Guidance for Prospective 

Ground-Water Monitoring Studies

	Environmental Fate and

	Effects Division

	Office of Pesticide Programs

	U.S. Environmental Protection Agency

	December 19, 2007



  TOC \o "1-3" \h \z \u    HYPERLINK \l "_Toc184799134"  CHAPTER 1 -
INTRODUCTION	  PAGEREF _Toc184799134 \h  7  

  HYPERLINK \l "_Toc184799135"  1.1 Environmental Exposure
Characterization	  PAGEREF _Toc184799135 \h  8  

  HYPERLINK \l "_Toc184799136"  1.11  Fate and Transport Studies	 
PAGEREF _Toc184799136 \h  9  

  HYPERLINK \l "_Toc184799137"  1.12  Conceptual Model	  PAGEREF
_Toc184799137 \h  11  

  HYPERLINK \l "_Toc184799138"  1.2.  Ground Water Exposure and
Estimating Risk	  PAGEREF _Toc184799138 \h  13  

  HYPERLINK \l "_Toc184799139"  1.21  Evaluation of Registered or
Proposed Uses	  PAGEREF _Toc184799139 \h  13  

  HYPERLINK \l "_Toc184799140"  1.22 Available Monitoring Data	  PAGEREF
_Toc184799140 \h  14  

  HYPERLINK \l "_Toc184799141"  1.23 Modeling Ground Water Exposure	 
PAGEREF _Toc184799141 \h  14  

  HYPERLINK \l "_Toc184799142"  1.24  Consideration of Risk	  PAGEREF
_Toc184799142 \h  15  

  HYPERLINK \l "_Toc184799143"  1.3  CASE STUDY	  PAGEREF _Toc184799143
\h  15  

  HYPERLINK \l "_Toc184799144"  1.31  Exposure Characterization	 
PAGEREF _Toc184799144 \h  15  

  HYPERLINK \l "_Toc184799145"  1.32  Monitoring	  PAGEREF _Toc184799145
\h  16  

  HYPERLINK \l "_Toc184799146"  1.33  Modeling	  PAGEREF _Toc184799146
\h  17  

  HYPERLINK \l "_Toc184799147"  1.34  Data Evaluation	  PAGEREF
_Toc184799147 \h  17  

  HYPERLINK \l "_Toc184799148"  1.4  STUDY COMPONENTS	  PAGEREF
_Toc184799148 \h  18  

  HYPERLINK \l "_Toc184799149"  1.5  STUDY RESULTS	  PAGEREF
_Toc184799149 \h  19  

  HYPERLINK \l "_Toc184799150"  CHAPTER 2 - SITE SELECTION	  PAGEREF
_Toc184799150 \h  19  

  HYPERLINK \l "_Toc184799151"  2.1  STUDY SCOPE	  PAGEREF _Toc184799151
\h  20  

  HYPERLINK \l "_Toc184799152"  2.11 Definition	  PAGEREF _Toc184799152
\h  20  

  HYPERLINK \l "_Toc184799153"  2.12  Compounds of Interest and
Analytical Methods	  PAGEREF _Toc184799153 \h  22  

  HYPERLINK \l "_Toc184799154"  2.2  A SET OF CANDIDATE SITES	  PAGEREF
_Toc184799154 \h  23  

  HYPERLINK \l "_Toc184799155"  2.21  Unconfined Aquifer	  PAGEREF
_Toc184799155 \h  24  

  HYPERLINK \l "_Toc184799156"  2.22  Shallow Depth	  PAGEREF
_Toc184799156 \h  24  

  HYPERLINK \l "_Toc184799157"  2.23  No Flow Restrictive Layers	 
PAGEREF _Toc184799157 \h  24  

  HYPERLINK \l "_Toc184799158"  2.24  Preferential Flow	  PAGEREF
_Toc184799158 \h  25  

  HYPERLINK \l "_Toc184799159"  2.25  Tile Drains	  PAGEREF
_Toc184799159 \h  25  

  HYPERLINK \l "_Toc184799160"  2.26  Single Soil Series Mapping Unit	 
PAGEREF _Toc184799160 \h  25  

  HYPERLINK \l "_Toc184799161"  2.27  Low Topographic Slope	  PAGEREF
_Toc184799161 \h  26  

  HYPERLINK \l "_Toc184799162"  2.28  Stable Hydraulic Gradient	 
PAGEREF _Toc184799162 \h  26  

  HYPERLINK \l "_Toc184799163"  2.3  COOPERATOR INTERVIEW	  PAGEREF
_Toc184799163 \h  27  

  HYPERLINK \l "_Toc184799164"  2.31  No Prior History of Test Pesticide
Use	  PAGEREF _Toc184799164 \h  27  

  HYPERLINK \l "_Toc184799165"  2.32  Long-Term Availability of Study
Site	  PAGEREF _Toc184799165 \h  27  

  HYPERLINK \l "_Toc184799166"  2.4  PRELIMINARY SITE CHARACTERIZATION	 
PAGEREF _Toc184799166 \h  28  

  HYPERLINK \l "_Toc184799167"  2.41  Absence of Dominant Fracture Flow	
 PAGEREF _Toc184799167 \h  28  

  HYPERLINK \l "_Toc184799168"  CHAPTER 3 - SITE CHARACTERIZATION AND
CONCEPTUAL MODEL	  PAGEREF _Toc184799168 \h  30  

  HYPERLINK \l "_Toc184799169"  3.1  EXISTING LOCAL DATA AND BASE MAP	 
PAGEREF _Toc184799169 \h  30  

  HYPERLINK \l "_Toc184799170"  3.11  Compile Existing Local Data	 
PAGEREF _Toc184799170 \h  31  

  HYPERLINK \l "_Toc184799171"  3.12  Develop a Base Map	  PAGEREF
_Toc184799171 \h  31  

  HYPERLINK \l "_Toc184799172"  3.13  Information Sources	  PAGEREF
_Toc184799172 \h  32  

  HYPERLINK \l "_Toc184799173"  3.2  SOIL AND VADOSE ZONE INVESTIGATION	
 PAGEREF _Toc184799173 \h  32  

  HYPERLINK \l "_Toc184799174"  3.21  Exploratory Coring Program and
Field Testing	  PAGEREF _Toc184799174 \h  33  

  HYPERLINK \l "_Toc184799175"  3.22  Number and Locations of Soil Cores
  PAGEREF _Toc184799175 \h  34  

  HYPERLINK \l "_Toc184799176"  3.23 Field Testing	  PAGEREF
_Toc184799176 \h  35  

  HYPERLINK \l "_Toc184799177"  3.24  Preservation and Transportation of
Formation Samples	  PAGEREF _Toc184799177 \h  35  

  HYPERLINK \l "_Toc184799178"  3.25  Quality Assurance and Quality
Control Procedures	  PAGEREF _Toc184799178 \h  36  

  HYPERLINK \l "_Toc184799179"  3.26  Test Pit Excavation	  PAGEREF
_Toc184799179 \h  36  

  HYPERLINK \l "_Toc184799180"  3.27  Abandonment of Soil Core Holes	 
PAGEREF _Toc184799180 \h  37  

  HYPERLINK \l "_Toc184799181"  3.3  SATURATED ZONE INVESTIGATION	 
PAGEREF _Toc184799181 \h  37  

  HYPERLINK \l "_Toc184799182"  3.31  Hydraulic Head	  PAGEREF
_Toc184799182 \h  37  

  HYPERLINK \l "_Toc184799183"  3.32  Direction of Ground-Water
Flow and Hydraulic Gradient	  PAGEREF _Toc184799183 \h  38  

  HYPERLINK \l "_Toc184799184"  3.33  Hydraulic Conductivity	  PAGEREF
_Toc184799184 \h  38  

  HYPERLINK \l "_Toc184799185"  3.34  Background Water Quality	  PAGEREF
_Toc184799185 \h  38  

  HYPERLINK \l "_Toc184799186"  3.4  CONCEPTUAL MODEL	  PAGEREF
_Toc184799186 \h  39  

  HYPERLINK \l "_Toc184799187"  3.41  Soils and the Vadose Zone	 
PAGEREF _Toc184799187 \h  39  

  HYPERLINK \l "_Toc184799188"  3.42  Saturated Zone and Water Quality	 
PAGEREF _Toc184799188 \h  40  

  HYPERLINK \l "_Toc184799189"  CHAPTER 4 - MONITORING PLAN DESIGN	 
PAGEREF _Toc184799189 \h  41  

  HYPERLINK \l "_Toc184799190"  4.1  SETTING UP	  PAGEREF _Toc184799190
\h  41  

  HYPERLINK \l "_Toc184799191"  4.11  Agricultural Management Practices	
 PAGEREF _Toc184799191 \h  41  

  HYPERLINK \l "_Toc184799192"  4.12  Irrigation	  PAGEREF _Toc184799192
\h  42  

  HYPERLINK \l "_Toc184799193"  4.13  Initial Post-Pesticide Application
Irrigation Event	  PAGEREF _Toc184799193 \h  42  

  HYPERLINK \l "_Toc184799194"  4.14  Irrigation After Initial Event	 
PAGEREF _Toc184799194 \h  43  

  HYPERLINK \l "_Toc184799195"  4.15  Mixing and Loading Area	  PAGEREF
_Toc184799195 \h  43  

  HYPERLINK \l "_Toc184799196"  4.16  Control Plot	  PAGEREF
_Toc184799196 \h  43  

  HYPERLINK \l "_Toc184799197"  4.17  Decontamination Area	  PAGEREF
_Toc184799197 \h  44  

  HYPERLINK \l "_Toc184799198"  4.18  Weather Station	  PAGEREF
_Toc184799198 \h  44  

  HYPERLINK \l "_Toc184799199"  4.2  Application of Pesticide and Tracer
  PAGEREF _Toc184799199 \h  44  

  HYPERLINK \l "_Toc184799200"  4.21  Pesticide	  PAGEREF _Toc184799200
\h  44  

  HYPERLINK \l "_Toc184799201"  4.22  Tracer	  PAGEREF _Toc184799201 \h 
44  

  HYPERLINK \l "_Toc184799202"  4.3  SOIL MONITORING PLAN	  PAGEREF
_Toc184799202 \h  45  

  HYPERLINK \l "_Toc184799203"  4.31  Soil Sampling Methods and
Instrumentation	  PAGEREF _Toc184799203 \h  45  

  HYPERLINK \l "_Toc184799204"  4.32  Number and Location of Soil Cores	
 PAGEREF _Toc184799204 \h  45  

  HYPERLINK \l "_Toc184799205"  4.33  Soil Sampling Timing and Frequency
  PAGEREF _Toc184799205 \h  46  

  HYPERLINK \l "_Toc184799206"  4.4  SOIL-WATER MONITORING PLAN	 
PAGEREF _Toc184799206 \h  46  

  HYPERLINK \l "_Toc184799207"  4.41  Soil Water Content Measurements	 
PAGEREF _Toc184799207 \h  46  

  HYPERLINK \l "_Toc184799208"  4.42  Instrumentation	  PAGEREF
_Toc184799208 \h  46  

  HYPERLINK \l "_Toc184799209"  4.43  Location and Frequency of Sampling
  PAGEREF _Toc184799209 \h  47  

  HYPERLINK \l "_Toc184799210"  4.44  Soil water Sampling	  PAGEREF
_Toc184799210 \h  47  

  HYPERLINK \l "_Toc184799211"  4.45  Instrumentation	  PAGEREF
_Toc184799211 \h  47  

  HYPERLINK \l "_Toc184799212"  4.46   Depth and Number of Lysimeters	 
PAGEREF _Toc184799212 \h  47  

  HYPERLINK \l "_Toc184799213"  4.47  Time of Emplacement	  PAGEREF
_Toc184799213 \h  48  

  HYPERLINK \l "_Toc184799214"  4.48  Sampling Frequency	  PAGEREF
_Toc184799214 \h  48  

  HYPERLINK \l "_Toc184799215"  4.5  GROUND-WATER MONITORING PLAN	 
PAGEREF _Toc184799215 \h  48  

  HYPERLINK \l "_Toc184799216"  4.51  Monitoring Well Design	  PAGEREF
_Toc184799216 \h  49  

  HYPERLINK \l "_Toc184799217"  4.52  Number, Emplacement, and Screen
Lengths of Wells Within a Cluster	  PAGEREF _Toc184799217 \h  49  

  HYPERLINK \l "_Toc184799218"  4.53  Number and Location of Monitoring
Well Clusters	  PAGEREF _Toc184799218 \h  49  

  HYPERLINK \l "_Toc184799219"  4.54  Time of Emplacement	  PAGEREF
_Toc184799219 \h  50  

  HYPERLINK \l "_Toc184799220"  4.55  Sampling Frequency	  PAGEREF
_Toc184799220 \h  50  

  HYPERLINK \l "_Toc184799221"  4.56  Instrumentation	  PAGEREF
_Toc184799221 \h  50  

  HYPERLINK \l "_Toc184799222"  4.57  Sampling Methods	  PAGEREF
_Toc184799222 \h  51  

  HYPERLINK \l "_Toc184799223"  4.58  Integrated Sampling Schedule	 
PAGEREF _Toc184799223 \h  51  

  HYPERLINK \l "_Toc184799224"  CHAPTER 5 - SITE CHARACTERIZATION AND
MONITORING PLAN DESIGN REPORTS	  PAGEREF _Toc184799224 \h  56  

  HYPERLINK \l "_Toc184799225"  5.1  SITE CHARACTERIZATION REPORT	 
PAGEREF _Toc184799225 \h  56  

  HYPERLINK \l "_Toc184799226"  5.11  Site Base Map	  PAGEREF
_Toc184799226 \h  57  

  HYPERLINK \l "_Toc184799227"  5.12  Surficial Soil Characteristics	 
PAGEREF _Toc184799227 \h  57  

  HYPERLINK \l "_Toc184799228"  5.13  Field Testing Methods and Results	
 PAGEREF _Toc184799228 \h  57  

  HYPERLINK \l "_Toc184799229"  5.14  Historical Water Needs and Net
Recharge	  PAGEREF _Toc184799229 \h  57  

  HYPERLINK \l "_Toc184799230"  5.15  Test Pit Excavation	  PAGEREF
_Toc184799230 \h  58  

  HYPERLINK \l "_Toc184799231"  5.16  Exploratory Boring Program	 
PAGEREF _Toc184799231 \h  58  

  HYPERLINK \l "_Toc184799232"  5.17  Saturated Zone Investigations	 
PAGEREF _Toc184799232 \h  58  

  HYPERLINK \l "_Toc184799233"  5.18  Background Water Quality	  PAGEREF
_Toc184799233 \h  58  

  HYPERLINK \l "_Toc184799234"  5.19  Conceptual Model	  PAGEREF
_Toc184799234 \h  58  

  HYPERLINK \l "_Toc184799235"  5.2  MONITORING PLAN DESIGN REPORT
(PROTOCOL)	  PAGEREF _Toc184799235 \h  59  

  HYPERLINK \l "_Toc184799236"  CHAPTER 6 - MONITORING PLAN
IMPLEMENTATION	  PAGEREF _Toc184799236 \h  62  

  HYPERLINK \l "_Toc184799237"  6.1  APPLICATION OF PESTICIDE AND TRACER
  PAGEREF _Toc184799237 \h  63  

  HYPERLINK \l "_Toc184799238"  6.2  IRRIGATION	  PAGEREF _Toc184799238
\h  63  

  HYPERLINK \l "_Toc184799239"  6.3  SOIL MONITORING	  PAGEREF
_Toc184799239 \h  64  

  HYPERLINK \l "_Toc184799240"  6.31  Decontamination of Sampling
Equipment	  PAGEREF _Toc184799240 \h  64  

  HYPERLINK \l "_Toc184799241"  6.32  Soil Sample Collection and
Handling	  PAGEREF _Toc184799241 \h  64  

  HYPERLINK \l "_Toc184799242"  6.4  PORE-WATER MONITORING	  PAGEREF
_Toc184799242 \h  65  

  HYPERLINK \l "_Toc184799243"  6.41  Instrumentation	  PAGEREF
_Toc184799243 \h  65  

  HYPERLINK \l "_Toc184799244"  6.42  Decontamination	  PAGEREF
_Toc184799244 \h  66  

  HYPERLINK \l "_Toc184799245"  6.43  Sample Collection	  PAGEREF
_Toc184799245 \h  66  

  HYPERLINK \l "_Toc184799246"  6.5  GROUND-WATER MONITORING	  PAGEREF
_Toc184799246 \h  67  

  HYPERLINK \l "_Toc184799247"  6.51  Instrumentation	  PAGEREF
_Toc184799247 \h  67  

  HYPERLINK \l "_Toc184799248"  6.52  Well Development	  PAGEREF
_Toc184799248 \h  68  

  HYPERLINK \l "_Toc184799249"  6.53  Decontamination	  PAGEREF
_Toc184799249 \h  69  

  HYPERLINK \l "_Toc184799250"  6.54  Sample Collection	  PAGEREF
_Toc184799250 \h  69  

  HYPERLINK \l "_Toc184799251"  6.6  SAMPLE HANDLING AND TRACKING	 
PAGEREF _Toc184799251 \h  70  

  HYPERLINK \l "_Toc184799252"  CHAPTER 7 - REPORTING	  PAGEREF
_Toc184799252 \h  72  

  HYPERLINK \l "_Toc184799253"  7.1  QUARTERLY REPORTS	  PAGEREF
_Toc184799253 \h  72  

  HYPERLINK \l "_Toc184799254"  7.11  Summary of Site Activities	 
PAGEREF _Toc184799254 \h  73  

  HYPERLINK \l "_Toc184799255"  7.12  Mass Balance	  PAGEREF
_Toc184799255 \h  73  

  HYPERLINK \l "_Toc184799256"  7.13  Protocol Deviations	  PAGEREF
_Toc184799256 \h  73  

  HYPERLINK \l "_Toc184799257"  7.14  Analytical Results	  PAGEREF
_Toc184799257 \h  73  

  HYPERLINK \l "_Toc184799258"  7.2  STUDY TERMINATION REPORT	  PAGEREF
_Toc184799258 \h  74  

  HYPERLINK \l "_Toc184799259"  7.3  FINAL REPORT	  PAGEREF
_Toc184799259 \h  74  

  HYPERLINK \l "_Toc184799260"  7.31  Field Practices	  PAGEREF
_Toc184799260 \h  75  

  HYPERLINK \l "_Toc184799261"  7.32  Sampling Activities	  PAGEREF
_Toc184799261 \h  75  

  HYPERLINK \l "_Toc184799262"  7.33  Analytical Results and Discussion
of Findings	  PAGEREF _Toc184799262 \h  75  

  HYPERLINK \l "_Toc184799263"  7.34  Quality Assurance	  PAGEREF
_Toc184799263 \h  75  

  HYPERLINK \l "_Toc184799264"  7.4  ELECTRONIC DATA REPORTING
GUIDELINES	  PAGEREF _Toc184799264 \h  76  

  HYPERLINK \l "_Toc184799265"  7.41  Study Area and Conceptual Site
Model	  PAGEREF _Toc184799265 \h  77  

  HYPERLINK \l "_Toc184799266"  7.42  Application of pesticide and
tracer	  PAGEREF _Toc184799266 \h  77  

  HYPERLINK \l "_Toc184799267"  7.43  Crop information	  PAGEREF
_Toc184799267 \h  78  

  HYPERLINK \l "_Toc184799268"  7.44  Soil properties	  PAGEREF
_Toc184799268 \h  78  

  HYPERLINK \l "_Toc184799269"  7.45  Ground-water data	  PAGEREF
_Toc184799269 \h  79  

  HYPERLINK \l "_Toc184799270"  7.46  Weather data	  PAGEREF
_Toc184799270 \h  79  

  HYPERLINK \l "_Toc184799271"  7.47  Irrigation input	  PAGEREF
_Toc184799271 \h  80  

  HYPERLINK \l "_Toc184799272"  7.48  Chemical monitoring results	 
PAGEREF _Toc184799272 \h  80  

  HYPERLINK \l "_Toc184799273"  CHAPTER 8.0 - REFERENCES	  PAGEREF
_Toc184799273 \h  81  

 ACKNOWLEDGEMENT

Many scientists in the Environmental Fate and Effects Division deserve
thanks for their roles in the design of these studies and development of
this Guidance.  We would like to acknowledge Michael Barrett, Elizabeth
Behl, Kevin Costello, and James Wolf, who developed the design of the
field study described in this document and who wrote substantial
sections of the document.  Other scientists provided significant
technical input and editing of the guidance and/or participated in the
public workshop and Scientific Advisory Panel meetings were Jonathan
Angier, Mark Corbin, R. David Jones, Robert Matzner, Laurence Libello,
David Wells and Amy McKinnon.  Finally, the original concept of
designing a prospective ground-water monitoring study for pesticides was
developed by Stuart Z. Cohen and Catherine Eiden.

CHAPTER 1 - INTRODUCTION tc \l1 "CHAPTER 1  - INTRODUCTION 

This document provides guidance for conducting a Prospective
Ground-Water (PGW) monitoring study for the registration of pesticides
in the United States (listed as guideline number 166-1 in 40 CFR
158.29).  The PGW study, which is required on a case-by-case basis, is
conducted in a controlled setting and provides the Agency with data for
evaluating the impact of legal pesticide use on ground water quality. 
After assessing the overall environmental fate of a pesticide, the
Agency may require the pesticide manufacturer (registrant) to conduct a
PGW study, with input from EPA on key aspects of the study design.  The
Agency’s assessment is based on a review of laboratory data on
mobility and persistence of the compound, estimates of potential
exposure, available monitoring and modeling information, and a
consideration of the potential for risk from drinking water exposure. 
Data generated from these field studies have proven valuable to EPA
scientists and risk managers as they are specifically designed to relate
pesticide use specified on the label to measurements of the pesticide
and its degradates in ground water used as a source of drinking water. 
This document provides guidance on how to conduct a PGW monitoring
study, describes milestones for consulting with EPA, and describes how
results should be reported to EPA. 

EPA uses the results of PGW monitoring studies to help answer questions
such as: (1) Will the pesticide leach in portions of the pesticide use
area that are similar to the study area? (2) How do pesticide residues
change over time? (3) What measures might be effective in mitigating the
pesticide leaching?  Monitoring data generated in these studies provide
a time-series of concentrations that can be used in exposure and risk
assessments as a reasonable surrogate for pesticide concentrations in
drinking water drawn from shallow private wells in agricultural areas.
PGW studies have been used to test alternative mitigation strategies for
pesticides that have adversely affected ground water quality to
determine, for example, if a reduction in application rate or specific
irrigation technology will reduce or eliminate the impact.  Data from
these studies also have been used to develop the EPA regression
screening model SCI-GROW, (  HYPERLINK
"http://www.epa.gov/oppefed1/models/water/models4.htm#scigrow" 
http://www.epa.gov/oppefed1/models/water/models4.htm#scigrow  ; see also
ILSI, 1998), which is used to estimate screening-level pesticide
concentrations in ground water used as a source of drinking water. 
Currently, the results of these studies are being used to evaluate
models of subsurface pesticide transport, and as a basis for model
scenarios for estimating pesticide concentrations in shallow ground
water.

In the past, the Agency has required both retrospective and PGW studies
on a case-by-case basis. The prospective study was designed to eliminate
factors that confound the interpretation of retrospective monitoring
studies.  For example, in the site selection process, sites with prior
use of the pesticide or with point sources of contamination are not
selected for study.  Also, since the pesticide is applied according to a
current or proposed label, concentrations observed during the study can
be directly linked to a known and current labeled use. The PGW studies
are conducted at a field scale rather than a larger scale to ensure that
adequate field quality assurance/quality control (QA/QC), collection of
ancillary data (climatic data, soil characteristics), and level of
instrumentation can be implemented at a reasonable cost, while
maintaining a scale that captures the natural variability in soils,
hydrology, and other environmental factors, and under which standard
agronomic practices can be implemented.

The original draft guidance for PGW monitoring studies was developed
primarily in the early 1990s and has been subjected to substantial
public review and comment, including a public workshop sponsored by EPA
in 1995 and a Scientific Advisory Panel (SAP) review in 1998.  The
comments received during the workshop and SAP meeting provided valuable
suggestions from both a technical and practical perspective and were
used to revise this guidance and to address other issues identified in
the Agency’s review of studies conducted for the registration of over
50 pesticides.  The recommendations in this guidance document also
represent the Agency’s substantial experience, over the last decade,
in developing and articulating effective procedures for collecting high
quality data on pesticide movement into ground water. 

 1.1 Environmental Exposure Characterization

PGW studies may be required on a case-by-case basis, depending on an
assessment of the pesticide’s potential to impact ground water and the
Agency’s consideration of risk.  Before a pesticide can be sold in the
United States, EPA evaluates its safety to humans and to terrestrial and
aquatic animals and plants, based on a wide range of laboratory and
field studies. The environmental studies examine both the ecological
effects (toxicity) of a pesticide and its chemical fate and transport. 
After EPA scientists review all the available information on toxicity,
chemical fate and transport, and proposed use of a pesticide, they
develop an environmental exposure characterization, which includes an
exposure profile and conceptual model.  The exposure characterization
estimates the potential exposure of plants, animals, and water resources
to pesticide residues in water, food, and air.  The exposure profile
describes:

Degradation of the pesticide active ingredient (how fast and by what
means it is degraded in the environment) and how persistent it is in the
environment;

Breakdown products or degradates that result from the degradation
processes; 

Mobility of the pesticide active ingredient and its degradates and how
these chemicals may be transported from the application site (e.g.
volatilize into the atmosphere, move into ground or surface waters, or
bind to the soil); and 

Accumulation of the pesticide and it’s degradates in the environment.

These environmental fate studies are designed to help identify which
dissipation processes are likely to occur when a pesticide is released
into the environment and to characterize the breakdown products that are
likely to result from these degradation processes. The diagram below
illustrates the potential dissipation pathways for a pesticide after it
is applied. 

Figure 1.  Pesticide Dissipation Pathways

Based upon results of environmental fate and transport studies, EPA
develops a preliminary, qualitative exposure assessment. This, in turn,
may be used to design or trigger additional conditional field studies,
such as the PGW study.

1.11  Fate and Transport Studies 

EPA reviews many laboratory and field studies to determine the fate of
pesticides in the environment. The types of studies required depend on
the use of the pesticide. Certain laboratory studies (e.g., hydrolysis,
photolysis, and soil metabolism) are routinely conducted for all
outdoor-use pesticides. Other conditional studies (e.g., PGW studies,
photo-degradation in air, and field volatility) may be triggered by data
from the initially required laboratory studies and/or use or application
patterns and basic product chemistry data. The basic studies provide the
following critical information for a pesticide active ingredient and its
major degradates:

Half-life of the parent (persistence) 

Identity of degradates 

Rates of formation and decline of degradates

Bioconcentration potential

Mobility of the parent and degradates 

The Agency regulations found in 40 CFR 158.29 describe the types and
amounts of data that the Agency needs for assessing the environmental
fate of a pesticide active ingredient. These controlled laboratory and
field studies, which are conducted under approved Guidelines and Good
Laboratory Practices, are used to determine the persistence, mobility,
and bioconcentration potential of a pesticide active ingredient and its
major degradates.  Generally, degradates formed at greater than or equal
to 10% of the amount of applied pesticide are considered significant
(i.e., major degradate) and should be identified in the study.  In
addition, degradates of known toxicological or ecotoxicological concern
should be quantified and identified, even when present at less than 10%
of the applied pesticide. 

Physicochemical Degradation:  This includes hydrolysis and
photo-degradation in water, soil, and air. Hydrolysis studies determine
the potential of the parent pesticide to degrade in water, while
photo-degradation studies determine the potential of the parent
pesticide to degrade in water, soil or air when exposed to sunlight.
During these studies, data are also collected concerning the identity,
formation and persistence of degradates.

Biological Degradation:  These studies include aerobic and anaerobic
soil metabolism, and aerobic and anaerobic aquatic metabolism. The soil
metabolism studies determine the persistence of the parent pesticide
when it interacts with soil microorganisms living under aerobic and
anaerobic conditions. The aquatic metabolism studies produce similar
data that are generated by pesticide interaction with microorganisms in
a water/sediment system. These studies also identify degradates that
result from biological metabolism.

Mobility:  These studies include leaching and adsorption/desorption,
laboratory volatility, and field volatility. The leaching study assesses
the mobility of the parent pesticide and its’ degradates through
columns packed with various soils. The adsorption/desorption study
determines the potential of the parent pesticide and its’ degradates
to bind to soils of different types. The potential mobility of the
parent pesticide and each degradate is determined by examining the data
from both of these studies and may range from immobile to highly mobile.

Bioconcentration:  These studies use aquatic organisms to estimate the
potential of a pesticide, under controlled laboratory conditions, to
partition to the organisms from respiratory and dermal exposures. These
studies also provide information on the degree a pesticide or degradate
can be depurated should levels of the pesticide in the surrounding
aquatic environment be reduced.

Field dissipation:  These studies track the dissipation of a pesticide
from the surface soil layer, and the formation and dissipation of
degradates.  While laboratory environmental fate studies are designed to
assess one dissipation process at a time, field dissipation studies
assess pesticide loss as a combined result of chemical and biological
processes (e.g., hydrolysis, photolysis, microbial transformation) and
offsite transport (e.g., volatilization, leaching, runoff) as well as
loss from plant uptake. These studies provide a field dissipation
half-life, a lumped parameter that takes all routes of dissipation into
account.  Several field studies are usually conducted for each pesticide
in typical use areas.  

EPA’s assessment may also identify whether pesticide mobility or
persistence is affected by pH, temperature, or other factors.  The
exposure profile, combined with an evaluation of use and consideration
of risk may trigger a PGW monitoring study.

1.12  Conceptual Model

The potential for pesticide movement to ground water depends on a
variety of factors, including hydrologic properties of the overlying
soil and vadose zone that affect downward movement of water and
chemicals, travel time through the unsaturated zone to ground water,
aquifer properties (conductivity, porosity, depth, type, location of
recharge area), leaching potential of the pesticide (persistence and
mobility), and type of well drawing water for drinking purposes (Focazio
et al, 2002).  These factors can vary significantly throughout the use
area of a pesticide. While pesticide persistence and mobility parameters
derived from laboratory studies are useful as a starting point for
assessment, these parameters are not always sufficient to adequately
characterize leaching of chemicals under actual field conditions.  Data
collected in PGW monitoring studies represent the integration of effects
of multiple environmental and agronomic practices at a site where a
specific crop is grown.  The term prospective is based on a key aspect
of the study design, namely, the pesticide has not been used previously
at the site.  If the pesticide is detected, then it is the result of the
application during the study rather than a prior application (e.g., at a
different label rate) or mishandling of the pesticide during mixing,
loading, or disposal activities.

  

A PGW monitoring study begins with the application of a pesticide and a
mobile tracer compound to a site that has been instrumented (i.e. wells
and other monitoring equipment has been installed) and where the crop is
(or will be) planted.  The crop is grown in a field during the study,
following standard agronomic practices (e.g., tillage, irrigation, crop
cultivation).  Figure 2 below depicts a generic conceptual model for
pesticide transport to shallow, private rural wells in an agricultural
area.  Following pesticide application, residues can be washed off plant
surfaces by precipitation or irrigation.  They may adsorb to soils to
varying degrees and may degrade as a result of chemical or biological
processes.  As water infiltrates through the vadose zone to the water
table, pesticide residues can be transported to the subsurface and can
adsorb and degrade further.  Pesticides can be transported from a field
in runoff after precipitation or irrigation, adsorbed to eroded soil, or
volatilized in air.  Pesticides also can be taken up to a varying extent
by plants.  A PGW study is designed to minimize the effect of some of
these transport processes (i.e., runoff or the impacts of artificial
drainage) in the site selection process and to track the overall impact
of other processes on water quality.

Figure 2.  Conceptual Model for Pesticide Transport to Shallow, Private
Rural Wells.

The vadose and saturated zones under the field are monitored over time
(usually at least two years) for residues of the pesticide, significant
degradates, and a conservative tracer.  The tracer identifies the depth
to which recharge has moved following the application of the pesticide. 
Weather data is also collected during the study.  The pesticide and
tracer are only applied one time, to enable the movement of the
pesticide and the tracer to be tracked without interference.  These
studies track the movement of the pesticide, degradate, and applied
water (using a tracer compound) through the soil into the water table
and produce a time-series of concentrations over a period of several
years.  Adequate ancillary data are collected (e.g., climate, timing and
mass of pesticide applied, irrigation, soil characteristics) to enable
the results to be interpreted.  Study results should be evaluated, and
concentrations adjusted accordingly to take into consideration the
numbers and frequencies of application allowed on the label.  The goal
of the study is to determine whether a pesticide will move to ground
water in some locations where it can be applied, and to determine the
time-course concentrations in ground water of the pesticide, major
degradates, and degradates of toxicological concern.  

In order for the results to be applicable to regulatory decisions, the
site selected for study should have certain characteristics.  Depending
on the objective of a particular study, a study site may be selected to
represent an environment that is highly susceptible to leaching (e.g.,
sites with coarse-textured soils that facilitate rapid transport) or a
site that represents other conditions under which the pesticide is most
typically used.  Sites selected for study represent a specific use (or
set of uses) of the pesticide, as well as soil, hydrology, and climatic
conditions common to a use area; these conditions should be explicitly
described in the site selection report.  Site selection should also
include consideration of other factors that dominate ground-water flow
systems, e.g. regions dominated by karst topography or tile drains,
especially if such factors dominate in an important use area.  Ideally,
multiple sites should be selected for monitoring that exhibit a range of
characteristics of the broader use area.  For example, selecting several
sites that are highly vulnerable to leaching along with several sites
presenting more typical vulnerability for a spatially diverse pesticide
use area can provide a more complete understanding of the potential
range of pesticide movement.  Having results from a range of sites will
enhance the Agency’s ability to extrapolate results across the
composite use area.  When a single site is chosen for monitoring, the
site should represent a highly vulnerability site. If the behavior of a
pesticide (i.e., its soil mobility and persistence) varies greatly from
site to site, EPA may request site-specific measurements of degradation
rates or sorption coefficients in the PGW study test soil.  These data
would aid in interpreting study results and in modeling.

1.2  Ground Water Exposure and Estimating Risk

 tc \l3 "Use of Modeling 

Some pesticides and pesticide degradates pose a high risk at very low
concentrations, while others pose less risk at these same low
concentrations.  Because of the substantial costs associated with
conducting a PGW study, consideration is given to potential risk based
on estimates of exposure from available monitoring data and from
screening-level models.  

1.21  Evaluation of Registered or Proposed Uses tc \l3 "Evaluation of
Registered or Proposed Uses 

The way in which a pesticide is used can play a critical role in
determining its impact on the environment.  For example, pesticides that
are exclusively used indoors pose negligible risk of direct ground-water
contamination in comparison to those with outdoor uses.  Some typical
indoor uses include baits, greenhouse uses, and use in food handling
establishments.  While ground-water impacts associated with those uses
can occur from improper handling or disposal, the PGW study focuses on
water quality impacts resulting from use according to the registered
label.  Thus, a consideration of how the pesticide will be used is an
important factor in assessing whether a study would provide data needed
to reduce uncertainty in water exposure assessments.

 

1.22  Available Monitoring Data

For the pesticide of concern, EPA may have available ground-water
monitoring data collected by academic institutions, federal and state
agencies, or pesticide registrants.  Sources of these data include state
monitoring databases,  other federal agencies [e.g., United States
Geologic Survey (USGS) monitoring  programs like the National Water
Quality Assessment Program (NAWQA) or the Toxic Substances Hydrology
Program], Office of Pesticide Program's (OPP) Pesticides in Ground Water
Database (USEPA, 1992), reports submitted to EPA under FIFRA § 6(a)(2),
EPA’s STORET database, the open literature, and monitoring conducted
by public water supply facilities in compliance with the Safe Drinking
Water Act.  OPP compiles and evaluates available water monitoring data
and examines the quality of the studies.  In general, most monitoring
studies are not designed to target and document impacts from the use of
a specific pesticide at a specific rate, nor are they conducted with the
level of quality assurance and quality control of a PGW study. 
Monitoring data typically provide a lower bound on potential exposure,
especially where data are available to determine the amount of a
pesticide applied (both the rate and numbers of applications) and the
location of treated areas relative to sampling sites.

While most available monitoring data are not likely to be of adequate
spatial and temporal resolution to address uncertainties in exposure for
a specific pesticide, data are useful in EPA’s determination of the
need for a PGW study and may also be helpful in determining preferred
test sites.  These data may highlight uses for which impacts appear to
be lower, and, thereby help EPA focus evaluation efforts or further
monitoring on specific uses or geographical areas where impacts may be
higher.  

1.23  Modeling Ground Water Exposure

EPA routinely uses the screening-level model (SCI-GROW) to estimate
potential ground water exposure for pesticide water assessments. 
SCI-GROW is an empirical regression model developed by EPA and is based
on monitoring results of PGW studies.  This model requires limited input
parameters (e.g., Koc, aerobic soil metabolism half-life, and annual
pesticide application rate).  Using these values, the model estimates
the concentration of the pesticide (90-day peak) in shallow, unconfined
aquifers that are subject to relatively rapid recharge and under
conditions similar to sites where the monitoring was conducted).  The
model can simulate multiple applications of the pesticide and the
results are useful when reviewed in conjunction with the field study.  A
detailed description of this model can be found at EPA's Web site:  
HYPERLINK "http://www.epa.gov/oppefed1/models/water/index.htm" 
www.epa.gov/oppefed1/models/water/index.htm .

When the screening model estimates that a particular pesticide may leach
into ground water at levels of concern, risk managers may determine that
a PGW study will provide quality data to reduce the uncertainty in the
assessment. 

EPA is currently evaluating mechanistic models such as LEACHM (Hutson
and Wagenet, 1992), PRZM (Carsel et al., 1997), RZWQM (DeCoursey et al.,
1989), and PEARL (Leistra, et. al., 2001) and comparing estimates to
monitoring data from PGW studies and other studies.  OPP’s overall
ground water modeling approach and conceptual model has been peer
reviewed by the FIFRA Scientific Advisory Panel at meetings in February
2005 (USEPA, 2005a) and August, 2005 (USEPA, 2005b).  This methodology
was implemented in water modeling conducted for the Revised N-Methyl
Carbamate Cumulative Risk Assessment (USEPA, 2007).  

1.24  Consideration of Risk

Before requiring a PGW study, risk managers at EPA take into
consideration the potential for human exposure to pesticide residues in
drinking water and related uncertainties.  Consideration of risk may
also take into account the potential for ground water containing
pesticide residues to impact the quality of ecologically sensitive
surface water, as well as the intrinsic value of ground water as an
important natural resource. Ground water contamination can be difficult
and costly to remediate, and it can take many years for contaminants to
naturally degrade even when point sources are removed.  Water from
private rural wells is typically not treated prior to consumption, and
over 27 million people in the United States rely on private rural wells
as their primary water source.  

1.3  CASE STUDY tc \l2 "4.  CASE STUDY 

The following case study is an example of the exposure assessment
process that occurs before a ground-water study is required for a
(hypothetical) herbicide, Chemical H, proposed for use on corn and
soybeans.  

1.31  Exposure Characterization tc \l3 "Environmental Fate Assessment  

The registration standard for Chemical H required the full complement of
environmental fate studies, and data submitted by the registrant were
acceptable.  Overall, Chemical H is characterized as a potentially
persistent pesticide (half-lives up to a few months) that can be mobile
in a variety of soils.  However, field dissipation studies suggest that
Chemical H degradation may be more rapid (i.e., within a few weeks)
under certain conditions in some soils.  

The aerobic soil metabolism half-life was determined to be 35 to 70 days
in studies conducted in several soils, and the anaerobic soil metabolism
half-life averaged about 170 days.  Based on these studies, it appears
that Chemical H could be persistent enough in the field for significant
leaching to occur.  However, at some field dissipation study sites,
Chemical H dissipated more rapidly (half-lives were less than three
weeks at four of the eight study sites) than other soil-applied
pesticides that have been found to reach ground water.  Overall, at
eight study sites, field dissipation half-lives for the upper six inches
of soil ranged from 8 to 46 days.  The field dissipation data indicates
that Chemical H appears to degrade more rapidly in acidic soils in the
southern part of its use range; however, it is not clear whether the
enhanced dissipation in these soils was entirely due to more rapid
degradation as opposed to soil leaching or other dissipation routes. 
Although residues were analyzed to a 3-foot depth at several of the
field dissipation study sites, there were no consistent detections of
Chemical H or its major degradate, Chemical H-acid, below 18 inches at
any of these sites.  The minimum detection limit was 10 μg/L for both
compounds (the maximum application rate for Chemical H is 0.10 lb ai/A).
 

Chemical H is fairly resistant to abiotic hydrolysis. It hydrolyzes
slowly in sterile water at pH 5 (extrapolated half-life is 91 days) and
does not appreciably hydrolyze at pH 7 and 9 over the 30-day study
period.  Chemical H, though, is very susceptible to photolysis, with an
aqueous photolysis half-life of 1 day and a soil photolysis half-life of
7 days.

In general, the laboratory data show that Chemical H is persistent in
most soils with a degradation half-life of 5 to 10 weeks.  Chemical
H-acid, the primary degradate, appears to persist for several months or
longer in neutral or alkaline soils.  However, this degradate has not
been found to persist in photolysis studies.  No other degradates were
found to accumulate at more than 5% of the applied parent compound.  In
the field, the accumulation of Chemical H-acid residues was highly
variable, ranging from a maximum of 5% of the applied Chemical H at one
site to a maximum of 50% of the applied Chemical H at another site.  

Chemical H partitions primarily into the soil water in most soils.  In
soil column leaching studies, it is mobile in a sandy soil containing
1.4% organic matter (5% to 10% leaching through the column) and
moderately mobile in sandy loam (1.1% O.M.) and loamy sand (2.0% O.M.)
soils (1% to 5% leaching through the column).  In batch equilibrium
studies, Kd (in this case equivalent to Freundlich adsorption constants)
values ranged from 0.8 to 3.4 in five soils tested.  The degree of
adsorption was roughly proportional to soil organic matter content.  The
Koc  ranged from 34 to 72; the median Koc was 47.  The only Kd greater
than 1.4 in four soils tested was associated with a soil containing 12%
organic matter.  It should also be noted that Chemical H solubility is
considerably reduced in alkaline soils.  

Chemical H-acid is even more mobile than Chemical H, with Koc values
from batch equilibrium studies ranging from 4 to 17 in the same four
soils in which Chemical H sorption was studied.  The degradate was not
confirmed to leach below 18 inches in field dissipation studies sampled
to a 3-foot depth, but the soil analytical method could only detect
residues exceeding about 20% of the applied pesticide, even if it was
applied at the maximum rate and was fully retained in the upper six
inches of soil.	

1.32  Monitoring tc \l3 "Monitoring 

Chemical H parent was detected in ground water sampled in a small number
(5) of studies reported in the Office of Pesticide Program’s (OPP's)
Pesticides in Ground Water Database (USEPA, 1992).  Although three
detections exceeded the pesticide's Maximum Contaminant Level (MCL) and
Health Advisory Level (HAL) of  7 μg/L, the majority of the detections
(75%) were below 1 μg/L.  No monitoring data are available for Chemical
H-acid in ground water.  Sufficient monitoring data, though, are
available for the parent to demonstrate that Chemical H does leach to
ground water after registered applications in some areas.  However, some
of the higher concentrations reported may be due to chemical spills or
other accidents.  The monitoring data have not been collected in a
sufficiently systematic way to determine under what specific conditions
Chemical H is most likely to reach ground water.  Based on a gross
examination of the monitoring data, it appears that ground-water
contamination may be more likely in the northern part of the Chemical H
use area.

1.33  Modeling tc \l3 "Modeling 

Initially, evaluation of Chemical H was performed with the screening
model SCI-GROW.  Screening modeling demonstrates that Chemical H has the
characteristics (at least in the majority of use sites) of other
pesticides with long-established uses that have been found in ground
water.  This is especially true of Chemical H-acid, which is both more
mobile and more persistent than Chemical H parent.  The soil half-life
of this degradate has not been directly measured, but it appears to be
much longer than 6 months in at least some soils.  Based on SCI-GROW
concentration estimates, residues of Chemical H alone exceed the
aggregate risks for drinking water alone in OPP’s human dietary risk
assessment; similar exposure estimates for the degradate, which is
assumed to have similar toxicity, will add to the risk.

PRZM modeling was conducted at 10 representative use sites.  A
simulation of leached residues for Chemical H was compared with
simulated Chemical P residues, the corn and soybean herbicide most
commonly detected in ground water.  Twenty separate application years
were simulated at each site.  At 1 of the 10 sites, measured Chemical P
residues from a vadose zone and ground-water monitoring study were
compared with simulations for both chemicals.  PRZM only roughly
predicted the overall amount of Chemical P and its chemical behavior as
it leached through the soil profile.  At this, and at most other sites,
when aerobic metabolism half-lives and average Koc values were used,
modeling always predicted that Chemical H would leach to a depth of 3 or
6 feet more than Chemical P (as a percentage of the application rate). 
However, if the Chemical H degradation half-life was shorter (e.g., less
than two weeks), then predicted leaching as well as the magnitude of
residues was generally less than that of Chemical P.  Chemical H-acid,
when formed in sufficient quantities, was also predicted to leach
substantially at many use sites.  

1.34  Data Evaluation  tc \l3 "Data Evaluation  

The weight-of-evidence of the environmental fate properties of the
pesticide are enough to raise concern about its potential to reach
ground water.  Since the photolysis half-life for Chemical H is short,
the foliar application for this chemical is considered less of a concern
than the soil-incorporation method.  

μg/L in water over a period of a few weeks exceed Levels of Concern
(LOCs) for freshwater fish (Risk Quotient (RQ) of 12-30).  This
exceedance may pose a risk in areas where ground water discharges to
surface water bodies.  A more definitive analysis of the scenarios under
which Chemical H residues leach significantly to ground water cannot be
made at this time because of the uncertainty regarding the subsurface
behavior of Chemical H and Chemical H-acid.  Such data could be
obtained, however, from PGW studies.

μg/L.

This case study illustrates the complex analysis that is involved in
determining the environmental fate of a pesticide and in evaluating its
potential to impact the quality of ground water as a result of normal
agricultural use.  The uncertainty in this analysis may be greater for
chemicals that have never been used and for degradation products that
have little environmental fate data.  In these cases, scientists should
rely exclusively on the environmental fate assessment to determine the
likelihood of leaching, and on predictions of models to estimate the
concentrations that may occur.  PGW studies may provide EPA risk
assessors and risk managers with particularly valuable information in
these circumstances.

1.4  STUDY COMPONENTS tc \l2 "5. STUDY COMPONENTS 

This guidance is intended to be performance-based, rather than a
definitive description of how to install wells and how to collect
samples.  The goal is to provide the study director with adequate
flexibility in selecting equipment and methods needed to provide high
quality results, while at the same time standardizing the study design. 
This flexibility also allows the study director to install more sampling
devices and collect more samples than stipulated to meet the goal of the
study, when needed.  For example, if EPA approves a site where the
hydrology is more complex and the depth to ground water is greater, for
the study to be successful, more site instrumentation may be needed, and
the term of the study is likely to be longer in order to determine the
concentrations of the pesticide and major degradates 

The major design components for PGW monitoring studies and guidance on
how to carry out these studies are explained in detail in the following
chapters of this document:

Site Selection

Site Characterization and Site-Specific Conceptual Model

Monitoring Plan Design

Site Characterization and Monitoring Plan Design Reports

Monitoring Plan Implementation

Reporting 	

1.5  STUDY RESULTS tc \l2 "6.  STUDY RESULTS 

As specific stages of a PGW study are completed, results should be
reported to EPA.  These different reports require varying levels of
effort and detail and are described more fully in subsequent chapters of
this guidance.  The reports should include the following information:

Site Selection Report:  Maps, tables, and a brief interpretive text. 
EPA will select the study site from the set of candidate sites proposed
by the registrant.  

Site Characterization and Monitoring Plan Design Reports: Site-specific
data, more detailed interpretation, and a proposed monitoring plan,
including maps.  The Site Characterization and Monitoring Plan Design
Reports should be submitted to and approved by EPA before the monitoring
plan implementation phase of a ground-water study can begin.

Quarterly Progress Reports:  Brief data summary relying on summary
tables and graphs.  New data for the quarter are highlighted in these
reports, and any deviations from protocol, equipment failures, or other
complications are identified.  Typically, reviews of these quarterly
reports will not prompt any action, unless results of analysis or
irregularities in the performance of the study warrant further action.  

Termination Report:  Brief letter report that indicates study results
and rationale for termination along with accompanying data summary.

Final Report: The final report will consist of a final review of study
results and appendices, containing earlier submissions.  This final
report will serve as a comprehensive primary reference for the study.

The following chapters describe, in more detail, the components of a PGW
monitoring study.

CHAPTER 2 - SITE SELECTION tc \l1 "CHAPTER 2 - SITE SELECTION 

Careful selection of ground-water monitoring study sites is critical in
ensuring that study results are useful to aid risk assessors and
regulatory managers in pesticide regulatory decisions. The soils,
hydrogeology, and climate at the study site (or sites) should be
accurately described or characterized in order to properly instrument
the site and to interpret the results of the study.  Also, the range of
soils, hydrogeology, and climatic characteristics represented by the use
site should be established to properly interpret the data collected. 
The characteristics of candidate sites will depend on the specific use
and the conditions the study is intended to explore (e.g.,"high
exposure" or "typical use," irrigated or dryland sites).  For example, a
site may be selected because it has the combination of environmental
characteristics typically associated with ground water quality problems.
 Another aspect to consider in site selection is that the conditions are
such that the study can be conducted within a reasonable and predictable
time frame.  Ultimately, the success of the site selection will be
performance based.  The study should be able to clearly track an applied
tracer through the vadose zone to the saturated zone and track any
downward movement of pesticide residues.

OPP recommends that the registrant consider a number of sites in the
preliminary site selection process.  The following four-step process for
the selection of field sites is suggested.  These steps are described in
detail in the following sections:

Study Scope

A Set of Candidate Sites

Cooperator Interview

Preliminary Site Characterization

All proposed sites that meet the criteria discussed in this chapter
should be suitable for study.  Sites should be ranked according to soil
type, hydrogeologic characteristics and other relevant factors, and this
information should be submitted to EPA in tabular form.  Pesticide
application and data collection cannot begin before the study site is
approved in writing by EPA.  Therefore, in the interest of saving time
and resources, the study director should take special care during site
selection to identify candidate sites.  Full site characterization
activities (Chapter 3) may begin following EPA approval of the study
site(s).

2.1  STUDY SCOPE tc \l2 "1.  STUDY SCOPE 

2.11 Definition tc \l3 "Definition 

The first step in selecting a study site is for the registrant to
describe where and how the pesticide will be or is used.  Included in
the preliminary assessment should be usage (application rates, number of
applications, maximum application) information for all use sites,
stratified by geographic area (region, state, and county).  The
registrant should also provide information on the pesticide formulation,
relevant agronomic practices (e.g., application timing or irrigation
requirements), mode of action and environmental fate characteristics of
the pesticide or soil properties that affect the mobility or persistence
of a pesticide in the field. 

Since a pesticide use area may have some locations with a greater
probability for contamination of ground water than others, the
registrant should assess the ground-water "vulnerability" throughout the
use area.  Ground-water vulnerability depends on many factors, and can
be characterized using overlay (GIS) and indexing methods (Leaching
Potential) (Kellog et al., 1992; Diaz-Diaz et al., 1998),  process-based
methods (modeling), or statistical methods.  The assessment can be as
simple as county-scale ranking, or as sophisticated as layered GIS data
layer maps (Burkart et al., 1994) or vulnerability surfaces. 
Appropriate State Agencies may be contacted to determine whether areas
highly susceptible to contamination of ground water have already been
identified in the usage areas.  The registrant should use any of these
methods to:  1) describe the overall vulnerability of the pesticide use
area to contamination of ground water; 2) identify the vulnerability
associated with a "typical use site"; 3) identify sites throughout the
use area that are most vulnerable to contamination of ground water; and
4) characterize the vulnerability of the sites they propose to study. 
The registrant should provide a complete description of the tool used to
assess vulnerability and how this tool was used to select the candidate
sites.

Based on this information, EPA will determine the uses for which the
monitoring study is required, the number of studies for each use, the
implementation schedule, and the conditions of the study (application
method, soil type, geographic area).  More than one study site may be
needed because of major differences between uses (e.g. rice or corn), or
if use occurs in very different geographic areas (e.g., CA and NY).  A
careful definition of study scope will assure that the answers to
regulatory questions such as these are obtained: 

Will the pesticide leach at any location in the pesticide use area? Will
fate             properties be important or influence study results
(e.g., soil pH and pesticide              hydrolysis)?

Which uses pose the greatest risk of leaching?  

Is there a high risk that leaching will occur in a specific geographic
area or for a     specific use; if so, what measures can mitigate this
risk?

It is important to design individual prospective ground-water studies
to answer questions particular to the pesticide in question.  The
chemical properties of a pesticide may require that the registrant
evaluate leaching potential for application to different soil types, for
different application methods, formulations or for applications at
different label rates.  If a single study is performed on a site
representing high vulnerability for leaching within a pesticide's use
area, and pesticide residues are not found in the ground water or deep
within the soil column, it can be assumed that this chemical is not
likely to leach unless subsequent monitoring data show otherwise.  On
the other hand, studies performed on a highly vulnerable site and at a
less vulnerable site that may be more "typical" of the pesticide's use
would provide some basis for extrapolation of leaching potential between
these different scenarios, perhaps through the use of computer models.  

This preliminary assessment is intended to identify acceptable sites
that are candidates for extensive site characterization activities.  The
regional assessment of candidate areas should yield a list of areas
where vulnerable and relatively homogeneous sites might be found.  Study
sites that are approximately 2 to 5 acres are then identified within
these candidate regions.

2.12  Compounds of Interest and Analytical Methods tc \l3 "Compounds of
Interest and Analytical Methods 

All pesticides, major pesticide degradates in the study and the
conservative tracer compound to be used on the site are considered
compounds of interest.  A major degradate is one accounting for > 10% of
the applied at any time during the laboratory studies, or one that has
been identified as of potential toxicological, environmental or
ecological concern.  The test pesticide should be applied only once
using the method of application stated on the product label.  The
application should be made at the highest recommended label rate for the
crop used in the study.  

A comprehensive description of the methods (USEPA, 1992) selected for
the analysis of all compounds of interest should be provided. 
Information on the analytical procedures to be used for both water and
soil samples, and on the method detection limits (MDL) (USEPA, 1992)
should also be reported.  Any background information and references that
might assist EPA in the evaluation of the nature, accuracy, and
selectiveness of all proposed analytical methods should also be
included.  If no standard analytical method is available for the
compounds of interest, methods should be developed, validated, and
approved by EPA before beginning the prospective study, to ensure that
the study is acceptable.  

μg/L, whichever is lower.  PQL refers to the lowest concentration at
which the laboratory can confidently quantify the concentration of the
compound of interest.  The study authors should report all samples with
concentrations above the MDL as detections, including those below the
PQL in which the concentration cannot be quantified.  In addition, the
study authors should provide sample equations to demonstrate how the PQL
was calculated.

Analytical methods used should also be selective for the compound of
interest and free of any interference problems from other substances
likely to be present in the sample.  If less selective methods are used
(e.g., ELISA (immunoassay) methods, gas chromatography (GC) with
electron capture detection or nitrogen/phosphorous detection for sample
screening), all detections should be confirmed using a different method
(e.g., a second GC column with a different polarity).  The procedure
used to analyze significant degradates identified in the Subdivision N
Environmental Fate studies should also be reported.

2.2  A SET OF CANDIDATE SITES tc \l2 "2.  A SET OF CANDIDATE SITES 

The second step in the site selection process is a regional assessment
of sites within the pesticide use area and identification of candidate
sites.  The characteristics of candidate sites will depend on the
specific use and the conditions the study is intended to explore ("high
exposure" or "typical use," irrigated or dryland, etc.).  

A regional assessment for candidate sites involves several steps.  It is
important to first investigate certain general factors including
pesticide use, vulnerability of the use area, soil type, and general
hydrologeology including aquifer type and depth, and climate.  Aquifers
are herein defined as a saturated geologic unit that can transmit
significant quantities of water under ordinary hydraulic gradients. 
However, many individuals rely on shallow ground water sources (i.e.
shallow saturated soils) that do not necessarily meet this definition. 
The term “aquifer” used throughout this guidance is intended to
cover both types of drinking water sources.  This reconnaissance work
can be done easily using spatially distributed data such as a GIS
display.  Once an area is found that appears to meet these factors, the
next step is to look for individual fields that might be appropriate for
the study.  At this time, it is important to focus on specific site
characteristics including aquifer characteristics and other criteria
listed below. 

With few exceptions, all candidate sites for a prospective ground-water
study should meet the following criteria (ordered by expected
significance):

Unconfined aquifer,

Less than 30-foot depth to the water table, 

No flow restrictive layers between the surface and water table, 

Single Soil Series Mapping Unit

Less than or equal to 2% topographic slope (generally level), 

Two to five acres in area, and

Sufficient distance from drainage features to ensure stable hydraulic
gradient         conditions.

2.21  Unconfined Aquifer    tc \l3 "Unconfined Aquifer    

Prospective ground-water monitoring studies are designed to monitor the
downward movement of pesticides toward the water table.  The quality of
ground water in shallow, unconfined aquifers where recharge is rapid is
most likely to be affected by pesticide use.  The impact of pesticide
use under these conditions is manifested reasonably quickly.  Under
different conditions, for example, where the aquifer is deep or recharge
is not rapid, it may take several years for the impact of a pesticide to
be measured in ground water.  Therefore, the time it takes for a
pesticide to leach from its point of application to ground water (its
travel time) can be quite variable and highly dependant upon transport
pathways.  It is therefore important to consider the “travel time”
of the tracer or pesticide residues to reach ground water when selecting
a site.  Travel time will most likely increase with increasing depth. 
Thus, the study maybe required to continue for a longer period of time. 
Registrants should therefore consider travel time while the site
selection process is occurring.

Unconfined aquifers are defined here as those where the water table
forms the upper boundary and where no significant low-permeability
layers overlie that boundary.  The water table is defined as the top of
the saturated zone, where the fluid pressure is approximately equal to
atmospheric pressure (Freeze and Cherry, 1979).

2.22  Shallow Depth tc \l3 "Shallow Depth 

Depth to the uppermost aquifer material is an important variable in
determining the vulnerability of shallow unconfined aquifers to
contamination of agricultural chemicals.  Kolpin et al. (1993) stated
that the greater the depth to the top of the aquifer, the smaller the
frequency of herbicide detection.  In Mehnert et al. (1995), study
results showed that the occurrence of agricultural chemicals was higher
when the well depth was less than 30 feet.  Therefore, to determine the
potential for a pesticide to leach during the time frame in which the
study occurs, shallow is defined here to be an average depth to ground
water of less than or equal to 30 feet and the depth to the water table
suggests a recharge zone.  While no specific depth is considered “too
shallow,” sites with shallow water tables may actually have an upward
flux rather than downward flux.  Therefore, professional judgment should
be exercised to avoid picking a site with too shallow a ground water
table.  Sites with drain tiles, drainage ditches, etc. may also need to
be considered for some pesticide uses particularly in those geographic
use areas where they dominate.  As noted above, sites with preferential
flow and tile drains will require specialized protocols which will need
to be reviewed on a case-by-case basis.

2.23  No Flow Restrictive Layers tc \l3 "No Flow Restrictive  Layers 

Sites with soil layers that may restrict the downward movement of water
should be avoided.  Often the definition of restrictive zones is limited
to those layers such as clays and hard pans that restrict downward water
movement.  These are soil layers that normally have low hydraulic
conductivity values (less than 0.5 cm per hour (Soil Survey Staff,
1992).  Soil particle size distribution (texture), soil structure, and
pore size distribution are factors that significantly influence the
leaching of pesticides through the soil profile to ground water (USEPA,
1990).  However, soil layers with highly contrasting soil textures may
also inhibit water flow (e.g., sandy loam overlying a coarse sand or
fine gravel) and should not be considered.  Sites should be carefully
evaluated for soil properties that may inhibit water flow.

2.24  Preferential Flow tc \l3 "Preferential Flow 

Consideration should be given to selecting sites with a documented
history of preferential flow where the pesticide may be used in that
area.  Pesticides which will be used in areas dominated by preferential
flow (i.e. soils with macropores or fingered flow in sandy soils) may
leach faster in these soils than conventional flow transport processes
and may be more representative of a “high exposure” scenario for
that chemical.  The consideration of sites dominated by preferential
flow should be considered on a case by case basis. 

Completion of test pits are a quick and inexpensive method for
evaluating soil variability and determining if preferential flow is
likely to be an important process at a site.  Data collected during a
study may also indicate if preferential flow processes are important. 
Site specific data can answer questions which provide insight into the
presence of preferential flow processes.  Examples of the types of
questions are “did the tracer reach ground water quicker than
expected, or not at all?”, “did pesticide leach to ground water
faster than expected from modeling?”, and “is there variability in
occurrence time and concentration of tracer and pesticide in
lysimeters?”.  The answers to these questions can provide information
which suggests that preferential flow process may, or may not, be
important at a specific site.

2.25  Tile Drains tc \l3 "Tile Drains 

In some instances, a pesticide may be proposed for use in an area
dominated by tile drains.  Site selection should consider the occurrence
of tile drains.  However, care should be used when considering a site
with tile drains.  Installation of tile drains can fundamentally alter
the structure of subsurface soils and result in “artificial”
pathways for leaching.  In no cases, should a site selected with tiles
drains eliminate ground-water monitoring as part of the design due to
the presence of tile drains.  Sampling of tile drains may be considered
as a supplement to the study, but not as a substitute to other required
elements.  The consideration of sites dominated by tile drains should be
considered on a case by case basis.

2.26  Single Soil Series Mapping Unit tc \l3 "Single Soil Series Mapping
Unit 

Single soil series mapping units in the field are desirable to best
define the conditions represented by multiple samples collected over the
extent of the field.  While no field is truly homogeneous, sites can be
selected to minimize site variability and sampling designs can be used
to better understand pesticide fate.  The site should have uniform soil
characteristics in three dimensions: aerially or spatially (same series)
and vertically (similar properties from the soil surface to the water
table).  It is likely to be easier to ensure that soils are uniform
spatially, than that they do not vary with depth.

The study director should at least ensure that each 2- to 5-acre study
site be a single soil mapping unit as defined by the National Resource
Conservation Service (NRCS) (formerly Soil Conservation Service or SCS).
 The mapping unit should be a consociation, which is a delineated unit
dominated by a single soil series and similar soils.  In general, at
least three-quarters of the mapping unit consists of the named soil
series and similar soils (from a hydrologic standpoint).  The total
amount of dissimilar inclusions are generally less than 15 % if the soil
properties are more limiting and  25 % in not limiting (Soil Division
Staff, 1993).

Once a particular study area has been identified, specific soil mapping
units containing the soil series on the candidate site can be found by
consulting county soil surveys published by NRCS.  Refinement of NRCS
maps may be necessary to achieve the level of detail necessary for site
selection and characterization.  The soils maps should be evaluated and
refined as needed by a qualified soil scientist.

In addition to being relatively homogenous over the candidate study
site, the soil physical properties should be consistent with the
conditions the study is intended to evaluate.  For instance, soils
appropriate for high-exposure ground-water monitoring studies should be
among the most vulnerable soils allowed on the product label for a
particular use.  Two types of soils are appropriate in these situations:


Coarse-textured soils with low organic matter content: These soils are
characterized by high sand content, low silt and clay content, and low
organic matter (less than 2%) in the uppermost soil horizons; or

Structured soils with high hydraulic conductivity.

Sites that do not consist of either of these types of soils would be
removed from further consideration.  

The selection of a "typical use" study site would be carried out in a
similar fashion, but the main selection criteria would favor a site
representative of the most common conditions to which the pesticide will
be applied, which might not reflect the highest vulnerability to
leaching.  A determination of the areas with the greatest use cannot be
the sole criterion in the selection of a study site.  "Typical use"
studies will only be requested if there is a question as to whether the
pesticide will leach under those conditions. 

2.27  Low Topographic Slope tc \l3 "Low Topographic Slope 

The site should be as level as possible to minimize runoff or run-on. 
The topographic gradient of proposed study sites should not exceed 2%. 
In addition to slope, the shape of the land surface should also be
considered.  For example, concave land surfaces will encourage
infiltration and convex land surfaces would tend to encourage runoff,
and should therefore be avoided.

2.28  Stable Hydraulic Gradient tc \l3 "Stable Hydraulic Gradient 

It is recommended that study sites not be located within the radius of
influence of irrigation or production wells.  Sites also should not be
located near surface-water bodies or tides that control the direction of
ground-water flow.  The Agency has a concern that surficial water bodies
could cause extreme fluctuations in the direction of ground-water flow. 
Whatever information that might be gained concerning the leaching
potential of a pesticide would be obscured by the effects of outside
influences on the height of the water table and direction of
ground-water flow.  Further information on local conditions may be
obtained from area reconnaissance and an investigation of wells and
surface drainage features on surrounding properties.

2.3  COOPERATOR INTERVIEW tc \l2 "3.  COOPERATOR INTERVIEW 

The third step in the site selection process is to interview farmers
("cooperators") to investigate the history of pesticide use at each site
and to secure permission to use individual fields as study sites.  Once
the registrant has narrowed the search for appropriate study sites to
the county or soil-series level, individual candidate sites can be
identified.  Individual farmers should be contacted about past
agricultural practices and the long-term availability of the site for
extended monitoring.  If the farmer has not owned the property for at
least the past five years, the previous owner should be contacted if
possible to establish additional site history.

2.31  No Prior History of Test Pesticide Use tc \l3 "No Prior History of
Test Pesticide Use 

The history of the site should be known in order to identify use of the
test pesticide, degradates, tracer, or other compounds which could
interfere with analytical procedures or interpretation of the study
results.  Therefore, the registrant should demonstrate that there has
been no use of the test pesticide on the test site during the previous
five-year period.  For pesticides with extremely long half-lives
(greater than six months), study directors should investigate a longer
prior use history (an additional two to five years of site history, when
possible).  

Pesticide use information should be verified using the cooperator's
written records.  In addition, the study director should be thorough in
inquiring if any pesticide spills, pesticide storage near wells, or
other point sources have occurred at or near the site.  In addition,
sites that have received fill material from off-site sources should be
identified due to potential contamination issues.  It is incumbent upon
the study director to fully investigate the site and report results
before the commencement of the monitoring study.  Sites where such
potential point sources occur should be eliminated from further
consideration at this stage.

2.32  Long-Term Availability of Study Site tc \l3 "Long-Term
Availability of Study Site 

Ground-water monitoring studies are typically conducted over a 2 to 3
year period.  The length of the required monitoring period is determined
by several factors, the most important of which is the pattern of
movement of both the pesticide and tracer through the soil column, as
determined by the analysis of pore-water and well-water samples.  The
site owner should be made aware that time estimates are imperfect, and
that study conditions or chemical properties (i.e. very persistent
chemicals) may require the site to be available for more than 3 years. 
Additionally, in cases where leaching of the pesticide is being
investigated at multiple sites or in cases where application to sandy
soils has already been excluded from the registration label, then
studies may need to be conducted at sites where travel times to ground
water are longer.  If a site is not available for a minimum 2 to 3
years, the site should be eliminated from further consideration at this
stage.

2.4  PRELIMINARY SITE CHARACTERIZATION tc \l2 "4.  PRELIMINARY SITE
CHARACTERIZATION 

The fourth step in the site selection process is to undertake a
reconnaissance of candidate sites.  The final result should be a set of
proposed study sites.  Once a set of candidate fields has been
identified and access is secured, preliminary characterization should be
carried out.  This investigation includes estimations of soil
characteristics and variability, a description of site hydrogeology,
identification of topographic and surface features that could impact the
study, and site access considerations.  Utilizing benchmark soil series
as established by the NRCS will provide the registrant with additional
soils data.  Because these Benchmark series fall within a specified
range of criteria and is available in GIS coverage, the spatial
distribution of the soil and the range of properties could be
characterized to identify how vulnerable the site actually is and how it
fits within the entire use area.

 

Information about pesticides used on and near the site should be
gathered to ensure that contamination of the aquifer has not occurred. 
In addition, it is important to ensure that no chemicals were applied
that would be difficult to analytically separate from the test compound.
 The results of these investigations should be submitted to the Agency
in the form of tables presenting the characteristics of the candidate
sites, maps indicating locations of candidate sites, a description of
which sites are most preferred, and why.  The presence of compounds that
interfere analytically with the test pesticide will result in rejection
of the site.  

Ranking of the various sites should be based on how likely each site
would be to meet study guidelines after full characterization.  A small
number of soil samples should be collected for analysis from each
candidate site, with the intent of determining the texture, organic
matter, and permeability of the uppermost soil layers.  Local water
table depth should be determined by consulting the local NRCS office,
examining existing wells on the site, or by installing piezometers.  The
natural configuration of the land surface should also be considered;
sites containing depressions or low-lying areas that could facilitate
ponding should be avoided.  Any additional information that can be
collected during this phase of the characterization should further the
goal of ensuring that a chosen site will be accepted after a more
resource-intensive, full site characterization.

Upon receiving the preliminary site characterization data from the
registrant, EPA will give conditional acceptance of sites that appear to
be consistent with study guidelines.  Full site-characterization can
then commence.

2.41  Absence of Dominant Fracture Flow tc \l3 "Absence of Dominant
Fracture Flow 

The hydraulic gradient, the configuration of the piezometric (or
potentiometric) surface, and textural variations in the aquifer media
are typically used to estimate the average direction and velocity of
ground-water flow.  This technique is not appropriate for the
determination of ground-water flow and velocity in karst or highly
fractured regions.  For this reason, areas where prevalent ground-water
flow occurs along karst or fracture-flow features are generally
unacceptable for highly vulnerable study sites, unless significant use
of the pesticide is anticipated in such an environment.  Special
monitoring techniques should be planned for such situations.  

CHAPTER 3 - SITE CHARACTERIZATION AND CONCEPTUAL MODEL tc \l1 "CHAPTER
3 - SITE CHARACTERIZATION AND CONCEPTUAL MODEL 

Interpretation of the results of a prospective ground-water monitoring
study largely depends upon whether the hydrogeology of the study site is
adequately understood.  Site characterization data are necessary to more
accurately assess site vulnerability, thereby placing into context
results of the study relative to conditions throughout the pesticide use
area.  

Site characterization includes a description of topography at the site
and in the vicinity, soil characteristics, and vadose and saturated zone
hydrogeology.  Descriptions of agronomic practices (including irrigation
and tillage) and climate (rainfall frequency, amount, and seasonal
distribution) are also fundamental.  This information is needed before
monitoring equipment is installed.  Information collected in this phase
of the study may be used as input parameters for computer models.

A conceptual model should be developed to understand how the site
characteristics may affect the fate of the test pesticide.  This model
involves the analysis and interpretation of data collected during site
characterization for soils, the vadose zone, and the saturated zone. 
Various methods exist to compile, analyze, and present these data in
both graphical and tabular form.  Visual displays of data are usually
the most convenient and useful for presenting site characterization
data.  Once the flow system is understood, and the conceptual model is
developed, a monitoring plan can be designed that is suited to the study
site (Chapter 4).

Site characterization activities are divided into four steps.  These
steps are described in detail in the following sections:

Existing Local Data and Base Map

Soil and Vadose Zone Investigation

Saturated Zone Investigation

Conceptual Model 

Products of site characterization are:  1) a summary of existing local
data; 2) a detailed base map; 3) site- specific characterization data;
and 4) a conceptual hydrogeologic model of the site.  All these data and
the conceptual model should be summarized and described in the Site
Characterization Report (Chapter 5).

3.1  EXISTING LOCAL DATA AND BASE MAP tc \l2 "1.  EXISTING LOCAL DATA
AND BASE MAP 

The first step in the site characterization process is to gather all
available information about the geology, topography, soils, hydrology,
climate, and agricultural practices that could affect the fate and
transport of the pesticide at the study site.  These data are used to
characterize the local hydrogeologic and agricultural conditions, and
relate site-specific conditions to the regional framework.  The base map
of the study site provides a spatial reference for all site
characterization information and monitoring results.

3.11  Compile Existing Local Data tc \l3 "Compile Existing Local Data 

A description of the regional hydrogeology is important background
information for developing the conceptual model of flow and transport at
the study site.  An understanding of the hydrogeologic framework is
typically needed to interpret the results of monitoring and to
understand field observations.  

Soil is a primary factor in regulating whether rainwater runs off or
infiltrates.  Data obtained from soil surveys are used to create maps of
soil classes, where average values of soil properties are estimated
within a defined region of a mapping unit (Webster, 1985; Cambardella et
al., 1994).  Thus, an initial set of possible study site locations can
be determined in part with a published United States Department of
Agriculture (USDA) Soil Conservation Survey.  Site-specific soil
characterization and delineation, in addition to the Soil Survey, will
normally be necessary.  

The timing and intensity of rainfall has a strong impact on the
transport of pesticide residues off a field due to leaching or runoff. 
National Oceanic and Atmospheric Administration (NOAA) has a nationwide
system of weather stations that measures rainfall and computes
statistics (averages, return frequencies).  During the course of a
prospective ground-water study, an onsite weather station to measure
rainfall amount and intensity, soil and air temperature and pan
evaporation is strongly recommended.  Historical rainfall at or near the
study site should be determined to ensure that water input during the
study is consistent with historical data.  A water balance should be
developed to provide an estimate of the net historical recharge at the
site.

3.12  Develop a Base Map tc \l3 "Develop a Base Map 

An accurate base map of each study site should be developed to provide a
spatial reference for site characterization observations and for
subsequent monitoring data.  The base map should fully represent the
significant features of the study site and the surrounding area;
particularly those that may affect ground and surface water flow
systems.  It is strongly recommended that all base maps include:  

The location of the test site by latitude and longitude (and by township
range, and section).  The use of more exact methods, such as a Global
Positioning System (GPS) or standard survey methods should also be
considered,

The location of nearby roads, surface water bodies, fences, and
municipal boundaries,

The location of nearby wells (including identification of irrigation
source), canals, and drainage systems,

The date the base map was developed and the sources of base map
information,

The organization and individual responsible for the base map,

The area and slope of the control plot and test plot,

Ground surface elevations and topographic features in the vicinity of
the study site, and

Map scale, map title, county name, and complete legend including
topographic contour interval, explanation of map symbols, and north
arrow.

Detailed information on site topography is needed to identify areas
within a field where leaching is more likely to occur.  Although a study
site should have a low slope overall, small-scale natural variations in
slope within a field can direct the flow of water to runoff or cause it
to pond. Identification of these areas is important for developing a
conceptual model of the site, and in interpreting results of monitoring.
 We strongly recommend surveying the study site and adjacent areas to
provide elevation data at a one foot or less contour interval (depending
on the slope of the site).  

Base maps are used to record the locations of all pertinent study
features and sampling sites  including the location of soil cores,
infiltration tests, piezometers, monitoring wells, lysimeters, drinking
and irrigation wells, buried drainage tiles, weather stations, pesticide
mixing and loading areas, pesticide storage facilities, disposal areas,
and buildings.  In addition, the location of a control area
hydrologically upgradient of the study site should be identified and
located on the base map, as well as a site for the test pit excavation. 
The Site Characterization Report should include this base map.

3.13  Information Sources tc \l3 "Information Sources 

Sources of information on soils, geology, hydrology, topography and
climate include:  local experts, USDA agricultural extension service,
the USGS and state geologic surveys, USDA NRCS soil surveys, and the
NOAA climatic databases.  Information on pertinent surficial features
obtained from aerial photogrammetric surveys may also be of use in base
map development.  State transportation departments, environmental
protection departments, and county planning departments often maintain
such information for land areas under their jurisdiction.  Private
companies may also be a source for aerial photogrammetric information in
some areas.  

3.2  SOIL AND VADOSE ZONE INVESTIGATION tc \l2 "2.  SOIL AND VADOSE ZONE
INVESTIGATION 

Soil structure and variations in soil texture, surficial geology,
topography, hydrology, and the impact of years of agricultural practices
(e. g. tillage, irrigation, drainage structures) influence the extent to
which  precipitation or irrigation will infiltrate or runoff from a
field.  If site characterization is inadequate, these real-world
complexities will limit the interpretation of the monitoring data. 
Thus, characterization of the subsurface is fundamental and necessitates
substantial sampling, particularly between the soil surface and the
saturated zone.  The following sections group the investigation into two
categories: an exploratory coring program in which sampling and testing
occur throughout the study site, and a test pit excavation, located
adjacent to or near the study site.  The sections below describe
parameters that should be characterized during the coring and test pit
investigations.  There is significant flexibility as to which methods
can be used to measure the parameters for site characterization.  The
emphasis is on performance-based methods as dictated by site specific
conditions.  Techniques are to be approved by the EPA prior to use.  

3.21  Exploratory Coring Program and Field Testing  tc \l3
"Exploratory Coring Program and Field Testing  

All site characterization programs should include an exploratory coring
program to directly investigate and characterize the vadose zone.  The
purpose of the exploratory coring program is to obtain information about
selected soil properties which reflect a soil's capacity to hold and
transmit water, to bind or retain a pesticide, and to degrade or
transform a pesticide; or those factors which considered together affect
a pesticide's mobility and persistence at a specific study site.  The
soil coring program is also a means to assess the vertical and
horizontal homogeneity of these parameters across a study site.  Data
collected from exploratory coring is used to develop an initial
conceptual model of subsurface conditions at the test site.  In this
phase of the study, soil heterogeneities or barriers to leaching not
discovered in preliminary site selection can be identified.  Before
initiation of the exploratory coring program, an effort should be made
to identify and locate utilities, irrigation systems, tile drains, etc.
to avoid damage and costly repairs.   

At least one continuous soil core (from the surface to the water table)
from at least eight locations throughout the study site, as well as one
continuous core from a control area assumed to be up-gradient of the
study site, will be collected.  A detailed drilling log should be
prepared by a trained soil scientist or geologist to describe the
texture, color, structure, and moisture content of the soils as they are
collected over the complete core.  Methods for collecting soil samples
(such as split spoon or thin-walled Shelby tube) can be found in the
open literature.  A soil core log should give special attention to
confining layers, abrupt changes in texture or color, and other features
needed to characterize the physical and chemical properties of the
vadose and saturated zones.  In addition, depth to the water table
should be recorded.

Soil sub-samples should be taken from each core for laboratory analysis.
 Special attention is to be paid to the top six feet of the soil column,
to allow comparison with NRCS soil surveys (which describe soils to a
depth of six feet).  The top six feet of the core should be divided into
either six-inch intervals or by soil diagnostic horizon, whichever is
less.  Emphasis is placed on the surface six feet because soil texture,
porosity, structure, and organic matter content have a large influence
on the persistence and mobility of the applied pesticide.  Below the top
6 feet of the soil core, sub-samples should be collected every four
feet, except when a visible change in soil properties (color, texture,
structure) is observed.  In this case, at least two sub-samples should
be taken from the 4-foot interval, to characterize the differences
between soil types.  Each sample should be described in the field by an
experienced geologist and/or soil scientist.  In addition, all soil
sub-samples should be analyzed for the following information:

soil texture class, particle density, bulk density, porosity, fraction
sand, fraction silt and fraction clay,

organic matter content or organic carbon content,

field capacity (1/3 bar), 1 bar, 5 bar, and wilting point (15 bar) (all
measured on undisturbed soil samples),

saturated hydraulic conductivity,

hydraulic conductivity vs.  soil water content and matric potential,

field soil water content, residual water content and saturated water
content,

matric potential vs.  soil water content (water characteristic function)

Munsell color (specify moisture condition, i.e., wet or dry), and

pH and cation exchange capacity or anion exchange capacity (if
appropriate).

These samples should not be composited.  Compositing of samples
precludes obtaining information about the variability of these important
parameters across the field.  Standard methods for the parameters listed
above are available from ASTM and are described in Mason (1983), Klute
et al.  (1986), Jury et al. (1991) and Wilson et al.  (1995).
Consideration should be given to conducting these tests on undisturbed
samples where possible.

The compounds of interest (ie. pesticide, degradates and tracer), should
also be analyzed for from soil collected in each horizon to ensure there
has been no prior use of these compounds at the study site.  If the test
compound has not been registered, this need not be done.  

3.22  Number and Locations of Soil Cores tc \l3 "Number and Locations of
Soil Cores 

Given that the study will be conducted in a field that is approximately
two to five acres in size, a minimum of eight soil cores are needed to
characterize the vadose zone.  A greater number of cores will likely
increase the reliability of interpretations of subsurface conditions.

There are a number of ways of determining where these soil cores should
be collected.  The most important factor to consider is that core
locations be distributed throughout the field in such a manner that a
strong conceptual model can be developed.  This can be accomplished by
locating the cores randomly, along a grid, or stratifying them according
to some predetermined criterion.  The grid may be oriented perpendicular
or parallel to the ground-water flow field.  The field may be segmented
into sectors, gridded and cores randomly located in each sector.  If
piezometers will be installed at core locations, these locations should
be located at or near the corners of the study site.  

Coring methods should be selected based on consideration of the
anticipated textures of the vadose and saturated zones, the anticipated
borehole depth, stability of the borehole, and ease of collection of
samples for analysis.  Drilling methods appropriate for these
considerations are described in the ASTM standards manual.

3.23 Field Testing tc \l3 "Field Testing 

The description or prediction of processes which influence pesticide
dissipation, specifically leaching, in the field requires an
understanding of infiltration, recharge, and internal drainage (water
redistribution).  Thus there is a need to characterize soil hydraulic
properties, such as soil water content, matric potential vs. soil water
content (water characteristic function) relationships and hydraulic
conductivity.  Because soils in a field are typically heterogeneous,
solute transport is controlled by properties which vary both spatially
and temporally, and these are also often scale dependant.  Therefore, it
is important that these parameters be measured in the field.

In these two to five acre study sites, we recommend that the saturated
and unsaturated hydraulic conductivity be measured at a minimum of six
locations dispersed across the study site (and indicated on the site
base map) to take into account field variability of soils.  If
significant variability in hydraulic conductivity is evident, then
measurements should be made in additional locations to further define
the range of variability across the site.  In general, measurements are
made for at least two depth horizons at each measurement location - one
at the soil surface and for each soil horizon below the surface to a
depth of six feet.  The soil water content should also be measured at
these sites from the surface to the water table.  These data will be
correlated with the water characteristic function determined in the lab
and the matric potential will be estimated for these locations.  The
matric potential indicates the direction of water movement in the vadose
zone.  The field determined soil water content will also be correlated
with the hydraulic conductivity and compared to the lab results from the
soil cores.  This will provide insight into how well the results of the
lab tests represent actual conditions in the field.  Consideration
should also be given to developing breakthrough curves to determine
dispersivity and the likelihood for preferential flow and to estimate an
effective porosity for soil samples.

3.24  Preservation and Transportation of Formation Samples  tc \l3
"Preservation and Transportation of Formation Samples  

ASTM provides guidance for preserving and transporting soil samples for
analysis.  Although some flexibility in these procedures might be
necessary due to the practical considerations in sampling a farm field,
certain procedures should be followed in every case.  The field
personnel should follow all relevant Department of Transporation (DOT)
and International Air Transport Association (IATA) hazardous materials
and dangerous goods regulations concerning the shipping of dry ice. 
These samples should be sent by overnight mail the day they are
collected, or kept frozen until they arrive at the laboratory.  

3.25  Quality Assurance and Quality Control Procedures  tc \l3 "Quality
Assurance and Quality Control Procedures  

Procedures for ensuring the quality of all soil samples and the data
derived from those samples are an integral part of the exploratory
coring program.  Mason (1983) and Barth et al. (1989) present details on
quality assurance for soil and formation sampling activities.  Good
laboratory practices relevant to field investigations should be
followed.  

All soil core logs and subsurface descriptions recorded during the
drilling operation should be included in the Site Characterization
Report.  State or local regulations concerning the permitting and/or
documentation of exploratory coring activities should be followed. 
Chain-of-custody forms should be prepared and archived for all
subsurface samples, and subsurface samples that are not destroyed by
analytical procedures should be retained as reference samples for the
duration of each study.  

3.26  Test Pit Excavation tc \l3 "Test Pit Excavation 

The Agency views the completion of test pit excavations during the
initial phases of the site characterization process as a quick and
inexpensive way to assess the heterogeneity of a site and the potential
for preferential flow.  The 1998 Scientific Advisory Panel (SAP)
identified the presence of preferential flow as a critical element to be
assessed in the site selection/site characterization process.  If a
pesticide is to be used in an area dominated by preferential flow (e.g.
in a karstic region or with extensive tile drainage) then site
characterization should evaluate this process and consider sites with
documented preferential flow.  The completion of test pits at the
subject site is a quick and inexpensive way to assess whether
preferential flow is likely (at least in the near surface) at a site. 
Unusual conditions which may prove problematic for a Prospective
Ground-Water Study (i.e. restrictive layers) can quickly be identified
and result in significant cost savings.  Test pits may also be
considered during the course of the study when unusual conditions are
noted.  Test pits should not be located within the active monitoring
area but should be located in close proximity to the area of pesticide
application (i.e. immediately adjacent to the site or within a control
plot).

Test pit excavations are particularly useful in characterizing the
lateral extent or thickness of low-permeability layers noted during soil
survey and exploratory boring activities or in identifying dominant
patterns at a site (Mason, 1983).  Soil structure or other features that
may result in significant preferential flow should be noted and
reported.  Such features are common and should be investigated through
use of test pits when considering a site.  The excavation should be
located adjacent to or near the area of the site where the compounds of
interest are to be applied and monitored.  The locations of the test
pits should be indicated on the base map.  The walls of the test pits
should be described using methodology and nomenclature which is
consistent with the Soil Survey Manual (Soil Survey Division  Staff,
1993), Soil Taxonomy (Soil Survey Staff, 1975), and Keys to Soil
Taxonomy (Soil Survey Staff, 1992).  Photographs of pit walls could also
be considered.  

Field workers should take care when entering a test pit to characterize
soil properties.  All test pit activities should be conducted under the
supervision of an Occupational Safety and Health Administration (OSHA)
required “competent person”.  OSHA standards state that test pits
should not be excavated to deeper than five feet unless a shoring system
(e.g. trench box or trench shield) is installed to support the pit
walls.  However, since the stability of pits five feet deep and
shallower can also vary with soil texture and moisture, safety
precautions should be considered in these scenarios as well.  Proper
abandonment procedures for test pits should be undertaken and documented
in the First Quarterly Report.  

3.27  Abandonment of Soil Core Holes  tc \l3 "Abandonment of Soil Core
Holes  

Characterization of the shallow saturated zone requires the installation
of at least four piezometers.  Some of the cores drilled for soil
characterization may be converted into piezometers.  The holes created
by soil coring that are not converted to piezometers should be properly
abandoned prior to the application of the compounds of interest. 
Guidance on proper abandonment of soil coring locations may be found in
Aller et al. (1990) and American Water Works Association (1984).  Boring
abandonment procedures should also comply with any state or local
regulations for agricultural fields.  If additional fill material is
required to complete the abandonment process, “pesticide-free” soil
should be used.  

3.3  SATURATED ZONE INVESTIGATION  tc \l2 "3.  SATURATED ZONE
INVESTIGATION  

A limited investigation of the saturated flow regime should be conducted
for each study site.  This information is needed to develop the
conceptual model and to interpret monitoring data.  The following
sections describe the recommended procedures for characterizing the
ground-water flow characteristics of the aquifer.  These procedures
include collecting hydraulic head data and conducting pumping tests
and/or slug tests.  The data derived from these activities are then used
to estimate the direction of ground-water flow, the hydraulic
conductivity of the aquifer, and the ground-water velocity at the study
site.  

3.31  Hydraulic Head tc \l3 "Hydraulic Head 

Piezometers should be installed at the site to measure the hydraulic
head.  If done simultaneously, piezometers may be placed in the same
borehole where the exploratory soil cores were collected, to save
resources.  At least four piezometers should be installed at the corners
of the study site to establish the water-table surface.  These
piezometers should remain in place for the duration of the study so that
these simple measurements can continue to be made.  Since suitable sites
for ground-water monitoring studies should exhibit low topographic
relief, small errors in surface elevation measurements can seriously
impact the interpretation of subsurface conditions.  Therefore, care
should be taken to measure and record elevation data accurately.  A
small cut or indelible mark should be placed on the piezometer well
casing for use as a measuring point (MP), and this point should be
surveyed relative to the local U.S. Geodetic Vertical Datum.  The
location and height of this point should be measured to an accuracy of
plus or minus 0.01 foot.  

Procedures for measuring depth to water in monitoring wells are detailed
in ASTM Standards.  Initial measurements of water levels should not be
collected until after the piezometer or well has had time to stabilize
from the effects of construction and development activities.  Piezometer
locations should be specified on the base map, and initial water level
data should be presented on a map in the Site Characterization and
Monitoring Plan Report.

3.32  Direction of Ground-Water Flow and Hydraulic Gradient tc \l3
"Direction of Ground-Water Flow and Hydraulic Gradient  

A map of the potentiometric surface of the surficial aquifer should be
prepared for each study site.  This map should use the site base map for
location information and should include the locations of piezometric
head measuring points.  Contour lines representing equal hydraulic head
should be constructed.  Methods for constructing water-table maps and
estimating hydraulic gradient and ground-water flow direction from these
maps are provided in Freeze and Cherry (1979).

3.33  Hydraulic Conductivity tc \l3 "Hydraulic Conductivity 

The hydraulic conductivity of an aquifer controls the rate at which
ground water flows under a given hydraulic gradient.  The velocity of
the ground water can be used to approximate how long it will take a
conservative tracer (or pesticide) to travel beyond the test site
boundaries.

Hydraulic conductivity is typically measured in the field by means of
slug tests or pumping tests. Slug tests should be conducted at locations
where the soil cores indicate very low hydraulic conductivity aquifer
materials.  A pumping test under these conditions is usually not
possible because the yield of the aquifer is too small to collect
sufficient data to analyze using typical methods.  Slug tests sample a
very small region around the well and the results only represent the
aquifer properties in that region.  Therefore, they are of limited value
and one should be done at every well.  Pumping tests should be used when
the hydraulic conductivity values are large enough to collect sufficient
data to analyze using typical methods.  Pumping tests sample a much
larger region of the aquifer and give a more representative hydraulic
conductivity value for the aquifer.  Also, fewer pumping tests would
have to be conducted because they do sample a much larger portion of the
aquifer.  Methods for conducting and analyzing slug tests and pumping
tests are provided in Freeze and Cherry (1979), Walton (1987) and Fetter
(1988).  The results and interpretations of all slug tests and pumping
tests should be included in the Site Characterization Report.

3.34  Background Water Quality tc \l3 "Background Water Quality 

Basic data should be collected to establish the background quality of
ground water, irrigation water and precipitation at the study site. 
Analyses should include major ions (dissolved oxygen, alkalinity, etc.),
major nutrients (nitrate, nitrite, ammonia, organic nitrogen, and
phosphate), temperature, electrical conductivity and pH.  Additionally,
water should be analyzed for the test compound (to ensure that there are
no residues, and to check the analytical method) and the tracer compound
(typically bromide).

 

If the irrigation source is a well within a quarter mile of the test
plot, the study director should determine if pumping this well has any
effect on the water table below the test site.  This can be accomplished
by using a data logger probe in the monitoring well nearest the
irrigation well, and monitoring any drawdown of the depth to water when
the irrigation well pump is turned on.  Ensure that the irrigation well
is run long enough to ensure communication with the underlying aquifer.

3.4  CONCEPTUAL MODEL tc \l2 "4.  CONCEPTUAL MODEL 

Site characterization data are analyzed and interpreted to produce a
three-dimensional representation of the characteristics of the study
site.  The site-specific conceptual model should include graphical
displays of interpreted hydrogeologic characteristics that illustrate
the relationship between soil and hydrogeologic features.  The
conceptual model should be discussed with reference to graphs, figures,
and maps and the data collected during site characterization.  The
discussion should integrate site hydrogeology, surface hydrology, and
historical climatic data.  The minimum graphical tools and analyses
needed to develop the model are described in the following sections.

3.41  Soils and the Vadose Zone tc \l3 "Soils and the Vadose Zone 

The results of the soil analyses including preliminary surface
investigations and NRCS information, exploratory coring program, and
test pit excavation should be analyzed and integrated.  At a minimum,
the following are needed to interpret these data:  

At least two stratigraphic cross sections (or fence diagrams) for each
study site, one parallel to the direction of ground-water flow and one
perpendicular to ground-water flow,

A detailed map of surface soils (1:100 to 1:1,000),

Graphs or tables of particle-size distribution vs.  depth for each core,

Graphs or tables of matric potential head vs.  depth and soil water
content, 

Graphs or tables of hydraulic conductivity vs.  soil water content,

Graphs or tables of organic matter content vs.  depth for each core,

Tables and/or graphs that display ranges of hydraulic conductivity,

Ranges of bulk density and hydraulic conductivity values for significant
subsurface horizons,

An estimate of the amount of water needed for the tracer to reach ground
water in two years and

An estimate of travel time needed for the tracer and/or pesticide to
reach ground water.

A brief discussion of the above information should identify areas in the
study site (at the surface or at depth) where variations in topography,
soil texture, or other factors could cause differences in recharge.  All
data analysis techniques and the results of those techniques should be
documented in the Site Characterization Report.

3.42  Saturated Zone and Water Quality tc \l3 "Saturated Zone and Water
Quality 

The results of saturated zone investigations and background water
quality analyses are used to interpret the subsurface hydrogeology of
the site.  At a minimum, the following are needed to interpret these
data:

Contour map of the water table surface indicating the direction of
ground-water flow,

Analyses of slug tests and/or pump tests

Estimate of hydraulic gradient and flow velocity of the aquifer,

Comparison of the spatial distribution of hydraulic conductivity using
data obtained from laboratory and field investigations,

Graphical display of water quality data from the onsite wells, the
irrigation source and precipitation and

Sample chromatogram from an analysis of the test compound(s) and tracer
in onsite water.  

These and other data analysis techniques and the results of those
techniques should be documented in the Site Characterization Report. 
The discussion accompanying these data should address water table
fluctuations based on the collection of local historical data.  Regional
recharge and discharge areas should also be discussed, including nearby
features such as irrigation wells and canals that could influence the
flow system.  The discussion should also include a description of the
variations in hydraulic conductivity, the presence of confining layers,
and the overall aquifer flow system at the site, using historical data
where necessary.  Any interferences identified when analyzing the water
collected at the site should also be discussed.



CHAPTER 4 - MONITORING PLAN DESIGN tc \l1 "CHAPTER 4 - MONITORING PLAN
DESIGN 

Once the site has been characterized, the variability of soil properties
and the ground-water flow system are understood, and a conceptual model
developed, a monitoring plan can be designed that is suited to the study
site.  The number of wells and other sampling devices required to
provide a high degree of statistical certainty in the study results
would likely prevent the cooperating farmer from growing a crop on the
field using standard agronomic practices, and would make the study
prohibitively expensive.  However, with a good conceptual model and a
reasonable number of sampling locations, monitoring data will be
adequate to answer regulatory questions.  The clear advantages of
testing a pesticide in the field under conditions that as closely as
possible resemble those in which it will actually be used, as discussed
in Chapter 1, outweigh any disadvantages.  Additional tools such as
lysimeters and computer models can provide useful data to augment the
field data obtained.  It is strongly recommended that studies be
conducted under FIFRA GLP, as described in 40CFR160.  Written standard
operating procedures (SOP) should be developed and maintained by the
study director.

The compounds of interest (Chapter 2) will be monitored in surface
soils, the vadose zone, and the saturated zone.  A conservative tracer
will be used to follow water movement through the system and weather
will be monitored throughout the study.  Aspects to consider, and
minimum data collection needs, are described in the following sections:

Setting Up

Soil Monitoring Plan

Soil Water Monitoring Plan

Ground-Water Monitoring Plan

Design decisions should be integrated into one Monitoring Plan Design
Report for the Prospective Ground-Water Monitoring Study.  

4.1  SETTING UP tc \l2 "1.  SETTING UP 

4.11  Agricultural Management Practices tc \l3 "Agricultural Management
Practices 

Standard agricultural practices for the target crop and the intended use
of the test pesticide should be followed while conducting the
Prospective Ground-Water Monitoring Study.  All pesticides, fertilizers,
and farming, maintenance, and sampling equipment should be stored away
from the study site so as to eliminate the possibility of contamination.
 

4.12  Irrigation tc \l3 "Irrigation 

The following guidelines assume that leaching of the pesticide is being
investigated at a site selected because conditions exist at that site
that are more likely to promote ground-water vulnerability and will
provide data on the leaching of the pesticide under those conditions. 
Some alterations may be approved in the irrigation scheme at selected
sites when leaching at multiple sites representing different levels of
ground-water vulnerability is being investigated.  Irrigation should be
scheduled at regular intervals, as well as applied at critical periods
in the growing season, to meet the target water input.  The initial
irrigation event should be scheduled to occur within three days after
the pesticide application, unless sufficient precipitation occurs during
this time.  Following the first irrigation event, dates should be
established when additional water will be applied to the field if
monthly targets of total applied water are not reached as a result of
natural precipitation.  The schedule should be flexible enough to ensure
that adequate water is applied to meet the needs of the crop,
particularly in critical moisture periods (such as the period of
tasseling through silking for corn, or during fruit development for
orchard crops).  The Monitoring Plan Design Report should indicate the
irrigation method, rate, schedule, and duration.  Actual dates of
irrigation events should be documented and reported in the Final Report.
 

Estimate target water requirement by month (120% of crop water demand or
120% of historical rainfall data, whichever is greater).  These goals
should be maintained at the study site through each and every agronomic
season starting from the initial pesticide application date throughout
the entire monitoring period for the study unless alternate goals are
agreed to by the Agency during the latter years of the study.
Calculations for target water requirements should be based on 20-year
data distributions (crop, study site/region, rainfall, irrigation, etc).
 Document calculations, assumptions, and reference 20-year data used in
determining target water demand.  Procedures used to determine the
timing and amounts of water as a function of rainfall and other climate
conditions should be provided.  The type of irrigation system, the
frequency of irrigation, and the minimum amount of irrigation applied
should conform with local agronomic practices for the specific crop and
study soil.  All irrigation events should be conducted so as to minimize
surface pooling and runoff while maximizing the potential for
infiltration.  

4.13  Initial Post-Pesticide Application Irrigation Event tc \l4
"Initial Post-Pesticide Application Irrigation Event 

In general, the timing and rate of irrigation is more important during
the initial days and weeks after application than it is as the study
progresses into the second year and beyond.  The relationship between
rainfall timing and intensity and pesticide leaching has been reported
by a number of researchers (Isensee et al, 1990; McLay et al., 1991,
Shipitalo et al., 1990; Sigua et al., 1993;1995).  Since rainfall is
both spatially and temporally variable, it is necessary to supplement
rainfall so that a study can be conducted within a reasonable time
period.  Therefore, it is recommended that an initial irrigation be
applied to the study area within three days after the pesticide
application.  

After initial pesticide application, a minimum of 1.0 inch of natural
rainfall or irrigation should occur within 3 days and the application
rate should be between 0.5 and 1.0 inches per hour.  The first month’s
targeted rainfall plus irrigation amounts should be divided into four
periods of 7-8 days each, and at least one fourth of the target monthly
water requirement should occur in each of the four periods (apply
additional irrigation water amounts in increments of 0.3 inches or
greater as needed to meet the total month’s targeted amount).  

4.14  Irrigation After Initial Event tc \l4 "Irrigation After Initial
Event 

The intent of the Prospective Ground-Water Monitoring Study is to
evaluate a pesticide’s potential to contaminate ground water and to
provide an idea as to the concentrations that could be seen in ground
water through normal agricultural activities.  It is therefore necessary
that enough water be added to the site so that ground water is recharged
during the study.  Due to the stochastic nature of precipitation, to
rely strictly on precipitation may result in the study having to be
conducted for many years.  Thus irrigation can be applied to reduce the
length of time that a study may need to run.

Beginning with the second month after application, at least the target
water requirement for the specific month (as specified in
Agency-approved Monitoring Plan Design report) should occur either in
the form of natural rainfall or applied as irrigation.  Irrigation does
not have to be applied when the crop is not present.  For example,
irrigation should not be applied during winter months when freezing
would destroy irrigation equipment.  On occasion, at sites where
precipitation has fallen well below historical norms for months or
longer, some irrigation water might be applied during fallow months in
order to meet the previously established water balance targets. 
Irrigation is not required at times when damage to the crop would occur
(during times when drying is essential).  

Sprinkler irrigation is preferred except in instances where other
crop-specific methods (flood irrigation as an example) are required to
assess movement under typical agronomic practices.  Documentation should
be provided, including references and names, for such crop-specific
irrigation practices.  

4.15  Mixing and Loading Area tc \l3 "Mixing and Loading Area 

The location of pesticide mixing and loading activities should be
identified on the base map.  Ideally these activities should take place
down gradient and down slope from the site to minimize the possibility
of point-source contamination.  Other activities that could take place
in this area include calibration of the sprayer equipment with water,
sampling of the application (tank) mixture, and sampling equipment
cleaning.

4.16  Control Plot tc \l3 "Control Plot 

To establish background ground water quality, at least one well should
be placed hydraulically up gradient of the field where the test
pesticide will be applied.  Control plots should be planted and
maintained the same as the treated field.  Control wells should be
sampled on the same schedule as monitoring wells in the treated field. 
The control area and control well location(s) should be identified on
the base map.

4.17  Decontamination Area  tc \l3 "Decontamination Area  

Prior to sampling soils or ground water, equipment should be cleaned to
minimize the likelihood of cross-contamination.  This should be done far
enough away from the study site so that activities and onsite disposal
of rinsate will not affect study results.  The decontamination area
should be identified on the base map.  Additionally, rinsate should not
be disposed of in “ecologically sensitive” areas, such as wetlands
or down other wells.

4.18  Weather Station tc \l3 "Weather Station 

Onsite climatic monitoring is essential in evaluating pesticide leaching
relative to the timing and magnitude of precipitation.  Precipitation
data are also needed to determine the required amount of monthly
irrigation.  Daily rainfall amount and intensity, pan evaporation, and
temperature data are also key input parameters for several computer
simulation models.  A variety of automated weather stations and data
logging equipment are commercially available that record daily
precipitation, pan evaporation, wind speed, solar radiation, minimum and
maximum air temperature, and soil temperature.  Special care should be
taken to protect parts of the weather station that can easily be damaged
by birds and other animals, such as rain gauges and evaporation pans.  

4.2  Application of Pesticide and Tracer tc \l3 "Application of
Pesticide and Tracer 

4.21  Pesticide tc \l4 "Pesticide 

Decisions about pesticide application rates are made when the study
scope is defined.  Application method, calibration procedures and the
amount applied should be documented for the test pesticide and reported
in the Site Characterization and Monitoring Plan.  Only one application
of the pesticide should be made.  The tank mixture should be sampled and
the concentration confirmed.  The pesticide application rate should be
verified using pan samplers, shallow soil samples, application cards or
other in situ collection devices.  Nominal and actual application rates
should be reported.

4.22  Tracer tc \l4 "Tracer 

A conservative tracer should be applied along with the test pesticide to
provide information on the direction and rate of movement of water
through the vadose and saturated zones.  

When selecting a tracer, the chemistry of the compound should be
considered along with potential sources of background interference,
achievable detection limits, and potential losses due to adsorption,
volatilization, and plant uptake.  Bromide and chloride have typically
been used to trace the movement of soil water in agricultural studies. 
Other tracers may be acceptable if approved by EPA.  

Appropriate tracer application rates should be determined prior to
initiation of the study, taking into consideration analytical methods
and limits of detection and quantification, and concentrations in
background soil and water samples (higher background levels of bromide,
for example, at a study site can interfere with the ability to track the
subsurface movement of the ion unless a relatively high initial
application rate is used).  Analytical methods, calibration procedures
and amount of tracer applied should be documented and reported in the
Monitoring Plan Design and Final Reports.  The tracer should only be
applied once at the same time as the initial pesticide application.

4.3  SOIL MONITORING PLAN tc \l2 "2.  SOIL MONITORING PLAN 

The primary purpose of soil sampling in these studies is to verify
pesticide application rate and to provide information on the dissipation
of the compounds of interest in the zone of application, and not to
track the movement of the test compound through the subsurface. 
Experience with prospective studies over the past 10 plus years
indicates little correlation between pesticide detections in soil cores
and detections in ground water.  Some subsurface soil samples are
collected early in the study to identify residues that remain in top
meter of the soil column, above the uppermost lysimeters.  Deeper
vertical transport will be tracked using suction lysimeters and wells
and not soil cores.  Soil samples are to be analyzed for residues of the
test pesticide, degradates, and tracer compounds.  The soil moisture
content should be measured for each sample collected.

4.31  Soil Sampling Methods and Instrumentation  tc \l3 "Soil Sampling
Methods and Instrumentation  

Soil samples to verify the application rate should be collected using
methods that ensure that pesticide-free soil does not dilute the samples
to which the pesticide has been applied.  When the pesticide is applied
as a spray, soil samples for application verification should be
collected from the surface soil without adding deeper pesticide-free
soil.  In this case, a sampler such as the box sampler will allow the
collection of a wide (30 cm) and shallow (8 cm) sample.  If the
pesticide is soil incorporated, the initial soil samples should be
collected to the depth of the disturbed zone.  If a banded application
is used, soil samples should be collected in the band to the depth of
the disturbed zone.  To avoid discarding any of the applied pesticide,
surface plant residue should not be removed from these samples.  

4.32  Number and Location of Soil Cores tc \l3 "Number and Location of
Soil Cores 

A sufficient number of soil samples should be collected from a study
site to qualitatively demonstrate the variability in pesticide
application rates across the study site.  The distribution of soil
sampling locations across each study site should be dictated by the
method of pesticide application and the degree of soil homogeneity on
the site.  For example, the collection of a minimum of 15 individual
soil cores is required at each sampling period for a 2- to 5-acre study
site with relatively homogeneous soil conditions.  Sites that exhibit
marked soil heterogeneities will require a greater number of soil
samples.  

4.33  Soil Sampling Timing and Frequency  tc \l3 "Soil Sampling Timing
and Frequency  

In general, soil samples should be collected until a pattern of
persistence or decline of the compounds of interest has been
established.   Soil cores collected during the first two soil sampling
rounds (pre-application and immediately post-application) should only
sample surface soil.  Shallow soil cores (0 - 10 cm) should be collected
during rounds 3 and 4.  Slightly deeper cores (0 - 100 cm) may be
collected following the initial irrigation event, or earlier if a
precipitation event occurs.  Analysis of soil samples for pesticide and
tracer residues should be continued until at least three consecutive
(normally monthly) samples show no residues above the minimum detection
(not quantitation) limit or until termination of soil sampling is
approved by EPA.  

4.4  SOIL-WATER MONITORING PLAN tc \l2 "3.  PORE-LIQUID MONITORING PLAN


Tracer and pesticide residues in soil water are monitored to provide an
indication of the movement of water and the test pesticide through the
vadose zone.  Soil-water samples, collected with soil-solution samplers,
suction lysimeters, or other devices, qualitatively track the downward
transport of pesticide residues.  Analytical methods for pesticides in
soils commonly have higher minimum detection limits than those in water,
typically by more than an order of magnitude.  Also, water is likely the
medium via which the solutes will be transported.  Thus, soil-water
samples can be used to better track the movement of pesticide residues
or tracer in vadose zone media with a greater power of detection than in
soil samples.

4.41  Soil Water Content Measurements  tc \l3 "Soil Water Content
Measurements  

The amount of water in soil, or the soil water content, is an important
component of assessing a site's overall water balance.  It is also
important for providing water to plants and for transporting solutes. 
Evaporation of water from the soil, transpiration by plants, movement of
water, and the transport of solutes in soil are functionally related to
the soil water content.  Soil water, therefore, is a dynamic property
which varies both spatially and temporally.  

Soil water content throughout the site should be measured at least
monthly (preferably more frequently).  Soil moisture measurements are a
necessary piece of information needed for modeling flow and for onsite
water management; for example, to determine when irrigation is needed. 
Soil water content should be determined for soil samples collected for
pesticide and tracer residue analysis because these parameters should be
reported on a dry-weight basis.

4.42  Instrumentation tc \l4 "Instrumentation 

A number of direct and indirect methods are available to measure soil
water content (Gardner, 1986; Topp, 1993).  The gravimetric method (a
direct, destructive procedure) is a standard technique commonly used to
collect reference data on soil water content.  Indirect methods include:
electrical conductivity, capacitance and resistance, neutron
thermalization, and gamma ray and neutron attenuation.  Of these
methods, the three that appear to have the greatest use and utility are:
gravimetric soil-water content; Time Domain Reflectometry (TDR), an
electrical capacitance method; and neutron probe (neutron
thermalization).  Techniques such as TDR or frequency domain capacitors
have the advantage of real-time readouts and no radioactive source.

Tensiometers or other suitable methods should be used to determine the
availability of soil water for sample collection (Cassel and Klute,
1986; Rawlins and Campbell, 1986).  Stannard (1990) provides a summary
of the theory, design, installation, and use of vacuum-gauge, manometer,
and pressure-transducer tensiometers in field investigations.  The types
of tensiometers used at each study site, and their locations, should be
documented and reported in the first quarterly report.

4.43  Location and Frequency of Sampling tc \l4 "Location and Frequency
of Sampling 

Soil water content measurements should be collected near the suction
lysimeters and wells.  Soil water content should be measured when
lysimeters are sampled to at least a depth of one meter.

4.44  Soil water Sampling tc \l3 "Pore water Sampling 

Because water in the vadose zone is held at negative matric potentials,
water will not flow freely into sampling devices.  Suction, in excess of
the soil matric potential, should be applied  to induce the flow of
water into sampling devices.  Therefore, suction lysimeters or other
pore-liquid samplers are required.   There is an extensive body of
literature on the function and limitations of different devices and
techniques for extracting water from soil using a pressure differential.
 Reliable, documented methods should be used to collect samples of soil
water for analysis of the applied chemical, degradation products,
tracers and other species of interest.

4.45  Instrumentation tc \l4 "Instrumentation 

The operation and effectiveness of suction lysimeters have been
described by Morrison (1983); Everett, Wilson and Hoylman (1984); and
Everett and McMillon (1985).  The function and limitations of various
suction sampler designs are presented in Wilson (1990).  Vacuum samplers
can be used to obtain soil-liquid samples from up to 6 feet below the
ground surface.  Pressure-vacuum lysimeters are recommended for water
sample collection to a depth of 50 feet (Parizek and Lane, 1970). 
Limitations are discussed by Litaor (1988).  

The porous sampling membrane of suction lysimeters can be constructed
from a number of materials.  Testing has shown that sampling membranes
constructed of PTFE (Teflon) cannot sustain a sufficient vacuum to
collect samples under high matric potentials.  Prior to installation,
however, laboratory studies should be conducted to assess the degree of
sorption exhibited by the compounds of interest onto the ceramic
membranes.

4.46   Depth and Number of Lysimeters tc \l4 "Depth and Number of
Lysimeters 

A minimum of eight clusters of four lysimeters each should be installed
within the boundaries of the treated study site.  The lysimeters at each
cluster should be installed at four different depths (e.g. 3, 6, 10 and
15 feet) to provide the greatest coverage of the vadose zone.  If the
study is conducted at a site with a ground water table less than 15 feet
below grade, fewer lysimeters will be required per cluster. 

4.47  Time of Emplacement tc \l4 "Time of Emplacement 

Lysimeters should be in place a minimum of 2 weeks, and preferably one
month, prior to the application of the test pesticide to the study site.
 In most cases, this will allow materials in the lysimeter to seal the
annular space and to equilibrate with soil-moisture conditions.  In some
instances, a longer period of time may be necessary to achieve reliable
and consistent samples from suction lysimeters.  It should be noted that
Litaor (1988) generally recommended that solution sampler systems be
installed one year before sampling begins so that the samplers can
equilibrate with the surrounding soil.  Suction lysimeters should
therefore be tested for operational effectiveness prior to the field
application of the compounds of interest.  

4.48  Sampling Frequency tc \l4 "Sampling Frequency 

Tensiometers should be regularly monitored to assess the availability of
soil water for collection, and to determine the level of suction
required to draw water from soil pores.  Samples should be collected
from lysimeters prior to pesticide application and frequently in the
early part of the study.  Soil pore water sampling activities should be
coordinated with the collection of ground-water samples.  A typical
sampling scheme is as follows:  

ROUND	

TIMING	

DEPTH



Sample 1	

Pre-application	

3, 6, 9, 15 feet (ALL DEPTHS)



Sample 2	

7 days after application	

3, 6 feet



Sample 3	

14 days after application	

3, 6, 9 feet



Sample 4	

1 month after application	

3, 6, 9 feet



Sample 5	

2 months after application	

3, 6, 9 feet



Sample 6	

3 months after application	

3, 6, 9, 15 feet



Sample 7 - ?	

continue monthly sampling	

3, 6, 9, 15 feet (ALL DEPTHS)



Samples should be drawn from lysimeters at each sampling period and
analyzed individually.  In the event that an insufficient volume of
water is collected from a lysimeter, samples from two lysimeters located
at the same depth increment may be composited.  Criteria for termination
of sampling are presented in Chapter 6.  Approval for termination of
monitoring should be received from EPA in writing.  

4.5  GROUND-WATER MONITORING PLAN tc \l2 "4.  GROUND-WATER MONITORING
PLAN 

The purpose of monitoring tracer and pesticide residues in ground water
is to provide an indication of the movement of water, the test pesticide
and its degradates through the vadose zone to ground water. 
Ground-water samples should be collected and analyzed for all compounds
of interest (Chapter 2).

4.51  Monitoring Well Design tc \l3 "Monitoring Well Design 

The success of a ground-water monitoring program for a prospective
monitoring study depends in part on the proper installation of
monitoring wells.  Installation of these wells by licensed professional
monitoring well installers, according to published standards
specifically related to the construction of monitoring wells, should
ensure that the wells will provide representative ground-water samples. 
Auger, direct push and other acceptable methods of well installation may
be used provided the wells are installed and constructed to ensure
reliable sampling of ground water, and that well materials do not affect
sample quality.  Local and state monitoring well construction,
installation and location requirements should be taken into account in
planning well design.  Studies have recommended against using existing
drinking water wells for monitoring pesticide concentrations, finding a
significant difference in detections between existing wells and
stainless steel monitoring wells (Smith et al., 1998). Well abandonment
at the completion of the study should be done in accordance with local
and state regulations.  To minimize site disturbance, borings completed
for site characterization should be used to install monitoring wells.

4.52  Number, Emplacement, and Screen Lengths of Wells Within a Cluster
tc \l3 "Number, Emplacement, and Screen Lengths of Wells Within a
Cluster 

Ground-water monitoring wells should be installed as clusters.  At each
ground-water sampling location at least two depths should be sampled. 
The magnitude of seasonal fluctuations in the water table should be
determined prior to monitoring well installation.  The shallowest well
at each location should be placed to intercept the shallowest occurrence
of ground water.  This generally means that it will be screened across
the water table.  The top of the screen for the second well should be
placed at the depth of the bottom of the shallow well screen.

In order to avoid excessive dilution of a pesticide residue or tracer
and to focus on a discrete portion of the aquifer, screen lengths should
be no longer than 1.5 meters; generally a smaller screen is preferable. 
If the depth to the water table does not fluctuate drastically, each
cluster should monitor the top 3 meters of the aquifer.  Where the water
table fluctuates due to seasonal or other influences a greater thickness
of the aquifer should be screened.

4.53  Number and Location of Monitoring Well Clusters tc \l3 "Number and
Location of Monitoring Well Clusters 

Monitoring wells should be located up gradient of the treated field in
the control plot, within the treated field and down gradient of the
treated field.  A minimum of eight monitoring well locations should be
spatially distributed within the treated field.  State and local
requirements for ground-water monitoring should be included in planning.

The locations of wells should be randomly distributed within the field. 
They may be placed at randomly chosen nodes on a regular grid to
simplify data analysis and to reduce interference with agronomic
practices such as planting, pesticide applications, and irrigation. 
Alternatively, the field may be divided into sectors and more wells
located in selected sectors based upon the site characterization data
and the conceptual model.  Factors that might induce differential rates
of infiltration and solute transport through the soil and subsoil
include soil texture and structure, surface topography (shape and
gradient), and hydraulic conductivity.  Monitoring wells should not be
placed in areas susceptible to runoff.

4.54  Time of Emplacement   tc \l3 "Time of Emplacement   

Wells should be installed a minimum of 2 weeks prior to pesticide
application.  Time should be allowed for development and stabilization
of the wells prior to use.   They should be in place to allow background
sampling of ground water for site characterization prior to pesticide
application.

4.55  Sampling Frequency tc \l3 "Sampling Frequency 

Ground-water samples should be collected more frequently in the early
part of the study and coordinated with the collection of soil and soil
water samples and irrigation events.  One pre-application sample should
also be collected from all wells.  Ground-water samples should be
collected 14 days after the initial application, and at least once a
month after that time from all monitoring wells.  Additional samples
should be collected before 14 days if there is reason to believe the
compounds of interest may move rapidly (for example, following a large
rainfall or irrigation event).  Some researchers have indicated that
pesticides may leach to very shallow ground water beneath agricultural
fields shortly after major recharge events.  Based on analytical results
of soil and soil water sampling, additional ground-water sampling events
may be scheduled.  Criteria for termination of sampling are presented in
Chapter 6.  Approval for termination of monitoring should be received
from EPA in writing.  A typical sampling scheme is:

ROUND	

TIMING



Sample 1	

Pre-application



Sample 2	

14 days after application



Sample 3	

1 month after application



Sample 4	

2 months after application



Sample 5	

3 months after application



Sample 6 - ?	

continue monthly sampling

4.56  Instrumentation  tc \l3 "Instrumentation  

The study director should ensure that all sample collection equipment
will not alter the quality of ground-water samples during transfer or
collection activities.  A wide range of sampling devices suitable for
sampling nonvolatile organic chemicals in ground water is available, but
only a few are suitable for volatile organic compounds.  For instance,
most pumps and bailers are not suitable for the collection of volatiles.
 Also, certain types of sampling equipment may not be appropriate in any
situation: i.e., peristaltic pumps generally cannot sample as deep as 30
feet.  Sampler parts should be constructed of materials that will not
contaminate or alter sample integrity.  Typically teflon or stainless
steel sampling equipment is preferred (USEPA, 1986b).  In addition,
pesticides may adsorb to certain types of tubing such as silicone
rubber, Nalgene 180, Tygon R-3603, and low-density polyethylene.  Teflon
or stainless steel bailers should alleviate this problem in most
situations.  Dedicated sampling pumps are recommended to avoid
cross-contamination.  If these will not be used, then decontamination
procedures which are appropriate for the situation should be used.  

4.57  Sampling Methods tc \l3 "Sampling Methods 

Before any well is sampled, the static water levels should be obtained. 
Water levels should also be measured in each piezometer during the
sampling round.  This information will be used to construct a water
table map for each sampling period.  Wells should be purged before
sampling.  Samples should be drawn from each monitoring well during each
sampling period and analyzed individually.  The first ground-water
samples from each round should be drawn from the furthest up gradient
well clusters.  Sampling should then progress down gradient.  Sampling
for subsequent events should remain in the same order unless analytical
results indicate contamination of up gradient wells.  In this case,
sampling should progress from the well displaying the lowest pesticide
residues to the well displaying the greatest pesticide residues.

4.58  Integrated Sampling Schedule tc \l3 "Integrated Sampling Schedule 

Once design decisions have been made about how and when to sample soil,
soil water, and ground water, these decisions should be integrated into
one monitoring plan for the ground-water monitoring study.  An example
of a coordinated monitoring schedule is given below:

ROUND	

TIMING	

MEDIA SAMPLED



Sample 1	

Pre-application	

Soil (0 - 3 inches), ALL Soil Water, ALL Monitoring Wells.  



Sample 2	

Immediately post-application	

Soil (0 - 3 inches)



Sample 3	

1 day after application	

Soil (0 - 1 foot), 



Sample 4	

3 days after application, (irrigate)	

Soil (0 - 1 foot), 



Sample 5	

7 days after application	

Soil (0 - 1 foot), Soil Water (3, 6 feet)



Sample 6	

14 days after application	

Soil (0 - 1 foot), Soil Water (3, 6, 9 feet), ALL Monitoring Wells



Sample 7	

1 month after application (irrigate)	

Soil (0 - 2 feet), Soil Water (3, 6, 9 feet), ALL Monitoring Wells



Sample 8	

2 months after application (irrigate)	

ALL Soil Water, ALL Monitoring Wells



Samples 9 - ?	

3 months after application - study termination (irrigate)	

ALL Soil Water, ALL Monitoring Wells



Sampling of soil water and ground water should continue until the
patterns of transport and decline have been established for the test
pesticide and associated degradates.  No study will be terminated before
the questions for which the study was designed have been reasonably
answered.  The registrant may suspend sample analysis with EPA approval
(but not continued sample collection) if they believe these criteria
have been met while awaiting formal response from EPA as to whether the
Agency agrees that the criteria for study termination have been met.

	

CHAPTER 5 - SITE CHARACTERIZATION AND MONITORING PLAN DESIGN REPORTS tc
\l1 "CHAPTER 5 - SITE CHARACTERIZATION AND MONITORING PLAN DESIGN
REPORTS 

	

Reports summarizing the site characterization process and the
development of monitoring plans for each study site should be submitted
to EPA for approval prior to the installation of the monitoring system. 
The Monitoring Plan Design Report should be prepared simultaneously with
the Site Characterization Report.  Although both reports should be
submitted before the implementation phase of the study can begin, they
do not have to be submitted together.  Final approval of monitoring
plans will be provided after review.  Required elements of both of these
reports are described below.  All reports and supporting data should be
submitted in an editable electronic format and as many hard copies as
required by Registration Division or Special Review and Reregistration
Division.  

5.1  SITE CHARACTERIZATION REPORT tc \l2 "1.  SITE CHARACTERIZATION
REPORT 

The Site Characterization Report should be completed after the site
characterization process.  The required elements of this report have
been described in detail in Chapter 3.  They will be briefly summarized
here and include:

A summary of regional conditions,

A site base map,

Description of surficial soil characteristics,

Description of field testing methods and results in the vadose zone
(saturated and unsaturated hydraulic conductivity, soil water content)

Description of historical water needs of crop and net recharge at the
site,

Descriptions and results of test pit excavations,

Description of the design, implementation, and results of the
exploratory boring program,

Results of shallow saturated zone investigations,

Description of the irrigation, ground water and precipitation water
quality,

Development of a conceptual model of the site, and 

Any additional information that may impact the design, performance, or
conclusions of the study.



Summary of Regional Conditions tc \l3 "Summary of Regional Conditions 

Regional hydrogeology and agriculture should be described to provide a
framework for interpreting the site-specific data collected during the
site characterization process.  A description and map depicting the site
location with respect to geographic features, regional topography,
dominant soil types, major aquifers (including those used for drinking
water), regional water table depths and direction of ground-water flow,
regional irrigation trends, and other regional agricultural practices
should be included.  Maps and figures to illustrate the regional
conditions are encouraged.

5.11  Site Base Map tc \l3 "Site Base Map 

An accurate base map of each study site displaying the information
collected during the site characterization process should be included in
the Site Characterization Report.  The required elements of a site base
map are listed in Chapter 3, Section 1.  

5.12  Surficial Soil Characteristics tc \l3 "Surficial Soil
Characteristics 

The results of detailed soil investigations conducted by a qualified
soil scientist should be presented.  A map depicting the soil series
present at each study site should accompany a description of the
characteristics of the soils present on each site.  A site-specific soil
profile describing the various soil horizons typical at each study site
should be included.  Soil profile descriptions should follow the
conventions established by the U.S. Department of Agriculture.

5.13  Field Testing Methods and Results tc \l3 "Field Testing Methods
and Results 

The procedures used to determine the hydraulic conductivity, matric
potential head and soil water content of each test site should be
reported.  A map indicating the locations of test sites should be
presented along with the results of the tests.

5.14  Historical Water Needs and Net Recharge tc \l3 "Historical Water
Needs and Net Recharge 

The data used to establish a baseline value for the average historical
water needs of the crop and net recharge at the site should be
summarized.  If historical weather data is derived from readily
available sources, such as the nearest NOAA weather station, the average
of the monthly precipitation and evaporation data should be summarized
in a concise table, and the data source cited.  If these data were
derived from a local source near the study site, the summary table
should be accompanied by a more detailed description of the data source,
as well as the name of a contact that is willing to discuss and verify
the data.  If historical irrigation records are available, these should
be described in text and summary tables.  If such data are not
available, the method used to estimate irrigation requirements should be
described in detail.  Copies of the historical irrigation records or
calculations used to estimate irrigation needs should be included as an
appendix to the Site Characterization Report.

5.15  Test Pit Excavation tc \l3 "Test Pit Excavation 

Test pit investigation results should be reported.  All excavations
should be located on a site map, and sketches and descriptions of
significant features in the test pit walls should be included in the
report.  

5.16  Exploratory Boring Program tc \l3 "Exploratory Boring Program 

The design of an exploratory boring program is described in Chapter 3,
Section 2.  Documentation of all exploratory borings is critical to the
characterization of subsurface conditions at each study site.  This
documentation should include a reference to the boring methods and
subsurface sample collection methods used, copies of all drilling logs,
reference to the preservation and transportation procedures for soil
samples, a summary of the methods used to analyze soil sample
properties, and the physical and chemical characteristics of all soil
samples.  Quality assurance procedures ensuring the integrity of soil
samples and the data derived from those samples should also be reported.
 

5.17  Saturated Zone Investigations tc \l3 "Saturated Zone
Investigations 

The procedures used to gather information on the hydraulic
characteristics of the shallow saturated zone should be reported. 
Contour maps illustrating the potentiometric surface of the shallow
aquifer at each study site should be constructed, and estimates of the
hydraulic gradient at each site should be reported.  Any information on
water-table fluctuations associated with each study site should be
reported, along with estimates of the magnitude and potential impacts of
the fluctuations on the study.  Hydraulic conductivity estimates
obtained at each study site should be reported, and the methods used to
determine these estimates should be described.  The range of hydraulic
conductivity values obtained from different locations across the site,
the results of pump testing, if used, and the results of laboratory
permeability tests should be compared to obtain an estimate of the
variability in hydraulic conductivity at the site.

5.18  Background Water Quality tc \l3 "Background Water Quality 

Basic data should be collected to establish the background quality of
ground water, irrigation water and precipitation at the study site. 
Analyses should include major ions, major nutrients, temperature,
electrical conductivity and pH.  Additionally, water should be analyzed
for the test compound (to ensure that there are no residues, and to
check the analytical method) and the tracer compound (typically
bromide).

5.19  Conceptual Model tc \l3 "Conceptual Model 

Information required for each study site is presented in Chapter 3,
Section 4 and includes:

A topographic map of the site,

A detailed map of surface soils (1:100 to 1:1,000),

Graphs or tables of particle-size distribution vs. depth,

Graphs or tables of matric potential head vs. depth and soil water
content, 

Graphs or tables of hydraulic conductivity vs. soil water content,

Graphs or tables of organic matter content vs. depth for each core,

An estimate of the amount of water needed for the tracer to reach ground
water in two years

An estimate of travel time needed for the tracer and/or pesticide to
reach ground water.	

Graphs or tables of infiltration rates and saturated and unsaturated
hydraulic conductivity measured across each study site, and

Contour maps of site hydraulic conductivity, soil water content, matric
potential head and hydraulic head.  The latter map should illustrate the
direction of ground-water flow and give estimates of the hydraulic
gradient.	

Geologic cross-sections should be constructed from soil core information
collected during site characterization.  At least two cross-sections
should be prepared for each study site that depicts significant
stratigraphic and hydrogeologic features.  One cross-section should be
oriented parallel to the direction of ground-water flow; the other
should be perpendicular to the flow direction.  The following
information should be included on each cross-section:

Orientation of the section across the site,

Description of all stratigraphic units,

Structural features,

Zones of high and low hydraulic conductivity,

Location of each borehole intersecting or projected into the section,
with the total depth of the borehole and the depth to the water table
indicated,



Indication of the rate and direction of ground-water flow.	

5.2  MONITORING PLAN DESIGN REPORT (PROTOCOL) tc \l2 "2.  MONITORING
PLAN DESIGN REPORT (PROTOCOL) 

In contrast to the level of site-specific detail required in a Site
Characterization Report, extensive detail in the Monitoring Plan Design
Report should only be provided for chemical-specific information, or
when elements of the proposed study design vary from the recommendations
provided in the remaining chapters of this Guidance Document.  Study
directors are discouraged from submitting "draft protocols."  If the
design requirements spelled out in this guidance document are met, then
timely approval of the Monitoring Plan Design Report will allow the
experimental phase of the study to begin on schedule.  Most subsequent
changes to the study design can be addressed in a series of memoranda,
rather than by submitting a series of draft reports.  

If the study director believes that some aspect of the Monitoring Plan
Design cannot be consistent with the guidelines in this document, a
detailed description and justification should be submitted.   This
situation may be caused by the conditions of the study site or chemical
characteristics of the pesticide or degradates.

The Monitoring Plan Design Report should clearly detail how the
pesticide application, sampling, and analysis will provide the data
necessary to evaluate the leaching potential of the pesticide and its
degradates under the site-specific study conditions.  The following
chemical-specific data should be provided:

Application rates,

Compounds to be analyzed, including degradates and tracer,

Analytical methods,

Application method,

Equipment calibration methods, and

Method used to confirm the application rate.  

The above information should be provided in summary form, with reference
to readily available standard operating procedures.  Field personnel
should document referenced procedures in official field notebooks to
comply with Good Laboratory Practice requirements.

The design of the proposed monitoring program for each study site
should also be fully described in the Monitoring Plan Design Report. 
The following information, detailed in Chapter 4, should be provided in
the Monitoring Plan Design Report:

The number of monitoring wells and suction lysimeters that will be
installed,

A diagram showing proposed well and lysimeter locations,

A description of the proposed soil water sampler design,

A schematic diagram of the proposed well construction details, 

Intended method, rate, schedule, and duration of irrigation, 

Proposed experimental start and finish dates, and

Soil, soil water, soil water content, matric potential and ground-water
sampling schedules.

The Monitoring Plan Design Report should also detail the field
procedures that will be used to instrument the site, conduct the
sampling, and abandon the site at the conclusion of the study.  These
required elements are described in Chapter 4.  These procedures should
be described in summary form, with reference to readily available
standard operating procedures.

	



CHAPTER 6 - MONITORING PLAN IMPLEMENTATION tc \l1 "CHAPTER 6 -
MONITORING PLAN IMPLEMENTATION 

Once the Monitoring Plan Design has been approved, work on
instrumentation can begin.  At this stage all design decisions have been
made.  What remains is to install monitoring devices, apply the
pesticide and tracer, to collect samples, and to send them off for
analysis.  This chapter describes factors to be considered in the field
during instrumentation, application, sample collection, and sample
handling.  

EPA anticipates that field-scale ground-water monitoring studies will be
conducted over a minimum of a 3-year period.  This period includes 1
year for site selection, site characterization, the development of a
monitoring plan, and the installation of the monitoring system, and at
least 2 years for post-application monitoring.  Additional time will
likely be required for the preparation of the final study report.  The
duration of these studies may vary depending on the results obtained. 
Termination of monitoring at study sites requires EPA approval. 
Generally, conditions appropriate for termination of the study include:

The tracer has peaked in concentration in all monitoring wells at the
site, and has shown a marked decline for at least three months and

Residues of the pesticide (parent and degradates of concern) have
completely degraded and dissipated in the entire profile (vadose and, if
applicable, saturated zone).  This is generally defined as no detections
for three consecutive sampling times over an interval of at least two
months, or

Pesticide residues have clearly peaked (parent and degradates of
concern) in ground water beneath the treated field (for each of the well
clusters) or concentrations have leveled off for an extended period
(usually about 4 to 8 months) while significant  pesticide residues and
tracer substance no longer remain in the vadose zone.

Sampling of soil water and ground water should continue until the
patterns of transport and decline have been established for the test
pesticide and associated degradates.  No study will be terminated before
the questions for which the study was designed have been reasonably
answered.  The registrant may suspend sample analysis with EPA approval
(but not continued sample collection) if they believe these criteria
have been met while awaiting formal response from EPA as to whether the
Agency agrees that the criteria for study termination have been met.

This chapter is divided into the following sections:

Application of Pesticide and Tracer

Irrigation

Soil Monitoring

Soil Water Monitoring

Ground-Water Monitoring

Sample Handling and Tracking

6.1  APPLICATION OF PESTICIDE AND TRACER tc \l2 "1.  APPLICATION OF
PESTICIDE AND TRACER 

The field crew should document that the application of the test
pesticide and tracer corresponds to the rates and methods defined in the
Monitoring Plan Design Report.  Background concentrations of the tracer
in the vadose and saturated zones need to be established ahead of time
and the application rate should be sufficient that breakthrough of the
tracer into shallow ground water can be clearly detected with the
analytical method used.  Application methods, calibration procedures,
amount applied, and the date and time of each application should be
documented carefully in the field notebook and reported in the First
Quarterly and Final Report.  The tracer identified in the Monitoring
Plan Design Report should be applied the same day as the test pesticide.

Field notes should record the climatic conditions on the day of
application, including wind speed, temperature and precipitation.  It is
particularly important to document in detail soil water content and
temperature conditions on the day of application and for following days.
 The field crew should take detailed notes (supported by photographs
when appropriate) on the amount, type, and positioning of plant residues
or organic amendments relative to the planting rows (if applicable),
surface roughness, row spacing, ridge height and depth and method of
plowing, crop stage and vigor, weed composition and cover, and other
factors which may significantly influence pesticide dissipation
especially in the critical first few hours and days after application. 
Application should not take place on a day when conditions could cause
pesticide loss due to spray drift or runoff, or if conditions are
inconsistent with label directions.  All entries to the field notebook
throughout the study should be consistent with FIFRA Good Laboratory
Practices (GLP).  

6.2  IRRIGATION

Detailed guidance on how to determine the amount of irrigation water
needed throughout the course of the study is provided in Chapter 4.  The
cooperating farmer tending the study field should be familiarized with
the schedule and method of irrigation identified in Monitoring Plan
Design.  With the exception of the irrigation event during the first
week after pesticide application, times when irrigation is needed will
not necessarily correspond to days field personnel are scheduled to
conduct sampling.  Soil water content determinations up to a one meter
depth should always be made prior to any irrigation event as well as for
all sampling events (normally several in the first month after
application and once a month thereafter).  The Study Director should
keep in close communication with the cooperating farmer to ensure that
monthly irrigation targets are being met, and that records of the dates
and amounts of irrigation are being kept.  

6.3  SOIL MONITORING tc \l2 "3.  SOIL MONITORING 

Soil sampling is important for verification of field application rate. 
For at least the month after application (normally including samples
taken 0, 1, 3, 7, 14, and 30 days post-treatment) samples should not be
composited before analysis in order to establish spatial variability of
the application.  Analysis of soil samples for pesticide and tracer
residues should be continued until at least three consecutive (normally
monthly) samples show no residues above the minimum detection (not
quantitation) limit.  

For soil monitoring, permanent equipment will not be installed in the
field.  Therefore, the first step in the field procedure is
decontamination of sampling equipment, followed by sample collection and
handling.  Careful attention to avoid cross contamination of samples is
important, especially in the early sampling intervals when pesticide
residues on the field are highest.  The field crew should carefully
document procedures in the field notebook, noting any problems or
deviations from the Monitoring Plan Design.  

6.31  Decontamination of Sampling Equipment tc \l3 "Decontamination of
Sampling Equipment 

Decontamination minimizes the likelihood that pesticide or tracer
residues will be introduced into deeper soil horizons during sampling. 
A decontamination area should be designated in a location downgradient
of the study plot.  Soil-sampling equipment should be cleaned prior to
sample collection at each sampling interval.  Field-blank water samples
should be taken with each sampling round to test the effectiveness of
the soil-equipment decontamination methods.  All rinsate used in the
decontamination process should be disposed of away from the study site. 
 Additionally, rinsate should not be disposed of in “ecologically
sensitive” areas, such as wetlands or down other wells. 

Field personnel can take additional precautions beyond equipment
decontamination to prevent sample cross-contamination.  For example,
each person collecting samples should wear a clean pair of gloves during
collection of each soil core.  Decontaminated sampling equipment should
never come in contact with the ground until the actual sample
collection.  Decontaminated sampling equipment should be placed in a
clean plastic bag between uses to avoid accidental contact with
contaminated soil or water.  

6.32  Soil Sample Collection and Handling  tc \l3 "Soil Sample
Collection and Handling  

The primary concern at the time of soil sampling is that representative
samples be collected, being careful not to cross-contaminate samples
from different depths or cores.  Surface plant residue should be
included with shallow soil samples to account for pesticide residues
clinging to this material.  When collecting successive samples for a
deeper core, the top portion of each core should be carefully scraped to
remove soil from the previous depth increment.  The locations of
sampling cores should be carefully measured and recorded in the field
notebook, to avoid re-sampling in a location previously disturbed by
coring.  After sampling, core holes should be refilled with
pesticide-residue free soil according to State and local regulations.  

6.4  PORE-WATER MONITORING tc \l2 "4.  PORE-LIQUID MONITORING 

The primary purpose of soil water monitoring is to track the movement of
dissolved pesticide and tracer toward the water table.  Detection of
tracer in the soil column indicates that downward movement is occurring;
detection of tracer in the ground water indicates that recharge has
occurred.  Monitoring pesticide residues gives an indication of the
relative rate of transport of the pesticide.  

6.41  Instrumentation tc \l3 "Instrumentation 

The proper installation of soil water content monitoring devices is
described in manufacturer's materials and in USEPA (1986b), ASTM (1994),
Nielsen and Johnson (1990), Everett, Wilson, and Hoylman (1984), and
Morrison (1983).  All lysimeters should be cleaned and leak tested
before installation in the field to ensure that they will be able to
hold sufficient vacuum to draw a soil-water sample.  Testing of
lysimeters prior to installation is of special practical importance,
since any lysimeter that does not function properly during the study
will require that a replacement be installed.  Recommended methods for
pre-installation cleaning and leak testing of pore-water samplers are
described in US EPA (1986b).  In some instances, the manufacturer of the
sampling device may recommend other cleaning procedures that are
appropriate for the specific device.  

The maximum suction that can be applied to a lysimeter before contact
with soil-water is broken is the bubbling pressure (or air entry
pressure).  If a suction greater than the bubbling pressure is applied
to a lysimeter, only air will be drawn into the collection cup.  If the
bubbling pressure for a lysimeter is not provided by the manufacturer,
this value should be determined before lysimeters are installed in the
field.  This can be done by saturating the collection cup with water,
immersing the cup in water, and applying pressure to the lysimeter.  The
bubbling pressure is the pressure at which air escapes from the ceramic
cup into the surrounding water.  

Pressure-vacuum lysimeters offer some advantages over suction
lysimeters.  For example, the maximum operating depth of pressure-vacuum
lysimeters is 15 meters, as opposed to 6 meters for suction lysimeters. 
 Also, pressure-vacuum lysimeters collected samples through tubing which
is part of the sample equipment, thus tubing is not reused eliminating
this as a potential source of contamination.  Good hydraulic contact
between the porous segment of the sampler and the unsaturated media is
needed to minimize leakage along the annulus of the borehole.  This may
be accomplished by packing silica flour around and beneath the porous
segment of suction samplers.  The use of other materials, such as sand
or soil backfill will not provide as strong a hydraulic connection and
may necessitate equipment replacement.  Bentonite powder should be used
to form a tight seal in the annular space immediately above the porous
component of the sampler to prevent contamination from the surface.  The
supervising scientist should record problems encountered during
installation or deviations from procedures and describe them in the
First Quarterly Report and in the Final Report.

6.42  Decontamination tc \l3 "Decontamination 

Sample collection tubing in a pressure-vacuum lysimeter is a dedicated
part of the sampling device, and need not be decontaminated.  Other
types of lysimeters, for example suction lysimeters, have sampling
tubing that is attached at the time of sampling and should be
decontaminated if it is used for multiple lysimeters.  In all cases,
sampling tubing should not be allowed to come in contact with the ground
and should be handled with clean gloves during sample collection.  Any
rinsate should be disposed of away from the study area. Additionally,
rinsate should not be disposed of in “ecologically sensitive” areas,
such as wetlands or down other wells.

6.43  Sample Collection  tc \l3 "Sample Collection  

The following procedures pertain to the collection of samples from
pressure-vacuum lysimeters.  Methods for the collection of pore-water
samples are generally provided by the equipment manufacturer and are
summarized in ASTM (1994), Nielsen and Johnson (1990), and USEPA
(1986a).  

Pore-water samples should be collected from suction lysimeters by
maintaining a constant level of suction on the porous cup of the
lysimeter for at least 24 hours.  The suction induces the flow of water
from the surrounding unsaturated media into the sampler.  To collect a
sample, pressure is applied to the second line and water is forced from
the porous cup through the discharge tubing into the collection bottle.

The appropriate amount of suction for each lysimeter depends upon the
type of soil and the ambient soil moisture at the time of sampling.  The
suction placed on the lysimeter should be greater than the suction
naturally occurring in the soil in order to induce flow into the
collection container and to prevent backflow from the porous sampling
cup to the soil matrix.  The pressure applied to the lysimeter to force
sample water from the collection cup to the surface should not exceed
the bubbling pressure of the lysimeter, or the collected sample will be
forced from the ceramic cup back into the surrounding soil.

The following should be included in the field notes for each lysimeter
sampled:  

Amount of suction applied, 

Date and time that suction was applied, 

Remaining suction at time of sampling, 

Date and time of sampling, 

Pressure applied for sampling and 

Volume of sample collected



If the volume of available pore water or ground water is not sufficient
for both pesticide and tracer analyses, pesticide analyses should be
given first priority.  If sample volume allows, duplicate and
field-spike samples should be collected.  A trip blank sample should be
included to ensure cross-contamination of samples does not occur during
shipment to the laboratory.

Any problems or variations in procedures in the Monitoring Plan Design
Report should be described in the Quarterly Reports and in the Final
Report.  Reasonable effort should be made to follow the prescribed
sampling program.  Adjustments may have to be made during periods of bad
weather but samples should still be collected according to the
prescribed intensity (i.e., still at an average frequency of once every
month unless a deviation from the protocol is approved by the Agency)
and at times closest to the scheduled date that are feasible.

6.5  GROUND-WATER MONITORING tc \l2 "5.  GROUND-WATER MONITORING 

As with the soil pore-water sampling devices, monitoring well design
decisions have been made and described in the Monitoring Plan Design
Report.  Problems or variances from these procedures should be
documented and discussed as they arise in each Quarterly Report and in
the Final Report.

6.51  Instrumentation  tc \l3 "Instrumentation  

The ability to collect representative ground-water samples depends on
the proper installation of monitoring wells.  Most states require that a
permit be filed prior to the installation of monitoring wells and that
well construction records are returned to the state within a specific
time following the emplacement of monitoring wells.  States may also
have specific monitoring-well construction requirements that should be
followed.  Wells should be installed by licensed drillers familiar with
all relevant state and local requirements and supervised by an
experienced geologist, professional engineer or environmental scientist.
 In addition, before initiation of the monitoring well installation
program, an effort should be made to identify and locate utilities,
irrigation systems, tile drains, etc. to avoid damage and costly
repairs.   

All information pertaining to work performed during the well
construction should be recorded in detail in a bound project notebook
using waterproof ink.  Field-book entries for each monitoring well
should be sufficiently detailed to allow the preparation of a detailed
well log.  The following minimum information should be provided on every
well log:

Well number and permit number,

Well location,

Well depth,

Elevation of the top of the casing,

Depth to the water table,

Well construction details including: materials; length and diameter of
the casing, screen, and surface casing,

Well annulus construction details including:  depth, thickness, and
materials selected for the filter pack, plug, and surface pad,

Geologist's field observations of soil characteristics from continuous
split-spoon samples including: soil texture, color, moisture, and
structure,

Geotechnical information, such as blow counts necessary to advance the
split spoon and sample recovery and

Names of the drilling contractor and supervising geologist and,

Weather conditions during the drilling activities.

Any deviations should be recorded and described in the First Quarterly
Report and in the Final Report.

6.52  Well Development tc \l3 "Well Development 

Well development procedures should be undertaken once a monitoring well
has been installed and sufficient time has passed to allow the annular
seal to cure.  The purpose of developing a monitoring well is to improve
the hydraulic characteristics of the filter pack by removing
fine-grained materials from the pack, and causing coarser materials to
settle around and stabilize the screen.  Once this is accomplished, the
monitoring well can be used to collect representative ground-water
samples.

Removal of fine materials may be more difficult if the surrounding soil
itself is fine-textured, or if the soil water is naturally turbid.  In
these cases, indicator parameters such as pH and conductivity should be
monitored during development (Driscoll, 1986).  Development should
continue until parameters stabilize or the turbidity of the discharge
water is less than 5 nephelometric turbidity units (NTU), as recommended
in USEPA (1986b).  If the parameters do not stabilize, this is an
indication that the development method is not effective and an alternate
method is needed.  Information recorded during the development of each
well should include:  date of development and development method, volume
of water removed, and a log of parameters monitored.

6.53  Decontamination  tc \l3 "Decontamination 

Unless dedicated pumps are used for sampling, all ground-water sampling
equipment should be cleaned before use, and between wells. 
Non-dedicated sampling equipment should be washed with a nonphosphate
detergent, rinsed with tap water then distilled water, and finally
rinsed with a pesticide-grade acetone (or hexane or methyl alcohol) to
aid in drying and to remove any organic residue (Barcelona at al.,
1985).  Other options are given in Driscoll (1986).  All solvents used
in decontamination activities should be disposed of in accordance with
State or local regulations.



If a single pump will be used to purge multiple wells or collect
ground-water samples, tubing should be dedicated to individual
monitoring wells.  Any non-dedicated equipment should be designed so
that it can be disassembled for cleaning at the decontamination area
before a different well is sampled.  Tubing removed from a well after
each purging or sampling event should be rinsed with deionized water
before placing in a clean storage container and sealed.  Field blanks
should be collected from sampling equipment between wells to test the
effectiveness of decontamination.  Bailers should be filled once and
then decanted into sample collection bottles.  If non-dedicated pumps
are used for sample collection, spectrographic-grade water should be
pumped through equipment after decontamination and a sample collected
for analysis.

Some States have developed guidelines for decontamination protocols
(Mickam et al., 1989).  State regulatory agencies should be consulted to
obtain current information on standard decontamination practices for
saturated and vadose zone monitoring programs.  These standards should
be used to supplement the guidelines outlined in this document.  

The water purged from the wells should be discharged away from all well
clusters.  Additionally, purge water should not be disposed of in
“ecologically sensitive” areas, such as wetlands or down other
wells.  Field personnel can take precautions beyond decontamination of
sampling equipment to ensure that cross-contamination between wells does
not occur.  Decontaminated equipment should be handled using rubber
laboratory gloves, and should not be placed directly on the ground.  It
is best to store equipment in clean sealed containers after
decontamination (e.g., plastic bags or coolers) for relocation to the
well site.  If bailers are used for purging and sampling wells, bailer
cords should be discarded after a single use.

6.54  Sample Collection tc \l3 "Sample Collection 

Prior to sampling any of the monitoring wells at a study site, field
conditions should be described in the field notebook.  This includes
observations of weather and soil surface conditions, and the height of
the water table in all wells and piezometers.

 

In order to collect a ground-water sample from a monitoring well that is
representative of the water in the surrounding aquifer, standing water
should be removed from the well casing, screen, and surrounding filter
pack.  This procedure is called purging.  The volume of water purged,
the rate at which it is withdrawn, and the location of the sampling
intake all determine how representative the sample is to the water in
the aquifer.  Typically parameters such as dissolved oxygen, specific
conductivity, oxidation-reduction potential, turbidity and pH are
continuously monitored throughout purging.  When these parameters
stabilize, the well is considered purged (Driscoll, 1986). 
Alternatively, a specific number of well casing volumes can be removed. 
Meters used to monitor pH, temperature, and specific conductance should
be calibrated before each use.  

Bailers should be gently lowered into the water column to a measured
depth just below the water table.  Samples for volatile pesticides
should be headspace-free.  Only a bladder pump is suitable for sampling
for volatile pesticides.

Ground-water samples should be collected in containers that will not
interact with the sample.  Consult with the laboratory that the samples
will be analyzed at to determine if preservation methods beyond the use
of ice will be necessary to prevent additional degradation of the target
compounds.  Ensure that use of chemical preservatives will not interfere
with analysis of target compounds.  Ground-water samples should not be
composited, but placed directly into sample collection bottles.  The
techniques used need to be validated for providing a representative
sample in which the analytes are stable under the conditions of
transport and subsequent storage before analysis.  A trip blank sample
should be included to ensure cross-contamination of samples does not
occur during shipment to the laboratory.

If the volume of available pore water or ground water is not sufficient
for both pesticide and tracer analyses the pesticide analyses should be
given first priority.  The analytical procedures described in the
Monitoring Plan Design should be used and documented.  Duplicate samples
and field spike samples should be collected.

6.6  SAMPLE HANDLING AND TRACKING tc \l2 "6.  SAMPLE HANDLING AND
TRACKING 

Water and soil samples should be placed directly into coolers after
collection.  To ensure against breakage and temperature fluctuations in
the samples, the following sample packing and shipping procedures should
be followed:  

Samples should be shipped in insulated boxes or coolers.  Devices are
available to automatically monitor and record temperature while the
samples are in transit.

Individual glass sample containers should be wrapped either in plastic
bubble wrap, placed in Styrofoam holders, or somehow packaged to
separate the sample bottles   during shipping.  

Gel-Cold packs or other materials to maintain stable temperatures can be
placed in each cooler, but should not be in direct contact with any of
the glass sample containers.  To help maintain the Gel-Cold pack
temperature and keep the temperature of the coolers around 4 (C,  ice
sealed in plastic bags may be added.  The ice should be bagged to
prevent seepage during transport.  Soil samples should   be packed in a
container at or below 0 (C as soon as possible after collection.  If
dry ice is used to preserve soil samples during shipment, field
personnel should follow all hazardous material labeling requirements.  

It is important that all sample tracking paperwork (i.e.
chain-of-custody) be included with the shipment and that the chest be
sealed according to chain-of-custody procedures.

All samples should be stored after collection according to GLP-compliant
procedures and the stability should be validated by a storage stability
study.  Coordination with the laboratory concerning frequency and number
of samples is important for sample preservation and to ensure that
sample holding times are not exceeded.  The laboratory should therefore
be notified prior to sample collection to ensure that samples will be
processed and analyzed quickly.  

The sample tracking procedure described in the Monitoring Plan Design
portion of the Study Protocol should be followed.  A number should be
assigned to each sample collected.  That number should be marked on the
sample container and recorded on the tracking form and in the project
notebook.  Weather conditions or field comments should also be recorded
on the tracking form or in the field notebook.  A three-part label
should be used that includes numbered descriptive information to be
placed on the sample container.  In general, sample labels should be
placed in duplicate on the sample container and should include:  

Date and time of collection,

pH, temperature, and specific conductance,

Identification of sample location,

Analytes, and

Signature of field technician.

If samples are shipped to a laboratory, samples should be shipped in
such a way as to avoid breakage of sample containers and maintain sample
integrity.

CHAPTER 7 - REPORTING tc \l1 "CHAPTER 7 - REPORTING 

Quarterly status reports for each prospective ground-water monitoring
study should be submitted following the application of the compounds of
interest.  Required elements of these status reports are described in
Section 7.1.  These status reports are required to allow adjustment to
the study design, if necessary, and for the determination of when the
stated goals of the study have been fulfilled.  However, in the interest
of efficiency, quarterly reports will not be formally reviewed (i.e. no
formal write-up of review will be submitted to registrant from the US
EPA) unless the results presented warrant further action.

The monitoring plan implementation phase of a prospective ground-water
study may end once the EPA approves a Study Termination Report submitted
by the registrant.  While ground-water sampling in a prospective study
would ideally be completed two years after the application of the test
chemical, the appropriate termination point of a study is a function of
site-specific and chemical-specific characteristics.  Section 7.2
describes milestones in the ground-water study that should occur before
the Study Director considers submitting a Study Termination Report.

At the conclusion of each study, a Final Study Report should also be
submitted to EPA.  Required elements of this report are described in
Section 7.3.  As this document should be able to stand alone as a full
report on the small-scale prospective study, it will include information
already presented in previous submissions.  This report is the vehicle
in which the registrant can provide interpretation of the study results,
suggest further mitigation measures, and extrapolate the results through
modeling, or comparison to other available data.   All information
referenced to sampling locations should conform to EPA's minimum data
elements standards which can be found at the US EPAs’ Water Quality
Data Submissions: OPP Standard Operating Procedure home page ( 
HYPERLINK
"http://www.epa.gov/oppsrrd1/registration_review/water_quality_sop.htm%2
3appendix_a%20" 
http://www.epa.gov/oppsrrd1/registration_review/water_quality_sop.htm#ap
pendix_a ).  All reports and supporting data should be submitted in an
editable electronic format and as one hard copy.

7.1  QUARTERLY REPORTS tc \l2 "1.  QUARTERLY REPORTS 

Quarterly status reports should be submitted to EPA beginning with the
first quarter following the application of the compounds of interest to
each study site.  The required elements of these reports include:

A summary of the activities at the site during the quarter,

Concentrations or mass accounting for the conservative tracer and total
pesticide residues at each cluster,      

Protocol deviations from the approved monitoring plan, and

Results of all chemical analyses for samples (including quality control
samples)      collected during the quarter.  Individual results should
be reported.  Results should not be averaged over samples or time.

Provide graphical representation of chemical analysis

These report elements are described further in the following sections. 
The submittal of additional information that may impact the design,
conduct, or findings of the study is encouraged.

7.11  Summary of Site Activities tc \l3 "Summary of Site Activities 

The summary of site activities should include all activities related to
agronomic practices, monitoring, and irrigation.  The application dates
for fertilizers or other compounds applied to the study area should be
reported along with information on other agronomic practices conducted
during the quarter.  Similarly, the dates of sample collection should be
reported along with information on weather conditions during the
quarter.  If irrigation water was applied to the study site during the
quarter, then the dates and amounts of water applied should be reported,
and compared to the targets set in the Irrigation Plan.  The results of
field measurements such as soil water content and matric potential
should be reported along with a water budget indicating the amount of
net recharge to the site.

7.12  Mass Balance tc \l3 "Mass Balance 

A mass balance for the conservative tracer and total pesticide residues
should be reported for each cluster.  The mass balance at each lysimeter
and monitoring well should be approximated.

7.13  Protocol Deviations tc \l3 "Protocol Deviations 

Any deviations from the protocol established and approved as part of the
Monitoring Plan Design should be reported for each quarter.  Reporting
of deviations should include a discussion of the proposed and approved
procedures, a description of the revised procedures that were
implemented during the quarter, the reasons for the revisions, and the
anticipated effects on the study.

7.14  Analytical Results tc \l3 "Analytical Results 

The results of all chemical analyses (i.e., analyses for the test
pesticide, degradates, and tracer) conducted on samples should be
reported in tabular format.  MDLs and the results of quality control
analyses should also be reported.  Comments and a brief discussion of
the analytical results for the quarter may be included.

7.2  STUDY TERMINATION REPORT tc \l2 "2.  STUDY TERMINATION REPORT 

The sampling program of a prospective ground-water monitoring study
would ideally last two years.  However, in reality the duration of a
successful study is a function of how long it takes for applied water to
recharge to ground water and of how long it takes for the pesticide and
its degradates to leave the vadose zone by degradation and/or
dissipation.  This time frame is a function of the soil type, properties
of the pesticide, and the amount of net recharge at the site.

In order to consider proposing an end to the sampling phase of a
prospective study, the study director should assess whether the
following criteria have been met:

The tracer has peaked in concentration in all monitoring wells at the
site, and has shown a marked decline for at least three months, and

Residues of the pesticide (parent and degradates of concern) have
completely degraded and dissipated in the entire profile (vadose and, if
applicable, saturated zone).  This is generally defined as no detections
for three consecutive sampling times over an interval of at least two
months, or

Pesticide residues have clearly peaked (parent and degradates of
concern) in ground water beneath the treated field (for each of the well
clusters) or concentrations have  leveled off for an extended period
(usually about 4 to 8 months) while significant  pesticide residues and
tracer substance no longer remain in the vadose zone.

The Study Termination Report should detail the fact that the above
conditions have been met, give a brief summary of study results, and
propose a date for the termination of the sampling phase of the
monitoring study.  Sample collection should continue until EPA reviews
the Study Termination Report and concurs that sampling can end.  EPA
will review the Study Termination Report within sixty days of receipt of
the report.  No study will be terminated before the questions for which
the study was designed have been reasonably answered.  

7.3  FINAL REPORT tc \l2 "3.  FINAL REPORT 

A  Final Report should be submitted to EPA at the conclusion of each
study.  This report should include

Documentation of the application of the compounds of interest, climatic
monitoring, and irrigation practices; 

Documentation of all sampling and sample analyses activities; 

Results of all chemical analyses and discussion of findings.  Individual
results should be reported.  Results should not be averaged over samples
or time; and

Documentation of quality assurance activities.

These report elements are described in more detail in the following
sections.  The submittal of additional information that may impact the
interpretation of study results is encouraged.

7.31  Field Practices tc \l3 "Field Practices 

The agricultural practices conducted during the course of the study
should be summarized in the Final Report.  Information on the
application methods, rates, and dates for the compounds of interest
should be reported.  The results of climatic monitoring at each study
site should be reported along with information on the irrigation methods
used, and irrigation rates, dates, and duration.

7.32  Sampling Activities  tc \l3 "Sampling Activities  

Information collected during each sampling episode should be reported,
including

Static water levels in monitoring wells and piezometers,

Weather conditions and field comments,

Tensiometer readings and the amount of suction used to collect lysimeter
samples, and

Soil moisture content at the time of sample collection.

7.33  Analytical Results and Discussion of Findings tc \l3 "Analytical
Results and Discussion of Findings 

The results of all chemical analyses should be presented.  Analytical
results for all compounds of interest should be presented along with
information on analytical detection limits that were achieved.  The
study findings should be summarized, and the significance of the
findings with respect to the demonstrated environmental fate of the test
pesticide and degradates should be discussed.  The use of graphics
and/or computer models to illustrate this discussion is encouraged.

7.34  Quality Assurance tc \l3 "Quality Assurance 

Compliance with good laboratory practices (GLPs) should be documented. 
For field activities, a description of the system for sample numbering
and/or identification should be presented 

For laboratory operations, the following should be reported:

Identification of responsible party who acted as sample custodian, 

Copies of laboratory sample custody logs consisting of serially numbered
standard lab-tracking report sheets, and 

Description of laboratory sample custody procedures for sample handling,
storage, and dispersion for analysis.

7.4  ELECTRONIC DATA REPORTING GUIDELINES  tc \l2 "4.  ELECTRONIC DATA
REPORTING GUIDELINES  

Data generated from PGW studies have proven valuable to OPP scientists
and risk managers in better understanding the potential for a pesticide
to: (1) impact ground water quality, (2) contaminate drinking water, and
(3) reach ecologically important surface water systems, when used in
accordance with label directions.  As part of an effort to update the
Agency guidance for the PGW studies OPP has developed specific guidance
for data submissions to improve the reliability, completeness,
transparency, and consistency in the PGW reports and facilitate further
use of these data for complete assessments of exposure to pesticides
through ground water (e.g., using leaching models to explore the
potential for the pesticide of interest to leach under a variety of
conditions).  Specific requirements on the submission of electronic data
are a matter that will be addressed for each study by EPA when
Prospective Ground-Water study candidate site information is submitted
to the Agency for approval.  In general though, submission of this data
electronically is likely to be requested and will help the Agency not
only in the specific interpretation of the implications of the study
results for the overall potential to impact ground water of the test
pesticide but also to develop higher tier models and continue the
advancement of pesticide risk assessments.

The following guidelines have been developed to assist in reporting of
PGW monitoring information in electronic format.  Listed below are eight
major information fields which focus on the key areas for prospective
ground-water monitoring data collection and reporting.  These major
information fields are;

 

study area and conceptual site model; 

application of pesticide and tracer;

crop information;

soil properties;

ground water data;

weather data;

irrigation application and 

chemical monitoring results.

Each major information field lists specific data types and requested
data formats which serve as guidelines for submission of prospective
ground-water monitoring study data.  

7.41  Study Area and Conceptual Site Model  tc \l3 "Study Area and
Conceptual Site Model  

The following study area information is requested to provide background
information as well as to develop a study-site conceptual model.  The
conceptual model should include graphs, charts, maps and data collected
during site characterization.  Integration of site hydrogeology, surface
hydrology, and historical climatic data is acceptable.

Study Area Information

Base map in GIS readable format (E.g., Arc shape files, *.dxf files, a
format specifically approved by EPA);

NRCS soil surveys;

Other historical information and

Site Characterization Data of Study Area.

Sample locations identified and reported in consistent coordinate system
format (GPS; x,y coordinates; northing,easting; lat,long).

Soil cores (coordinates) see soil properties below for listing of data
to be reported, unsaturated and saturated hydraulic conductivity
measurements at a minimum of 6 locations (coordinates) and soil horizons
with depth (bgs, ft) and soil water content measurements at same 6
locations.

Piezometers - if not placed in soil core holes need coordinates,
measuring point surveyed with U.S.  Geodetic Vertical Datum, hydraulic
head measurements, hydraulic conductivity (slug tests and/or pumping
test results), potentiometric surface diagrams, background water quality
data from upgradient well and influence of existing irrigation wells in
the area on subsurface hydraulics.

7.42  Application of pesticide and tracer tc \l3 "Application of
pesticide and tracer 

The following pesticide and tracer information is requested.  

Pesticide information

Chemical properties of test substance;

molecular weight;

CAS number; 

formulation and

verification of formulation (method and results).

Date(s) of pesticide application;

Incorporation depth;

method of application;

total amount applied; 

rate; 

area covered (coordinates of locations where pesticide applied and/or
boundary where pesticide applied) and 

soil monitoring results after application (field dissipation data).

Topographic map detailing results of all surface soil samples collected
to confirm application rate of pesticide.  Determine if any hot spots of
pesticides were detected post-application.  This may be used to
determine if any detection of pesticides in monitoring wells,
lysimeters, etc. can be correlated to a “hot spot” detected in
surficial soil samples.

If determined, any site-specific measurements of degradation or soil
sorption should be reported

Tracer information

Chemical; 

Formulation; 

locations where tracer applied (coordinates);

method of application; 

rate of application and

total amount applied.

7.43  Crop information  tc \l3 "Crop information  

The following crop information is requested (include this for the entire
course of the study, not just the year in which the pesticide is
applied).

Type of crop; 

planting dates; 

emergence dates; 

harvest date; 

date when chemicals applied (pesticide, herbicide, fertilizer, etc.) and


other relevant crop maintenance activities and crop growth / land cover
information.

7.44  Soil properties tc \l3 "Soil properties 

All data need to be separately reported for each depth increment of each
soil core analyzed.  Some soil characteristic data may have been
collected as part of the site characterization testing of the study
area.  If so, there is no need to repeat that information here. 
Pesticide property data essential for modeling of leaching of the test
pesticide (KOC and other measures of soil sorption and measures of soil
degradation rate) for the specific test soil should be provided (along
with background data relevant to the determination of these properties)
if specifically collected in association with the prospective
ground-water monitoring data in electronic format.  In cases where
pesticide property data are not specifically collected for the test
soil, the extrapolated property data should be submitted along with the
methodology for their calculation and citations for the studies these
property data are derived from.  

 

Soil core location (coordinates);

Minimum depth of the soil sample;

Maximum depth of the soil sample;

textural properties; 

sand/silt/clay fractions (%);  

CEC, or AEC;

Mineralogy; 

bulk density; 

KOC of the pesticide in the test soil or extrapolated from data for
other soils; 

Kd of the pesticide in the test soil or extrapolated from data for other
soils; 

Kf (Freundlich) adsorption constant of the pesticide in the test soil or
extrapolated from data for other soils;

degradation rate of the pesticide in the test soil or extrapolated from
data for other soils, organic matter content; 

field capacity (1/3 bar);

1 bar soil water content;

5 bar soil water content; 

wilting point (15 bar); 

saturated hydraulic conductivity; 

soil water content; 

matrix potential;  

Munsell color and 

pH.   

7.45  Ground-water data  tc \l3 "Groundwater data  

Some of these data may have been collected as part of the site
characterization of the study area.  If so, there is no need to repeat
that information here.  

Well location (coordinates); 

total depth of well; 

depth to water table; 

screened interval; 

background water chemistry; 

hydraulic head; 

flow; 

subsurface geology,; 

cross sections (descriptions, fence diagrams) and 

location (in 3-dimensions) of known aquitards.  

7.46  Weather data tc \l3 "Weather data 

The following site-specific weather data collected during the PGW study
is requested;  

location of monitoring station (coordinates);

rainfall, daily time step or shorter;

air temperature and

soil temperature (including depth measured at).

In addition, site-specific historical weather data for the previous
20-years (or as recent a 20+ year period that is available) should be
provided or referenced for analyses purposes.

7.47  Irrigation input tc \l3 "Irrigation input 

The following site-specific irrigation information is requested;

irrigation method; 

irrigation application date (days after treatment (DAT)); 

rate and 

total amount applied.

7.48  Chemical monitoring results tc \l3 "Chemical monitoring results  

The following chemical monitoring data for soil and ground water is
requested.  All headings should be clearly labeled and explanations
provided in an accompanying text file for clarity.  See attached
template for example.  All analyses above the minimum detection limit
should be reported as the nominal concentration.  If the nominal
concentration of a sample is below a Minimum Reporting Limit or Minimum
Quantification Limit is applicable (whether calculated as a uniform
limit or on a sample-by-sample basis) this information should be
captured in a separate data field.  Specific data fields are;

study identifier;

study type;

media sampled; 

analytes (CAS numbers for parent compound and metabolites); 

sample location (coordinates); 

date of sample; 

depth of sample; 

analytical result  (not averaged over samples or time) and 

analytical QA/QC data (method description, method quantification limit,
method reporting limit, sample quantification limit, data qualifiers).

At a minimum, provide analytical results for each monitoring well in
bar-graph format so a trend in increase and/or decrease will be easily
visualized.  Graph results for each monitoring well separately for
entire sampling period (i.e. 24 months).

All tabular data should be in either ASCII or MS Access format (or a
format specifically approved by EPA).

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