EPA510-R-97-001
PIRI
ISSUE PAPERS
July 2, 1997
PIRI'S (PARTNERSHIP IN RBCA IMPLEMENTATION) OFFICIAL MEMBERS INCLUDE
REPRESENTATIVES FROM THE MAJOR OIL COMPANIES (I.E., AMOCO, BP, CHEVRON, EXXON,
MOBIL, AND SHELL), ASTM, EPA's OUST, AND STATES. : THE PAPERS CONTAINED HERE
REPRESENT THE POINTS OF VIEW OF THE VARIOUS PIRI AUTHORS AND NOT THE COMPANIES OR
STATES WITH WHICH THEY ARE AFFILIATED. THIS DOCUMENT IS NOT AN EPA DOCUMENT. THIS
DOCUMENT WILL BE UPDATED AS CHANGES IN TECHNOLOGIES AND POLICIES REQUIRE. IT IS
CRITICAL THAT READERS CHECK WITH THE IMPLEMENTING AGENCY IN THEIR STATES BEFORE
ACTING UPON THE POLICIES DISCUSSED IN THESE PAPERS.
Issues Associated With Natural Attenuation 1
The Definition Of Contaminant In Risk-Based Corrective Actions 4
No Further Action Letters In Risk-Based Corrective Actions 7
Selection Of Carcinogenic Target Risk Levels For Soil And Groundwater Remediation 9
Off-Site Movement Of Chemicals Of Concern In Risk-Based Corrective Actions 13
Institutional Controls In Risk-Based Corrective Actions 16
Groundwater Nondegradation Policies In The Development And Implementation Of
Risk-Based Corrective Action Programs 19
Using TPH In Risk-Based Corrective Action 21
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PIRI
ISSUE PAPER
Issues Associated With Natural Attenuation
by
Dana S. Tulis, United States Environmental Protection Agency
There are a multitude of technical and policy issues associated with using natural attenuation to
remediate leaking USTs containing petroleum. The U.S. Environmental Protection Agency (EPA)
believes that natural attenuation is a viable option for remediating leaking UST sites and that it is
compatible with the risk-based corrective action approach. The majority of States allow natural
attenuation, and most State Funds reimburse for associated expenditures. Some State implementing
agencies do not, however, allow the use of natural attenuation.
Background
The use of natural attenuation at UST sites with petroleum releases has increased significantly
over the past few years. As of 1995, natural attenuation is the second most popular option for soil sites; it
is being used at roughly 29,000 sites or at 28 percent of the active contaminated soil universe. Natural'
attenuation is the most common treatment option at groundwater sites; it is being used at 17,000 sites or
about 47 percent of the active contaminated groundwater universe.
The first issue for natural attenuation is whether or not it is accepted as a remediation option by a
State. Although most States allow the use of natural attenuation, there are at least seven States that do not
allow it as the sole remediation option. About 43 States have established or are planning to establish
guidance, regulations, or statutes on natural attenuation. At this time, MTBE does not appear to readily
biodegrade. EPA, therefore, does not currently believe that natural attenuation is an appropriate
remediation option for MTBE. EPA encourages States to incorporate MTBE as a chemical of concern
into their RBCA programs. About 10 States do not allow natural attenuation if MTBE is a chemical o*f
concern; this number may'begin to increase as more States start testing for the presence of MTBE.
However, the presence of MTBE at a site should not preclude natural attenuation as a remedy for other
contaminants (e.g., BTEX) at a site.
Natural attenuation is one of several remediation options possible at a site; it is not a "default"
option. As with any remediation option, natural attenuation should be evaluated for its appropriateness
based on the risks, the site characteristics, and the potential to achieve remediation objectives at each
individual site.
The next issue is "how to implement" the use of natural attenuation. EPA is developing an
EPA/OSWER Directive entitled Use of Monitored Natural Attenuation at Superfund, RCRA Corrective
Action, and Underground Storage Tank Sites for use at petroleum and hazardous waste sites and hopes to
release it by September 1997. ASTM is developing a Standard Guide for Remediation by Natural
Attenuation at Petroleum Sites and plans to release it soon. These documents will assist States in
developing processes and criteria for implementing natural attenuation as a remedy.
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Natural Attenuation Versus No Further Action
»
If natural attenuation is chosen as a remediation option, then, by definition, the site is not
"protective [of human health and the environment]." The site would be designated as a No Further
Action (NFA) site if it were "protective [of human health and the environment]"; hence, work is still
needed at the site. Natural attenuation is an active process that includes site characterization, risk
assessment, and monitoring of remediation progress. EPA believes that free product removal is essential
when remediating by natural attenuation and that the cleanup is not complete until the site has reached the
cleanup levels of the State or local implementing agency. EPA also believes that it is important for the
implementing agency to include contingency measures in its planning, in case natural attenuation is
shown through monitoring to be unable to meet the cleanup levels.
Of course, States can and do incorporate flexibility in how they implement and oversee free
product removal. One must remember that the Federal UST regulations pertain only to Federally
regulated USTs that contain petroleum (and hazardous substances). Petroleum from other sources is not
subject to the Federal UST regulations, although EPA's Oil Pollution Act, Resource Conservation
Recovery Act (RCRA), or Safe Drinking Water Act (SDWA) may apply. In addition, the Federal UST
regulations state that "...owners and operators must remove free product to the maximum extent
practicable as determined by the implementing agency." For example, site-specific (e.g., geological)
conditions may render free product removal impractical. In this case or at other sites as determined by
the implementing agency, free product removal would probably be assessed within a risk-based
framework base that evaluates proximity to potential receptors, land use, groundwater classification, and
other factors as determined by the State or local implementing agency. EPA recommends that the
responsible parry work closely with the implementing agency to ensure that it complies with State
requirements.
Site Characterizations
As with any remediation alternative, an adequate site characterization is essential. Three types of
site-specific information or "lines of evidence" may be used: Primary, secondary, and tertiary. Each, is
described below.
+ Primary lines of evidence are data from historical groundwater and/or soil chemistry samples that
demonstrate a clear and meaningful trend of declining contaminant mass and/or concentrations at
appropriate monitoring or sampling points. Primary lines of evidence are used to determine
whether plumes are shrinking or stable.
4 Secondary lines of evidence include data from the site characterization that indirectly
demonstrate the type of natural attenuation processes active at the site and determine the rate at
which such processes will reduce contaminant concentrations to required levels. For example,
the rate of biodegradation can be indirectly determined by measuring the levels of dissolved
oxygen and nitrate, iron (IT), sulfate, methane, carbon dioxide, and other parameters.
4- Tertiary lines of evidence include data from field or microcosm studies (conducted in or with
actual contaminated site media) that directly demonstrate microbial activity in the soil or aquifer
material and its ability to degrade the contaminants of concern.
EPA recommends collecting both primary and secondary lines of evidence unless there are
sufficient historical data (as determined by Hie State or local implementing agency) to adequately
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characterize the site. The amount and type of information necessary will depend upon site-specific
factors including the hydrogeological settings, the size and nature of the problem, the existence and
proximity of any receptors, and the potential risk to receptor!. For petroleum sites, EPA does not expect
that tertiary lines of evidence will be necessary. ASTM is developing similar recommendations.
Nineteen States currently require secondary lines of evidence (i.e., geochemical indicators) for natural
attenuation.
Remediation Objectives
Every remediation action plan must have clearly defined objectives. These objectives include
identifying cleanup levels or performance requirements, determining points of compliance, and
establishing acceptable timeframes for cleanup. Once the remediation objectives are established, natural
attenuation can be evaluated for suitability as a remediation alternative. Natural attenuation may'be the
sole remediation option, a component of the remediation action plan, or unsuitable—depending on the site.
Performance Monitoring
EPA emphasizes that performance monitoring is essential when relying on natural attenuation as
a remediation option. Performance monitoring is needed to demonstrate that natural attenuation is
occurring according to expectations, to detect contaminant migration or any new releases from the site,
and to verify the attainment of cleanup objectives. EPA stresses that performance monitoring is required
as long as contamination levels remain above required cleanup levels at points of compliance as
determined by the State implementing agency. The majority of States require quarterly monitoring
generally for a period of 1 to 3 years or until definite trends are established or standards are attained.
Practical and Economic Issues
The potential advantages of natural attenuation include: The generation of less remediation
wastes; less disruption of the environment; ease of use in conjunction with other remediation
technologies; no equipment down time; and likelihood of lower overall costs than from active
remediation. There are, however, a number of disadvantages including: Longer timeframes may be
required to achieve remediation goals; the public may not perceive the process correctly; site
characterizations can be more costly and complex; responsibility must be assumed for performance
monitoring; the potential exists for continued migration; and implementing a contingency plan that uses a
more active remediation alternative might be necessary if natural attenuation fails.
The disadvantages can have economic implications: Properly transfers may be delayed or
stopped; longer timeframes may not be compatible with future land uses; active remediation may be more
economical than performance monitoring at certain sites; and liability could be an issue for present and
future land users. In addition, the owner and operator may find it more difficult to obtain insurance.
EPA and the States are working closely with the private sector to overcome some of these issues, but
many of them will need to be resolved on a site-specific basis.
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PIRI
'* ISSUE PAPER
The Definition Of Contaminant In Risk-Based Corrective Actions
by
Karen Lyons, Shell Oil Co.
When State regulatory agencies are integrating risk-based corrective action (RBCA) into their
UST programs, they may need to reconsider their definition and use of terms such as contaminant,
contamination, and contaminated media. Historically, many programs have defined a contaminant as any
detection of a chemical in environmental media. To be consistent with the underlying concepts of
RBCA, it may be more appropriate to define contaminant in terms of the conditions that pose an
unacceptable threat to human health and/or the environment.
Defining Contaminant
In adopting a RBCA program, the acceptance that limited quantities of chemicals of concern
(COCs) may remain in environmental media without presenting an unacceptable threat to human health
and the environment is fundamental. In other words, the mere presence of a chemical in a medium does
not necessarily make that medium contaminated. One of the goals of RBCA is to establish those specific
conditions which pose an unacceptable threat to human or environmental receptors. As a starting point
for defining the key terminology, the following questions must be addressed:
+ What is a chemical of concern (COC) and how does it differ from a contaminant!
+ When does the presence of a COC result in contaminated media*!
f How does a State agency regulate contaminated medial
4 How does one determine which concentration levels of COCs will pose an unacceptable present
or future threat to human health or the environment?
Chemical of concern (COC) can be defined by referring to the statutory and regulatory
definitions for solid waste, industrial solid waste, municipal solid waste, radioactive waste, hazardous
waste, hazardous substance, petroleum substance, and other regulated substances. To define these
substances, individual States should look to their own administrative code and/or the Code of Federal
Regulations. For petroleum underground storage tanks, the list of COCs should be relatively limited.
A COC becomes a contaminant when the COC occurs at a concentration that poses an
unacceptable threat to human health and the environment. The RBCA program will establish that
particular concentration limit specific to land use and exposure scenario.
Contaminated media means soil, sediment, groundwater, surface water, or air that contains COCs
at levels which exceed human health or environmentally protective levels as determined consistent with
the State's RBCA program. Most States regulate contaminated media, that is, specific chemicals as they
occur in air, water, soil, and sediment.
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Historical Perspective
Historically, it has not been unusual ftrf a State to u's"e contaminant to mean any occurrence of a
regulated chemical in soil, sediment, groundwater, surface water, air, or other media above the currently
established level of detection. By defaulting to this definition, the State may feel that it is enacting its
responsibility for protecting the public; the State cannot provide the regulated community with anything
that may be misinterpreted as a permit to pollute or discharge. This definition of contaminant may be
perceived to be protective [of human health and the environment], but it has not necessarily resulted in
the remediation or removal of more contaminated media or other measurable benefits of reducing human
health risks or ecological impacts. The following problems have been identified with a definition based
on limit of detection:
4 Many chemicals occur at background concentrations in soil, water, or air by their natural
occurrence in the environment. Typically, these chemicals are not regarded as contaminants
solely because they are detected in the laboratory.
4 There is a stigma associated with the words contaminant and contamination, potentially resulting
in property devaluation and/or third-party concerns. By defining contamination on the basis of
occurrence only, unnecessary concern is generated and this stigma is automatically attached to a
property before the potential risks associated with the occurrence of a chemical have been
evaluated. This thinking is certainly not consistent with rational risk-based decision-making.
4 There are inherent problems with the use of the laboratory levels of detection that will impart
much uncertainty to the definition.
4 The level of detection for a chemical may be specific to the laboratory method used to analyze
for that particular chemical; one'chemical can have various detection limits depending on the
laboratory method used in mat particular State or agency program.
4 Detection limits are ever changing with advances in analytical chemistry and availability of better
laboratory equipment. In many cases, chemicals can be detected well below background levgls.
4 The accurate detection of a chemical in a sample can be impeded by the occurrence of other
chemicals in the sample (e.g., matrix interference).
Alternatively, the risk-based definition for contaminant takes into account the acceptable level of
risk, land-use definitions (i.e., current and reasonable potential future), and exposure scenario (i.e.,
completed pathways). Inherent in the State-implemented RBCA program will be the demonstration that
the regulated chemical is present at a concentration that is deemed to pose an unacceptable risk to human
health or the environment and, therefore, is undesirable. A critical change in philosophy as it applies to
these definitions might help to eliminate the automatic assignment of the "contamination" stigma to all
properties where COCs are detected.
Precedent Setting Programs
There is a precedent in many State and Federal regulatory programs to allow levels of chemicals
of concern to remain in environmental media without becoming contaminated media. Most States have
accepted this concept in their adoption of MCLs or State drinking water standards and permitted air
emissions and surface water discharges. Each State can look to its specific programs for numerous
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examples of situations when acceptable levels of chemicals in soil, water, or air do not create
contaminated media.
Recommendation
Establish the goals of the State-specific RBCA program. Develop definitions that are consistent
with the goals as part of the implementation process. Consider existing statutory and regulatory
definitions to avoid conflict with existing State regulatory programs.
LAST REVISED JUNE ZO, 1997.
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PIRI
ISSUE PAPER
No Further Action Letters In Risk-Based Corrective Actions
by
Chet Clarke, Texas Natural Resource Conservation Commission
A primary goal of environmental regulatory programs is the protection of human health and the
environment. Beyond protection of human health and the environment, a primary goal of responsible
parties is to achieve in a timely and cost-effective manner "No Further Action" (NFA) status which
supports some degree of certainty. NFA letters are significant in that they should:
4 Represent an official regulatory affirmation that a site adequately protects human health and the
environment for the intended use of the site;
4 Note the end to corrective action; and
4 Document any property use restrictions.
Regulators, responsible parties, landowners, investors, and lenders all benefit from NFA status.
Unfortunately, the vague language often included in NFA letters (e.g., no further action at this time; no
further action but case may be reopened at a future time) thwarts much of the benefit derived from NFA
status for all parties involved. Responsible parties need to have reasonable confidence that a corrective
action matter is resolved. Landowners also need an NFA letter that imparts reasonable certainty to the
closure to avoid an unnecessary stigma on the property which may diminish property values and rum an
otherwise lucrative property transaction into an unacceptable economic risk for investors and lenders.
Regulators may be concerned that the NFA status may be inappropriately viewed as an end to
environmental liability. Generally, there is no end to environmental liability with the issuance of an NFA
letter. The NFA letter is a notice of the end of corrective action based on reported site conditions and
land use and generally does not address environmental liability. (Each regulatory entity should verify.)
Because the NFA letter dpes not address environmental liability, "at this time" language imparts
uncertainty and complicity into the NFA statement.
Clearly, the issuance of NFA letters is important, and the wording of NFA letters is critical. In
developing NFA letters, several factors should be considered. The first is that environmental regulatory
agencies generally have clear authority to compel corrective actions when necessary to protect human
health and the environment from contamination sites regardless of any assigned NFA status. In other
words, "at this time" language may be duplicative and may cause unnecessary concern as NFA status
may not terminate regulatory authority. Regulatory agencies may want to investigate their authority in
this regard.
Second, signed statements from responsible parties and consultants attending to the
appropriateness of the site-for NFA status may impart a greater regulatory confidence in assignment of
NFA status in that all parties have a vested interest/responsibility in the closure decision. More
confidence in the completeness and validity of site information imparts greater confidence in decision
making on the part of all parties involved.
Third, specific conditions for closure may be incorporated into NFA letters when restricted land
use or other conditions must be maintained for NFA status to remain in effect. Such NFA letters should
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clearly indicate what actions/conditions will necessitate further corrective action. For example, language
such as *NFA status will be in effect so long as the site is not used for residential purposes" can be
incorporated into NFA letters to indicate to all parties involved that the property is suitable for other land
uses which, in fact, may represent greater economic advantage than residential land use. Using this
language may not limit authority to reopen cases when needed to protect human health and the
environment, but it will lay out use of the property that can be confidently exercised. In some instances,
institutional controls may be necessary to ensure long term protection and notification when land-use
limitations are the basis for closure.
LAST REVISED JUNE 2O, I 997.
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PIRI
ISSUE PAPER
Selection Of Carcinogenic Target Risk Levels For Soil And Groundwater Remediation
by
Mark Malander, Mobil Oil Corporation
Target risk levels dictate the degree of human health protection to be achieved by risk-based soil
and groundwater cleanup standards. The degree of conservatism incorporated in the selection of
applicable target risk levels significantly affects cleanup standard calculations and associated remediation
action cost. This paper reviews the significance of the carcinogenic target risk level and provides
background information regarding target risk values incorporated in various regulatory programs. This
paper does not discuss target risk levels for non-carcinogenic chemicals.
Significance of Target Risk Levels
The target risk level serves as a starting point in the development of soil and groundwater cleanup
standards. The adverse human health effect is quantified by the individual excess lifetime cancer risk
(IELCR). The IELCR represents the incremental (over background) probability of an exposed
individual's getting cancer (i.e., a risk occurring in excess of or above and beyond other risks for cancer
such as diet, smoking, heredity). Cleanup standards calculated on the basis of excess risk limits
correspond to allowable levels in excess of the background concentrations of the chemicals of concern
normally present in the source media. In the "forward mode" of risk assessment, the end result of a
baseline risk assessment is an estimated IELCR at the point of exposure. If the IELCR exceeds the
regulatory specified target risk level, remediation measures are necessary. In the "backward mode" of
risk assessment, the acceptable level of risk at the point of exposure, as specified by the regulatory
authority, is used to back-calculate soil or groundwater target cleanup concentrations for the source area.
If the target concentrations exceed the actual concentrations in the source area, no remediation measures
are necessary.
Back-calculated cleanup standards are directly proportional to the applicable target risk level.
For example, if the acceptable risk level for benzene in residential drinking water is increased from 10~6 to
10"4, the target concentration for benzene changes from 2.94 ug/1 to 294 ug/1 (ASTM, 1995), based on
the application of standard reasonable maximum exposure (RME) factors. In practical terms, this means
that persons ingesting water containing 2.94 ug/1 of benzene on a daily basis for 30 years will incur an
additional 1 in 1,000,000 risk of cancer, while persons ingesting water containing 294 ug/1 of benzene,
incur an additional 1 in 10,000 risk of cancer. Persons who do not ingest this water incur no additional
risk. Soil and groundwater cleanup standards for all exposure pathways exhibit a similar sensitivity to the
acceptable risk levels.
Examples Of Acceptable Carcinogenic Risk Levels In Existing Regulatory Programs
There is a general perception that a carcinogenic risk limit of 10"s represents a standard risk
protection factor embodied in State and Federal regulations. However, careful review of historical
standards reveals use of a broad range of effective risk limits, wherein 10's represents a lower bound zero
risk value (FSC, 1980). Also, there is an apparent historical trend for the use of greater acceptable risk
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levels a$ the conservative nature of risk assessment calculations has been recognized. Examples of
existing regulatory standards are listed below.
4 U.S. Food and Drug Administration (FDA): A risk-based recommended standard of 10'8 was
first proposed by Mantel and Bryan in 1961. In 1977, the FDA instead used 10'6 as a risk-based
standard for food residues of animal drugs after originally proposing the 1O'8 risk level in 1973.
The 10"6 target risk level used by the FDA for meat products represents essentially zero risk.
4 Mean Regulatory Trigger: Travis et al (1987) reviewed over 132 Federal regulatory decisions
and concluded that every situation involving a risk due to chemical exposure of 4x10'3 triggered a
regulation. Further, action was never taken to reduce upper-bound cancer risks below 1x10'5.
The decisions to regulate at levels between 4xlO'3 and IxlO'6 were based on size of exposed
population, technical feasibility, and costs.
f Superfund NCP: Li its final National Contingency Plan for Superfund site remediation (USEPA,
1990a), EPA codified a range of acceptable risks (i.e., IxlO'4 to IxlO'6) as a basis for remediation
of Superfund sites. The decision to use a range of acceptable risk levels and not specify IxlO'6 as
the ultimate cleanup goal was reaffirmed in subsequent Agency guidance (USEPA, 1991).
4 Safe Drinking Water Act: The starting point for most MCLs is a 10'6 carcinogenic target risk
level, but many MCLs exceed the 10'6 risk level for practical and economic reasons. For
example, the Federal MCL for beryllium is based on a carcinogenic target risk level of 2xlO'4 for
these reasons.
+ State RBCA Target Risk Policies: A recent survey of States participating in the EPA/ASTM
RBCA Training Initiative shows that roughly one-third of them have selected carcinogenic target
risk limits in the range of 10'5 to'10"4 for development of risk-based soil and groundwater cleanup
standards. Of the 14 States responding to the 1995 RBCA Policy Issue Survey, nine had
tentatively selected a 10'6 carcinogenic target risk level or a drinking water MCL as the basis for
derivation of cleanup limits, while five intend to employ either a 10'5 or 10"4 target risk limit
depending on applicable land-use conditions (Conner et al., 1997).
t EPA Hazardous Waste Management System Toxicity Characteristics Revision: In its Hazardous
Waste Management System Toxicity Characteristics Revisions (USEPA, 1990a), USEPA has
selected a single risk level of IxlO'5. EPA believes that "due to the conservative nature of the
exposure scenario and the underlying health criteria," a 10'5 target risk level is the highest risk
level that is likely to be experienced by an exposed population.
* Clean Air Act Amendments (1990b): The Clean Air Act, as amended, 42 USC 741209, contains
a provision which specifically references and endorses the basis on which EPA determined
acceptable risk and margin of safety in the benzene NESHAP regulations. Under this policy,
EPA considers all relevant risk factors, including uncertainty in the risk estimates, with a
presumptive risk of approximately 1 in 10,000 (10'4) in making acceptable risk decisions under
Section 112 (hazardous air pollutants) of the Clean Air Act (USEPA, 1989).
4 National Council on Radon Protection: While evaluating radon exposures, the National Council
on Radiation Protection and Management adopted a remediation action level corresponding to a
LAST REVISED JUNE 20, 1997. I O
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^lifetime risk of 2.8xlO~2. This was adopted to balance risk and feasibility. A lower level would
have resulted in "a great societal cost." „«
Thus, although the common belief is that Federal regulations are written with an acceptable risk of 10'6,
this is not true as is clear from the above examples.
Options For Defining An Acceptable Carcinogenic Level Of Risk
Considering that 10"6 is an arbitrary number as is any other number (e.g., 10'5 or 10"4), the
following are a few policy options available to the decision makers:
+ A single specified acceptable risk level applicable for all carcinogens (i.e., the Bright-line
standard such as 10'6, lO'5).
+ Different specified risk levels depending on the weight-of-evidence classification of a chemical
(i.e., 10'6 for A carcinogens, and 10'5 for B and C carcinogens, or 10'5 for A carcinogens and 10'4
for B or C carcinogens).
4 A range of acceptable risk levels (e.g., 10"4 to 10'6) with accompanying discussion as to how the
range is to be used (e.g., land use) .
4 Lower acceptable risk level for actual exposures, higher acceptable risk level for potential future
exposures. This may be justified on the basis that most of the petroleum-derived chemicals are
known to naturally attenuate. '
References
American Society for Testing and Materials (ASTM). 1995. Standard Guide for Risk-Based Corrective
Action Applied at Petroleum Release Sites. ASTM E 1739.
Conner, J.A., R.K. McLeod, and J.P. Nevin. 1997. State RBCA Policy Issue Database, American
Petroleum Institute.
Food and Drug Administration (FDA). 1973. Compounds used in food-producing animals. Procedures
for determining acceptability of assay methods used for assuring the absence of residues in edible
products of such animals—proposed rule. Federal Register 35:19226-19230.
Food and Drug Administration (FDA). 1977. Compounds used in food-producing animals. Criteria and
procedures for evaluating assays for carcinogenic residues in edible products of animals. Federal
Register 42:10412-10437.
Food Safety Council (FSC). 1980. Fd. Cosmet. Toxicol. 18:711-734.
Mantel, N. and W. Bryan. 1961. Safety testing of carcinogenic agents. J. Natl. Cancer Inst. 27:455-470.
LAST REVISED JUNE 2O, I 997.
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Travis, p.C., S.A. Richter, E.A. Crouch, R. Wilson, and E. Wilson. 1987. Cancer risk management: A
review of 132 Federal regulatory decisions. Environmental Science and Technology 21(5):415~420.
US Environmental Protection Agency (USEPA). 1989. National emission standards for hazardous air
pollutants: Benzene emissions for maleic anhydride plants, ethylbenzene/styrene plants, benzene storage
vessels, benzene equipment leaks and coke by-product recovery plants—final rule. Federal Register
54:38044.
US Environmental Protection Agency (USEPA). 1990. Hazardous waste management system toxiciry
characteristics revisions. Federal Register 55:11798-11863.
US Environmental Protection Agency (USEPA). 1990a. National oil and hazardous substances pollution
contingency plan-final rule. Federal Register 55:CFR Part 300:666.
US Environmental Protection Agency (USEPA). 1990b. Clean Air Act. 42 USC 7412(f).
US Environmental Protection Agency (USEPA). 1991. Role of the Baseline Risk Assessment in
Superfund Remedy Selection Decisions, OSWER Directive 9355.0-30.
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PIRI
ISSUE PAPER
Off-Site Movement Of Chemical(s) Of Concern In Risk-Based Corrective Actions
by
Jim Rocco, BP Oil Corporation
The term "off-site" refers to properties or areas that are not within the boundaries of the property
on which the release occurred or where the source area(s) is located. The primary driver (from a pure
risk-based corrective action perspective) for considering the off-site movement of a chemical of concern
is the actual or potential exposure of a receptor to a chemical of concern at a concentration that presents
an unacceptable risk. There are, however, a number of non-risk-related issues that impact (and many
times drive) the decisions associated with off-site movement. These issues include:
+ "Trespass" or the concept that the chemical of concern was caused to exist off-site without the
permission or consent of the property owner;
4 "Property devaluation" or the concept that the property value has been lessened by the stigma
associated with the presence of the chemicals of concern on a property even though the presence
of that chemical does not present a risk;
4 "Diminished use" or the concept that the property can not be fully utilized or that its use is
partially restricted by the presence of chemical of concern; and
+ ''Nondegradation" or the concept that the environment has been degraded and should be restored
to its original quality even though the chemicals of concern do not present a risk. (This is
particularly true for ground water.)
Off-site movement is a difficult issue for a State program to address because it is driven not only
by protection of human health and the environment but also by subjective criteria, emotional responses,
and non-health-based considerations. From a RBCA perspective, the ideal approach to this issue is to
address it based purely on the actual or potential risk that is posed by the chemical of concern, leaving the
other issues to be resolved among the stakeholders under common law principles. This approach
addresses the acceptable risk associated with a source area based on known or reasonably anticipated
point(s) of exposure. Although this approach provides considerable flexibility, implementing it may be
difficult because of current State policies (e.g., nondegradation) and a general reluctance to accept the
concept of site-specific acceptable concentrations of chemicals of concern in the groundwater or soil.
Different Approaches For State Programs
As described in the following paragraphs, there are several alternate approaches being considered
by State programs. The most restrictive approach is to establish groundwater standards (i.e., apply
drinking water standards or background levels) and require that all groundwater, on or off the site, meet
these standards. This approach does not take into account the use of the groundwater, the potential for
exposure to the chemicals of concern, or the technological limitations of remediation methods. It requires
the implementation of a complex and sometimes extensive remediation action system to reduce
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concentrations of chemicals of concern in the soil and groundwater simply to achieve the standard. It
assumes that all soil and groundwater can be restored to pre-release condition.
A State could allow a demonstration showing that existing levels of chemicals of concern do not
present a current or future unacceptable risk but requiring that concentrations of chemicals of concern in
the groundwater ultimately reach established groundwater standards within an identified timeframe
through natural attenuation. This approach recognizes that natural attenuation processes will reduce the
concentrations of chemicals of concern over distance and time. This approach does, however, require
that an established groundwater standard be achieved; typically, it will require the implementation of a
remediation action plan if the standard cannot be achieved in the timeframe identified.
A State could assume that the property line is the point of exposure for the purpose of calculating
site-specific target levels at the source area. This approach recognizes the use of a point of exposure
(e.g., a drinking water well, surface water) but artificially fixes the location of this point rather than
specifically establishing it at the actual or reasonably potential future point where a receptor may be
exposed to the chemicals of concern. For smaller sites or sites where the source is close to the property
line and there is no likely future receptor in close proximity, this approach is not significantly different
from the one above.
A State could assume an arbitrary point of exposure set at a defined (limited) distance (often set
as groundwater travel time) down-gradient of the source, regardless of property size, for the purpose of
calculating site-specific target levels at the source area. This approach recognizes both the difficulty of
establishing reasonably potential future points of exposure and the problems associated with using the
property line as a point of exposure. It still does not address actual points of exposure unless they are
within the defined distance; it could, therefore, be conservative in some cases.
Policy Considerations
There are three considerations or policy decisions that must be evaluated in order to define an
approach to the off-site movement of chemicals of concern: Land use, groundwater use, and poimXs^of
exposure. Land use (current and reasonably potential future) includes the land use of the site and the *
surrounding property. Determination of land use should be based on the following factors:
+ The current land use of the property;
* The current land use of properties immediately adjacent and across any streets from the properly;
4 The current zoning or planning designation for the property;
4- The current zoning or planning designation for the surrounding properties;
4 Reasonably potential future land use of the property using the duration of exposure as the
maximum time into the future to evaluate; and
4- Reasonably potential future land use of the surrounding properties using the durations of
exposure as the maximum time into the future to evaluate.
Groundwater use (current and reasonably potential future) includes the quality and potential use
of the groundwater (groundwater classification) as a drinking water source and State nondegradation
policies. While this determination can be linked to the use of the property, it is typically addressed as a
separate issue. Determination and documentation of groundwater use could include the development of a
groundwater classification system based on characteristics such as urban setting, yield rates, existing
quality (both ambient chemicals resulting from human activities and natural quality as measured against
the primary and secondary drinking water standards).
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Determination of the location of the point(s) of exposure, specifically when a known or
reasonably potential future receptor is not identified, could include:
•f S|f
+ An actual or known location of a current or future receptor;
+ The determination of an assumed location for a receptor in cases where future use is likely, but
the exact circumstances for that use cannot be determined; or
4 A calculated position based on a time/distance relationship (e.g., groundwater travel time).
It is important that a RBCA program identify these three policy decisions to ensure a consistent approach
that clearly defines unacceptable risk.
LAST REVISED JUNE 2O, I 997.
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PIRI
*» ISSUE PAPER
Institutional Controls In Risk-Based Corrective Actions
by
Kevin Kratina, New Jersey Department Of Environmental Protection
The use of institutional mechanisms to memorialize land and resource-use constraints and
provide for safety has been used extensively throughout the United States. Federal, State and local laws
and codes have required various institutional control mechanisms for conservation area protection,
aquifer protection, historic preservation, development limitations, hazardous and solid waste facility
closure, notice of contaminated sites, notice of buried utilities, and the like. Whenever institutional
controls are used, a control requirement (or notice) is recorded with the appropriate regulatory agency (or
agencies) where reasonable diligent inquiry (required by law in many instances) would uncover the
existence of such notice. Examples of different types of institutional controls are: Structure-use
restrictions, land-use restrictions, natural resource-use restrictions, well restriction areas, deed
restrictions, deed notices, declaration of environmental restrictions, access controls, monitoring
requirements, site posting requirements, information distribution, notification in closure letter, restrictive
covenants, and Federal/State/county/local registries.
In the area of site remediation, returning land and groundwater to conditions acceptable for
unrestricted residential use would be ideal, but the limitations of public and private-party funds tell us that
this goal can never be achieved. Through the experience in risk-based corrective action and the need for
remediation that is "protective [of human health and the environment]" and cost effective, the doors have
opened for the use of institutional controls. In a 1 995 survey of States conducted by the Association of
State and Territorial Solid Waste Management Officials (ASTSWMO), 14 of 27 responding States
acknowledged the use of institutional controls in site remediation. New Jersey defines "institutional
controls" as "...a mechanism used to limit human activities at or near a contaminated site, or to ensure
effectiveness of the remediation action, over time, when contaminants remain at a contaminated site in
levels or concentrations above the applicable remediation standard that would allow for unrestricted use
of that property. Institutional controls may include, without limitation, structure, land, and natural
resource-use restrictions, well restriction areas, and deed notices."
Institutional controls are effective when the definition of "what contamination can remain at a
site and under what conditions" or "how clean is clean" is defined based upon current land-use and
exposure scenarios; particularly when the continued existence of such "protective" conditions is beyond
the control of the regulatory agency. As an alternative to cleaning a site to levels that would be
considered "safe" for unrestricted use, an institutional control can provide notice of exposure elimination,
system maintenance (e.g., engineering control, capping), or land-use constraints (e.g., nonresidential use
only). The institutional control, for example, could require notification to the approving agency prior to
any disturbance of the land or change of land use that would create an unacceptable exposure.
The goal of State and Federal cleanup programs is to provide a regulatory structure in which cost-
effective remediation decisions that are protective of human health and the environment can be made; the
use of institutional controls provides for flexibility in remediation decision making. Institutional controls
should be designed to remain protective over time, especially when risk-based remediation decisions are
made based upon current land and resource use and maintenance of engineering controls. Remediation
decisions memorialized in institutional controls should "run" with the land (e.g., deed notices, use
LAST REVISED JUNE zo, 1 997.
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restrictions) or property file (i.e., be filed with the appropriate local/county/State land/resource-use
control agencies) and, as needed, have affirmative obligations for maintenance requirements which are
passed on to the prospective purchaser/operator.
Future land-use consideration should also be a critical factor in determining the nature and use of
institutional controls. The scope of the remediation strategy, which should be defined early in the
remediation process, should be based upon future land-use considerations. Especially if property
purchasers are involved, the scope of the remediation effort and the use of any institutional controls
should be consistent with the purchaser's intended use of the property. Prospective property transactions
may be affected or complicated by the existence of contamination that remains above levels acceptable
for unrestricted use when liability is unclear or contamination is not well defined.
Generating the data necessary to define the "scope" of the institutional control is a regulatory
policy issue. The precision of soil and groundwater requirements and the reliance on field data versus
modeling efforts should be considered. This is especially true for instances when the institutional control
(e.g., deed notice) requires concurrence from the property owner. Delineation in these circumstances
must be conducted in a manner to ensure that the ability of a property owner, purchaser, or neighboring
property owner to use his/her property in a manner he/she chooses, to allow an understanding of any
potential property value impacts, if any, and to allow for concurrence with the requested use restriction.
There are many factors that must be considered in designing a remediation program that
incorporates and relies upon the use of institutional controls. Some of these public policy issues include:
4 What are the State's land-use and population pressures for a change in the exposure scenario
(e.g., conversion from industrial to residential use)?
4 Should a State have penalty/enforcement capability if the maintenance requirements of the
physical site are not followed (e.g., an allowance for breeches in exposure control mechanisms)?
4 Will a responsible party have the option to place a "use restriction" on property he does not own?
Will this be considered a taking of property?
4 Should there be a preference for permanent remedies consistent with the National Contingency
Plan and should the cost of permanent versus protective non-permanent remedies be considered?
4 Are the repositories for the institutional controls reasonable for noticing current users, future
purchasers, and resource and land-use decision makers? Is there redundancy in the multi-level
notice requirements to prevent "system" notification failure? Can the diligent inquiry for such
notices be required in law at the time of property transfer?
4 Can the existing government structure be used to memorialize the institutional control
mechanism? (E.g., will a county repository for deed notices serve to provide notice to future
property purchasers?)
4 Will local officials be notified of restrictions that may limit property use in a manner inconsistent
with local zoning plans?
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Should the institutional control have an affirmative obligation to allow site inspections? Should
this be required only if some form of "maintenance" is required?
What level of public notice should be required?
Is groundwater under a site considered State or private party property? If the site is located in a
non-groundwater-use area, should all property owners be notified?
Should a State establish a mechanism to evaluate the effectiveness of institutional controls over
time?
References
ASTSWMO Leaking Underground Storage Tanks Task Force. 1996. "Toolbox " of Administrative
Procedures for Managing Contaminated Sites - Survey Results.
Clancy-Hepburn, M. et al. 1995. Research Report "Institutional Controls In Use," Environmental Law
Institute.
Gimello, R. 1995. Final Guidance Memorandum, "Classification Exception Areas." New Jersey
Department of Environmental Protection.
New Jersey Department of Environmental Protection. 1994. "Future Land Use: A Key Consideration in
Remedy Selection," Site Remediation News, Vol 6, No. 1.
Senate Bill 1070, Public Law 1993, Chapter 139, State of New Jersey, March 15, 1993.
LAST REVISED JUNE ao, 1997. I 8
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PIRI
ISSUE PAPER
Groundwater Nondegradation Policies In The Development And Implementation Of
Risk-Based Corrective Action Programs
by
Geoffrey L. Gilman, Amoco Corporation
Since the development and publication of the American Society for Testing and Materials
(ASTM) E 1739-95 Standard Guide for Risk-Based Corrective Action at Petroleum Release Sites and
EPA's OSWER Directive 9610.17, Use of Risk-Based Decision Making in UST Corrective Action
Programs, the majority of State UST programs have pursued some application of risk-based cleanup
standards within their respective environmental programs. Regulators in numerous States have, however,
voiced concerns that risk-based corrective action (RBCA) conflicts with the groundwater nondegradation
policies of their agencies. As a result, the degree to which ASTM/RBCA can be successfully
implemented has been limited in these States.
While virtually every State's environmental regulatory agency adheres to a nondegradation
policy of some sort, the form, substance, and interpretation of these policies vary greatly. Usually found
in the "Introduction" or "General" sections of the State's environmental protection act, nondegradation
language can also be found in specific statutes or laws in the preambles and/or actual texts of the
regulatory codes. Some States have no enforceable nondegradation language; rather, the agency has
merely stated such a policy. Nondegradation policies can take the form of groundwater standards or
classifications, of remedial goals or objectives and, in rare cases, of actual enforceable remedial
standards. As a rule, the intent of nondegradation policies is usually to prevent pollution and to protect
the viability of natural resources and not to establish "zero tolerance" cleanup standards. Through broad
interpretation, though, some States have historically used nondegradation policies for just that purpose.
In attempting to deal with a nondegradation policy in the process of implementing a RBCA .,
program in any State, the first step is to fully understand the intent and meaning of the policy. Is the
policy being properly interpreted by the implementing agency? Who is interpreting it? Is the language
being interpreted literally or has supposition been applied? Can all parties agree upon an official
interpretation and application?
The next step is to determine if the policy presents a hurdle or a road block. How invested is the
implementing agency in seeking a solution? There may be an opportunity to seek a more favorable
interpretation, and there may be some flexibility in the agency's application of the policy. A number of
approaches can be applied to successfully implement an ASTM/RBCA program in States with '
nondegradation policies.
Legislation/Rulemaking
The most direct approach to dealing with a nondegradation policy is to change it through
legislation or rulemaking. This approach, however, should generally be pursued after other approaches
have been exhausted. The processes of legislative change and environmental rulemaking are time-
intensive and unpredictable.
LAST REVISED JUNE 2O, I 997. I 9
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Strict Interpretation
»
Assuming that a consensus interpretation of the nondegradation policy has not been achieved
among the parties, the opportunity exists for them to agree on an interpretation more favorable to the RBCA
process. For example, it can be argued that the intent of a nondegradation policy is to prevent the degrada-
tion of a natural resource, and that once it becomes degraded other policies will have to be put in place to
apply to the remedial efforts. This argument, however, should not be interpreted as a "license to pollute."
Standards Versus Objectives
In many cases, groundwater standards, cleanup standards, and cleanup objectives are considered
synonymous. The most likely intent of groundwater standards is to protect the viability of potable
aquifers and not to determine the level of cleanup necessary to apply to a contaminated aquifer.
Groundwater standards may also serve to define classifications of groundwater. The argument should be
made that not all groundwater is potable and that drinking water standards need only apply to aquifers
which produce potable groundwater. Furthermore, there is a tremendous difference between objectives
and standards. Arguably, cleanup standards should be set at realistically achievable levels commensurate
with the risk posed by the contamination and the designated use of the aquifer, while cleanup objectives
should represent targets or goals which might be technically, practicably, and financially unachievable.
Point Of Compliance
In the case of stringent generic cleanup standards, there may be an opportunity to apply the
concept of risk by extending the point of compliance beyond the point of release. Many State codes
allow for mixing zones. Also, many States base their cleanup standards on drinking water MCLs. By
strict interpretation of the federal definition, MCLs apply only at the tap and not to the aquifer. Following
this interpretation would allow for some flexibility to apply the principles of RBCA to the remedial effort.
k
>
Natural Attenuation
Although ASTM/RBCA applies the concepts of natural attenuation to the models that determine
Tier It risk-based cleanup levels, there is still an opportunity to utilize natural attenuation in States that
mandate strict concentration-based cleanup levels. Natural attenuation is,one of many acceptable
remediation options atUST sites. Please see the PIRI Issue Paper on natural attenuation for a discussion
in greater detail.
Summary
There are certainly other approaches to dealing with nondegradation policies, probably as many
as there are variations of the policies themselves. It is necessary for all involved parties to understand the
intent and meaning of the policies and to develop a relationship that is conducive to seeking a solution.
Finally, it is important to realize and understand that, notwithstanding their misinterpretation and
misapplication, nondegradation policies are a vital part of an agency's environmental protection program.
It should be the goal of all who endeavor to implement risk-based corrective action programs to achieve a
balance between pollution prevention, exposure prevention and remedial action.
LAST REVISED JUNE S.O, 1997. 2O
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ISSUE PAPER
Using TPH In Risk-Based Corrective Action
by
John B. Gustafson, Shell Development Company
Total Petroleum Hydrocarbon (TPH) analysis is widely used as a general measure of the presence
of crude oil or petroleum product in soils. TPH is defined as the measurable amount of petroleum-based
hydrocarbon in an environmental media (e.g., soil, water, sediments) and, thus, is dependent on analysis
of the medium in which it is found. While providing an overall concentration of petroleum hydrocarbons,
TPH itself is not a direct indicator of the risk (i.e., mobility, toxicity, and exposure to human and
environmental receptors) posed by petroleum hydrocarbon contamination. Both mobility and toxicity are
very dependent upon the relative amounts of individual (or groups or families of) constituents within a
hydrocarbon mixture. For example, a crude oil may contain different types and amounts of aromatic
compounds than does a gasoline. Other analysis or information in addition to a single TPH number must
be used to relate TPH concentrations to risk.
This paper presents an overview of the measurement of TPH and the methods that have been
used in the past to estimate the risk from TPH contamination. More recent developments, including those
of the Total Petroleum Hydrocarbon Criteria Working Group (TPHCWG), which is a national ad hoc
committee that was formed to develop technically defensible risk-based approach to TPH, are also
discussed. The paper concludes with examples of how the TPHCWG technology might be used by State
regulatory agencies to incorporate TPH into a risk-based corrective action program.
Measurement Of TPH
A TPH method of analysis often used and required by many regulatory agencies is EPA Method
418.1. This method provides a "one number" value of TPH in an environmental media; it does not ,.,
provide information on the composition (i.e., individual constituents such as benzene) of the hydrocarbon
mixture. The amount of TPH measured by this method depends on the ability of the solvent used to
extract the hydrocarbon from the environmental media and the absorption of infrared (IR) light by the
hydrocarbons in the solvent extract. Method 418.1 is not specific to hydrocarbons; in fact, it can give
false positive results when organic matter is extracted from the environmental media for analysis. In
other words, TPH measurements do not always indicate petroleum contamination (e.g., humic acid).
Another analytical method commonly used for TPH is EPA Method 8015 Modified. This
method reports the concentration of purgeable and extractable hydrocarbons which are also sometimes
referred to as gasoline and diesel range organics (i.e., GRO and DRO) because the boiling point ranges of
the hydrocarbon in each roughly corresponds to that of gasoline (i.e., C6 to C1(M2) and diesel fuel (i.e.,
C8.I2 to C24.26), respectively. Purgeable hydrocarbons are measured by purge-and-trap gas
chromatography (GC) analysis using a flame ionization detector (FID), while the extractable
hydrocarbons are analyzed by GC following extraction with a solvent and subsequent concentration of
the extract by evaporation. While more detailed information is generated by this method (e.g., GC
chromatograms), the results are most frequently reported as single numbers for purgeable and extractable
hydrocarbons.
The Massachusetts Department of Environmental Protection (MADEP) has developed a method
LAST REVISED JUNE 2O, IQ97. 21
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based op 8015 Modified which gives a measure of the aromatic content of the hydrocarbon in each of
several darbon number ranges. In the MADEP method, the lighter hydrocarbon fractions (i.e., carbon
numbers from C6 to C12) are analyzed by purge-and-trap GC analysis using a flame ionization detector
(FID) to measure the total hydrocarbons and a photo ionization detector (PDD) to measure the aromatics
(e.g., benzene) with the aliphatic (e.g., hexane) component of the TPH being found by difference. The
aromatic and aliphatic fractions are divided into carbon number fractions based on the normal alkanes
(e.g., n-octane) as markers. The heavier hydrocarbons (i.e., C12 to C26) are analyzed using an extraction
procedure followed by a column separation using silica gel (Modified EPA Method 3630) of the aromatic
and aliphatic groupings or fractions. The two fractions are then analyzed using GC-FID. PAH markers
and n-alkane markers are used to divide the heavier aromatic and aliphatic fractions by carbon number,
respectively.
The MADEP method is based on standard EPA methods (i.e., 8020/8015 Modified) which allows
it to be easily implemented by contract laboratories. However, there are some concerns or issues about
the method. One issue is that the PID is not completely selective for aromatics (i.e., it does respond to
some aliphatic compounds). Thus, this approach can lead to an overestimate of the more mobile and
toxic aromatic content Another issue with this analytical approach is that the results from the two
analyses (i.e., purgeable and extractable hydrocarbons) can overlap in carbon number and thus may not
be simply added back together to get a total TPH concentration. The performance of this method on real
hydrocarbon products may be limited.
The TPH Criteria Working Group has developed a method for identifying and quantifying the
presence of the groups or fractions with similar mobility in soils. The technique is based on EPA Method
3611 (Alumina Column Cleanup and Separation of Petroleum Wastes) and EPA Method 3630 (Silica Gel
Cleanup), which are used to fractionate the hydrocarbon into aliphatic and aromatic fractions. A gas
chromatograph equipped with a boiling point column (non-polar capillary column) is used to analyze
whole soil samples as well as the aliphatic and aromatic fractions to resolve and quantify the fate-and-
transport fractions selected by the TPH Criteria Working Group. The method is versatile and
performance-based and, therefore, can be modified to accommodate data quality objectives.
»
Estimates Of Risk For TPH
There are three basic approaches that have been used in the past to estimate potential human
health risks posed by TPH contamination. The one most generally applied and most appropriate for
evaluation of the carcinogenic risk from TPH is an "Indicator" approach. This approach assumes that the
estimated risk from TPH is characterized by a small number of indicator compounds (e.g., BTEX, PAHs).
This approach was necessitated by the inability to analyze for the large number of constituents in TPH
and the lack of toxicological and other relevant data for many of those constituents that could be
individually identified. The indicator approach is generally accepted and used by state regulatory
agencies for carcinogenic risk posed by TPH. The use of the indicator approach for determining non-
carcinogenic risk has, however, not been fully developed.
Another approach, the "Surrogate" approach, assumes that TPH is not specifically included as an
indicator and can be characterized by a single surrogate compound. This approach could overestimate
toxicity and mobility because of the compounds typically available for use as surrogates. For example
with respect to toxicity, benzene is the surrogate compound for the aromatics; it is also the most carceno-
genic. With respect to mobility, benzene is, again, the surrogate compound because it travels at a faster
rate than other petroleum constituents. Benzene is, however, the least abundant of the constituents found
in petroleum mixtures. A variant of the "Surrogate" approach is the "Whole Product" approach in which
LAST REVISED JUNE EO. 1997. 22
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the toxijiry and mobility of the TPH product are based o| that of a whole product of similar character
Neither the "Surrogate" nor the "Whole Product" approach is capable of taking into account the effects of
weathering (i.e., changes in composition and tdxicity and mobility over time) and the wide range of
mobility of the constituents of the typical hydrocarbon product. Because the lighter and more mobile
constituents tend to weather faster, weathered crude oils and hydrocarbon products are typically less
mobile and, thus, could pose a lower risk (although mobility is only one of several factors used to deter-
mine risk). These approaches are similar to the "Indicator" approach in that they use specific knowledge
of a single or a few constituents to characterize the many constituents in a hydrocarbon mixture.
More recently, approaches have been developed which are a compromise between the "Indicator"
and the "Surrogate" or "Whole Product" approaches. In these approaches, carcinogenic risk is estimated
based on indicators (e.g., benzene and the carcinogenic PAHs) while the non-carcinogenic risk from the
TPH is estimated based on a relatively small number of groupings or fractions. Each of these groups or
fractions is composed of constituents of TPH that have similar toxicity and mobility characteristics. The
risk as a result of TPH contamination can be estimated for each of the groupings or fractions as individual
contaminants or for the measured TPH (i.e., the sum of all the groups or fractions) by assuming additivity
of risk. The estimated risk approach to TPH developed by the Massachusetts Department of
Environmental Protection and the Total Petroleum Hydrocarbon Criteria Working Group are examples of
this compromise approach.
TPH Criteria Working Group
The TPHCWG approach is a combined indicator and grouping or fraction approach. Note that
the non-carcinogenic indicators (i.e., TEX and non-carcinogenic PAHs) are included in the grouping or
fraction analysis and do not need to be analyzed as indicators (although, this can be done if desired by
backing them out of the TPH analysis). The basic approach is similar to that developed by MADEP in
that the TPH is split into a small number of groups or fractions that have similar properties. The main
difference between the approaches is that in the TPHCWG approach, the groups or fractions of TPH are
defined based on the potential mobility of the hydrocarbons within each group; in the MADEP approach,
they are based on the available toxicity data. ...
The TPHCWG approach is not a surrogate approach in which the physical/chemical and
toxicological properties of the grouping or fractions are based on single surrogate compounds. The
physical/chemical and toxicological properties of each of the groups or fractions are based on all
available data for individual constituents, well defined mixtures, and/or whole products that are
representative of each group or fraction. Thus, the TPHCWG approach is an extension of the MADEP
approach, based on a more complete database of physical/chemical and toxicological properties and
specifically taking into account the variability in the potential mobility of the petroleum hydrocarbon
groups or fractions. The approach developed by MADEP does an adequate job of assessing the risk from
TPH for direct exposure scenarios, while the approach developed by the TPHCWG is better suited for
addressing cross media exposure pathways such as soil leaching to groundwater.
The TPHCWG has essentially completed its effort and final reports are available on the Internet
(http://voyager.wpafb.af.mil). The working group is still finalizing the document (Volume 5) which
incorporates all of the findings into a sample risk-based decision making framework. The TPHCWG
approach is, however, summarized in a technical overview document that is available on the web page
and has been presented at numerous conferences and workshops.
US.ST REVISED JUNE 2O, 1 997. 23
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Incorporating TPH Into A Risk-Based Corrective Action Program
•
The petroleum fate-and-transport fractions and toxicity criteria developed by the Working Group
can be used in the ASTM/RBCA framework to cpmpare certain fractions obtained from sampling results
to previously developed RBSLs or to develop a compound-specific risk-based screening level (RBSL).
The soil risk-based screening levels (RBSLs) that are calculated for the indicator compounds and for the
fatc-and-transport fractions can be used individually as a basis for the management of a contaminated
site. In this instance, site remediation will be governed by the most restrictive or lowest soil RBSL.
Alternatively, the composition of the total petroleum mixture present at a site can be used to yield a soil
RBSL for TPH. The RBSL for TPH is calculated by assuming that the risk for the individual compounds
and fate-and- transport fractions can be added, each weighted by their composition in the total petroleum
mixture. The Working Group's Volume 5 provides a thorough discussion of how the approach may be
used within the RBCA framework, including risk calculations and results from demonstration sites where
this new approach has been used.
The approach developed by TPHCWG is intended to provide the technical basis for a broad
range of regulatory programs. Thus, while it can be used to develop risk-based analysis for the individual
TPH groupings, the approach can also be used to develop a risk assessment or risk-based screening levels
for TPH (i.e., the sum of the fractions). In addition, the application of the full analytical method and risk
analysis may not be needed for all soil samples collected at a petroleum-contaminated site. Once the
petroleum composition has been fully characterized at a site, additional sampling can rely on traditional,
less expensive TPH analysis rather than the new Working Group method (if the TPH fingerprint is similar
across the site). This simplification can be carried further if process knowledge for a site can be used to
characterize the hydrocarbon contamination such that the composition of the petroleum hydrocarbons at
the site can be based on non-site specific analysis (e.g., typical jet fuel at an Air Force base).
These simplifications are important for application of the TPHCWG technology at sites where the
cost of the more detailed analysis is not justified. For example, the full TPHCWG analysis may not be
cost effective at heavy hydrocarbon sites where significant concentrations of the indicator compounds are
not anticipated, historical data for TPH does not allow identification of the individual groupings, and/or
additional analysis is not cost effective. The full TPHCWG analysis may also not be cost effective for
sites such as retail/marketing sites with underground storage tanks where information about the type of
hydrocarbon is available (i.e., the contamination is known to be gasoline from an underground storage
tank). For these cases, generic risk-based TPH screening levels based on typical composition data (i.e., a
typical weather gasoline) can be developed, and less expensive TPH analysis or indicator analysis can be
used to characterize the site. The TPHCWG technology can be adapted to fit within and support a broad
range of regulatory programs.
One possible use of the TPHCWG technology is to provide the technical basis for the assumption
that the risk from TPH other than the indicator compounds (e.g., BTEX and the PAHs) is not significant
under certain exposure scenario assumptions. In this case, the risk from TPH contamination would be
evaluated based on the analysis of indicator compounds or on some non-risk-based criteria such as the
potential mobility of the TPH as a non-aqueous phase liquid or NAPL. Ohio is a good example of a State
that has developed a look-up table for TPH based on soil types and the boiling range of the hydrocarbon
contamination. The criteria were developed using models to estimate the percent of saturation required
for the non-aqueous phase liquid (NAPL) hydrocarbon to be mobile. The States of Hawaii and Louisiana
have developed similar policies where the upper limit for TPH screening levels (i.e., 5000 mg/kg and
10,000 mg/kg, respectively) are based on aesthetics or some other non-risk-based criteria.
LAST REVISED JUNE 20, 1997. 24
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Another possible use of the TPHCWG teehnologf' is to develop generic criteria for TPH based on
typical compositions of fresh and/or weathered hydrocarbon mixtures. A good example is a recent
analysis of crude oils in the State of Michigan. Analyses (of five representative crude oils from across the
State were used to support cleanup levels of 10,000 mg/k|. At this concentration of TPH (i.e., 10,000
mg/kg), the concentrations of the carcinogenic indicator PAHs and the TPHCWG fate-and-transport
fractions are below levels of concern (i.e., concentrations are less than RBSLs). The state regulatory
agency is currently adopting 10,000 mg/kg as a generic screening level for TPH at all crude oil
contaminated sites.
NOTE: The technical documents of the TPHCWG are in press or in preparation. Some of these
documents are now available or will be soon on the U.S. Air Force Toxicology Division web site (http://
voyager.wpafb.af.mil). At this web site, Working Group publications may be downloaded from the
"recent publications" icon. Additional Working Group resources will be added to this web site as they
become available. EPA has neither reviewed nor endorsed the TPHCWG approach. EPA recognizes that
TPH may be used as a screening tool for the measurement of total hydrocarbon contamination, but
cautions states that it is inconsistent with a risk-based approach that focuses on individual chemicals and
their risk to human health.
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