U.S. Environmental Protection Agency Plan for Developing Interim
Preliminary Remediation Goals for Dioxin in Soil

In May 2009, the U.S. Environmental Protection Agency’s (EPA)
Administrator, Lisa P. Jackson decided that EPA needs to accelerate work
underway to reassess the human health risks from exposures to dioxin. 
EPA’s Science Plan for Activities Related to Dioxins in the
Environment (2009) details a plan, with interim milestones, for
completion of the Agency’s dioxin reassessment.  By the end of 2010,
EPA expects to complete the dioxin reassessment and release it to the
public, subject to further consideration of the science and the scope
and complexity of the revisions that will need to be made. 

Several key site-specific decisions involving dioxin may need to be made
before the dioxin reassessment is finalized.  EPA’s Office of Solid
Waste and Emergency Response (OSWER) will be reviewing current dioxin
cleanup guidance set by the Agency and other entities, with the goal of
recommending interim preliminary remediation goals (PRGs) informed by
the latest science. These interim recommended PRGs would be used until
EPA issues its dioxin reassessment and OSWER issues final recommended
PRGs based on the reassessment.  After publication of the dioxin
reassessment and final PRG guidance, EPA will re-evaluate cleanup
decisions at Superfund, Federal Facilities, Brownfields, and Resource
Conservation and Recovery Act (RCRA) sites that were based on the
interim PRGs to ensure that cleanups are protective. 

In developing these interim recommended PRGs, OSWER and EPA’s Office
of Research and Development (ORD) are reviewing current soil cleanup
levels and dioxin toxicity values used by the states, the Agency for
Toxic Substances and Disease Registry, and other countries.  Based on
this evaluation, OSWER may reconsider EPA’s currently recommended PRGs
for Superfund, Federal Facilities, Brownfields and RCRA sites, which are
1 ppb (parts per billion) (or 1,000 ppt (parts per trillion)) for dioxin
toxicity equivalents (TEQs) in residential soil, and a level within the
range of 5 ppb (or 5,000 ppt) and 20 ppb (or 20,000 ppt) in
commercial/industrial soil, where exposure is due to direct contact. 
Three key components of EPA’s current recommended PRGs will be
re-evaluated: the EPA dioxin toxicity value adopted in 1985, generic
exposure assumptions, and the cancer risk level. OSWER intends to
recommend interim PRGs informed by the latest science and the work of
state and other agencies.  

The proposed plan for the development of the OSWER interim recommended
PRGs for dioxin in soil is as follows:

Open public comment period on this OSWER plan              

for developing interim recommended PRGs  	                              
   October  2009                                                        
                          

Interim recommended PRGs available for public comment                   
    

in the Federal Register                          				  December 31, 2009

End of public comment period					          February 2010

Issuance of guidance that addresses interim recommended                 
          

PRGs								   	     June 2010*

                                                          

*Schedule subject to change based on the extent of public comments
received.

EPA will make this information available to the public through the
following: 1) the EPA Superfund program web site; 2) Clu-in, a web site
maintained by EPA that has technical information related to cleanups; 3)
postings on regional web sites and used at public meetings; and 4)
distribution generally to the regions.

To comment on the proposed plan for developing interim recommended PRGs
for dioxin in soil, please send comments to:  OSWER_Dioxin_PRGs@epa.gov 


Frequently Asked Questions

How are PRGs Used?

Consistent with the National Contingency Plan, PRGs generally are
initial chemical-specific concentration goals for specific media (e.g.
soil, sediment, water and air) and land uses at Superfund, Federal
Facilities, Brownfields and RCRA sites.  These goals normally should
both be protective of human health and the environment and comply with
all applicable, relevant and appropriate regulations (ARARs) for all
exposure pathways being addressed. 

Risk-based PRGs generally are developed using estimates for the toxicity
of a chemical, as well as generic exposure assumptions.  An example of
an exposure assumption is exposure frequency, or the number of days in a
year that a person is exposed to contamination.  A generic exposure
frequency of 350 days per year is typically used for Superfund, Federal
Facilities, Brownfields, and RCRA sites for residential settings.

A PRG is usually calculated for cancer and for non-cancer effects.  The
more conservative value typically is then selected as the recommended
PRG.  PRGs for carcinogens commonly are set at levels that correspond to
one in a million (1 x 10-6) individual excess cancer risk5 as a point of
departure.  However, they may be revised to a different risk level
within the acceptable risk range of 10-6 to 10-4 based on consideration
of exposure factors, uncertainty, or technical issues. PRGs for
non-carcinogens are typically set at a level corresponding to a hazard
quotient6 equal to 1.0.

It is important to note that PRGs are not intended to act as
site-specific cleanup levels; rather they are intended to serve as
initial guidelines for use in scoping characterization and remediation
alternatives at Superfund, Federal Facilities, Brownfields, and RCRA
sites.  Final cleanup levels for a site typically would be developed by
modifying the PRGs based on consideration of site specific factors
(e.g., exposure frequency or acceptable cancer risk level).7

For specific information on how PRGs are calculated, see EPA’s Risk
Assessment Guidance for Superfund (RAGS) Part B, Chapter 1 and Chapter
3.  Available online at:   HYPERLINK
"http://www.epa.gov/oswer/riskassessment/ragsb/index.htm%20" 
http://www.epa.gov/oswer/riskassessment/ragsb/index.htm  

What are the current PRGs for dioxin in soil?

For Superfund, Federal Facilities, Brownfields, and RCRA sites,
OSWER’s 1998 soil dioxin guidance  NOTEREF _Ref237845794 \h  \*
MERGEFORMAT  2  recommends a PRG of 1 ppb (or 1,000 ppt) for dioxin
toxicity equivalents (TEQs)  NOTEREF _Ref237845810 \h  \* MERGEFORMAT  3
 in residential soil, and a level within the range of 5 ppb (or 5,000
ppt) and 20 ppb (or 20,000 ppt) in commercial/industrial soil, where
exposure is due to direct contact. A range in levels has been
recommended for commercial/industrial soil due to the greater
variability in human exposures associated with these land uses.

The currently recommended PRGs are based on an EPA dioxin toxicity value
adopted by the Agency in 1985. This toxicity value is considered a Tier
3 toxicity value under the 2003 OSWER memorandum on the hierarchy of
sources of toxicological information8 that should be considered for
site-specific risk assessments (the interim recommended PRGs will also
be based on a Tier 3 toxicity value.)  The categories for toxicity
values are as follows:

Tier 1- EPA’s Integrated Risk Information System (IRIS)9

Tier 2- EPA’s Provisional Peer-Reviewed Toxicity Values (PPRTVs) –
The Office of Research and Development/National Center for Environmental
Assessment/Superfund Health Risk Technical Support Center develops
PPRTVs, at the request of EPA’s Superfund program, for chemicals not
found in IRIS. 

Tier 3- Other Toxicity Values – Tier 3 includes additional EPA and
non-EPA sources of toxicity information. Priority should be given to
those sources of information that are the most current, the basis for
which is transparent and publicly available, and which have been
peer-reviewed. 

The currently recommended PRGs are also based on generic exposure
assumptions and cancer risk levels used at Superfund, Federal
Facilities, Brownfields, and RCRA sites.  The 1 ppb (or 1,000 ppt)
represents a lifetime excess cancer risk of 2.5 x 10-4 for residential
soil, and 5 ppb (or 5,000 ppt) represents a lifetime excess cancer risk
of 1.4 x 10-4 for commercial/industrial soil.  

Why is EPA considering modifying the existing PRGs for dioxin in soil?  

While EPA finalizes its ongoing dioxin reassessment, EPA Administrator
Jackson has asked that Agency staff consider the newest science to help
evaluate the protectiveness of current PRGs for dioxin in soil.  

How will the interim PRGs for dioxin in soil be used?

The interim PRGs will be used to evaluate pending cleanup decisions.
These decisions will be re-evaluated when the final PRGs for dioxin in
soil are developed. As noted above, the interim PRGs being developed for
dioxin are not site-specific cleanup levels. They are intended to serve
as recommended PRG levels that can generally be used as a starting point
in the process used for determining cleanup levels at Superfund, Federal
Facilities, Brownfields, and RCRA sites.  Final cleanup levels for a
site would typically be developed by modifying the PRGs based on
consideration of site-specific information (such as exposure frequency
or acceptable cancer risk level) obtained as part of the site-specific
baseline risk assessment. 

October 15, 2009

  PAGE  1 

 U.S. Environmental Protection Agency.  May 26, 2009.  EPA’s Science
Plan for Activities Related to Dioxins in the Environment.  Press
Release.  Available online:    HYPERLINK
"http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=209690" 
http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=209690 .

 U.S. Environmental Protection Agency.  April 13, 1998.  Approach for
Addressing Dioxin in Soil at CERCLA and RCRA Sites.  OSWER Directive
9200.4-26.  Available at:    HYPERLINK
http://www.epa.gov/superfund/resources/remedy/pdf/92-00426-s.pdf
http://www.epa.gov/superfund/resources/remedy/pdf/92-00426-s.pdf .

 Toxicity equivalents consider the toxicity of the less toxic
dioxin-like compounds as fractions of the toxicity of the most toxic
compound (2,3,7,8-TCDD). Each compound is attributed a specific “Toxic
Equivalency Factor” (TEF). This factor indicates the degree of
toxicity compared to 2,3,7,8-TCDD, which is given a reference value of
1.

 40 CFR 300 Section 430(e)(2)(i)(A)(2)

5  Cancer risks normally are estimated as the incremental probability of
an individual developing cancer over a lifetime as a result of exposure
to a contaminant.  This incremental or excess individual lifetime cancer
risk is generally expressed as the probability (e.g., 1 x 10-6 or one in
a million) of an individual developing cancer.

6  A hazard quotient generally is the ratio of an exposure level for a
single substance to a reference dose, which is an estimate of the daily
exposure that is likely to be without an appreciable risk of deleterious
effects during a lifetime.

7  EPA's Risk Assessment Guidance for Superfund, Part B, Development of
Preliminary Remediation Goals 1991, EPA/540/R-92/003

8  U.S. Environmental Protection Agency.  Office of Solid Waste and
Emergency Response.  December 5, 2003.  Human Health Toxicity Values in
Superfund Risk Assessments.  OSWER Directive 9285.7-53.  Available at:  
 HYPERLINK "http://www.epa.gov/oswer/riskassessment/pdf/hhmemo.pdf" 
http://www.epa.gov/oswer/riskassessment/pdf/hhmemo.pdf .

9  IRIS develops human health risk information for an EPA database that
addresses potential human health effects that may result from long-term
exposure to environmental contaminants.   Dioxin toxicity values
established based on the final dioxin reassessment will be incorporated
into IRIS.

What is a PRG?

Preliminary remediation goals (PRGs) are chemical-specific concentration
goals for specific media (e.g. soil, sediment, water and air) and land
use combinations at Superfund, Federal Facilities, Brownfields and RCRA
sites.  They serve as a target to use during the initial development,
analysis, and selection of cleanup alternatives.  These goals should
both be protective of human health and the environment and comply with
all applicable, relevant and appropriate regulations (ARARs) for all
exposure pathways being addressed.

