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OCR for page 34
3
Some Approaches to Setting
Cleanup Goals at
Hazardous Waste Sites
HALINA SZEJNWALD BROWN
During the past decade the assessment and cleanup of haz-
ardous waste sites has come to occupy a prominent position in the
activities of federal, state, and local governments. Currently, EPA
estimates over 23,000 potential sites nationwide and over 850 on
the Superfund national priority list. In Massachusetts alone, there
are about 400 confirmed hazardous waste sites, of which 21 are on
the Superfund list.
Cleanup of these sites raises a vexing question: How clean is
clean enough? The question is neither new nor unique to haz-
ardous waste sites. Yet compared to direct emissions of toxic
materials into water or air, soil contamination presents a signifi-
cantly more complex problem. As illustrated in Figure 3-1, human
and nonhuman exposure to soil contaminants can occur through a
variety of pathways. Also, because hazardous waste sites usually
contain large numbers of toxic substances with a wide combined
spectrum of adverse effects, cleanup standards must be sensitive
to this multiple route/multiple agent exposure pattern. Finally,
specific circumstances of human intake of the substances through
multiple media are difficult to predict or measure.
Determining the extent of cleanup of hazardous waste sites
can be approached using one of two general methods: absolute or
relative. The absolute approach is based on the assumption that
we can define acceptable concentrations of hazardous materials in
the environmental media from which no significant risk of adverse
34
OCR for page 35
APPROACHES TO SETTING CLEANUP GOALS
iN
WATER
J
WATER
.',j \"".
- ~
DRY -]
SOIL ~ _
~-
FIGURE 3-1
(1980).
35
_ i~
ROOT CROP
~ ~ .,,.''' ~
J MOISTURE
Jr:
) GROUND WATER
+:
WATER
A A
-
PLANT CROP
~ Ale
A,; _
FOLIAGE
_ ~
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ANIMAL
.;
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, I HYDRO SOIL
' :-
FILTER/
BOTTOM FEEDER
.,, ~
B -VAPOR)
MOISTURE ATMOSPHERE (PARTICLES)
J
Pollutant pathways from soil to man. SOURCE: Dacre et al.
effects to humans and the environment would be expected. For
toxic effects to humans that have a threshold, this level would
be somewhere below the expected threshold for the population at
risk. For nonthreshold effects such as cancer, the definition of
"clean" is often linked to some acceptable or, as some (Kasperson,
1983) argue, tolerable risk level.
The common feature of absolute approaches is their search
for universally acceptable numbers (i.e., standards, guidelines,
and criteria). Once established, these numbers drive the cleanup
process because they, in effect, define the term "clean."
In contrast to the absolute, standard-based approach to man-
aging environmental pollution, the relative approach defines
"clean" for each particular situation. It may be driven by technol-
ogy, costs, comparison with other current and historical hazards,
or risk/benefit analysis, or it may be expressed as a percentage
OCR for page 36
36
HAZARDOUS WASTE SITE MANAGEMENT
reduction of a hazardous material (for example, 99.99 percent). In
essence, an acceptable level of contamination is defined as that as-
sociated with the most acceptable option in a particular decision
problem. Hence, the acceptable level is defined for each situa-
tion through the risk management process rather than used as an
absolute goal for hazard management.
It has been argued (Fischhoff et al., 1981) that the absolute
approach to acceptable risk (or, by analogy, to "How clean is
clean?" ~ is simplistic and unworkable in most situations and that
the issue should be viewed as a decision problem, unique for each
specific situation. Despite the criticism, however, the standard-
based approach has been consistently the favored one for risk
managers. There are several reasons for this:
. Once a standard is adopted, its application is simple and
noncontroversial.
It is easy to justify and defend in court.
It provides a means of communication among all the techni-
cal and nontechnical participants of the risk management process
on both sides of the issue.
It appears to be an objective process grounded in scientific
analysis and free of value judgments.
~ It relieves policymakers from the cumbersome burden of
dealing with uncertainty and from being charged with imposing
their own values and beliefs on society.
.
It simplifies the problem by automatically determining the
goals of risk management activities.
It reflects a recurrent hope that we will find a scientific
method for objectively resolving the problem of "How clean is
clean?"
The purpose of this paper is to review five currently used
approaches to determining "How clean is clean?" at hazardous
waste sites. The paper focuses on the general concepts that are
used as well as on specific methods. The work of the follow-
ing agencies is reviewed: U.S. Environmental Protection Agency,
U.S. Army, California Department of Health Services, Washington
State Department of Ecology, and the New Jersey Department of
Environmental Protection.
OCR for page 37
APPROACHES TO SETTING CLEANUP GOALS
TlIE EPA SUPERFUND PUBLIC EEAITlI
EVALUATION MANUAL
General Concepte
37
This document is a comprehensive manual for site assessment
and the establishment of cleanup goals. Conceptually, the EPA
methodology is similar to that of California in its view of the en-
vironmental migration of chemicals, the role of chemical analysis
and dispersion modeling in determining media-specific concentra-
tions of chemicals, and the reliance on toxicity-based criteria to
determine cleanup levels. There are, however, differences between
the two methodologies. One notable difference is that California
concerns itself with all chemicals found at a site, whereas the
EPA manual recommends the use of indicator compounds, chosen
on the basis of minimum effective dose (MED) for toxic effects,
carcinogenic potency, environmental mobility, and persistence.
The following terminology is used in the EPA manual.
Critical Toxicity Value
This is a property of toxic substances that reflects the quan-
titative relationship between daily dose and magnitude of adverse
effect of that substance. Three types of critical toxicity values are
used:
~ Acceptable intake for subchronic exposure (AlS). The high-
est human intake of a chemical, expressed as milligrams per kilo-
gram (mg/kg) x day, that does not cause adverse ejects when
exposure is short-term (but not acute). This AlS is usually based
on subchronic animal studies.
~ Acceptable intakefor chronic exposure (AlC). The highest
human intake of a chemical, expressed as mg/kg x day, that does
not cause adverse effects when exposure is long term. The AIC is
usually based on chronic animal studies.
~ Carcinogenic potency factor. A measure of carcinogenic
potency of a chemical, derived from animal data. It corresponds
to a lifetime cancer risk per unit dose (mg/kg x day)-t
Estimated Daily Intake
.
This is a daily dose of a substance by a specified route of
OCR for page 38
38
HAZARDOUS WASTE SITE MANAGEMENT
exposure under some particular exposure conditions related to the
site. Two types of estimated daily intake values are used:
.
Subchronic daily intake (SDI). The projected human intake
of a chemical averaged over a short period of time, expressed as
mg/kg x day. The SD! is calculated by multiplying the peak short-
term concentration (STC) in an exposure medium by the human
intake factor for that medium and by the body weight factor.
. Chronic daily intake (CDI). The projected human intake of
a chemical averaged over 70 years, expressed as mg/kg x day. The
CDI is calculated by multiplying the peak long-term concentration
(LTC) in an exposure medium by the human intake factor for that
medium and by the body weight factor.
Critical toxicity values are derived from studies on animals or
observations made in human epidemiologic studies. Each is spe-
cific for the route of exposure specified in the experiment on which
it is based. Thus, AlS (oral) is different from AlS (inhalation),
and they cannot be used interchangeably. Acceptable intake val-
ues and carcinogenic potency index are properties of a substance
administered under specified conditions and are therefore appli-
cable at any site for any exposure scenario. Estimated chronic
and subchronic daily intakes (SD! and CDI) are calculated for a
particular site and reflect conditions at that site as well as the
estimated route, magnitude, and duration of human exposure.
Derivation of Acceptable Intakes for
Subchronic and Chronic Exposure
A distinction is made between chemicals that produce carcino-
genic effects and those that do not. Acceptable intake values are
calculated only for compounds that do not exhibit carcinogenic
properties.
The evaluation manual is not specific on details of the deriva-
tions of the AlSs and AICs beyond the fact that they are derived
from no observed adverse effect levels (NOAELs) and that the
protection of sensitive members of the population is considered.
Based on that information, it is reasonable to assume that AlSs
and ATCs are derived from quantitative toxicity data by applying
uncertainty factors to experimentally derived NOAELs.
OCR for page 39
APPROACHES TO SETTING CLEANUP GOALS
Estimation of Daily Stake
39
The methodology is based on the assumption that human ex-
posure to toxic materials present at the site can originate from
the following media: air, ground water, surface water, soil, and
contaminated fish. Human intake of toxicants from these me-
dia can occur through ingestion, inhalation, and skin absorption.
Although soil as a medium and skin as a route of absorption are ac-
knowledged, the methodology does not specify how human intake
should be calculated for these. Instead, the manual recommends
that the agency be contacted on a case-by-case basis when intake
from soil and through skin (or both) is expected to be significant.
Human intake is estimated separately for each indicator com-
pound/route of exposure/duration of exposure/population ex-
posed. Duration of exposure is divided into chronic and sub-
chronic. Thus, for a particular population, SD! and CDI are
estimated for each chemical X and route Y using the general
formulas:
and
SDIX,y (mg/kg x day) = STCx,y x human intake factory
CDIX,y (mg/kg x day) = LTCx,y x human intake factory,
where SDIX y and CDIX y are subchronic and chronic daily intakes
of chemical X by route Y; STCx y and LTCx y are short- and
long-term concentrations of chemical X in a medium associated
with route of exposure Y; and the human intake factor of the
medium is associated with route of exposure Y. This is illustrated
below for two routes and three media:
SDIX,inha~ = STCX'air x human intake factorair,
CDIX,inha~ = LTCX,air x human intake factorair,
and
SDIX,ora~ = STCX~wa~er x human intake factorwa~er
+ STCX,fi~h x human intake factoring.
These examples show that for each route of exposure to a
chemical, the total human daily intake is a sum of the daily in-
takes from all media by the same route. The additivity applies
OCR for page 40
40
HAZARDOUS WASTE SITE MANAGEMENT
only to the same population exposed at the same time and for
approximately the same duration (chronic versus subchronic).
For carcinogenic substances, CDI values are also used to cal-
culate lifetime carcinogenic risk, according to the formula:
Lifetime riskx,y = CDIX y x carcinogenic potency factory y.
The value of lifetime risk is later used to determine cleanup levels
for the site.
Daily intake values for chronic and subchronic exposure, as
well as carcinogenic risk, are calculated for specific exposure con-
ditions and are therefore specific for each site.
Exposure to Multiple Chemicals by Multiple Routes
Noncarcinogenic Effects
The methodology assumes that the effects of simultaneous
exposure to several chemicab that cause the same type of toxicity
are additive. Therefore, total daily intake of each chemical must
be adjusted to meet the acceptable intake level. This is shown in
the following:
~ CDI (route)) < 1
i 1 AIC (route))-
SDI (route)) < 1
i 1 AIS (route))- '
where i is the substance number. Once again, the acceptable
intakes for chronic and subchronic exposures are specific for the
duration of exposure and the route of exposure (oral or inhalation).
The methodology also assumes that the effects of exposure to a
particular substance through several exposure routes are additive,
as shown in the following:
~ CDI (subst)j
I 1 AIC (subst)
~ SDI (subst)
I 1 AIS (subs")`
where j is a route number.
OCR for page 41
APPROACHES TO SETTING CLEANUP GOALS
41
The overall hazard index for multiple routes of exposure to
multiple chemicals with similar toxic effects can be expressed as a
sum of hazard indices for each route. Thus, for chronic exposure:
m rat
Hazard index = ~ ~ CDIij/AICij.
i=1 j=1
No significant adverse effects would be expected in the population
if the hazard index does not exceed 1 (hazard index < 1~.
Carcinogenic Effects
The assumption of additivity is also applied to compounds
producing carcinogenic effects. For multiple carcinogenic com-
pounds absorbed through a specific route, the total risk is:
m
Cancer risk for route Y = ~ CDIyi x carcinogenic potency factory).
i=1
Likewise, the risks from multiple routes of exposure to substance
X are additive:
n
Cancer risk for substance X = ~ CDIjX
j=1
x carcinogenic potency factorjx.
The total carcinogenic risk for multiple substances and multiple
routes is:
m n
Cancer risk = ~ ~ CDIij x carcinogenic potency factorij.
i=1 j=1
Only chronic, 70-year exposure duration conditions are used for
calculating cancer risks.
Cleanup Criteria
Site Assessment
Site assessment involves the following steps:
Step 1. Selection of indicator compounds.
OCR for page 42
42
HAZARDOUS WASTE SITE MANAGEMENT
Step 2. Estimation of concentrations of indicator compounds
in environmental media at the points of maximum human expo-
sure, both for short and long periods of time (STC and LTC).
Step 3. Comparison of STCs and LTCs in specific media
with environmental criteria such as drinking water standards and
guidelines, ambient air standards, and water quality criteria. The
assessment stops here if standards/guidelines are available for all
indicator compounds. Otherwise, the process proceeds to Step 4.
Step 4. This step involves the most comprehensive health
assessment. Estimated human daily intakes (SDIs and CDTs) of
indicator compounds are estimated for each substance/route of ex-
posure/duration combination. Cancer risks associated with SDIs
and CDIs are also calculated. Also in this step the hazard in-
dex for multiple routes of exposure is calculated. Step 4 requires
knowledge of critical toxicity values such as acceptable intake for
subchronic exposure (AlS) and carcinogenic potency factors.
Target Levels
The goal of a cleanup is to meet target levels for indicator com-
pounds. Target levels are defined differently for compounds with
and without environmental standards. For a target concentration
for compound with a standard, an acceptable target concentra-
tion is one that does not exceed the specific standard for that
medium (requirements). Target concentrations for compounds
without standards are divided into two categories: potential car-
cinogens and chemicals with noncarcinogenic toxic effects.
For potential carcinogens, cleanup levels should maintain can-
cer risk in the range from 10-4 to 10-7 for a lifetime exposure,
with 10-6 as the desirable target risk level. This is a total risk for
a particular population. The target concentration is that concen-
tration that will produce chronic daily intake associated with this
range of risks. If only one carcinogenic substance is present, the
target concentration is calculated using the formula:
target chronic daily intake
Target concentration (medium) = . .
intake factor (medium)
Target concentration (medium) =
acceptable cancer risk
potency factor x intake factor (medium)
-
OCR for page 43
APPROACHES TO SETTING CLEANUP GOALS
43
For multiple routes/multiple agents, the target chronic daily in-
take (and therefore the target concentrations) can be apportioned
between media and chemicals in any combination as Tong as the
total cancer risk is within the 10-4 to 10-7 range.
For chemicals with noncarcinogenic toxic effects, the target
concentration is defined as that at which (1) chronic daily intake
does not exceed the acceptable intake for chronic exposure for indi-
vidual substances/routes; and/or (2) the hazard index for multiple
routes/multiple substances exposures does not exceed unity; that
IS
.O,
CDI (subst, route) < AIC (subst, route),
Hazard Index < 1.
As with carcinogenic substances, for multiple exposures the con-
centrations of individual substances in specific media can be ap-
portioned in any way as Tong as the two conditions are met.
CAI:~?O11~IA SITE MITIGATION DECISION T1tEE
General Concepts
This document provides state decision makers with a stan-
dardized approach to setting site-specific cleanup levels. It is
based on the assumption that a toxicant deposited in the soil will
be distributed among the environmental media in accordance with
its chemical and physical properties as well as the properties of
the media (air, soil, surface water, and ground water). It further
assumes that the biologic receptors (humans and terrestrial and
aquatic biota) will be exposed through contact with one or more of
these media. The system relies on environmental monitoring and
predictive formulas and models to estimate the actual concentra-
tions of toxic agents in each medium. The emphasis is on defining
acceptable concentrations of toxic materials in environmental me-
dia at points of contact with the biologic receptors. Three terms
are essential to understanding the system:
. The maximum exposure [eve! (MEL) is a daily dose (mg/
day) of a substance that is not expected to produce adverse health
effects in a 7~kg adult chronic exposure.
OCR for page 44
44
HAZARDOUS WASTE SITE MANAGEMENT
. The applied action level (AAL)is a concentration of a
substance in a particular medium that, when exceeded, presents
a significant risk of adverse impact to a biologic receptor. AALs
drive the cleanup process for a site.
. The cleanup level is a site-specific criterion that a remedial
action would have to satisfy in order to keep exposure at the
biologic receptor level at or below the AAL.
The maximum exposure level provides the toxicologic basis for
the derivation of AALs and is substance specific. AALs are derived
from the MEL and calculated for each medium (water, air, soil)
using the average daily human exposure level to that medium as
their basis. Like MELs, AALs are substance and species specific.
Thus, for a particular agent, human AAL(soil~is different from
human AAL (air) or AAL (water). Likewise, human AAL (water)
is most likely different from aquatic AAL (water). In essence,
AALs define "How clean is clean?"
Derivation of MEIs for Humans
For the purpose of developing MEI.s and AALs, toxic sub-
stances are divided into two groups: (1) threshold agents, which
produce effects for which there is a threshold; and (2) nonthreshold
agents, which produce effects for which no threshold level can be
assumed, such as cancer, mutations, and genotoxic or teratogenic
effects.
Threshold Substances
The following sources of quantitative and/or qualitative data
on the toxic properties of substances are recommended, in a de-
scending order of preference: human or animal toxicity data,
drinking water standards and guidelines, and occupational ex-
posure limits, which are used by the American Conference of
Governmental Industrial Hygienists to determine threshold limit
values (TEVs). These undergo internal review by professional staff
before being used as the basis for MEL derivation.
From human or animal toxicologic dose-response curves. The
derivation of MELs from toxicologic dose-response curves follows a
classic method of acceptable daily intake (ADI) derivation, which
is illustrated in the following formula:
OCR for page 56
56
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OCR for page 57
APPROACHES TO SETTING CLEANUP GOALS
57
those of the media. The methodologies differ, however, in their ap-
proaches to estimating the media-specific concentrations of chem-
icals. The Washington State methodology does not address the
topic in any detail. In the EPA and California approaches, media-
speciDc concentrations of chemicals in secondary media are deter-
mined by direct sampling and by environmental modeling. Thus,
the knowledge of current and future concentrations of chemicals
in the primary and secondary media is as close to the reality as
analysis and modeling permit. The goal of site cleanup under these
approaches is to ensure that these concentrations do not exceed
previously established chemical-/media-specific numerical criteria.
The U.S. Army and New Jersey methods take a different tack.
First, both view the environment as a set of compartments in equi-
librium with each other so that the concentrations of chemicals in
secondary media can be calculated from soil concentrations by
using a set of equilibrium constants. Of course, because in reality
equilibrium conditions occur only at compartmental boundaries
at best, the calculated concentrations of chemicals are often signif-
icantly overestimated. Further, the equilibrium assumption does
not apply to assessing the ambient air concentrations of contam-
inants. Second, by centering around the question "what cleanup
level is necessary in the primary medium such that the predicted
concentrations in the secondary media do not exceed the health-
based acceptable levels?" the two methods attempt to use math-
ematical formulas that link the last point in the environmental
pathway of a chemical to the first one. The EPA and California
methods do not do that. Instead, they rely only on comparing
concentrations of chemicals in individual media at the points of
human exposure with the acceptable health-based levels in these
media, with the implicit understanding that cleanup of the pri-
mary medium should somehow lead to acceptable levels in the
secondary media.
So, whereas the U.S. Army and New Jersey methods may be
overly simplistic and stringent, the EPA and California approaches
are narrower in scope.
Derivation of Media-Specific Numerical Criteria
As stated earlier, in each of the five methodologies reviewed
here, media-specific numerical criteria play an essential function
in defining cleanup levels at hazardous waste sites. In short, these
OCR for page 58
58
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OCR for page 59
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OCR for page 60
60
HAZARDOUS WASTE SITE MANAGEMENT
numbers determine "How clean is clean?" Therefore, the method
of derivation of these numbers is a cornerstone of each method-
ology. There are three main conceptual approaches to this task:
(1) use media-specific background levels of chemicals or their mul-
tiples; (2) use chemical-specific existing standards for air, soil,
and water; and (3) develop chemical-/media-specific criteria from
toxicity data.
The first approach is simple, but in practice it may be un-
achievable. Only one of the five methodologies, that of Washington
State, uses it.
The second approach is also simple and does not require a
knowledge of toxicology, but it suffers from three major limi-
tations. First, environmental standards and guidelines, derived
under different laws and based on different sets of requirements
and assumptions, are a mixed bag of numbers that are not nec-
essariTy protective of the public health of a diverse population.
Second, because these numbers are meaningful only when applied
to a particular substance in a particular medium, they can not
be used to address the multiple media/multiple chemical exposure
scenarios that are prevalent at many hazardous waste sites. Third,
the number of chemicals for which air and water standards, guide-
lines, or criteria have been developed is small. Perhaps for these
reasons, the use of ambient standards is limited. Only the Wash-
ington State methodology makes extensive use of them to define
cleanup levels. The EPA approach uses environmental standards
to a limited extent; namely, when all indicator compounds in all
media have them, a very rare event.
The third approach to deriving numerical criteria from tox-
icity data is the most popular (used by EPA, the U.S. Army,
California, and New Jersey) and the most difficult. In essence,
it consists of the derivation of a chemical-specific AD! (or its
conceptual analog), followed by its modification by media-specific
intake factors, according to the following formula: criterion (chem,
medium) = ADI (chem)/intake factor (medium). Because AD! is
a chemical-specific toxicity parameter, it can be modified accord-
ing to particular exposure conditions, which is the advantage of
this approach. Hence, multiple chemical/multiple media exposure
conditions can be considered. There are two ways by which the
acceptable daily intake is calculated:
1. Exclusive reliance on toxicity data. Here, the acceptable
OCR for page 61
APPROACHES TO SETTING CLEANUP GOALS
61
daily intake is calculated by applying an uncertainty factor to
a threshold daily dose. In the California and EPA methods the
NOAEL (no observed adverse effect level) serves as a threshold
dose. In the U.S. Army method the NEL (no-effect level) is used.
Only the EPA methodology relies exclusively on this approach.
California, the U.S. Army, and New Jersey use it in conjunction
with another approach, which is described in the next paragraph.
2. Conversion of existing guidelines, standards, and criteria
into acceptable daily intakes, according to the formula: Acceptable
daily intake (chem) = criterion (medium, chem) x intake factor
(medium). For instance, in the California and U.S. Army methods,
occupational exposure limits are converted into the MEL and DT,
respectively. Likewise, drinking water standards and food residue
limits are converted into DTS by the U.S. Army. The conver-
sion methods vary. In the California method, the conversion into
maximum exposure levels {MELs. expressed in m~/daY) is cer
~1
· ~. . 1 ~ ~1- ~ · ~·
formed oy in-house experts turougn tne appllcarlon OI UnCerFaIn£Y
factors, pharmacokinetic factors, intake factors, and professional
judgment. The U.S. Army method relies on uncertainty factors
and intake factors. The New Jersey method relies only on intake
factors to convert numerical criteria into allowable daily doses.
(See Tables 3-1 and 3-2 for a list of the uncertainty factors used
in the California and U.S. Army approaches.) Clearly, there are
differences among the methodologies.
The advantage of approach 1 is its firm reliance on toxicity
data and principles of toxicology. Its disadvantage is that it re-
quires extensive data and sophisticated scientific expertise and is
· ~
resource Intensive.
The advantage of approach 2 is its efficiency. Its main disad-
vantage is that, as stated before, standards and guidelines, derived
under different laws and based on different sets of requirements and
assumptions, are a mixed bag of numbers that are not necessarily
related to toxicity data for a particular chemical. Furthermore,
by converting these numbers into acceptable daily doses (MELs,
DTS), this approach erroneously implies that these are toxicity-
based numbers. Despite these clear limitations, approach 2 is used
extensively by California, New Jersey, and the Army.
It is apparent that there are significant differences among the
four methodologies (excluding Washington State, which uses a to-
tally different approach) in the derivation and use of chemical-/
OCR for page 62
62
HAZARDOUS WASTE SITE MANAGEMENT
media-specific numerical criteria. They diner in both their toxi-
cologic data bases and methods of conversion. It is thus unlikely
that criteria developed by different methodologies for the same
medium/chemical should be the same or even comparable to each
other. It is also evident that it is inappropriate to use numbers
originating from more than one source to solve a particular prob
lem.
Estimation of Carcinogenic Risks
In all four approaches the lifetime excess cancer risk is a prod-
uct of carcinogenic potency factor and dose. Where the approaches
differ, however, is in the interpretation of carcinogenic potency and
the data base used. The New Jersey and EPA methods use the
EPA Carcinogen Assessment Group's slope factors (expressed as
kg x day/mg). These are 95 percent statistical upper bounds risk
estimates that are derived mostly from animal experiments and
are not converted to human unit risk values. California relies on
its own in-house quantitative risk assessment. The potency fac-
tor is based on animal or human data and reflects a 95 percent
statistical upper bound of raw data, extrapolated to humans and
extrapolated to low doses using the multistage model. The U.S.
Army approach uses the unit risk values from EPA water quality
criteria documents. These are 95 percent statistical upper bounds
estimates, extrapolated to humans and extrapolated to Tow doses
using the one-hit model. Given the above differences one may
expect that carcinogenic risks calculated by each method for the
same substance/exposure conditions may differ by one or more
orders of magnitude.
Acceptability of Carcinogenic Risks
In the four methodologies reviewed here that use chemical-/
media-specific criteria to define "How clean is clean?" separate
treatment is given to substances with and without carcinogenic
properties. For substances with carcinogenic properties the cri-
teria are based on some cancer risk level set as a goal. The
three methodologies that address cancer risks for multiple sub-
stances/multiple media exposure conditions (California, EPA, and
the U.S. Army) assume additivity of cancer risks. The methods
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APPROACHES TO SETTING CLEANUP GOALS
63
vary in what they consider a goal risk level. New Jersey and Cali-
fornia use a total risk of 10-6, the U.S. Army uses 10-5, and EPA
uses a range of from 10-7 to 10-4 with 10-6 being a preferred goal.
Multiple Chem~cal/Multiple Route Exposures
The Washington State methodology, which relies mainly on
existing media-specific standards, does not address this issue. Nei-
ther does the New Jersey approach. Both California and EPA
consider cancer risks from multiple routes and/or multiple chemi-
cals to be additive. Also, the adverse effects of multiple chemicals
with similar types of toxic response are additive. Finally, the
total dose from multiple routes of exposure to a substance is ad-
ditive. The U.S. Army approach also assumes that multiroute
doses of a substance are somehow cumulative but does not specify
their exact mathematical relationship (additive, multiplicative, or
other). Multiple chemical and multiple carcinogenic risks are not
addressed.
SUMMARY AND CONCLUSIONS
Hazard management at waste sites is more complex than at
other locations because it involves multiple pathways of exposure.
All of the methods reviewed in this paper focus on the protection
of public health from the adverse effects of exposure to single tox-
icants as well as their mixtures, through single or multiple routes
of exposure. The most favored approach to defining Chow clean
is clean?" for hazardous waste sites is that based on chemical-/
media-specific numerical ambient acceptable concentrations for
specific toxic materials. These criteria are derived separately for
substances with and without carcinogenic properties, a practice
consistent with many past experiences in regulating air and water
contaminants. The rationale used by each method to derive these
health-based numbers, however, is unique to each method; thus
the results are not comparable.
The similarities and differences among the five approaches
were summarized in Table 3-4, which shows that, despite the sim-
ilarities in defining cleanup levels for hazardous waste sites, the
differences in applying the general concepts are vast. The con-
fusion in terminology, although frustrating, is the least of the
problem. The most serious differences stem from variations in
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64
HAZARDOUS WASTESITEMANAGEMENT
the basic assumptions about the environmental fate of chemicals,
stringency of application of principles of toxicology, data base, use
of existing standards/guidelines, use of safety factors, interconver-
sion among routes of human exposure, acceptability of cancer risk,
and extent of reliance on expert judgment. Because of this diver-
sity, acceptable ambient concentrations derived by one method are
not comparable with those from another. Furthermore, the adop-
tion of numbers derived through one method for use by another is
inappropriate.
Finally, it is instructive to Took at the results of this analysis
in the context of the current emphasis on the separation of risk
assessment from risk management. The application of numerical
criteria to the "How clean is clean?" question, all related to
toxicologic properties of compounds, would imply that this is
a risk assessment issue. An examination of the basis of these
criteria and the methods for their derivation shows, however, that
none of the five methodologies succeeds in the task of separating
risk assessment from management. In general, the practice of
converting the existing "numbers" into chemical-/media-specific
criteria, the need to simplify the complex scenarios, and the need
to fill the lack of data with assumptions make it clear that the
separation, however desirable, cannot be maintained.
REFE1lENCES
Department of Health Services, Toxic Substances Control Division, Alterna-
tive Technology and Policy Development Section. 1985. The California
Site Mitigation Decision Tree. Draft working document.
Dacre, J. C., D. H. Rosenblatt, and D. R. Cogley. 1980. Preliminary
pollutant limit values for human health effects. Environmental Science
and Technology 14:778-783.
Dime, R., and W. Greim. 1986. Calculation of Cleanup Levels for Con-
taminated Soils. New Jersey Department of Environmental Protection,
Hazardous Sites Mitigation Administration.
Fischhoff, B., S. Lichtenstein, P. Slavic, S. Derby, and R. Kenney. 1981.
Aceeptablc Risk. Cambridge: Cambridge University Press.
Kasperson, R. E. 1983. Acceptability of human risk. Environmental Health
Perspectives 52:1 5-20.
Rosenblatt, D. H., J. C. Dacre, and D. R. Cogley. 1982. An Environmental
Fate Model Leading to Preliminary Pollutant Limit Values for Human
Health Effects. Pp. 474-505 in Environmental Risk Analysis for Chemicals,
ed. Richard Conway. New York: Van Nostrand Reinhold.
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APPROACHES TO SETTING CLEANUP GOALS
65
Small, M. 1984. The Preliminary Pollutant Limit Volume Approach: Pro-
cedures and Data Base. U.S. Army Medical Bioengineering Research
and Development Laboratory, Ft. Detrick, MD 21701. Technical Report
8210.
U.S. EPA, Office of Emergency and Remedial Response. 1985. Superfund
Public Health Evaluation Manual. Washington, D.C.
Washington Department of Ecology. _
Guidelines. July.
1984. Final Cleanup Policy Technical
PROVOCATEUR'S COMMENTS
David Miller
Because the preceding paper is an excellent survey of state
approaches to cleanup goals, ~ would like to spend my time as
a provocateur discussing the basic concept of using numerical
criteria or setting standards for determining "How clean is clean?"
at hazardous waste sites. The thought ~ would like to get across
is that numerical criteria or standards, or whatever you want to
call them, are diversions. They are an impediment that removes
science from the process of developing rational solutions to soil
and ground water contamination problems. As one who has been
involved from the start in negotiations on "How clean is clean?"
~ have watched the numbers and the criteria become more and
more stringent. It is not worth arguing over the numbers because
almost none of them is achievable.
The natural characteristics of the soil and ground water system
at each particular site determine the effectiveness of pumping and
treating, capping, or flushing the soil. Aquifers do not give up
contaminants either uniformly or completely. Yet most sites can be
managed to minimize health and environmental impacts without
spending tens of millions of dollars to clean them up to background
levels. Contaminated portions of aquifers will never be developed
by the waterworks industry as potable water supplies anyway, and
further contamination of ground water and surface water sources
can be prevented. Our real challenge is not how to set the standard
but how to educate the legislator and the public to the reality of
the cleanup process.
The money and effort presently being expended to accom-
modate impossible cleanups should be spent on determining and
implementing the best way to protect the rest of the resource.
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HAZARDOUS WASTE SITE MANAGEMENT
For example, ground water pumping operations should be located
downgradient and not within the boundaries of waste sites where
treatment costs are highest and the time required to achieve
cleanup standards is greatest. Otherwise, the legacy of the Su-
perfund effort will be the endless operation and maintenance of
remedial action systems that originally were justified on the basis
of artificial criteria and unscientific risk assessments.
Finally, let me relate some statistics that perhaps can be
used later. The average proposed cleanup cost for key Superfund
sites has risen from $5 million to about $20 million. This rapid
escalation in cost over the past few years is principally driven by
a preoccupation with achieving numerical cleanup standards. The
potential number of such sites ranks in the thousands.
Investigating Superfund sites has become a million-dolIar pro-
cess, with a million more going into litigation. These expenditures
have created a giant data base describing the extent of the problem
but very rarely shed much light on the technical and economic fea-
sibility of remedial alternatives. Endless negotiations over "How
clean is clean?" have delayed the initiation of remedial actions for
more than 3 years at some of the better-known Superfund sites.
During these delays, plumes of contamination increase in size as
does, proportionately, the ultimate cost of the cleanup.
In conclusion, ~ am not advocating no action, but ~ am propos-
ing source control and the treatment of contaminants with the
principal objective of protecting what is left and reaching achiev-
able cleanup goals over a reasonable length of time.
Representative terms from entire chapter:
human intake
