e-CFR Data is current as of January 18, 2008 

Title 40: Protection of Environment

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Subpart U—Initial Distribution System Evaluations

Source:   71 FR 483, Jan. 4, 2006, unless otherwise noted. 

§ 141.600   General requirements.

(a) The requirements of subpart U of this part constitute national
primary drinking water regulations. The regulations in this subpart
establish monitoring and other requirements for identifying subpart V
compliance monitoring locations for determining compliance with maximum
contaminant levels for total trihalomethanes (TTHM) and haloacetic acids
(five)(HAA5). You must use an Initial Distribution System Evaluation
(IDSE) to determine locations with representative high TTHM and HAA5
concentrations throughout your distribution system. IDSEs are used in
conjunction with, but separate from, subpart L compliance monitoring, to
identify and select subpart V compliance monitoring locations.

(b) Applicability. You are subject to these requirements if your system
is a community water system that uses a primary or residual disinfectant
other than ultraviolet light or delivers water that has been treated
with a primary or residual disinfectant other than ultraviolet light; or
if your system is a nontransient noncommunity water system that serves
at least 10,000 people and uses a primary or residual disinfectant other
than ultraviolet light or delivers water that has been treated with a
primary or residual disinfectant other than ultraviolet light.

(c) Schedule. (1) You must comply with the requirements of this subpart
on the schedule in the table in this paragraph (c)(1).

If you serve this population	You must submit your standard monitoring
plan or system specific study plan1or 40/30 certification2to the State
by or receive very small system waiver from State	You must complete your
standard monitoring or system specific study by	You must submit your
IDSE report to the State by3

Systems that are not part of a combined distribution system and systems
that serve the largest population in the combined distribution system

(i) ≥100,000	October 1, 2006	September 30, 2008	January 1, 2009.

(ii) 50,000–99,999	April 1, 2007	March 31, 2009	July 1, 2009.

(iii) 10,000–49,999	October 1, 2007	September 30, 2009	January 1,
2010.

(iv) <10,000 (CWS Only)	April 1, 2008	March 31, 2010	July 1, 2010.

Other systems that are part of a combined distribution system

(v) Wholesale system or consecutive system	—at the same time as the
system with the earliest compliance date in the combined distribution
system	—at the same time as the system with the earliest compliance
date in the combined distribution system	—at the same time as the
system with the earliest compliance date in the combined distribution
system.

1If, within 12 months after the date identified in this column, the
State does not approve your plan or notify you that it has not yet
completed its review, you may consider the plan that you submitted as
approved. You must implement that plan and you must complete standard
monitoring or a system specific study no later than the date identified
in the third column.

2You must submit your 40/30 certification under §141.603 by the date
indicated.

3If, within three months after the date identified in this column (nine
months after the date identified in this column if you must comply on
the schedule in paragraph (c)(1)(iii) of this section), the State does
not approve your IDSE report or notify you that it has not yet completed
its review, you may consider the report that you submitted as approved
and you must implement the recommended subpart V monitoring as required.

(2) For the purpose of the schedule in paragraph (c)(1) of this section,
the State may determine that the combined distribution system does not
include certain consecutive systems based on factors such as receiving
water from a wholesale system only on an emergency basis or receiving
only a small percentage and small volume of water from a wholesale
system. The State may also determine that the combined distribution
system does not include certain wholesale systems based on factors such
as delivering water to a consecutive system only on an emergency basis
or delivering only a small percentage and small volume of water to a
consecutive system.

(d) You must conduct standard monitoring that meets the requirements in
§141.601, or a system specific study that meets the requirements in
§141.602, or certify to the State that you meet 40/30 certification
criteria under §141.603, or qualify for a very small system waiver
under §141.604.

(1) You must have taken the full complement of routine TTHM and HAA5
compliance samples required of a system with your population and source
water under subpart L of this part (or you must have taken the full
complement of reduced TTHM and HAA5 compliance samples required of a
system with your population and source water under subpart L if you meet
reduced monitoring criteria under subpart L of this part) during the
period specified in §141.603(a) to meet the 40/30 certification
criteria in §141.603. You must have taken TTHM and HAA5 samples under
§§141.131 and 141.132 to be eligible for the very small system waiver
in §141.604.

(2) If you have not taken the required samples, you must conduct
standard monitoring that meets the requirements in §141.601, or a
system specific study that meets the requirements in §141.602.

(e) You must use only the analytical methods specified in §141.131, or
otherwise approved by EPA for monitoring under this subpart, to
demonstrate compliance with the requirements of this subpart.

(f) IDSE results will not be used for the purpose of determining
compliance with MCLs in §141.64.

§ 141.601   Standard monitoring.

(a) Standard monitoring plan. Your standard monitoring plan must comply
with paragraphs (a)(1) through (a)(4) of this section. You must prepare
and submit your standard monitoring plan to the State according to the
schedule in §141.600(c).

(1) Your standard monitoring plan must include a schematic of your
distribution system (including distribution system entry points and
their sources, and storage facilities), with notes indicating locations
and dates of all projected standard monitoring, and all projected
subpart L compliance monitoring.

(2) Your standard monitoring plan must include justification of standard
monitoring location selection and a summary of data you relied on to
justify standard monitoring location selection.

(3) Your standard monitoring plan must specify the population served and
system type (subpart H or ground water).

(4) You must retain a complete copy of your standard monitoring plan
submitted under this paragraph (a), including any State modification of
your standard monitoring plan, for as long as you are required to retain
your IDSE report under paragraph (c)(4) of this section.

(b) Standard monitoring. (1) You must monitor as indicated in the table
in this paragraph (b)(1). You must collect dual sample sets at each
monitoring location. One sample in the dual sample set must be analyzed
for TTHM. The other sample in the dual sample set must be analyzed for
HAA5. You must conduct one monitoring period during the peak historical
month for TTHM levels or HAA5 levels or the month of warmest water
temperature. You must review available compliance, study, or operational
data to determine the peak historical month for TTHM or HAA5 levels or
warmest water temperature.

Source water type	Population size

category	Monitoring periods and frequency of

sampling	Distribution system monitoring locations1



	Total per monitoring

period	Near entry

points	Average residence

time	High TTHM

locations	High HAA5

locations

Subpart H









<500 consecutive systems	one (during peak historical month)2	2	1

1



<500 non-consecutive systems

2

	1	1

	500–3,300 consecutive systems	four (every 90 days)	2	1

1



500–3,300 non-consecutive systems

2

	1	1

	3,301–9,999

4

1	2	1

	10,000–49,999	six (every 60 days)	8	1	2	3	2

	50,000–249,999

16	3	4	5	4

	250,000–999,999

24	4	6	8	6

	1,000,000–4,999,999

32	6	8	10	8

	≥5,000,000

40	8	10	12	10

Ground Water









<500 consecutive systems	one (during peak historical month)2	2	1

1



<500 non-consecutive systems

2

	1	1

	500–9,999	four (every 90 days)	2

	1	1

	10,000–99,999

6	1	1	2	2

	100,000–499,999

8	1	1	3	3

	≥500,000

12	2	2	4	4

1A dual sample set (i.e., a TTHM and an HAA5 sample) must be taken at
each monitoring location during each monitoring period.

2The peak historical month is the month with the highest TTHM or HAA5
levels or the warmest water temperature.

(2) You must take samples at locations other than the existing subpart L
monitoring locations. Monitoring locations must be distributed
throughout the distribution system.

(3) If the number of entry points to the distribution system is fewer
than the specified number of entry point monitoring locations, excess
entry point samples must be replaced equally at high TTHM and HAA5
locations. If there is an odd extra location number, you must take a
sample at a high TTHM location. If the number of entry points to the
distribution system is more than the specified number of entry point
monitoring locations, you must take samples at entry points to the
distribution system having the highest annual water flows.

(4) Your monitoring under this paragraph (b) may not be reduced under
the provisions of §141.29 and the State may not reduce your monitoring
using the provisions of §142.16(m).

(c) IDSE report. Your IDSE report must include the elements required in
paragraphs (c)(1) through (c)(4) of this section. You must submit your
IDSE report to the State according to the schedule in §141.600(c).

(1) Your IDSE report must include all TTHM and HAA5 analytical results
from subpart L compliance monitoring and all standard monitoring
conducted during the period of the IDSE as individual analytical results
and LRAAs presented in a tabular or spreadsheet format acceptable to the
State. If changed from your standard monitoring plan submitted under
paragraph (a) of this section, your report must also include a schematic
of your distribution system, the population served, and system type
(subpart H or ground water).

(2) Your IDSE report must include an explanation of any deviations from
your approved standard monitoring plan.

(3) You must recommend and justify subpart V compliance monitoring
locations and timing based on the protocol in §141.605.

(4) You must retain a complete copy of your IDSE report submitted under
this section for 10 years after the date that you submitted your report.
If the State modifies the subpart V monitoring requirements that you
recommended in your IDSE report or if the State approves alternative
monitoring locations, you must keep a copy of the State's notification
on file for 10 years after the date of the State's notification. You
must make the IDSE report and any State notification available for
review by the State or the public.

§ 141.602   System specific studies.

(a) System specific study plan. Your system specific study plan must be
based on either existing monitoring results as required under paragraph
(a)(1) of this section or modeling as required under paragraph (a)(2) of
this section. You must prepare and submit your system specific study
plan to the State according to the schedule in §141.600(c).

(1) Existing monitoring results. You may comply by submitting monitoring
results collected before you are required to begin monitoring under
§141.600(c). The monitoring results and analysis must meet the criteria
in paragraphs (a)(1)(i) and (a)(1)(ii) of this section.

(i) Minimum requirements. (A) TTHM and HAA5 results must be based on
samples collected and analyzed in accordance with §141.131. Samples
must be collected no earlier than five years prior to the study plan
submission date.

(B) The monitoring locations and frequency must meet the conditions
identified in this paragraph (a)(1)(i)(B). Each location must be sampled
once during the peak historical month for TTHM levels or HAA5 levels or
the month of warmest water temperature for every 12 months of data
submitted for that location. Monitoring results must include all subpart
L compliance monitoring results plus additional monitoring results as
necessary to meet minimum sample requirements.

System Type	Population size

category	Number of monitoring

locations	Number of samples



	TTHM	HAA5

Subpart H:





  	<500	3	3	3

  	500–3,300	3	9	9

  	3,301–9,999	6	36	36

  	10,000–49,999	12	72	72

  	50,000–249,999	24	144	144

  	250,000–999,999	36	216	216

  	1,000,000–4,999,999	48	288	288

  	≥ 5,000,000	60	360	360

Ground Water:





  	<500	3	3	3

  	500–9,999	3	9	9

  	10,000–99,999	12	48	48

  	100,000–499,999	18	72	72

  	≥ 500,000	24	96	96

(ii) Reporting monitoring results. You must report the information in
this paragraph (a)(1)(ii).

(A) You must report previously collected monitoring results and certify
that the reported monitoring results include all compliance and
non-compliance results generated during the time period beginning with
the first reported result and ending with the most recent subpart L
results.

(B) You must certify that the samples were representative of the entire
distribution system and that treatment, and distribution system have not
changed significantly since the samples were collected.

(C) Your study monitoring plan must include a schematic of your
distribution system (including distribution system entry points and
their sources, and storage facilities), with notes indicating the
locations and dates of all completed or planned system specific study
monitoring.

(D) Your system specific study plan must specify the population served
and system type (subpart H or ground water).

(E) You must retain a complete copy of your system specific study plan
submitted under this paragraph (a)(1), including any State modification
of your system specific study plan, for as long as you are required to
retain your IDSE report under paragraph (b)(5) of this section.

(F) If you submit previously collected data that fully meet the number
of samples required under paragraph (a)(1)(i)(B) of this section and the
State rejects some of the data, you must either conduct additional
monitoring to replace rejected data on a schedule the State approves or
conduct standard monitoring under §141.601.

(2) Modeling. You may comply through analysis of an extended period
simulation hydraulic model. The extended period simulation hydraulic
model and analysis must meet the criteria in this paragraph (a)(2).

(i) Minimum requirements. (A) The model must simulate 24 hour variation
in demand and show a consistently repeating 24 hour pattern of residence
time.

(B) The model must represent the criteria listed in paragraphs
(a)(2)(i)(B)(1) through (9) of this section.

(1) 75% of pipe volume;

(2) 50% of pipe length;

(3) All pressure zones;

(4) All 12-inch diameter and larger pipes;

(5) All 8-inch and larger pipes that connect pressure zones, influence
zones from different sources, storage facilities, major demand areas,
pumps, and control valves, or are known or expected to be significant
conveyors of water;

(6) All 6-inch and larger pipes that connect remote areas of a
distribution system to the main portion of the system;

(7) All storage facilities with standard operations represented in the
model; and

(8) All active pump stations with controls represented in the model; and

(9) All active control valves.

(C) The model must be calibrated, or have calibration plans, for the
current configuration of the distribution system during the period of
high TTHM formation potential. All storage facilities must be evaluated
as part of the calibration process. All required calibration must be
completed no later than 12 months after plan submission.

(ii) Reporting modeling. Your system specific study plan must include
the information in this paragraph (a)(2)(ii).

(A) Tabular or spreadsheet data demonstrating that the model meets
requirements in paragraph (a)(2)(i)(B) of this section.

(B) A description of all calibration activities undertaken, and if
calibration is complete, a graph of predicted tank levels versus
measured tank levels for the storage facility with the highest residence
time in each pressure zone, and a time series graph of the residence
time at the longest residence time storage facility in the distribution
system showing the predictions for the entire simulation period ( i.e. ,
from time zero until the time it takes to for the model to reach a
consistently repeating pattern of residence time).

(C) Model output showing preliminary 24 hour average residence time
predictions throughout the distribution system.

(D) Timing and number of samples representative of the distribution
system planned for at least one monitoring period of TTHM and HAA5 dual
sample monitoring at a number of locations no less than would be
required for the system under standard monitoring in §141.601 during
the historical month of high TTHM. These samples must be taken at
locations other than existing subpart L compliance monitoring locations.

(E) Description of how all requirements will be completed no later than
12 months after you submit your system specific study plan.

(F) Schematic of your distribution system (including distribution system
entry points and their sources, and storage facilities), with notes
indicating the locations and dates of all completed system specific
study monitoring (if calibration is complete) and all subpart L
compliance monitoring.

(G) Population served and system type (subpart H or ground water).

(H) You must retain a complete copy of your system specific study plan
submitted under this paragraph (a)(2), including any State modification
of your system specific study plan, for as long as you are required to
retain your IDSE report under paragraph (b)(7) of this section.

(iii) If you submit a model that does not fully meet the requirements
under paragraph (a)(2) of this section, you must correct the
deficiencies and respond to State inquiries concerning the model. If you
fail to correct deficiencies or respond to inquiries to the State's
satisfaction, you must conduct standard monitoring under §141.601.

(b) IDSE report. Your IDSE report must include the elements required in
paragraphs (b)(1) through (b)(6) of this section. You must submit your
IDSE report according to the schedule in §141.600(c).

(1) Your IDSE report must include all TTHM and HAA5 analytical results
from subpart L compliance monitoring and all system specific study
monitoring conducted during the period of the system specific study
presented in a tabular or spreadsheet format acceptable to the State. If
changed from your system specific study plan submitted under paragraph
(a) of this section, your IDSE report must also include a schematic of
your distribution system, the population served, and system type
(subpart H or ground water).

(2) If you used the modeling provision under paragraph (a)(2) of this
section, you must include final information for the elements described
in paragraph (a)(2)(ii) of this section, and a 24-hour time series graph
of residence time for each subpart V compliance monitoring location
selected.

(3) You must recommend and justify subpart V compliance monitoring
locations and timing based on the protocol in §141.605.

(4) Your IDSE report must include an explanation of any deviations from
your approved system specific study plan.

(5) Your IDSE report must include the basis (analytical and modeling
results) and justification you used to select the recommended subpart V
monitoring locations.

(6) You may submit your IDSE report in lieu of your system specific
study plan on the schedule identified in §141.600(c) for submission of
the system specific study plan if you believe that you have the
necessary information by the time that the system specific study plan is
due. If you elect this approach, your IDSE report must also include all
information required under paragraph (a) of this section.

(7) You must retain a complete copy of your IDSE report submitted under
this section for 10 years after the date that you submitted your IDSE
report. If the State modifies the subpart V monitoring requirements that
you recommended in your IDSE report or if the State approves alternative
monitoring locations, you must keep a copy of the State's notification
on file for 10 years after the date of the State's notification. You
must make the IDSE report and any State notification available for
review by the State or the public.

§ 141.603   40/30 certification.

(a) Eligibility. You are eligible for 40/30 certification if you had no
TTHM or HAA5 monitoring violations under subpart L of this part and no
individual sample exceeded 0.040 mg/L for TTHM or 0.030 mg/L for HAA5
during an eight consecutive calendar quarter period beginning no earlier
than the date specified in this paragraph (a).

If your 40/30 certification is due	Then your eligibility for 40/30
certification is based on eight consecutive calendar quarters of subpart
L compliance monitoring results beginning no earlier than1

(1) October 1, 2006	January 2004.

(2) April 1, 2007	January 2004.

(3) October 1, 2007	January 2005.

(4) April 1, 2008	January 2005.

1Unless you are on reduced monitoring under subpart L of this part and
were not required to monitor during the specified period. If you did not
monitor during the specified period, you must base your eligibility on
compliance samples taken during the 12 months preceding the specified
period.

(b) 40/30 certification. (1) You must certify to your State that every
individual compliance sample taken under subpart L of this part during
the periods specified in paragraph (a) of this section were ≤0.040
mg/L for TTHM and ≤0.030 mg/L for HAA5, and that you have not had any
TTHM or HAA5 monitoring violations during the period specified in
paragraph (a) of this section.

(2) The State may require you to submit compliance monitoring results,
distribution system schematics, and/or recommended subpart V compliance
monitoring locations in addition to your certification. If you fail to
submit the requested information, the State may require standard
monitoring under §141.601 or a system specific study under §141.602.

(3) The State may still require standard monitoring under §141.601 or a
system specific study under §141.602 even if you meet the criteria in
paragraph (a) of this section.

(4) You must retain a complete copy of your certification submitted
under this section for 10 years after the date that you submitted your
certification. You must make the certification, all data upon which the
certification is based, and any State notification available for review
by the State or the public.

§ 141.604   Very small system waivers.

(a) If you serve fewer than 500 people and you have taken TTHM and HAA5
samples under subpart L of this part, you are not required to comply
with this subpart unless the State notifies you that you must conduct
standard monitoring under §141.601 or a system specific study under
§141.602.

(b) If you have not taken TTHM and HAA5 samples under subpart L of this
part or if the State notifies you that you must comply with this
subpart, you must conduct standard monitoring under §141.601 or a
system specific study under §141.602.

§ 141.605   Subpart V compliance monitoring location
recommendations.

(a) Your IDSE report must include your recommendations and justification
for where and during what month(s) TTHM and HAA5 monitoring for subpart
V of this part should be conducted. You must base your recommendations
on the criteria in paragraphs (b) through (e) of this section.

(b) You must select the number of monitoring locations specified in the
table in this paragraph (b). You will use these recommended locations as
subpart V routine compliance monitoring locations, unless State requires
different or additional locations. You should distribute locations
throughout the distribution system to the extent possible.

Source water type	Population size category	Monitoring frequency1
Distribution system monitoring location



	Total per monitoring period2	Highest TTHM locations	Highest HAA5
locations	Existing subpart L compliance locations

Subpart H:







  	<500	per year	2	1	1

	  	500–3,300	per quarter	2	1	1

	  	3,301–9,999	per quarter	2	1	1

	  	10,000–49,999	per quarter	4	2	1	1

  	50,000–249,999	per quarter	8	3	3	2

  	250,000–999,999	per quarter	12	5	4	3

  	1,000,000–4,999,999	per quarter	16	6	6	4

  	≥5,000,000	per quarter	20	8	7	5

Ground water:







  	<500	per year	2	1	1

	  	500–9,999	per year	2	1	1

	  	10,000–99,999	per quarter	4	2	1	1

  	100,000–499,999	per quarter	6	3	2	1

  	≥500,000	per quarter	8	3	3	2

1All systems must monitor during month of highest DBP concentrations.

2Systems on quarterly monitoring must take dual sample sets every 90
days at each monitoring location, except for subpart H systems serving
500–3,300. Systems on annual monitoring and subpart H systems serving
500–3,300 are required to take individual TTHM and HAA5 samples
(instead of a dual sample set) at the locations with the highest TTHM
and HAA5 concentrations, respectively. Only one location with a dual
sample set per monitoring period is needed if highest TTHM and HAA5
concentrations occur at the same location, and month, if monitored
annually).

(c) You must recommend subpart V compliance monitoring locations based
on standard monitoring results, system specific study results, and
subpart L compliance monitoring results. You must follow the protocol in
paragraphs (c)(1) through (c)(8) of this section. If required to monitor
at more than eight locations, you must repeat the protocol as necessary.
If you do not have existing subpart L compliance monitoring results or
if you do not have enough existing subpart L compliance monitoring
results, you must repeat the protocol, skipping the provisions of
paragraphs (c)(3) and (c)(7) of this section as necessary, until you
have identified the required total number of monitoring locations.

(1) Location with the highest TTHM LRAA not previously selected as a
subpart V monitoring location.

(2) Location with the highest HAA5 LRAA not previously selected as a
subpart V monitoring location.

(3) Existing subpart L average residence time compliance monitoring
location (maximum residence time compliance monitoring location for
ground water systems) with the highest HAA5 LRAA not previously selected
as a subpart V monitoring location.

(4) Location with the highest TTHM LRAA not previously selected as a
subpart V monitoring location.

(5) Location with the highest TTHM LRAA not previously selected as a
subpart V monitoring location.

(6) Location with the highest HAA5 LRAA not previously selected as a
subpart V monitoring location.

(7) Existing subpart L average residence time compliance monitoring
location (maximum residence time compliance monitoring location for
ground water systems) with the highest TTHM LRAA not previously selected
as a subpart V monitoring location.

(8) Location with the highest HAA5 LRAA not previously selected as a
subpart V monitoring location.

(d) You may recommend locations other than those specified in paragraph
(c) of this section if you include a rationale for selecting other
locations. If the State approves the alternate locations, you must
monitor at these locations to determine compliance under subpart V of
this part.

(e) Your recommended schedule must include subpart V monitoring during
the peak historical month for TTHM and HAA5 concentration, unless the
State approves another month. Once you have identified the peak
historical month, and if you are required to conduct routine monitoring
at least quarterly, you must schedule subpart V compliance monitoring at
a regular frequency of every 90 days or fewer.

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e-CFR Data is current as of January 18, 2008

Title 40: Protection of Environment

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Subpart V—Stage 2 Disinfection Byproducts Requirements

Source:   71 FR 488, Jan. 4, 2006, unless otherwise noted. 

§ 141.620   General requirements.

(a) General. The requirements of subpart V of this part constitute
national primary drinking water regulations. The regulations in this
subpart establish monitoring and other requirements for achieving
compliance with maximum contaminant levels based on locational running
annual averages (LRAA) for total trihalomethanes (TTHM) and haloacetic
acids (five)(HAA5), and for achieving compliance with maximum residual
disinfectant residuals for chlorine and chloramine for certain
consecutive systems.

(b) Applicability. You are subject to these requirements if your system
is a community water system or a nontransient noncommunity water system
that uses a primary or residual disinfectant other than ultraviolet
light or delivers water that has been treated with a primary or residual
disinfectant other than ultraviolet light.

(c) Schedule. You must comply with the requirements in this subpart on
the schedule in the following table based on your system type.

If you are this type of system	You must comply with subpart V monitoring
by:1

Systems that are not part of a combined distribution system and systems
that serve the largest population in the combined distribution system

(1) System serving ≥ 100,000	April 1, 2012.

(2) System serving 50,000–99,999	October 1, 2012.

(3) System serving 10,000–49,999	October 1, 2013.

(4) System serving < 10,000	October 1, 2013 if no Cryptosporidium
monitoring is required under §141.701(a)(4) or

October 1, 2014 if Cryptosporidium monitoring is required under
§141.701(a)(4) or (a)(6)

Other systems that are part of a combined distribution system

(5) Consecutive system or wholesale system	—at the same time as the
system with the earliest compliance date in the combined distribution
system.

1The State may grant up to an additional 24 months for compliance with
MCLs and operational evaluation levels if you require capital
improvements to comply with an MCL.

(6) Your monitoring frequency is specified in §141.621(a)(2).

(i) If you are required to conduct quarterly monitoring, you must begin
monitoring in the first full calendar quarter that includes the
compliance date in the table in this paragraph (c).

(ii) If you are required to conduct monitoring at a frequency that is
less than quarterly, you must begin monitoring in the calendar month
recommended in the IDSE report prepared under §141.601 or §141.602 or
the calendar month identified in the subpart V monitoring plan developed
under §141.622 no later than 12 months after the compliance date in
this table.

(7) If you are required to conduct quarterly monitoring, you must make
compliance calculations at the end of the fourth calendar quarter that
follows the compliance date and at the end of each subsequent quarter
(or earlier if the LRAA calculated based on fewer than four quarters of
data would cause the MCL to be exceeded regardless of the monitoring
results of subsequent quarters). If you are required to conduct
monitoring at a frequency that is less than quarterly, you must make
compliance calculations beginning with the first compliance sample taken
after the compliance date.

(8) For the purpose of the schedule in this paragraph (c), the State may
determine that the combined distribution system does not include certain
consecutive systems based on factors such as receiving water from a
wholesale system only on an emergency basis or receiving only a small
percentage and small volume of water from a wholesale system. The State
may also determine that the combined distribution system does not
include certain wholesale systems based on factors such as delivering
water to a consecutive system only on an emergency basis or delivering
only a small percentage and small volume of water to a consecutive
system.

(d) Monitoring and compliance —(1) Systems required to monitor
quarterly. To comply with subpart V MCLs in §141.64(b)(2), you must
calculate LRAAs for TTHM and HAA5 using monitoring results collected
under this subpart and determine that each LRAA does not exceed the MCL.
If you fail to complete four consecutive quarters of monitoring, you
must calculate compliance with the MCL based on the average of the
available data from the most recent four quarters. If you take more than
one sample per quarter at a monitoring location, you must average all
samples taken in the quarter at that location to determine a quarterly
average to be used in the LRAA calculation.

(2) Systems required to monitor yearly or less frequently. To determine
compliance with subpart V MCLs in §141.64(b)(2), you must determine
that each sample taken is less than the MCL. If any sample exceeds the
MCL, you must comply with the requirements of §141.625. If no sample
exceeds the MCL, the sample result for each monitoring location is
considered the LRAA for that monitoring location.

(e) Violation. You are in violation of the monitoring requirements for
each quarter that a monitoring result would be used in calculating an
LRAA if you fail to monitor.

[71 FR 488, Jan. 4, 2006; 71 FR 4645, Jan. 27, 2006]

§ 141.621   Routine monitoring.

(a) Monitoring. (1) If you submitted an IDSE report, you must begin
monitoring at the locations and months you have recommended in your IDSE
report submitted under §141.605 following the schedule in §141.620(c),
unless the State requires other locations or additional locations after
its review. If you submitted a 40/30 certification under §141.603 or
you qualified for a very small system waiver under §141.604 or you are
a nontransient noncommunity water system serving <10,000, you must
monitor at the location(s) and dates identified in your monitoring plan
in §141.132(f), updated as required by §141.622.

(2) You must monitor at no fewer than the number of locations identified
in this paragraph (a)(2).

Source water type	Population size category	Monitoring Frequency1
Distribution system monitoring location total per monitoring period2

Subpart H:



	  	<500	per year	2

  	500–3,300	per quarter	2

  	3,301–9,999	per quarter	2

  	10,000–49,999	per quarter	4

  	50,000–249,999	per quarter	8

  	250,000–999,999	per quarter	12

  	1,000,000–4,999,999	per quarter	16

  	≥ 5,000,000	per quarter	20

Ground Water:



	  	<500	per year	2

  	500–9,999	per year	2

  	10,000–99,999	per quarter	4

  	100,000–499,999	per quarter	6

  	≥ 500,000	per quarter	8

1All systems must monitor during month of highest DBP concentrations.

2Systems on quarterly monitoring must take dual sample sets every 90
days at each monitoring location, except for subpart H systems serving
500–3,300. Systems on annual monitoring and subpart H systems serving
500–3,300 are required to take individual TTHM and HAA5 samples
(instead of a dual sample set) at the locations with the highest TTHM
and HAA5 concentrations, respectively. Only one location with a dual
sample set per monitoring period is needed if highest TTHM and HAA5
concentrations occur at the same location (and month, if monitored
annually).

(3) If you are an undisinfected system that begins using a disinfectant
other than UV light after the dates in subpart U of this part for
complying with the Initial Distribution System Evaluation requirements,
you must consult with the State to identify compliance monitoring
locations for this subpart. You must then develop a monitoring plan
under §141.622 that includes those monitoring locations.

(b) Analytical methods. You must use an approved method listed in
§141.131 for TTHM and HAA5 analyses in this subpart. Analyses must be
conducted by laboratories that have received certification by EPA or the
State as specified in §141.131.

§ 141.622   Subpart V monitoring plan.

(a)(1) You must develop and implement a monitoring plan to be kept on
file for State and public review. The monitoring plan must contain the
elements in paragraphs (a)(1)(i) through (a)(1)(iv) of this section and
be complete no later than the date you conduct your initial monitoring
under this subpart.

(i) Monitoring locations;

(ii) Monitoring dates;

(iii) Compliance calculation procedures; and

(iv) Monitoring plans for any other systems in the combined distribution
system if the State has reduced monitoring requirements under the State
authority in §142.16(m).

(2) If you were not required to submit an IDSE report under either
§141.601 or §141.602, and you do not have sufficient subpart L
monitoring locations to identify the required number of subpart V
compliance monitoring locations indicated in §141.605(b), you must
identify additional locations by alternating selection of locations
representing high TTHM levels and high HAA5 levels until the required
number of compliance monitoring locations have been identified. You must
also provide the rationale for identifying the locations as having high
levels of TTHM or HAA5. If you have more subpart L monitoring locations
than required for subpart V compliance monitoring in §141.605(b), you
must identify which locations you will use for subpart V compliance
monitoring by alternating selection of locations representing high TTHM
levels and high HAA5 levels until the required number of subpart V
compliance monitoring locations have been identified.

(b) If you are a subpart H system serving > 3,300 people, you must
submit a copy of your monitoring plan to the State prior to the date you
conduct your initial monitoring under this subpart, unless your IDSE
report submitted under subpart U of this part contains all the
information required by this section.

(c) You may revise your monitoring plan to reflect changes in treatment,
distribution system operations and layout (including new service areas),
or other factors that may affect TTHM or HAA5 formation, or for
State-approved reasons, after consultation with the State regarding the
need for changes and the appropriateness of changes. If you change
monitoring locations, you must replace existing compliance monitoring
locations with the lowest LRAA with new locations that reflect the
current distribution system locations with expected high TTHM or HAA5
levels. The State may also require modifications in your monitoring
plan. If you are a subpart H system serving > 3,300 people, you must
submit a copy of your modified monitoring plan to the State prior to the
date you are required to comply with the revised monitoring plan.

§ 141.623   Reduced monitoring.

(a) any time the LRAA is ≤0.040 mg/L for TTHM and ≤0.030 mg/L for
HAA5 at all monitoring locations. You may only use data collected under
the provisions of this subpart or subpart L of this part to qualify for
reduced monitoring. In addition, the source water annual average TOC
level, before any treatment, must be ≤4.0 mg/L at each treatment plant
treating surface water or ground water under the direct influence of
surface water, based on monitoring conducted under either
§141.132(b)(1)(iii) or §141.132(d).

Source water type	Population size category	Monitoring

frequency1	Distribution system monitoring location per monitoring period

Subpart H:



	  	<500

monitoring may not be reduced.

  	500–3,300	per year	1 TTHM and 1 HAA5 sample: one at the location
and during the quarter with the highest TTHM single measurement, one at
the location and during the quarter with the highest HAA5 single
measurement; 1 dual sample set per year if the highest TTHM and HAA5
measurements occurred at the same location and quarter.

  	3,301–9,999	per year	2 dual sample sets: one at the location and
during the quarter with the highest TTHM single measurement, one at the
location and during the quarter with the highest HAA5 single
measurement.

  	10,000–49,999	per quarter	2 dual sample sets at the locations
with the highest TTHM and highest HAA5 LRAAs.

  	50,000–249,999	per quarter	4 dual sample sets—at the locations
with the two highest TTHM and two highest HAA5 LRAAs.

  	250,000–999,999	per quarter	6 dual sample sets—at the locations
with the three highest TTHM and three highest HAA5 LRAAs.

  	1,000,000–4,999,999	per quarter	8 dual sample sets—at the
locations with the four highest TTHM and four highest HAA5 LRAAs.

  	≥ 5,000,000	per quarter	10 dual sample sets—at the locations
with the five highest TTHM and five highest HAA5 LRAAs.

Ground Water:



	  	<500	every third year	1 TTHM and 1 HAA5 sample: one at the
location and during the quarter with the highest TTHM single
measurement, one at the location and during the quarter with the highest
HAA5 single measurement; 1 dual sample set per year if the highest TTHM
and HAA5 measurements occurred at the same location and quarter.

  	500–9,999	per year	1 TTHM and 1 HAA5 sample: one at the location
and during the quarter with the highest TTHM single measurement, one at
the location and during the quarter with the highest HAA5 single
measurement; 1 dual sample set per year if the highest TTHM and HAA5
measurements occurred at the same location and quarter.

  	10,000–99,999	per year	2 dual sample sets: one at the location
and during the quarter with the highest TTHM single measurement, one at
the location and during the quarter with the highest HAA5 single
measurement.

  	100,000–499,999	per quarter	2 dual sample sets; at the locations
with the highest TTHM and highest HAA5 LRAAs.

  	≥ 500,000	per quarter	4 dual sample sets at the locations with
the two highest TTHM and two highest HAA5 LRAAs.

1Systems on quarterly monitoring must take dual sample sets every 90
days.

(b) You may remain on reduced monitoring as long as the TTHM LRAA
≤0.040 mg/L and the HAA5 LRAA ≤0.030 mg/L at each monitoring
location (for systems with quarterly reduced monitoring) or each TTHM
sample ≤0.060 mg/L and each HAA5 sample ≤0.045 mg/L (for systems
with annual or less frequent monitoring). In addition, the source water
annual average TOC level, before any treatment, must be ≤4.0 mg/L at
each treatment plant treating surface water or ground water under the
direct influence of surface water, based on monitoring conducted under
either §141.132(b)(1)(iii) or §141.132(d).

(c) If the LRAA based on quarterly monitoring at any monitoring location
exceeds either 0.040 mg/L for TTHM or 0.030 mg/L for HAA5 or if the
annual (or less frequent) sample at any location exceeds either 0.060
mg/L for TTHM or 0.045 mg/L for HAA5, or if the source water annual
average TOC level, before any treatment, >4.0 mg/L at any treatment
plant treating surface water or ground water under the direct influence
of surface water, you must resume routine monitoring under §141.621 or
begin increased monitoring if §141.625 applies.

(d) The State may return your system to routine monitoring at the
State's discretion.

§ 141.624   Additional requirements for consecutive systems.

If you are a consecutive system that does not add a disinfectant but
delivers water that has been treated with a primary or residual
disinfectant other than ultraviolet light, you must comply with
analytical and monitoring requirements for chlorine and chloramines in
§141.131 (c) and §141.132(c)(1) and the compliance requirements in
§141.133(c)(1) beginning April 1, 2009, unless required earlier by the
State, and report monitoring results under §141.134(c).

§ 141.625   Conditions requiring increased monitoring.

(a) If you are required to monitor at a particular location annually or
less frequently than annually under §141.621 or §141.623, you must
increase monitoring to dual sample sets once per quarter (taken every 90
days) at all locations if a TTHM sample is >0.080 mg/L or a HAA5 sample
is >0.060 mg/L at any location.

(b) You are in violation of the MCL when the LRAA exceeds the subpart V
MCLs in §141.64(b)(2), calculated based on four consecutive quarters of
monitoring (or the LRAA calculated based on fewer than four quarters of
data if the MCL would be exceeded regardless of the monitoring results
of subsequent quarters). You are in violation of the monitoring
requirements for each quarter that a monitoring result would be used in
calculating an LRAA if you fail to monitor.

(c) You may return to routine monitoring once you have conducted
increased monitoring for at least four consecutive quarters and the LRAA
for every monitoring location is ≤0.060 mg/L for TTHM and ≤0.045
mg/L for HAA5.

§ 141.626   Operational evaluation levels.

(a) You have exceeded the operational evaluation level at any monitoring
location where the sum of the two previous quarters' TTHM results plus
twice the current quarter's TTHM result, divided by 4 to determine an
average, exceeds 0.080 mg/L, or where the sum of the two previous
quarters' HAA5 results plus twice the current quarter's HAA5 result,
divided by 4 to determine an average, exceeds 0.060 mg/L.

(b)(1) If you exceed the operational evaluation level, you must conduct
an operational evaluation and submit a written report of the evaluation
to the State no later than 90 days after being notified of the
analytical result that causes you to exceed the operational evaluation
level. The written report must be made available to the public upon
request.

(2) Your operational evaluation must include an examination of system
treatment and distribution operational practices, including storage tank
operations, excess storage capacity, distribution system flushing,
changes in sources or source water quality, and treatment changes or
problems that may contribute to TTHM and HAA5 formation and what steps
could be considered to minimize future exceedences.

(i) You may request and the State may allow you to limit the scope of
your evaluation if you are able to identify the cause of the operational
evaluation level exceedance.

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b)(1) of this section for submitting the written report. The State must
approve this limited scope of evaluation in writing and you must keep
that approval with the completed report.

§ 141.627   Requirements for remaining on reduced TTHM and HAA5
monitoring based on subpart L results.

You may remain on reduced monitoring after the dates identified in
§141.620(c) for compliance with this subpart only if you qualify for a
40/30 certification under §141.603 or have received a very small system
waiver under §141.604, plus you meet the reduced monitoring criteria in
§141.623(a), and you do not change or add monitoring locations from
those used for compliance monitoring under subpart L of this part. If
your monitoring locations under this subpart differ from your monitoring
locations under subpart L of this part, you may not remain on reduced
monitoring after the dates identified in §141.620(c) for compliance
with this subpart.

§ 141.628   Requirements for remaining on increased TTHM and HAA5
monitoring based on subpart L results.

If you were on increased monitoring under §141.132(b)(1), you must
remain on increased monitoring until you qualify for a return to routine
monitoring under §141.625(c). You must conduct increased monitoring
under §141.625 at the monitoring locations in the monitoring plan
developed under §141.622 beginning at the date identified in
§141.620(c) for compliance with this subpart and remain on increased
monitoring until you qualify for a return to routine monitoring under
§141.625(c).

§ 141.629   Reporting and recordkeeping requirements.

(a) Reporting. (1) You must report the following information for each
monitoring location to the State within 10 days of the end of any
quarter in which monitoring is required:

(i) Number of samples taken during the last quarter.

(ii) Date and results of each sample taken during the last quarter.

(iii) Arithmetic average of quarterly results for the last four quarters
for each monitoring location (LRAA), beginning at the end of the fourth
calendar quarter that follows the compliance date and at the end of each
subsequent quarter. If the LRAA calculated based on fewer than four
quarters of data would cause the MCL to be exceeded regardless of the
monitoring results of subsequent quarters, you must report this
information to the State as part of the first report due following the
compliance date or anytime thereafter that this determination is made.
If you are required to conduct monitoring at a frequency that is less
than quarterly, you must make compliance calculations beginning with the
first compliance sample taken after the compliance date, unless you are
required to conduct increased monitoring under §141.625.

(iv) Whether, based on §141.64(b)(2) and this subpart, the MCL was
violated at any monitoring location.

(v) Any operational evaluation levels that were exceeded during the
quarter and, if so, the location and date, and the calculated TTHM and
HAA5 levels.

(2) If you are a subpart H system seeking to qualify for or remain on
reduced TTHM/HAA5 monitoring, you must report the following source water
TOC information for each treatment plant that treats surface water or
ground water under the direct influence of surface water to the State
within 10 days of the end of any quarter in which monitoring is
required:

(i) The number of source water TOC samples taken each month during last
quarter.

(ii) The date and result of each sample taken during last quarter.

(iii) The quarterly average of monthly samples taken during last quarter
or the result of the quarterly sample.

(iv) The running annual average (RAA) of quarterly averages from the
past four quarters.

(v) Whether the RAA exceeded 4.0 mg/L.

(3) The State may choose to perform calculations and determine whether
the MCL was exceeded or the system is eligible for reduced monitoring in
lieu of having the system report that information

(b) Recordkeeping. You must retain any subpart V monitoring plans and
your subpart V monitoring results as required by §141.33.

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