TO:  Participants in the EPA Case Study
     on Risk and Decision Making

RE:  Purpose of the Case Study and Your Role
     An analysis of risk is becoming an  increasingly  important
component of regulatory decision making  within  EPA.   Even so,  the
specific ways in which the concept of risk can  be  used  in a
particular situation are not well defined.  The result  can be
confusion and ultimately frustration among those who  must carry
out or are affected by the regulations.

    The concept of risk, however, need not be overwhelming and
can provide guidance in thinking about an environmental problem.
The purpose of this workshop is to help  individuals in  the EPA
Regions understand the basis of risk assessment, develop a common
base of knowledge and terminology, use the concept in formulating
a site-specific decision, and help refine skills in communicating
those decisions.  The workshop is not intended,  however, as a
step-by-step "how to" on risk assessment.  Rather, we are trying
to explain the concepts of risk assessment, risk management, and
risk communication in the context of a case study. There are
many uncertainties and issues, and often no clear  "right"
answers.  As you proceed through the case, you  will be  asked to
consider those issues.  Some of the issues you  normally would  not
confront in your day-to-day activities,  and some of the terms  may
be new.  But, regardless of your background, we hope  you will
address those issues and develop your own conclusions.   By help-
ing you understand the issues, we hope to make  you more informed
consumers of information on risks and increase  your understanding
of both the potential and the limitations of the concepts.  In
addition, we hope to encourage discussion of the unique circum-
stances involved in developing risk assessments for the site-
specific, localized problems that confront individuals  in the  EPA
regional offices.

    The workshop case study will focus on a hypothetical site-
specific problem that EPA regional staff might  encounter in their
day-to-day work.  You will have to decide what  actions  should  be
taken at the site.
                             U.S. Environmental Protection Agency
                             Region 5, Library (PL-12J)
                             77 West Jackson Boulevard 1?th
                             Chicago, IL  60604-3590

The Company

     Electrobotics was formed 15 years ago as a privately held
company.  Its two owners have lived in the community for many
years.  Electrobotics manufactures electronic components for the
computer industry.  In the past few years, the bulk of the com-
pany's sales has been in parts for personal computers, particu-
larly the popular Bananachrome® personal computer.

     Electrobotics has had a rocky history and has  been close to
bankruptcy several times.  However, with the recent growth in
demand for personal computers, its performance has  improved.
Last year Electrobotics had revenues of $7.5 million, compared
with $1.5 million five years ago.  Even so, the company was only
marginally profitable, with after-tax profits of less than

     Electrobotics employs about 150 people and has a reputation
for treating its employees well.  It has never laid off an
employee, even during difficult periods.


     Electrobotics is situated in a sparsely populated region.  A
residential development was recently built near the facility's
western boundary, and approximately 80 people live  in 20 homes
there.  In addition, the town of Utopia lies a little more than
1 mile east of the facility.  The area between the  facility and
the town has few homes, none closer than three quarters of a mile
to.the plant's eastern boundary.  There has been some discussion
about building housing on the property, but no definite plans
exist at this time.  Utopia relies on ground water  for its public
water system and has 40 wells in a nearby well field.  The well
field supplies approximately 50,000 residents, including those in
the development west of Electrobotics.  The ground  water from the
Electrobotics site flows toward the public well field.  Initial
indications are that any ground-water contamination from the
Electrobotics site would affect only three of the public wells.
(Figure 1 provides a schematic of the Electrobotics site and the
surrounding area.)

                                   Rgure 1

                                  Site Plan
                    Electrobotics Property
   & "i?T-s"'* *'' f> """'• '<
                       I I
                                  Water Supply
                                                      Direction of
                                                 Ground-Water Row
Residential Area
                                     (Not to Scale)
  Nature of the Problem

        About five years ago, Electrobotics changed its production
  process as it introduced a new  product.  The process required the
  use  of an industrial solvent—dinitrochickenwire (DNC).   Waste-
  water containing  the spent solvent is stored in a flow  equaliza-
  tion lagoon that  is  part of the Electrobotics wastewater  treat-
  ment plant (see Figure 1).  After treatment, the wastewater is
  discharged to the Smith River.   Electrobotics1  treatment  plant
  uses an activated sludge process.

        EPA has classified the solvent as a hazardous waste.
  Studies on the carcinogenic risks from DNC were only recently
  presented and will be discussed'in more detail  as you assess the
  risks  at the site.


     The hazardous waste regulations developed under RCRA require
that owners and operators of hazardous waste facilities, like
Electrobotics1  storage lagoon, utilize design features and con-
trol measures to prevent the leaking of hazardous waste into
ground water.  Furthermore, all regulated units (a regulated
unit, such as the storage lagoon, is a facility that received
hazardous waste after July 26, 1982) are subject to monitoring
and corrective action requirements if a ground-water problem is
identified.  The ground-water protection standards require the
Regional Administrator to establish in the facility permit, for
each hazardous constituent entering the ground water from a regu-
lated unit, a concentration limit beyond which degradation of
ground-water quality is not allowed.  The concentration limits
determine when corrective action is required.

     Three possible concentration limits can be used to establish
the ground-water protection standards:

       •  Background levels of the hazardous constituents

       •  Maximum concentration limits (MCLs) established by

       •  Alternate concentration limits (ACLs)

Background levels and MCLs are established in the facility permit
unless the facility owner or operator applies for an ACL.  The
background level of DNC is zero, and no MCL exists for the

     In October 1985, the owners of Electrobotics submitted to
EPA, as required under the RCRA regulations, a Part B application
for an RCRA permit.  This application provides the Regional
Administrator with information necessary to evaluate the safety
of the site.  It generally includes:

       •  A description of the facility

       •  Chemical and physical analyses of the hazardous waste
          to be handled

       •  Information from a hydrogeological investigation of the

       •  The potential for the public to be exposed to hazardous
          wastes or hazardous constituents through releases
          related to the unit, including identification of the

          potential pathways of human exposure and the magnitude
          and nature of the human exposure resulting from such

     In addition, Electrobotics1 owners have been conducting
ground-water monitoring as required under the regulations.

     The wastewater treatment system has been permitted under
EPA's National Pollution Discharge Elimination System (NPDES).
The discharge permit issued by EPA sets forth effluent quality
standards, which Electrobotics must meet if it is to discharge
the plant's wastewater to the Smith River.  Under the require-
ments of the NPDES permit, conventional pollutants and indicator
parameters are monitored at the plant's outfall on a daily,
weekly, or monthly basis.  These parameters include the

       •  Biochemical oxygen demand

       •  Chemical oxygen demand

       •  Total organic carbon

       •  Total suspended solids

       •  Ammonia

       •  Temperature

       •  pH

These monitoring requirements serve to ensure the proper func-
tioning of the wastewater treatment system.

     DNC is not included among the pollutants monitored in
accordance with Electrobotics1 NPDES permit.  However, included
in Electrobotics1 Part B application is information on samples
taken from the plant's outfall to the Smith River and tested for

     The results presented in the Part B application and from
other sources indicate that DNC was found in the ground water
below the lagoon.  The initial monitoring wells were located at
the immediate edge of the lagoon, referred to as the "point of
compliance."  Additional monitoring wells have been installed to
characterize'the plume, and results indicate that it has moved to
the eastern edge of the facility boundary.  In addition, DNC was
found in the air around the plant.  No DNC was found in the
wastewater treatment plant effluent.


     You, as the EPA representative responsible for the Electro-
botics site, will evaluate the available information on the risks
posed by PNC and decide whether to issue a permit and what, if
any, corrective actions should be taken at the facility.

Part I

     During Part I, you wish to determine whether and to what
extent the DNC found at the Electrobotics plant endangers the
public health.  Thus, you have decided to conduct a risk
assessment.  Your staff has prepared a document summarizing much
of the information you will need for assessing the risks.  This
document, attached as Part I, reviews the potential risks from

     The first section, which contains toxicological data on the
solvent, constitutes the hazard evaluation.

     The second section of Part I contains a summary of data on
the exposure of various population groups to DNC.  Several issues
arise concerning the interpretation and use of this information,
and it will be necessary for you to formulate appropriate

     The relationship between exposure to DNC and the risk of
adverse health effects is determined by a dose-response evalua-
tion.  In the third section of Part I, you must review possible
approaches to defining this relationship for the solvent.  There
may be several plausible options for describing this relationship
in the region of human exposure.  Normally, you would not examine
the hazard evaluation data and the dose-response information;
these results would be provided by EPA headquarters.  However, in
this instance you have asked your staff to provide the material
for your review because you feel it is important to your under-
standing of the problem.

     In the final section of Part I, you must present your con-
clusions regarding the human health risks posed by DNC from the
Electrobotics facility, and the uncertainties in your knowledge.
You must characterize the risks.

     Part I will be completed during the first day of the

Part II

     Once you have assessed the  risks  from  DNC,  you  must decide
what actions should be required  by Electrobotics'  owners.  You
must manage the risks.  Part  II  of the case is  currently being
prepared by your staff.  It will be given to you at  the end of
the first day of the workshop, when you have completed your
assessment of the risks, and  will be discussed  the next morning.
The new document will contain information on the options for
cleaning up the storage lagoon and ground water  at the
Electrobotics site.  In particular, you will have an approach
proposed by the owners of Electrobotics and alternatives
identified by your staff.

     For each of the options, you will be presented  with informa-
tion describing the approach, predicting the effect  of the option
on the risks identified in Part  I, and estimating the costs.

     At each of the steps in  Part I and Part II,, issues and data
will be presented and alternative conclusions listed.  After
discussion, you may select the conclusion that  seems most appro-
priate; if none seems appropriate you  should offer your own.

     Your review and evaluation will take place  within a working
group of 10 to 12 people.  After you discuss the issues with the
other members, your group should attempt to reach a  consensus on
what action should be taken about Electrobotics1  permit applica-
tion.  If you cannot reach a  consensus,  present  the  alternative
views.  You should note, however, that you  must  ultimately decide
what cleanup actions will be  required  of Electrobotics'  owners.

           Part I








       A.   Ground-Water Modeling Calculations and
           Associated Assumptions
       B.   Human Dose Calculations and Associated

                    AT THE ELECTROBOTICS SITE
Dinitrochickenwire (PNC)
       •  Solvent used to degrease fabricated metal parts
       •  Impurities:   commercial product contains trace amounts
          of trinitrochickenwire
       •  Physical state:  liquid, moderate volatility
       •  Stability:   degrades slowly in aqueous environments
       •  Solubility:   moderately soluble in water

                   II.  HAZARD EVALUATION
     Normally, you would not review information on the
hazards of specific chemicals;  the results would probably be
provided to you by EPA toxicologists.   But by working through
the material in this section,  you will develop an understand-
ing of the nature and quality of information used by the
toxicologists.  You will not become toxicologists, but we
hope you will become more informed users of the information
they provide.


     1.   The purpose of hazard evaluation is to identify the
          types of adverse health effects that may be associated
          with exposure to DNC, and to characterize the quality
          and strength of evidence supporting this identifica-

     2.   The specific hazard of concern in this review is
          cancer, although systemic toxic effects will also be

     3.   Epidemiological studies in exposed human populations
          are generally considered the best source of information
          for hazard identification.  Unfortunately, they are not
          available for most substances.  Moreover, establishing
          firm causal links between exposure and chronic human
          disease (such as cancer) is very difficult.

     4.   Studies with experimental animals also provide useful
          information for hazard identification.  Such studies
          can be controlled, and thus can more easily establish
          causality.  Results from such studies suffer from the
          obvious limitation that experimental animals are not
          the species of ultimate interest.

     5.   With one possible exception (arsenic), all known human
          carcinogens are also carcinogenic in one or more
          species of experimental animals.  Most animal carcino-
          gens have not been established as human carcinogens.

     6.   Biological data support the proposition that responses
          in experimental animals should be mimicked in humans.
          For some agents, however, species differences in
          response can be substantial.

     7.   The specific sites of tumor formation in humans may
          differ from those observed in experimental animals.

     8.   Data obtained by administering a substance by the same
          route of exposure experienced by humans are considered
          more predictive than data obtained by a different
          route.  If tumors form at internal body sites, however,
          the route of exposure may not be important.

          In general, a varied response in experimental animals--
          tumor formation or systemic effects in several species
          and both sexes, at different exposure levels with
          increasing response at increasing exposure, and at
          multiple body sites—provides more convincing evidence
          of potential human carcinogenicity or systemic damage
          than does a response limited to a single species or
          sex, or to body sites at which tumors or systemic
          effects commonly occur in untreated animals (e.g.,
          liver tumors in untreated male mice).

     The toxic properties of DNC were first investigated in the
1940s and 1950s.  In most of these tests, small groups of experi-
mental animals were exposed to very high amounts of DNC to iden-
tify the exposure conditions that would cause death.  Animals
received either a single exposure, or exposures covering only a
fraction of their lifetime.

     During the 1950s and 1960s, more extensive animal toxicity
tests were conducted, although none involved DNC exposures last-
ing more than about one-sixth of a lifetime.  These tests
revealed the range of doses that produced toxicity (the principal
site of toxic action was the liver) and the exposure level below
which no form of toxicity was identified.

     Information available in 1970 showed that the most highly
exposed humans received a daily DNC intake several hundred times
lower than the "no-observed toxic effect" intake identified in
the animal tests.  Because the liver toxicity produced by DNC was
of a type likely to occur only after a minimum threshold exposure
was exceeded, it was concluded that the most highly exposed
humans were protected from DNC toxicity by a wide safety margin.
This is discussed in more detail later.

     At least until 1980, no data had been published on the
effects of DNC on exposed humans.

The Frankenstein Study

     In late 1985, an article titled "Chronic Toxicity of Dini-
trochickenwire in Rats and Mice" appeared in a respected scien-
tific journal (Frankenstein, V., J. Environ. Tox.).  The Franken-
stein paper presented data on the effects of lifetime exposure to
DNC in two species of rodents.  These data revealed a form of

toxicity—carcinogenicity—that had not been seen before.   The
design of the Frankenstein experiment and the major findings are
presented in Tables 1 and 2.

     Remarks on the Frankenstein Study

1.   As far as can be determined from the published article, the
     Frankenstein study was carefully conducted,  and thera is no
     reason to doubt the accuracy of the reported data.

2.   DNC increased the incidence of tumors (percentage or  propor-
     tion of animals with tumors) in certain groups of animals.
     Not all animals in a group receiving DNC developed tumors.
     Tumor incidence is a measure of the risk (probability)  of
     tumor development.  Data in Table 2 can be interpreted as in
     the following example:  the lifetime risk of stomach  cancer
     in male rats exposed by gavage to the high dose of DNC
     daily, for their full lifetimes, is 0.40.

3.   Rats developed spleen and liver tumors after both inhalation
     and gavage exposures.  Lung tumors were produced only by
     inhalation, and stomach tumors only by gavage.  Females of
     both species showed fewer tumors than males, and mice, showed
     fewer tumors than rats.

4.   The stomach tumors appeared at the point where DNC contacted
     the stomach when introduced by stomach tube.  This point is
     in the rodent forestomach, an anatomical feature not  present
     in humans.

5.   Severe irritation was observed in the areas  of the rodents'
     stomachs that were exposed to high doses of  DNC delivered by
     stomach tube.  No signs of irritation were observed in low-
     dose control animals.  Dr. Frankenstein believes that the
     stomach tumors arose as a result of the severe toxic  insult
     caused by the direct stomach exposure.


                                     Tattle 1

                        DESIGN OF THE FRANKENSTEIN STUDY
   Species and
Rout* of Exposure

Rat, inhalation
Mouse, gavaqa>3



Low doaa
                                  Nuaber of
Mala   Feaale     Each OayJ
                  Amount of
                ONC Received






  Duration of
Expoaura (weeks)2



            of ONC par kiloqraa of the animal's body weight.  The concentration
 of ONC In the air in the inhalation experiment haa bean converted to a unit of
 •eight ao it can be compared with the unita in the gavage study.
^Approximate Ufeapana of the aniaala tftdar laboratory eonditlona.
'Gavaga ia administration of a substance by aaana of a stoaach tuba.
                                     Table 2

    Following ere the only groups in which a statistically significant exceaa
    of tuaor* »aa found.  Nearly 40 poaaible si tea of tumor formation Mara
    examined in each sax of both apaeiaa.

                                                  Percentage of
                                               Animla with Tuaors
                                                 (incidence rate)
      Study Group

    Rat, inhalation
    Rat, inhalation
    Rat, inhalation

    Rat, gavage
    Rat, gavaga
    Rat, gavaga
    Rat, gavaga


   Control   Low Ooaa   High Ooaa
     Mala     Stomach
     Female   Stoaach
     Mala     Liver
     Mala     Spleen
    Mouaa, gavaga





    'A statistically significant exceee of tuenrs ralativa to untreated
     control animals.  This i»aana it ia unlikely that the difference in tumor
     incidence between the treated and control aniswls ia due to chance.
     Bacauaa the only difference between tha control and treated animals wae
     the presence of ONC, it la likely that the excaaa tumor Incidence ia due
     to this eoapound.  Tuanra were found at other sites in both control and
     treated aninals, but no other tumors occurred in statistically
     significant axceaa.

Issues to Be Considered on the Carcinoqenicity  of  PNC
1.   How do these data conform  (or not conform)  to  the
     principles laid out on pages II-2 and  II-3—particu-
     larly the last principle?

2.   In view of these principles, is there  any reason to
     conclude that DNC is not carcinogenic  in rats  of both
     sexes (by gavage exposures) and in male mice  (by
     inhalation and gavage)?

3.   Should the stomach tumors be considered relevant to
     low-exposure risks to humans?

4.   Should the data obtained by gavage treatment be
     considered relevant to human exposure?

5.   Is there any reason to believe that humans  would not be
     at risk of developing the various tumors, assuming
     exposure to DNC?

6.   Is there any way to determine, from the data given,
     whether responses in humans are likely to be similar to
     those of rats or mice?  Males or females?

7.   Do the data provide sufficient evidence to  prove DNC
     is carcinogenic in animals?  Are the data too  limited
     or even inadequate?

Epidemiological Data
           the Frankenstein report was puolished, three DNC manu-
facturers decided to sucmit reports to EPA on their investiga-
tions into employee health.  The information from these three
reports is summarized below.

     Manufacturer A

     Manufacturer A had been producing DNC for 45 years, but none
of the 161 employees in the mortality study had been exposed for
more than 20 years; most were exposed for 10 to 15 years.  Al-
though employee exposure data were not extensive, they suggested
that past exposures were relatively high, sometimes approaching
the inhalation levels that produced an excess of tumors in
animals.  (Although the concentrations of air in the workplace
approached those used in the- animal experiment, the workers were
exposed to these high levels for only a fraction of their life-
time. )

     By January 1979, 35 of the 161 workers had died.  No
statistically significant increase in cancers (malignant
neoplasms) of any type was noted among these workers (3 cases
observed, 3.8 expected in a population of the same size, sex, and
age).  Cancers of the digestive system were elevated (2 cases
observed, 0.7 expected), but this elevation was not statistically
significant (i.e., it is not possible to say the observed
difference was not due simply to chance).  The workers were also
exposed to several other chemicals, at least two of which are
known animal carcinogens.

     Manufacturers B and C

     Reports from Manufacturers B and C are similar to the report
of Manufacturer A.  No cases of malignant neoplasms of the
stomach were reported by either manufacturer.  Both manufacturers
reported slight elevations in lung cancer, but neither elevation
was statistically significant.   No data on worker smoking habits
were available.  Manufacturer C reported 33 deaths among 290

Issue to Be Considered

1.   Should the information from the DNC manufacturers  alter
     earlier conclusions about the  inferences  to  be  drawn
     from the animal data?  If so,  how?  If  not,  why not?

2.   Are the epidemiological data sufficient evidence to
     prove DNC is carcinogenic in humans?  Are the data too
     limited or inadequate?

EPA's Risk Assessment Guidelines

     The Office of Health and Environmental Assessment (OHEA)
within EPA's Office of Research and Development has developed
guidelines for carcinogen risk assessment.  These guidelines
discuss weighing the evidence that a substance is a carcinogen
and classifying the chemical into one of five groups:

     Group A—Human carcinogen
     Group B—Probable human carcinogen
     Group C~Possible human carcinogen
     Group D—Not classified as to human carcinogenicity
     Group E—Evidence of noncarcinogenicity for humans

     OHEA developed an illustrative categorization of  substances
based on animal and human data/ as shown in Table 3.
Table 3
Animal Evidence
No data
No evidence




No Data
     You should note that the "No Data" category means no data
are available indicating a substance is or is not carcinogenic.
"No Evidence" means, for humans/ no association was found between
exposure and increased risk: of cancer in well-conducted,  well-
designed analytical epidemiologic studies.  When reviewing animal
data "No Evidence" means no increased incidence of neoplasms was
found in at least two well-designed and well-conducted animal
studies of adequate power and dose in different species.

Some Possible Conclusions
About PNC Carcinogenicity

1.  DNC is a human carcinogen (Group A).  There is suffi-
    cient evidence from epidemiological studies to support a
    causal association between DNC exposure and cancer.

2.  DNC is a probab.le human carcinogen  (Group B2).  There is
    sufficient animal evidence of carcinogenicity as demon-
    strated in the increased incidence of tumors at several
    sites in multiple species (rats and mice), in multiple
    experiments involving different routes of administration
    (inhalation, gavage), and at different dose levels.
    There is inadequate evidence of carcinogenicity from
    epidemiological studies.

3.  DNC is a possible human carcinogen  (Group C).  There is
    limited animal evidence of carcinogenicity because the
    data obtained when DNC was administered by stomach tube
    may not be relevant to any route of human exposure.
    Thus, DNC resulted in increased tumors in only one
    species (rat) and in one experiment involving only the
    inhalation route of exposure.  There is inadequate
    evidence of carcinogenicity from epidemiological

4.  DNC is not classifiable as to human carcinogenicity
    (Group D).  Because of the extreme conditions under
    which tumors were produced in the animal experiments,
    there is no reason to believe that DNC is a possible
    human carcinogen.  There is inadequate evidence of
    carcinogenicity from epidemiological studies.

5.  Other (formulate your own conclusion).


     Depending on the dose, exposure to a given chemical, such as
DNC, may result in a variety of toxic effects of which cancer is
only one.  These may range from gross effects, such as death, to
more subtle biochemical, physiological, or pathological changes.
Chemicals that give rise to toxic endpoints other than cancer
(and gene mutations) are often referred to as "systemic toxi-
cants" because they affect the function of various organ systems.
It should be noted that cancer-causing chemicals commonly also
evoke other toxic effects (systemic toxicity).

     So far, we have only discussed the carcinogenic properties
of DNC.  But as part of the hazard identification stage of a risk
assessment, the risk assessor considers each of the toxic end-
points from all studies evaluated in assessing the risk posed by
a chemical.

     A chemical such as DNC may elicit more than one toxic
effect, even in one test animal, in tests of the same or differ-
ent duration (acute, subchronic, and chronic exposure studies).
In general, the dose at which no adverse effect is demonstrated
will differ from one effect to another.  For example, the highest
dose at which statistically significant increases in kidney
damage are no longer observed may differ from the highest dose at
which statistically significant increases in liver damage are no
longer observed.

     Primary attention usually is given to the effect exhibiting
the lowest "no observed adverse effect level" (NOAEL), often
referred to as the critical effect.  In simplest terms, an exper-
imental exposure level is selected from the critical study that
represents the level at which "no adverse effect" was demon-
strated.  In our example above, if the highest NOAEL associated
with kidney damage is greater than the highest NOAEL associated
with liver damage, then liver damage is the critical endpoint for
examining systemic toxic effects of DNC.  This approach is based
on the assumption that if the critical toxic effect is prevented,
then all toxic effects are prevented.

The Shakespeare Study

     Only one chronic study of oral exposure to DNC was located
in the available literature.  That study, conducted by
Dr. Shakespeare et al. in 1978, presented data on the effects of
exposure to DNC in rats.  The design of the Shakespeare study and
the major findings are presented in the following quote from the


    "A total of 80 rats (40 males/40 females)  were exposed
     to either 0 mg/kg/day, 2 mg/kg/day,  10 mg/kg/day,  or
     20 mg/lcg/day of DNC for two years.   The method of
     exposure was gavage (in water).  At  the 20 mg/kg/day
     level of exposure, a statistically significant reduc-
     tion in the rate of body weight gain and weight changes
     in the kidney and liver were observed in both male and
     female rats.  Pigmentation of the liver and a statisti-
     cally significant reduction in the rate of body weight
     gain were observed in female rats exposed to at least
     10 mg/kg/day of DNC.  The 2 mg/kg/day level of exposure
     was reported as a chronic 'no observed adverse effect
     Remarks on the Shakespeare Study

1.   As far as can be determined from the published article/  the
     Shakespeare study was carefully conducted,  and there is  no
     reason to doubt the accuracy of the reported data.

2.   The Shakespeare study has been identified by your lab as th«
     critical study, with liver pathology as the critical effect
     or systemic toxic endpoint.  That is, the primary target
     organ for the systemic effects of DNC is the liver.

3.   DNC increased the incidence of liv'er and kidney changes  in
     certain groups of animals.  Not all animals in a group
     receiving DNC suffered from changes in liver or kidney
^-Shakespeare, et al., "Chronic Systemic Toxicity of Dinitrochick-
 enwire in Rats," Journal of Environmental Toxicology (1978).

Issues to Be Considered on the Systemic Toxi'city of PNC
1.   How do these data conform (or not conform) to the
     principles laid out on pages II-l and II-2—particu-
     larly the last principle?

2.   In view of these principles, is there any reason to
     conclude that DNC is not a systemic toxicant in rats of
     both sexes?

3.   Should the data obtained by gavage treatment be
     considered relevant to human exposure?

4.   Is there any reason to believe that humans would not be
     at risk of developing liver and kidney damage if
     exposed to DNC?

5.   Is there any way to determine, from the data given,
     whether responses in humans are likely to be similar
     to those of rats?

Some Possible Conclusions About the Systemic Toxicity of PNC

1.   DNC is a systemic toxicant to humans.   There is clear
     evidence from animal studies to support a conclusion
     that DNC exposure will cause kidney and liver damage in

2.   It is highly likely DNC is a systemic  toxicant to
     humans.  There is sufficient evidence  of toxicity as
     shown in the kidney and liver pathology found in rats
     exposed to DNC at relatively low doses.

3.   DNC is a potential human systemic toxicant.   We have
     reviewed a very limited amount of animal evidence
     showing that DNC is a systemic toxicant to rats result-
     ing in liver and kidney damage.

4.   DNC is not classifiable as to human systemic toxicity.
     The animal evidence is insufficient to make  a decision
     at this time.

5.   Other (formulate your own conclusion)


 1.  The purpose of exposure evaluation is to identify the magni-
     tude of human exposure to DNC, the frequency and duration of
     that exposure, and the routes by which humans are exposed.
     It may also be useful to identify the number of exposed
     people along with other characteristics of the exposed popu-
     lation (e.g., age, sex).

 2.  Exposure may be based on measurement of the amount of DNC in
     various media (air, water)  and knowledge of the amount of
     human intake of these media per unit of time (usually per
     day) under different conditions of activity.

 3.  Some individuals may be exposed by contact with several
     media.  It is important to consider total intake from all
     media in such situations.

 4.  Because only a limited number of samples of various media
     can be taken for measurement, the representativeness of
     measured values of environmental contaminants is always
     uncertain.  If sampling is adequately planned, the degree to
     which data for a given medium are representative of that
     medium can usually be known.

 5.  Sometimes air and water concentrations of pollutants can be
     estimated by mathematical models.  Although some of these
     models are known to be predictive in many cases, they are
     not thought to be reliable in all cases.

 6.  Standard average values and ranges for human intake of
     various media are available and are generally used, unless
     data on specific agents indicate that such values are

     As discussed earlier, the Electrobotics Company,  which manu-
factures parts for Bananachrome* personal computers,  operates a
production facility.  The facility employs 150 workers and

   includes a  wastewater treatment plant and equalization lagoon
   (surface impoundment).   (The  site plan is illustrated in
   Figure 2.)  Wastewater from the manufacturing  plant operations
   contains high  concentrations  of DNC and is  periodically dis-
   charged to  a  flow equalization lagoon, which  is  located within
   200 feet of the western  facility boundary.  There are no other
   potential sources of DNC releases in the surrounding area.
   Adjacent to this boundary  is  a residential  area  of 20 houses  in
   which 80 individuals reside.   Electrobotics has  built an 8-foot-
   high chain-link fence on the  property boundary separating  the
   residents from the facility grounds.  The area between the
   Electrobotics  facility and the threatened water  supply wells  to
   the east is undeveloped  and contains few residences.  There has
   been some discussion about building housing on the property/  but
   no definite plans exist  at this time.  The  Smith river is  located
   east of the facility about 1,500 feet from  the facility boundary.
   There are no  drinking water intakes along the  river, but some
   recreational  fishing and swimming occurs.

                                   Figure 2

               Site Plan and Points of Compliance and Exposure
                   Electrobotics Property
                                  [Smith River]

                                 r~\    x

         Air Monitoring
                            Compaance Monitoring Wells

                            Eastern Property Boundary
Residential Area
                    Treatment  I *
                                                      Direction of
                                                  Ground-Water Row
                                                                  Water Supply
Point of Compliance
Key Characterization Wells
                                                                     (Not to Scale)

     The equalization lagoon maintains a regular  flow  to  an
on-sits activated sludge wastewater treatment  facility.   The
equalization lagoon is maintained at an average fluid  depth of
10 feet and measures 10/000 square feet.  The  wastewater  from the
treatment plant is discharged to the river  in  compliance  with the
facility's NPDES permit.

     The equalization lagoon is underlaid by a compacted  natural
clay liner with a hydraulic conductivity (a measure  of the rate
at which it transmits water) of 3 x 10~s cm/sec,  which is
designed to provide substantial containment of the wastewater.
The uppermost geological formation beneath  the site  is composed
of approximately 75 feet of stratified glacial outwash, which
consists of layered sand and gravel with some  silt.  These
unconsolidated sediments form a productive  aquifer that is a
source of potable water to the surrounding  area.  A  well  field  is
located approximately 1.5 miles to the east (downgradient) of the
site and provides approximately 3 million gallons per  day (mgd)
of potable water to its 50,000 customers.   The well  field con-
tains 40 separate wells, each pumping 75,000 gallons per  day

     The hydraulic conductivity of the aquifer has been estimated
at 40 feet per day, based on field tests in the area.   However,
there may be thin continuous layers of significantly lower or
higher hydraulic conductivity within the glacial  outwash. The
water table is located about 10 feet below  the bottom  of  the
lagoon at the site.  The hydraulic gradient (a measure of the
slope of the water table), based on the best available potentio-
metric head measurements, is estimated at 0.005 feet/feet toward
the community well field.

     The site is located in a humid area.  The wind  direction is
seasonal; however, according to a wind rose from  a local  meteoro-
logical station (which describes wind direction and  frequency),
the wind blows west across the site toward  the 20 homes adjacent
to the lagoon approximately 30 percent of the  time.

     The owners of Electrobotics conducted analysis  of the lagoon
in preparing their Part B application.  The nature of  the materi-
als stored in the lagoon and the meteorological and  hydrogeolog-
ical conditions in the vicinity have resulted  in  some  concern by
EPA about possible exposure of workers at the  facility and resi-
dents in the vicinity to DNC via inhalation of air,  as well as
possible exposure of the community via contamination of drinking
water supplies.  In an attempt to respond to the  regulations  and
concerns of EPA staff, the owners undertook a  program  of  air,
surface-water, and ground-water monitoring.

     Measurements of concentrations of DNC on the site are
described in the next section.  A ground-water monitoring program
has been undertaken to comply with regulations promulgated under
the Resource Conservation and Recovery Act (RCRA).  Electrobotics
is monitoring contaminants in ground water at the downgradient
limit of the waste management unit, termed the "point of compli-
ance."  The point of compliance in this case is at the eastern
limit of the berm around the lagoon.  Three monitoring wells have
been installed at this point, and one well was installed upgradi-
ent (see Figure 2).  This conforms to the regulatory minimum.
No DNC was found in the sample from the upgradient well.  The
nearest downgradient property boundary is to the east, about
1,000 feet from the lagoon.

     Because DNC has been detected at the downgradient compli-
ance-monitoring wells, a ground-water assessment has been initi-
ated, and additional monitoring wells have been constructed at
the eastern property boundary to monitor chemical concentrations.
Further downgradient, the public well field represents a point of
potential human exposure.  Three of the 40 wells are located
directly downgradient of the lagoon.  The relative locations of
the point of compliance, eastern regulatory boundary, and actual
point of exposure are shown in Figure 2.

     Measurements of DNC concentrations in air along the western
site boundary, outdoors at the facility adjacent to the lagoon,
and indoors within the treatment plant have been made during a
single air-sampling program.  The sampling program was conducted
for a period of one week, during which 24-hour average concentra-
tions were measured at the western property boundary, adjacent to
the equalization lagoon and within the treatment plant.  During
the period of measurement/ wind was blowing generally west across
the lagoon toward the residential area.  The mean, standard devi-
ation, and range of measured chemical concentrations in air are
shown in Table 4.  Air measurements that were made concurrently
inside the wastewater treatment plant did not detect measurable
concentrations of the solvent.  Within the treatment plant, all
treatment units are closed and vapor-controlled to limit any
fugitive air emissions.

     Electrobotics1 NPDES permit requires monitoring only for
conventional pollutants and indicator parameters, so the effluent
from the treatment plant is not monitored for DNC before

it is discharged to the Smith river.  In preparing its Part  B
application, however/ the owners of Electrobotics collected  a
limited number of samples from the treatment facility outfall.
The results are presented in Table 4, and indicate that  no DNC
was detected.
Table 4
Ground water
Ground Mater
Ground water
Surface water
Inside treatment plant
At weatern boundary of site
Point of compliance
Eastern property boundary
Public well field
Treatment plant outfall
iftot detected at 1 /u.g/n? for air or 1 ng/l for
^Trace concentrations below detection limit of

Deviation Range
16 8-68
80 120-480
30 290-350
     The ground water has been periodically sampled and tested
for DNC both at the point of compliance, the monitoring wells on
the eastern boundary/ and at the water treatment plant at  the
community water system/ which draws water from  the aquifer for
the municipal supply.  Samples were taken at several depths  as
well.  The concentrations of chemicals in monitoring wells at the
point of compliance are indicated in Table 4.   The concentrations
detected at the compliance point indicate contamination of the
aquifer.  Trace concentrations of ONC have also been detected at
the eastern boundary in the most recent water tests/ but at  con-
centrations less than the method-detection limit of 1 ug/1
(or'ppb).  The municipal water supply has been  tested, and no
detectable concentrations of DNC were found.  However/ the
detection limit for DNC offered by available analytical methods
for ground water is 1 ug/1.

     A very simple description of the area's geology and the
current status of the DNC-contaminated ground-water plume  are
presented in Figure 3.  Available information suggests that  the
chemical plume has not yet migrated beyond the  eastern property
boundary/ but without corrective action the concentrations are
expected to increase in time in this vicinity,  eventually  affect-
ing offsite ground water.


                                                  Rgure 3

                                                 Site Plan
 Residential Area
                            Electrobotlcs Property
                             Smith River
                                                Water Supply
                                                                   DNC-Contamlnated Plume
                                                                            Direction of
                                                                     Ground-Water Row

                                                    (Not to Scale)
                                      Geological Cross Section
         In F«et  -30

                                  Monitoring Welle
             Characterization WeN

    DNC-Contamlnated Plume'
Water Supply
1  The outermost contour line la believed to be the edge of the edge of the DNC-contaminated plume.
  where the concentration Is below the detection limit of 1 ppb.

4  Tt'V'lS' surfac8 n«» a constant slope of 0.005 feet/feet.  The apparent change In slope Is an effect
  of the different horizontal scales.

      A mathematical model of the contaminant plume movement in
the aquifer  has been constructed to  estimate future concentra-
tions in  the aquifer.  A summary of  the  modeled environmental
concentrations in ground water is presented in Table 5.  Appen-
dix A contains the calculations and  the  associated assumptions
that  were applied in modeling these  environmental concentra-
                               Table 5

                       STEADY STATE IN GROUND WATER1

                    Eastern property boundary
                    Public well-field

     Human exposure to contaminated soil,  however, was considered
insignificant at this site because soils potentially contaminated
by ground water are located at least 10 feet below the land sur-
face.  No concentrations of DNC were found in a limited set of
soil samples taken from surface soils around the lagoon.   Conse-
quently, doses resulting from potential human exposure to soil
were not calculated.

     In order to estimate human exposure,  or dose of the consti-
tuent from each contaminated medium, certain data and assumptions
were applied.  These data and assumptions  relate to the extent
and frequency of human contact with these media and the degree of
absorption of chemicals for each route of  exposure.  When the
constituent is ingested, a certain fraction will be absorbed
through the gastrointestinal wall; when it is inhaled, a certain
fraction will be absorbed from the lungs.

     The method of dose calculation depends on the route of expo-
sure.  Certain standard values have been developed to estimate
contact with and intake of certain media.   For drinking water,
the EPA and other scientific groups generally assume that adults
drink 2 liters of water per day.  It is also generally assumed
that the average adult inhales from 20 to 23 cubic meters (m3) of
air per day.  We have assumed an adult inhales 23 mVday,
although EPA risk assessments are increasingly using 20 mVday.
It should be noted, however, that the data and assumptions
required for estimation of dose from most other routes of expo-
sure are not as readily standardized.

     The assumptions and calculations required to estimate DNC
dose to the 80 neighboring residents resulting from inhalation of
DNC-contaminated air are presented below to illustrate the ele-
ments of dose estimation.  A complete set of calculations and
associated assumptions for the critical pathways is shown in
Appendix B.

Inhalation of DNC-Contaminated
Air by Neighooring Residents


       •  An adult inhales 23 mVday °f air.

       •  Based on wind direction analysis, the duration of
          exposure is 30 percent of the time on an annual average

       •  The body weight of an adult is 70 kg.

       •  The inhalation absorption factor for DNC is 0.75.

       •  The adult lives in the home throughout his lifetime.


        0 .044 mg
                   (average  DNC air concentration  at boundary)
x 	  x  0.3  (percentage  of time exposed)
  70  kg
        x  0.75  (inhalation  absorption  factor)

        =  3.3 x  10-3 mg/kg/day

      Table 6 presents a summary  of all the  exposure calculations
performed to estimate doses from the  contaminated media to  the
identified exposed population groups.
                                    Table 6


        Air, neighboring residents1
        Air, workers on site (outdoors)^
        Ground water, point of compliance^
        Ground water, eastern property boundary-5
        Ground water, public well-field-*
                         DNC (mg/kg/day)
   x 10~3
4.7 x 10-3
9.5 x 10-3
7.8 x 10-3
1.6 x 10-*
Number of

        -'•Estimated exposures from DNC in the air are based on current concentrations
         in the air.
        Estimated exposures at the point of compliance are based on current
         concentrations of DNC at that point, although no individual is currently
         exposed to those concentrations.
        ^Estimated exposures at the eastern property boundary will not occur for three
         years, and no one currently receives their drinking water from that point.
         Exposure estimates for the public well-field will not occur for about
         22 years.

      The  ecosystem in the  ^mith  river  has  been  examined by  a
biologist employed by the  Electrobotics plant.   The resulting
study characterizes  the area upstream  and  downstream  from the
facility.   No major  evidence of  ecological damage was found,

although there was some discoloration of the river around the
outfall noted when the plant switched to the use of DNC.  This
discoloration has persisted.

     No threatened or endangered species were found near the
Electrobitcs site.  However, several threatened or endangered
species have been known to inhabit river ecosystems in the
vicinity.  Fish species include the Snail Darter, Slackwater
Darter, Amber Darter, and Spotfin Chub.  Terrestrial species
include the Eastern Indigo Snake.  Furthermore, several of these
species are acutely sensitive to compounds similar in structure
to DNC.  The data available on DNC are not adequace for estab-
lishing ambient water quality criteria for aquatic life.

     As noted earlier, the effluent discharged to the Smith river
from the Electrobotics treatment plant was tested for DNC.  No
DNC was detected at a detection limit of 1 /xg/1.

Remarks on Exposure Data

1.   Ground water directly beneath and adjacent to the regulated
     unit has been routinely sampled and analyzed for the
     presence of DNC.  Concentrations that have been measured
     have remained relatively constant for the past two years and
     indicate that DNC has leaked from the storage lagoon into
     the underlying aquifer.  Ground water moves toward a well
     field that provides drinking water for a community of
     50,000 people.  DNC has not been detected in the water sup-
     ply but may be present at concentrations below the current
     method detection limit, which is 1 ^g/1 (ppb).

2.   DNC is unstable in the environment and will decompose by
     biodegradation in shallow aquifer systems.  The decomposi-
     tion of the chemical in aquifers has been demonstrated in
     aquifer restoration programs at other sites, but the rates
     of decomposition are variable and have only been quantified
     in laboratory experiments.  The rate of decomposition at
     concentrations less than 10 ppb is uncertain.

3.   Trace concentrations (less than 1 jig/I) of DNC have been
     detected at the eastern facility boundary.  A mathematical
     model has been used to predict future concentrations of DNC
     in ground water downgradient of the regulated unit.  The
     model prediction indicates that the chemical will migrate in
     ground water and degrade at a slow rate.  On the basis of
     the model prediction, concentrations are expected to
     increase at the eastern property boundary if no corrective
     action is taken.  The degradation products are not believed
     to be carcinogenic.


4.   Estimates of  future concentrations  of  DNC  in  drinking  water
     are based on  analytical predictions from a ground-watar
     model.   Appropriate adjustments  regarding  ground-water
     dilution were made to estimate concentrations at  the tap.

5.   Estimates of  current exposure in air were  based on analyti-
     cal results obtained from measuring the  air concentrations
     in the  facility and at the boundary over a single seven-day
     period  in April 1986.  Twenty-four-hour  composite samples
     were taken each day over the sampling  period.  No other air
     data are available.

6.   Estimates of  current concentrations of DNC in treatment
     plant effluent are based on analytical results from samples
     taken over the same seven-day period in  April 1986.  Five
     samples were  taken during this period.

Issues to Be Considered

1.   Has Electrobotics adequately characterized  the
     ground-water contamination?  If not, what additional
     types of information would you require  them to  provide
     and why?

2.   The summary exposure data presented  in  Table 6  include
     some current exposure estimates and  some future expo-
     sure estimates.  Models are used to  predict concentra-
     tions of DNC at some point in the  future/ assuming  that
     releases of the substance from the lagoon occur at  the
     current rate.  Should the two types  of  exposure data
     (current and future) be treated the  same for purposes
     of characterizing human risk?  How should distinctions
     be reported?

3.   Should the ground-water concentration estimates that
     are based in part on modeling of a degradation  process
     be used at all?  How should this be  decided? If
     modeled concentrations are not used, how should the
     analyses of chemicals that are reported as  "below
     detection limit" or "not detected" in the water supply
     system be represented in exposure estimates?

4.   Are the estimates of DNC in surface  water acceptable?
     What additional information would you want?

5.   Is the mean concentration in the various media  the
     appropriate summary statistic to use to characterize
     human exposure?  Should the upper range or  statistical
     upper confidence limit be used as an alternative?

6.   Are the various assumptions about human intake  and
     average exposure to various media valid?  Should others
     be substituted or added?

7.   Should other routes of exposure to the  various  contami-
     nated media have been considered?

8.   Should the total exposure and risk for  the  regulated
     unit be represented by the sum of all incremental risks
     for each chemical/pathway?

 Issues to Be Considered (continued)

 9.   Was it appropriate to model the exposure based on an
      adult population?  Should other populations-at-risk
      have been considered?

10.   Should exposure and risk to workers at the facility be
      considered in the same context  as residents in the
      surrounding community?

11.   Do you believe DNC is affecting the ecosystem around
      the Smith River?

Some Possible Conclusions About
Human Exposure to PNC

     Which of the following conclusions best characterizes
the information you have seen?

1.   None of the exposure estimates is adequate for use in
     risk assessment.  Given the currently available data,
     the risk assessment should describe exposure in quali-
     tative terms only.  No quantitative risk assessment
     should be developed until better information is

2.   The exposure estimates presented in Table 6 for drink-
     ing water and air are reliable and can be used for risk
     assessment.  However, no risks should be assessed until
     more detailed data are obtained from other pathways of
     exposure, such as showering or ingestion of contami-
     nated soils.

3.   The exposure estimates presented in Table 6 and based
     on field measurements are reliable and can be used for
     assessing risks.  The exposure estimates based on
     modeling, however, are too uncertain to be used to
     assess the risks.

4.   Although the exposure estimates in Table 6 are based on
     different data and assumptions, they are all adequate
     and sufficient for assessing risks.  The risk manager
     should be made aware of the uncertainties in each of
     the data sets, but a quantitative risk assessment
     should be developed.

5.   In addition to Conclusion 2, it should be noted that
     all the exposures from various media should be added
     for those people exposed to all sources of DNC.

6.   Other (formulate your own).

     Normally, you would not be involved in reviewing dose- '
response information; the results generally would be pro-
vided to you.  As discussed before, however, we hope that by
having you evaluate this information and address the key
issues here, you will be able to better use the dose-
response information you will receive.

     We have given you the EPA approach to evaluating dose-
response relationships.  In addition, we have identified
alternative approaches so that you develop an understanding
of how others may perceive the issue.


     Because of the relative complexity of dose-response evalua-
tion, the following discussion is substituted for a statement of
key principles.

     Animal data showing that DNC is carcinogenic were obtained
in the high-exposure region of the dose-response curve.  Thus,
animal exposures were in the 30-to-300-unit range (see Table 1),
and these produced measurable risks in the range of 10 to 50 per-
cent (see Table 2).  Predictions of human exposure, as discussed
in Section III, are at much lower levels.  What can be said about
risks in the range of human exposure?

     At least three general approaches to this problem have been
proposed by various experts.

Approach 1

     Based on general theories of how carcinogens act to produce
cancer (largely derived from experimental studies and epidemi-
ological data), all finite exposure levels will produce a finite
risk.  The magnitude of the risk will decline as the magnitude of
exposure declines (clear even in the animal data).1

     If the quantitative relationship between exposure and risk
were known for all exposures, the risks to rodents exposed at
very low levels could be predicted from the measured exposure-
risk data.  The risks to humans could be predicted at these very
low levels if the relationship between rodent and human suscepti-
bilities were known.  Although these relationships cannot be
known with accuracy, a plausible upper limit on human risk can be
predicted with sufficient accuracy to be used as a guide to mak-
ing risk decisions.   Actual human risk is not likely to exceed
the upper limit, and it may be less.  This is the approach
generally adopted by EPA in evaluating the risk associated with
low-level exposure to carcinogens.
iThese two sentences are the proper formulation of the "no-
 threshold" concept.  It does not mean that all finite exposures
 will cause cancer; rather,  it means that all finite exposures
 will increase the probability (risk) that cancer will occur.

Approach 2

     The quantitative relationships between high-exposure and
low-exposure risks in rodents and between rodent and human risk
are not known with sufficient reliability to be used in risk
assessment.  Moreover, there is no reliable theory on which one
can conclude with assurance that low-level human exposure (i.e.,
exposure below the range producing detectable risks) poses any
risk at all.  As with other toxic effects, carcinogenicity will
not be initiated within an individual until a minimum threshold
of exposure is exceeded.  In such circumstances, the only reason-
able course is to report the magnitude of the margin-of-exposure
(MOE) by which humans are protected.  MOE is the maximum amount
of exposure producing no measurable tumorigenic response in ani-
mals divided by the actual amount of human exposure.  MOE gives
the risk manager adequate information on which to decide whether
exposures must be reduced or eliminated to provide human protec-
tion.  A relatively large MOE is desirable because it is likely
that the threshold for the entire human population is lower than
that observed in small groups of experimental animals.  This
approach is generally applied when evaluating the potential risk
of most noncarcinogenic effects.

Approach 3

     Although there is adequate theory and some evidence to per-
mit the conclusion that humans are at finite risk at all finite
exposure levels, there is insufficient knowledge to allow predic-
tion of the risks in quantitative terms.  The risk assessor
should simply attempt to describe risks qualitatively, perhaps
coupling this description with some information on the potency of
the compound and the magnitude of human exposure.  This type of
presentation is adequate for the risk manager, who should not be
concerned with the quantitative magnitude of risk in any case.
     Each of these views, and perhaps others as well, has some
merit.  The first approach is now used by most federal public
health and regulatory agencies, including EPA.  These agencies
emphasize that the predicted numerical risks are not known to be
accurate, but because of the nature of the models used to predict
them, they are likely to be upper-bound estimates of human risk.
An upper-bound estimate is one that is not likely to be lower
than the true risk and is likely to exceed the true risk (which
could be zero).

     For this exercise, we will estimate low-exposure risks using
the model currently used by EPA.  A model is a mathematical for-
mula that describes the relationships between various measures.
Two models are needed to predict low-exposure risks:

       •  A high to low exposure extrapolation model is needed to
          predict low-exposure risks to rodents from the measured
          high-exposure, high-risk data (see Table 2).  EPA
          currently uses a "linearized multistage model" for this
          purpose.  This model is based on general (not chemical-
          specific) , widely held theories on the biological pro-
          cesses underlying carcinogenesis.  Application of the
          model to the rodent exposure risk data produces an
          estimate of the lifetime risk for each unit of exposure
          in the low-exposure region.  This is called the unit
          cancer risk.  The linearized model is used to ensure
          that the unit cancer risk is an upper-bound estimate of

       •  An interspecies extrapolation model is used to extra-
          polate from rodent unit risks to human unit risks.  EPA
          assumes that rodents and humans are at equal risk at
          the same exposure measured in milligrams of carcinogen
          per square meter of body surface area per day.  Inter-
          species extrapolation models are commonly called
          "scaling factors" because they are used to scale doses
          between species.

     EPA's selection of these models is based on the agency's
view that they are the best supported for purposes of deriving an
upper-bound estimate of risk.  Alternative models are available
for both these forms of extrapolation, and several are equally
plausible.  In most cases, but not always, use of plausible
alternative models will yield lower estimates of risk than those
predicted by the two described here.  Differences can sometimes
be very large/ but are generally relatively small when the models
are limited to those that are linear at low exposures.

     Further discussions of various models and their plausibility
can be found in the handout "Principles of Risk Assessment:  A
Nontechnical Review."

     In this exercise we determine the upper-bound estimate of
unit cancer risks predicted for DNC using the models currently
preferred by EPA.  The effect of using alternative, plausible


models is  also described, as  are the animal.data that pertain to
the  second or third approaches described  above  for dose-response
evaluation (i.e.,  the  MOE or  qualitative  approaches).

Estimates  of Upper-Bound,
Lifetime  Slope Factors
Using Current EPA Models

      Application  of the EPA models  for high-to-low-dose and
interspecies extrapolation to the measured animal cancer data for
DNC  (Table 2) yields the results shown in Table 7.   The result of
such extrapolations is the slope factor.   In this exercise,  one
unit of exposure  is equal to  one milligram  (mg)  of the carcinogen
per  kilogram (kg)  body weight of the animal (or human) per  day
throughout the lifetime of the animal  (or human).  Thus, if  the
slope factor for  DNC is 0.0897 (8.97 x 10~2), the risk of
developing cancer  from 1 mg/kg/day  of lifetime  exposure to  DNC is
3.97 x 10-2 (a probability of about 9 in  100, or 1 in 10).
                                   Table 7

                               TO DNC TUMOR DATA

                               (based on Table 2)
          Species. Sex   Route of Exposure     Tumor Site

          Rat, male        Inhalation        Lung
          Rat, male        Inhalation        Spleen
          Rat, male        Inhalation        Liver
          Rat, male        Gavage           Stomach
          Rat, female       Gavage           Stomach
          Rat, male        Gavage           Liver
          Rat, male        Gavage           Spleen
          Mouse, male       Gavage           Liver
          Mouse, male       Gavage           Stomach
  Slope Factor
          *Risk for an average daily lifetime exposure of one unit.  Units are
           the same as those used earlier for describing the animal exposure
           (Table 1), such that one unit s one milligram per kilogram body weight
           per day. Risk is obtained from the slope factor by multiplying the
           latter by the actual number of units of human exposure.  For a given
           exposure, the higher the slope factor, the higher the risk.

     This relationship is presented graphically in Figure  4.  The
horizontal axis is the dose of DNC measured in mg/kg/day.  The
vertical axis is the response and is a probability.

                                Figure 4

                      Dose-Response Relationship for DNC
               (slope Factor)
                                         1    DOM

     To obtain the risk from other levels of exposure, the  slope
factor is multiplied by the number of units of exposure.  The
assumption is that at low doses the relationship between dose  and
response is linear.  Thus/ if a person were exposed to 0.003
units of DNC throughout his lifetime (0.003 mg/kg/day), the risk
would be 0.003 units times 0.0897/unit, or 0.00027  (2.7 x 10~4),
a probability of 2.7 cases arising in 10,000 individuals exposed
at this level.  The greater the slope of the line the more  potent
the carcinogen.

Estimates of Lifetime Slope
Factors Using Other Models

     Application of other models for high-to-low-dose extrapola-
tion yields slope factors equal to or slightly lower than  (less
than fivefold) those in Table 7, as long as the other models
incorporate the concept that risk increases in direct proportion
to exposure in the low-exposure region (linear models).  Use of
the most plausible alternative interspecies extrapolation model
(that generally used by FDA) yields slope factors sixfold  (for
rats) and thirteenfold (for mice) lower than those predicted in
Table 7.  Thus, alternative models predict slope factors about 30
to 65 times lower than those predicted using the EPA models.

      Adoption  of certain nonlinear models for high-to-low-dose
extrapolation  predicts  risks about 1,000  to 10,000 times  lower
than  those predicted by use of  the EPA model.  The nonlinear
models  are not used by  agencies charged with protecting human
health, but cannot be rejected  on purely  scientific grounds.

Carcinogenic Dose-Response
Evaluation not Involving
Formal  Extrapolation

      For those who believe formal extrapolation  beyond the
measurable dose-response data should not  be performed, it is
important to identify the exposures at which DNC produces tumors
and those at which no tumor excess is found (the "no observed
adverse effect level" or NOAEL).   Table 8 identifies NOAELs from
data  on DNC in Table 2.  This is not the  approach generally
applied by EPA for carcinogenic substances.
                                 Table 8

                      (NOAELs) FOR CHRONIC EXPOSURE TO DNC1

                             (based on Table 2)
                   Study Group      Sex     Tumor     NOAEL

                 Rat, inhalation    Male    Lung       JO
                 Rat, inhalation    Male    Spleen      30
                 Rat, inhalation    Male    Liver       30
                 Rat, gavage       Male    Stomach     50
                 Rat, gavage       Female   Stomach     SO
                 Rat, gavage       Male    Liver       50
                 Rat, gavage       Male    Spleen   None found
                 Mouse, gavage     Male    Liver    None found
                 Mouse, gavage     Male    Stomach     60
                 1Unita are identical to those in Tables 1 and 2.
                  "None found" means that a measurable excess of
                  tumors was found at both levels of exposure used
                  in the experiment.

Issues to Be Considered

1.   If explicit estimates of slope factors are made,  should
     only EPA's currently preferred models be used?  Should
     the results of applying other models also be displayed?

2.   Which species/sex/tumor site data from Table 7 should
     be used for slope factor assessment?  All, shown
     individually as in Table 7?  Only the data set yielding
     the highest slope factor?  A sum of all?  Other?

3.   Should the DNC stomach tumor data set be rejected
     because there is no exact anatomical counterpart in

4.   How should the uncertainties in use of models be

5.   Are the observed NOAELs true "no-effect" levels?  Could
     they simply reflect the fact that in experiments  with
     relatively small numbers of animals, the failure to
     observe a statistically significant increase of tumors
     is an artifact of the experimental design, and not a
     true absence of biological effect?  How should this
     uncertainty, if it is real, be taken into account?

6.   EPA has adopted the first approach, using slope factors,
     to extrapolate from the high doses used in the animal
     studies to the low doses at which humans are exposed.
     How might you respond to someone who argues for one of
     the other approaches?

Some Possible Conclusions About
Carcinogenic Dose-Response Evaluation

     Which of the following conclusions best characterizes
the information you have seen?

1.   The slope factors listed in Table 7 are true upper-
     bound estimates.   The true slope factor is not likely
     to exceed those listed, may be lower, and could be

2.   The same as the first conclusion, but add:  The use of
     alternative, plausible models yields slope factors
     about 10 to 100 times lower than those in Table 7.

3.   Slope factors should be reported for all plausible
     models, and the full range of estimates should be
     reported without  bias.

4.   There is no justification for calculating and reporting
     slope factors. What is critical for understanding the
     public health importance of low-level exposure to DNC
     is the margin of  exposure (MOE).  Estimation of the MOE
     is based on the NOAELs for its carcinogenic effects;
     these figures are reported in Table 8.

5.   Neither slope factors nor NOAELs are reliable indi-
     cators of human risk, and neither should be considered
     for risk assessment.  Dose-response relations for the
     human population  are not known for DNC;  risk should be
     described in qualitative terms only.

6.   Other (formulate  your own conclusion).


     As  discussed earlier,  "systemic"  effects  are  toxic  effects
 other than carcinogenicity  or mutagenicity,  such as  liver  or
 kidney damage,  induced by a chemical.  The EPA's approach  to
 assessing the risks associated  with  systemic toxicity  is
 different from  that for assessing the  risks  associated with
 carcinogenicity.  This is because different  mechanisms of  action
 are thought  to  be involved  in the two  cases.   In the case  of
 carcinogens, the EPA assumes that a  small number of  molecular
 events can evoke changes in a single cell that can lead  to
 uncontrolled cellular  proliferation.   This is  the  basis  for the
 no-threshold approach  discussed for  carcinogenicity  in the
 previous section.  The assumption for  carcinogens  is that  there
 is essentially  no level of  exposure  for  such a chemical  that does
 not pose a small, but  finite, probability of generating  a
 carcinogenic response.  In  the  case  of systemic toxicity,
 mechanisms must be overcome before the toxic endpoint  is
 manifested.  For example, a large number of  cells  could  be
 performing the  same or similar  function, and the population must
 be significantly depleted before the effect  is seen.

     Generally, based  on our understanding of  the  mechanisms of
 action,  systemic toxicity is treated as  if there is  an identifi-
 able exposure threshold (both for the  individual and for the
 population), below which effects are not observable.   The  thres-
 hold concept is important in the regulatory  context.   The  indi-
 vidual threshold hypothesis holds that a range of  exposures from
 zero to  some finite value can be tolerated by  an individual with
 essentially no  chance  of expression  of the toxic effect.
Reference Doses

     To evaluate systemic effects, the EPA has developed the
concept of a reference dose (RfD).  The RfD is an estimate, with
an uncertainty spanning perhaps an order of magnitude or greater,
of a daily exposure to the human population (including sensitive
subpopulations) that is likely to be without an appreciable risk
of deleterious systemic effects during a lifetime.

     The RfD is derived from the_NOAEIr^aentified during the      „
hazard evaluation stage_jQf—the risk assessment.  In particular, l^
the NOAEL^-is redujeedoy consistent application of uncertainty
factors «OTsJ)--that reflect various types of data and a modifying  v
factor (|MFT)that is based on professional judgment of the entire
chemicalVdatabase.  That is:
                      RfD - NOAEL/(UF X MF)

     The uncertainty factors account for such considerations  as
the variation in sensitivity among the members of the human popu-
lation, the uncertainty in extrapolating animal data to the case
of humans, the uncertainty in extrapolating from data obtained in
a study that is of less-than-lifetime exposure, and the uncer-
tainty in using data where a NOAEL was not identified.  Each
level of uncertainty usually adds a factor of ten.  Thus,  if  the
RfD for DNC was to be based on the animal study conducted  by
Dr. Shakespeare, we would have two factors of ten or an uncer-
tainty factor of 10 x 10 * 100.  The first factor of ten accounts
for sensitivity among the members of the human population, and
the second factor of ten is based on the extrapolation from
animal data to the case of humans.  The Shakespeare study  was a
chronic study and a NOAEL was identified, hence no other factors

     The modifying factor is greater than zero and less than  or
equal to ten, and reflects qualitative professional judgments
about scientific uncertainties not covered under the standard
uncertainty factors.  These include such considerations as the
completeness of the overall database and the number of species
and animals, tested.  The usual modifying factor is one.

     The concept of an RfD is presented graphically in Figure 5.

                              Figure 5

                          Reference Dose
                                 Critical Effects
                           NOAEL             Dose
     The RfD is useful as a reference point for gauging the
potential effects of various doses.  Usually, doses less than the
RfD are not likely to be.associated with any systemic health
risks and are therefore less likely to be of regulatory concern.
However, as the frequency of exposure exceeding the RfD
increases, and as the size of the excess increases, the probabil-
ity increases that adverse effects may be observed in a human
population.  Nonetheless, a clear conclusion cannot be categor-
ically drawn that all doses above the RfD are unacceptable.

      An alterantive  measure  that  is sometimes useful is  the mar-
gin  of exposure  (MOE) discussed earlier,  which  is  the magnitude
by which the  NOAEL of the  critical  toxic  effect  exceeds  the esti-
mated exposure/ or:
                          NOAEL for Critical  Effect
                                  Human Dose
      A summary of  the reference dose information  for DNC  is
presented  in  Table  9.
                                   Table 9

                       REFERENCE DOSE (RfD) FOR ORAL EXPOSURE
                                SUMMARY TABLE
         Critical Effect              Doses*          (F_

         Liver and kidney pathology   2 mgAg/day (NQAEL)   100

         Rat oral chronic study     10 mgAg/day (LOAEL)

         Shakespeare et al. (1978)

2 x 10-2
         *0oae conversion factors and assumptions: none.

Issues to Be Considered
On the Reference Dose for PNC

1..   Is the observed NOAEL from the Shakespeare study a true
     "no-effect" level?  Could it simply reflect the fact
     that in experiments with relatively small numbers of
     animals, the failure to observe a statistically signif-
     icant increase of systemic effects is an artifact of
     the experimental design, and not a true absence of
     biological effect?

2.   Do you think the reference dose approach adequately
     accounts for the uncertainties associated with NOAELs?

3.   Is the information presented in Table 9 an adequate
     description of the RfD?  What, if any, additional
     information would you like to see?

4.   The RfD for DNC is based on oral ingestion of DNC by
     rats.  Is it appropriate to use this RfD when evaluat-
     ing the potential health risks to residents near the
     Electrobotics plant who are exposed to DNC through the

5.   Should systemic health effects from exposure to DNC or
     carcinogenic effects be of greater concern?  Why?  Do
     we have enough information at this time to decide?

6.   Are the RfD and unit cancer risks reliable indicators
     of human risk?  Should they be used to conduct quanti-
     tative risk assessments, or should risks be described
     only in qualitative terms?

Some Possible Conclus-ions About
Systemic Toxicity Evaluation

     Which of the following conclusions best characterizes
the information you have seen?

1.   The RfD listed in Table 9, and the NOAJ3L from which it
     is derived, are sufficient to determine the systemic
     risks associated with exposure to ONC.

2.   There is no justification for calculating RfDs.  The
     uncertainty and modifying factors create an artificial
     sense of precision in an area involving tremendous
     uncertainty.  Risks from systemic toxicants should be
     described in qualitative terms only.

3.   Other (formulate your own conclusion).

                    V.  RISK CHARACTERIZATION

     In the last step of risk assessment, the information col-
lected and analyzed in the first three steps is integrated to
characterize the excess risk to humans.  In line with the alter-
native approaches for describing dose-response relationships, at
least four approaches to this step can be taken:

1.   Provide an explicit numerical estimate of excess lifetime
     cancer risk for each population group by multiplying the
     slope factor times the number of units of exposure
     experienced by each group:

     Excess lifetime = (slope factor) x (units of exposure)

     In this equation, excess risk is unitless—it is a probabil-

2.   Compare the exposure experienced by each group with the

3.   Estimate the margin of exposure (MOE) for each group by
     dividing the NOAEL from the critical study used to estimate
     the RfD by the exposure experienced by that group.

4.   Describe risks qualitatively for each population group.

     Risk characterization would normally include some combina-
tion of all four approaches, along with a description of their
relative merits.

     It is also essential that the statistical and biological
uncertainties in estimating the extent of health effects be
described in this step.

     Tables 10, 11, and 12 present the excess lifetime cancer
risks for each population group using data from Tables 6 and 7.
These risks are based on the highest slope factor for DNC.   If
other slope factors from Table 7 had been used, excess cancer
risks would be somewhat lower.  And if slope factors derived from
other dose response models had been used, the excess risks shown
in Tables 10, 11, and 12 would be 10 to 100 times lower.  The
risks in Tables 10, 11, and 12 are thought to be upper-bound
lifetime risks.

        Tables  10,  11,  and  12  also  report the  RfD  and  MOE for
systemic  health  effects  for each group.    The  MOE  is  not  an
expression  of  risk,  but  the ratio  of  the  NOAEL  identified  in  the
Shakespeare  study  to  the measured  or  modeled  human  exposure.
                                               T»ble 10

                                  MARGINS OF EXPOSURE FROM EXPOSURE TO DNC
                                     BASED ON POTENTIAL CONTAMINATION
                                        AT THE PUBLIC WELL-FIELD
        Current excess individual cancer risk from air1

        Potential excess individual cancer risk from water,
        assuming exposure at the public Hell-field
        22 years hence1

          Total exceaa individual cancer risk2

        Upper-bound estimate of excess cancer
          cases over a lifetime3

        Exposure (ao/kg/day)4


               3 x 10-*

1.6 x 10-4


3.5 x 10-3

               4 x 10-*

4.9 x 10-J

        ^Excess individual cancer risk obtained by Multiplying the highest slope factor from Table 7 (0.0897 for
         DNC) by the unite of exposure from Table 6.
        2Total excess individual cancer risk obtained by adding excess individual cancer risks from air and water
        'obtained by multiplying total individual excess cancer risk by the estimated number of people exposed.
        ^Exposures for nearby residents and workers are baaed on current air exposures and estimates of future
         exposures from drinking water obtained fro* the public well-field.
        5MOE for DNC obtained by dividing the NOAEL (2 mg/kg/day) from Table 9 by the appropriate DNC air and
         water exposures from Table 6.  If the MOE is less than 100, the exposure exceeds the RfD. The RfD is
         0.002 mg/kg/day.

                                                Table 11

                                MARGINS OF  EXPOSURE FROM EXPOSURE TO DNC
                                    BASED ON POTENTIAL CONTAMINATION
                                    AT THE  EASTERN PROPERTY BOUNDARY
   Current excess individual cancer  risk  from air'1

   Potential excess individual cancer  risk  from
   water, assuming all drinking water  is  obtained
   at the eastern property boundary1

     Total excess individual cancer  risk?

   Upper-bound estimate of excess cancer
     cases over a lifetime3

   Exposure (ma/kg/day)4


                   3 x  10-4

7.8 x 10-'


1.1 x 10-z


                   4 x 10-4

1.3 x 10-2

   ^Excess individual cancer risk obtained  by multiplying the highest slope factor from Table 7
    (0.0897 for DNC) by the units of exposure from  Table 6.
   2Total excess individual cancer risk obtained by adding excess individual cancer risks from air
    end water exposures.
   'Obtained by multiplying total individual excess cancer risk by the estimated number of people
   ^Exposures for nearby residents and workers  are  based on current air exposures and estimates of
    future expoeures from drinking water, assuming  it is obtained at the eastern property boundary.
   5MOE for DNC obtained by dividing the NOAEL  (2 mg/kg/day) from Table 9 by the appropriate DNC air
    and water exposures from Table 6. If the MOE is less than 100, the exposure exceeds the RfD.
                                               Table 12

                               MARGINS OF EXPOSURE FROM EXPOSURE TO DNC
                                       BASED ON CONTAMINATION AT
                                        THE POINT OF COMPLIANCE
Current excess individual cancer risk from air1

Potential excess individual  cancer risk from
water, assuming all  drinking water is obtained at
the point of compliance1

  Total excess individual cancer risk2

Upper-bound estimate of excess cancer
  cases over a lifetime'

Exposure (mg/kg/day)4

   9.5 x 10-3


                      3 x 10-*

    1.3  x 10-2


                      4 X 10-4
    9 x 10-4

    1 x 10-3


   1.4 x 10-2

^Excess individual cancer  risk obtained by multiplying the highest slope factor from Table 7  (0.0897 for
 DNC) by the units of exposure from Table 6.
2Total excess individual cancer riak obtained by adding excess individual cancer risks  from air and water
^Obtained by multiplying total individual excess cancer risk by the estimated number of people exposed.
'Exposures for nearby residents and workers are based on current air exposures and  estimates  of future
 exposures from drinking water, assuming it is obtained at the point of compliance.
5MOE for DNC obtained by dividing the NOAEL (2 mg/kg/day) from Table 9 by the appropriate DNC air and
 water exposures from Table 6.  If the .MOE is less than 100, the exposure exceeds the RfO.

Issues to Be Considered

1.   Are the results reported in Tables 10,  11,  or 12 an adequate
     characterization of DNC risks?  What else should be added?

2.   Risks are presented at three points:  the point of compliance,
     the eastern property boundary, and the  public well field.   What
     are the advantages and disadvantages of using each?  Which  one
     do you feel best represents the risks?

3.   Should risks derived using other slope  factors reported in
     Table 7 and slope factors obtained using alternative models
     also be discussed?  How would you present these uncertainties?

4.   The risks, MOE, and number of cases reported in Tables 10,  11,
     and 12 depend on the assumption that the number of people
     exposed and their level of exposure will remain constant over a
     lifetime.  Is this a plausible assumption?   Can alternative
     assumptions be used?

5.   Is it important to distinguish routes of exposure?  Should
     slope factors obtained from the gavage  data be used for popula-
     tion groups exposed by inhalation?  Should  gavage data be used
     at all?

6.   Is it appropriate to estimate the number of cancer cases by
     multiplying risk times population size?  Which is more impor-
     tant—risk to an individual, or risk to a population?

7.   Do you believe that animal data obtained from continuous, life-
     time exposure should not be used to characterize the risk of
     people exposed by certain routes intermittently, for a rela-
     tively small fraction of their lifetime?

8.   Is the RfD exceeded by any of the exposure  levels?  How do  the
     risks from cancer compare with the risks from systemic health
     effects?  Are they comparable?

9.   How would you characterize the risks to the ecosystem?  Would
     concern about ecosystem damages ever take precedence over
     concern about risks to human health?

Some Possible Conclusions
About PNC

     Which of the following best characterizes the informa-
tion you have seen?

1.   Upper-bound excess cancer risks to humans exposed to
     DNC are those reported in Tables 10,  11,  and 12.
     Although risks obtained from the use  of other models
     are lower, the risks could be as high as  those reported
     in the table.  The risk of systemic health effects are
     properly represented by the RfD and MOE.

     Same as Conclusion 1, except restrict estimates of
     excess risks for inhalation exposure  to slope factors
     estimated from inhalation data, and restrict risks for
     ingestion to gavage data.

3.   The excess cancer risks shown in Tables 10, 11, and 12
     as well as those obtained from all other  plausible
     models and all the various tumor site data should be
     reported, and all estimates should be given equal
     weight.  Such a presentation affords  the  decision maker
     a view of the uncertainty in the estimated risks.  In
     addition, a detailed discussion of the RfD should be

4.   Upper-bound estimates of excess lifetime  cancer risks
     to humans are those reported in Tables 10, 11, and 12.
     Use of all  other animal data sets and alternative
     cancer risk models used by some other agencies would
     result in prediction of lower cancer  risks, perhaps up
     to 65 times lower.  These risks are conditional on the
     assumption that DNC is a probable human carcinogen,
     based on observations  of carcinogenicity in two
     species of experimental animals.  Uncertainties in the
     exposure and population estimates are those described
     in the Exposure Assessment section.

5.   DNC is a probable human carcinogen, based on observa-
     tions of carcinogenicity in two animal species.
     Exposures needed to produce animal carcinogenicity are
     many times higher than those to which humans are
     exposed.  The margins of exposure by  which humans are
     protected from systemic health effects are shown in
     Tables 10, 11, and 12.

Some Possible Conclusions
About PNC (continued)

6.   DNC is a probable human carcinogen,  based on observa-
     tions of carcinogenicity in two species of experimental
     animals.  Humans  are exposed to DNC  through air and
     water.  In general, large numbers of people will oe
     exposed continuously to very low levels of DNC in
     drinking water, and a few groups are exposed to rela-
     tively high levels in air, some continuously, others
     intermittently.  The individual cancer risk in the
     general (larger)  population is probably low, and this
     translates to a very small number of cancer cases.  The
     individual risk to nearby residents  is moderate, and
     this also translates to a small number «1) of excess
     cancer cases.  The individual risk to workers at the
     plant is slightly higher than that of nearby residents,
     although because  of the relatively small number of
     workers, this again translates to less than one excess
     cancer case expected in this group.   In addition,
     potential exposures to all groups are below the RfD,
     indicating no significant risks of systemic health
     effects from DNC exposure.

7.   Other?  Some combination of the others?

Comparative Risks

     An obvious question associated with the quantitative results
presented in the risk characterization is, "are these big numbers
or small numbers?"  To help you think about this question, we
have provided a list of some commonplace risks.

(eaan values with
Motor vehicle accident (total)
Motor vahicla accident (pedeatrian only)
Ham accidents
Air pollution, aaatam United Statea
Cigaratta seeking, one pack par day
Sea- level background radiation (except radon)
All eancara
Tour tablaapoona peanut butter par day
Drinking Mater with EPA liait of chlorofora
Drinking water with EPA limit of trichlonathylene
Alcohol, light drinker
Police killed in line of duty (total)
Police killed in line of duty (by felona)
Frequent flying profeaaor
Mountaineering (Mountaineers)
Sources Baaed on annual risks presented by Wilson and

Lifetime Risk Uncertainty
1.7 x UP2
2.9 x ID'3
7.7 x IDT3
3.7 x 10-*
1.4 x Itr2
2.5 x ID-1
1.4 x ID-3
2 x 10-1
6 x HT*
4 x ID'5
i x ur7
i x ur3
1.5 x 10-2
9.1 x ur3
4 x 10-3
4 x 10~2
Crouch, Science.
Factor of 20 downward only
Factor of 3
Factor of 3
Factor of 3
Factor of 10
Factor of 10
Factor of 10
April 17, 1987.
     Which, if any of these, are relevant to the situation at
Electrobotics?  Why?

Acceptable daily intake (ADI).  Estimate of the largest amount
of chemical to which a person can be exposed daily that is not
anticipated to result in adverse effects (usually expressed in

Carcinogen.  A substance that increases the risk of cancer.

Control animals.  Animals that receive identical treatment as
test animals, except exposure to DNC, for the purpose of observ-
ing the natural or background rate of cancer in that type of

Dose.  Measurement of the amount received by the subject, whether
human or animal.

Dose-response evaluation.  A component of risk assessment that
describes the quantitative relationship between the amount of
exposure to a substance and the extent of toxic injury or

Dose-response relationship.  The quantitative relationship
between the amount of exposure to a substance and the extent of
toxic injury produced.

Epidemiological study.  Study of human populations to identify
causes of disease.  Such studies often compare the health status
of a group of persons who have been exposed to a suspect agent
with that of a comparable unexposed group.

Exposure.  To be accessible to the influence of a chemical or
chemical action.

Extrapolation.  The estimation of a value beyond the known range
on the basis of certain variables within the known range, from
which the estimated value is assumed to follow.

Gavaqe.  Type of exposure in which a substance is administered to
an animal through a stomach tube.

Hazard evaluation.  A component of risk assessment that involves
gathering and evaluating data on the types  of health injury or
disease (e.g., cancer) that may be produced by a chemical and on
the conditions of exposure under which injury or disease is

High-to-low-dose extrapolation.  The process of predicting low-
exposure risks to rodents from the measured high-exposure,
high-risk data.

Human exposure evaluation.  A component of risk assessment that
involves describing the nature and size of the population exposed
to a substance and the magnitude and duration of exposure.  The
evaluation could concern past exposures, current exposures, or
anticipated exposures.

Human health risk.  The likelihood (or probability) that a given
exposure or series of exposures may have or will damage the
health of individuals experiencing the exposures.

Incidence of tumors.  Percentage of animals with tumors.

Interspecies extrapolation model.  Model used to extrapolate from
results observed in laboratory animals to humans.

Linearized multistage model.  Derivation of the multistage model,
where the data are assumed to be linear at low doses.

Margin of exposure (MOE).  Maximum amount of exposure producing
no measurable adverse effect in animals (or studied humans)
divided by the actual amount of human exposure in a population.
Previously this was called the margin of safety.

Microgram (ug).  One-millionth of a gram (1 H9 • 3.5 x 10"8 oz. =
0.000000035 oz.).

Milligram (mg).  One-thousandth of a gram (1 mg « 3.5 x 10~5 oz.
- 0.000035 oz.).

Modifying factor.  An uncertainty factor, greater than zero and
less than or equal to ten inclusive; its magnitude reflects
professional judgment regarding aspects of the data used for the
assessment; e.g., the number of species tested and the complete-
ness of the overall database.

Multistage model.  Mathematical model based on the multistage
theory of the carcinogenic process, which yields risk estimates
either equal to or less than the one-hit model.

Neoplasm.  An abnormal growth of tissue, as a tumor.

No observed adverse effect level (NOAEL).  The highest experi-
mental dose at which there was no statistically or biologically
significant increase in a toxicologically significant endpoint.

One-hit model.  Mathematical model based on the biol oa i<\Hl theory
that a single "hit" of some minimum critical amount of a carcino-
gen at a cellular target—namely DNA—can initiate an irrevers-
ible series of events, eventually leading to a tumor.

Potency.  Amount of material necessary to produce a given level
of a deleterious effect.

ppb.  Parts per billion.

ppm.  Parts per million.

Reference dose (RfD).  An estimate (with uncertainty spanning
perhaps an order of magnitude or greater) of the daily exposure
to the human population (including sensitive subpopulations) that
is likely to be without appreciable risk of deleterious effects
during a lifetime.  The RfD is appropriately expressed in units
of mg/kg/day.

Risk.  Probability of injury, disease, or death under specific

Risk assessment.  The scientific activity of evaluating the toxic
properties of a chemical and the conditions of human exposure to
it both to ascertain the likelihood that exposed humans will be
adversely affected, and to characterize the nature of the effects
they may experience.

Risk characterization.  Final component of risk assessment that
involves integration of the data and analysis involved in hazard
evaluation', dose-response evaluation, and human exposure evalua-
tion to determine the likelihood that humans will experience any
of the various forms of toxicity associated with a substance.

Risk management.  Decisions about whether an assessed risk is
sufficiently high to present a public health concern and about
the appropriate means for control of a risk judged to be

Route of exposure.  Method by which the chemical is introduced
into the biological organism.

Safe.  Condition of exposure under which there is a "practical
certainty" that no harm will result in exposed individuals.

Scientifically plausible.   An approach or concept having substan-
tial scientific support but without complete empirical

Slope factor.  The increased likelihood of an individual
developing cancer from exposure to one unit of a substance over a
lifetime (exposure measured as mg of the substance per kg of body
weight per day—mg/kg/day).

Statistically significant.  The difference in tumor incidence
between the treated and control animals that is probably' not due
to chance.

Systemic effects.  Effects observed at sites distant from the
entry point of a chemical due to its absorption and distribution
into the body.

Threshold dose.  The dose that has to be exceeded to produce a
toxic response.

Total dose.  Sum of doses received by all routes of exposure.

Uncertainty factor.  Factors used in operationally deriving the
RfD from experimental data.  These factors are intended to
account for (a) the variation in sensitivity among the members of
the human population; (b) the uncertainty in extrapolating animal
data to the case of humans; (c) the uncertainty in extrapolating
from data obtained in a study that is of less-than-lifetime
exposure; and (d) the uncertainty in using LOAEL data rather than
NOAEL data.  Usually these factors are set equal to ten.   See
Table 1.

Unit cancer risk.  The increased likelihood of an individual
developing cancer from exposure to one unit of a substance over a
lifetime (exposure measured as concentration in a particular

Upper-bound estimate.  Estimate not likely to be lower than the
true risk.

                           Appendix A
Predicted Concentration of PNC
in Ground Water at Eastern Property
Boundary and Public Well Field
       •  Concentration in lagoon:   30 ppm (mg/1 )
       •  Concentration measured at compliance point:   332 ppo
       •  Half-life of DNC in aquifer:   10 years * 3/650 days
          — Degradation rate of DNC » 0.693/half-lif e
                                    » 1.9 x 10~4 day'1
          Distance from source to property boundary:  1,000 feet
       •  Travel time (T) from the source to property boundary:
              [distance traveled] x [effective porosity]
          T - -
              [hydraulic conductivity]  x [hydraulic gradient]
              1,000ft x 0.2
                                     1,000  days
              40 feet/day x 0.005
       •  Steady-state concentration at property boundary:
            [332 ppb]  x exp [(-1.9  x 1Q-4 day"1) x 1,000  days]
            » 275 ppo
       •  Distance from source to public well  field:
          1.5 miles •  8,000 feet

•  Travel time from the source to three threatened wells:
          8,000 x 0.2
         40 feet/day x 0.005
                               8,000  days
•  Steady-state concentration at the three threatened
    [332 ppb] x exp [(-1.9  x 10~4 day-1)  x 8,000  days]
    » 73 ppb
•  Steady-state concentration at actual  point  of  exposure
   (drinking water supply):
   The three threatened wells provide 7.5 percent of total
   drinking water supply; therefore,  the concentration  at
   the actual point of exposure (the drinking  water
    0.075 x 73 ppb * 5.5 ppb

                           Appendix B

Inhalation of PNC-Contaminated
Air by Neighboring Residents'
       •  An adult inhales 23 m3/day of air.
       •  Based on wind direction analysis, the duration of
          exposure is 30 percent of time on an annual average
       •  The body weight of an adult is 70 kg.
       •  The inhalation absorption factor for DNC is 0.75.
       •  The adult lives in the home throughout his lifetime.
          0.044 mg
                   (average DNC air concentration at boundary)
                           x 0.3 (human intake factor)
          x 0.75 (inhalation absorption factor)
          » 3.3 x 10~3 mg/kg/day

Inhalation of DNC-Contaminated
Air by Worker's
       •  An adult inhales 23 m^/day of air.
       •  The body weight of an adult is 70 kg.
       •  The inhalation absorption factor for DNC is 0.75.

  •  The duration of  exposure is  40  hours/week  for  a  30-yea:
     work period, or  10.2  percent of an  average lifetime.
     0.188 mg
              (average DNC air concentration  on-site)
       23 ra3      1
     x 	 x  	 x  0.102  (human  intake  factor)
        day     70 kg
     x 0.75 (inhalation absorption  factor)
     - 4.7 x  10-3 mg/kg/day

Inqestion of DNC-Contaminated
Drinking Water at Point of Compliance

          3.32 x 10-1 mg
                         (measured DNC concentration in ground
             liter        water at point of compliance)

            2 liters     1
          x 	 x  	 (human intake factor)
              day       70 kg

          x 1 (ingestion absorption factor)

          - 9.5 x 10-3 mg/kg/day

Ingestion of DNC-Contaminated
Drinking Water at Eastern
Property Boundary


       •  An adult consumes 2 liters of water per day.

       •  The body weight of an adult is 70 kg.

       •  Absorption is 100 percent.

       •  The water is consumed throughout the adult's  lifetime,


          0.275 mg
                   (predicted DNC concentration in  ground water
            liter   at eastern property boundary)

            2 liters    1
          x 	 x 	 (human intake factor)
              day      70 kg

          x 1 (ingestion absorption factor)

          » 7.8  x 10*3 mg/kg/day

Ingestion of PNC-Contaminated
Drinking Water at Public Well Field
          5.5 x 10"3 mg
                         (predicted DNC concentration  in  ground
                          ™      .    . . *     1 *  * •  * 9 \
             liter        water at public-well  field)
            2 liters     1
          x 	i	 x  	 (human intake factor)
              day       70 kg
          x 1 (ingestion absorption factor)
          * 1.6 x 10~4 mg/kg/day

          Part II






       Economic Impact of Options
       Changes in Risk


                        I.  INTRODUCTION
     You have just finished analyzing the potential risks from
DNC at the Electrobotics facility.   Your working group must now
decide what actions you will require of Electrobotics' owners to
deal with the situation.

     Your staff has reviewed several possible approaches to
managing the risks.  The first option was proposed by the owners
of the facility; the other four were developed by your staff.
This document briefly summarizes each option/ presents its costs
and economic impacts/ and describes how it alters the risks at
the Electrobotics site.  In addition, Appendix A describes the
hazardous waste treatment technologies available for use at the

     After reviewing this information/ you and your group must
choose one of these approaches or develop an alternative of your
own.  Your choice will be incorporated into a first draft of the
permit.  Your recommendation is expected at the end of this

                   II.  REGULATORY BACKGROUND
     As discussed earlier, RCRA regulations require that hazard-
ous waste facilities (such as Electrobotics1 storage lagoon) be
designed and operated in a manner that will prevent the leaking
of hazardous waste into ground water.  The regulations also
require ground-water monitoring and corrective action if a prob-
lem is identified.

     RCRA's ground-water protection standards require the
Regional Administrator to establish in the facility permit a DNC
concentration limit, beyond which degradation of ground-water
quality is not allowed.  The concentration limit determines when
corrective action is required and is set at the point of com-
pliance, immediately east of the storage lagoon.

     Three possible concentration limits can be used to establish
the ground-water protection standard:

       •  Background level of the hazardous constituent

       •  Maximum concentration limit (MCL) established by

       •  Alternate concentration limit (ACL)

     The background level and MCL are established in the facility
permit unless the facility owner or operator applies for an ACL.
In this case, the background level of DNC is zero, and no MCL
exists for the solvent.  An ACL may be available to Electro-
botics1 owners if they can demonstrate that the DNC will not pose
a substantial present or potential hazard to human health or the

     To continue operating the lagoon, the regulations also
require that Electrobotics1 owners retrofit the lagoon to ensure
no DNC leaches into the ground water.  The owners of
Electrobotics have proposed retrofitting the lagoon, which would
require them to:

       •  Pump out the free liquids from the lagoon

       •  Excavate the contaminated soil

       •  Install "minimum technology" to ensure no DNC leaches
          into the ground water.  In this case the owners would
          install a double liner under the lagoon.

     An alternative to retrofitting the lagoon is to close it and
install an above-ground storage tank.  Existing regulations allow
the owners to close the lagoon in one of two ways.   They must
either remove the hazardous waste and waste residues (clean
close) or retain the waste and manage the lagoon as a land
disposal unit.

     The owners have been advised that, because of  existing
ground-water contamination, it is probably not possible to meet
the standards for clean closure and terminate responsibility for
hazardous waste management in the near future.  As  a result, your
staff has developed a closure option based on the owners managing
the lagoon as a land disposal unit and installing an above-ground
tank.  To comply with regulations for this option,  the owners

       •  Eliminate the free liquids from the lagoon either by
          removing them from the impoundment or by  solidifying

       •  Stabilize the remaining waste and waste residues to
          support a final cover

       •  Install a final cover to minimize future  infiltration
          into the lagoon

       •  Perform post-closure care and ground-water monitoring

     You must now decide whether the facility's retrofitting plan
is adequate and what actions to require of the owners to clean up
both the lagoon and the associated ground-water contamination
problem.  You will not try to specify the particular concentra-
tion limits for the ground-water protection standard.  You must
only recommend the specific actions required at the site.  You
may accept the proposal from the owners, pick one of the options
presented by your staff, or develop an alternative  that you feel
is more appropriate.  Implicit in your decision, however, is the
concentration limit.

                          III.  OPTIONS

     You must now evaluate five possible approaches to addressing
the problem at the Electrobotics plant.   The first is the
proposal from the owners which involves  retrofitting the lagoon.
There are four alternative options that  have been developed by
your staff.


     The owners of Electrobotics have proposed retrofitting the
lagoon.  To accomplish this the owners would have to pump out the
liquids from the lagoon, excavate any contaminated soil, and
install a double liner under the lagoon  to stop any leaching of
DNC from the lagoon into the ground water.  The type of liner to
be used has been effective at test sites, although it is general-
ly recognized that there is always the possibility that the liner
will fail at some point.

     The owners have proposed a limited  retrofitting program
which does not include any treatment of  the current contamination
of the ground water.  They feel the current contamination of the
ground water does not pose a substantial present or potential
hazard to human health or the environment.

Alternative Control Options

     The four options reviewed by your staff are described below.
All four involve closing the lagoon and  managing it as a land
disposal unit.  In addition, all four would require the owners of
Electrobotics to install a new above-ground tank.  The first
involves installing a cap over the lagoon.  The second option
involves installing the cap and pumping  and treating the contami-
nated ground water.  The third option, which is somewhat more
expensive, contains the elements of the  first two options as well
as the construction of a slurry wall around part of the lagoon.
The last option requires the owners to excavate the material
under and around the lagoon and pump and treat the contaminated
ground water.

     Option 1:  Cap

     This option requires the installation of a cap over the
lagoon, which directly affects the lagoon but does not deal with
the current ground-water contamination.


        •  De-water the lagoon and excavate any accumulated
           sludges, which requires removing any free liquids and
           managing them as hazardous waste

        •  Solidify any remaining sludges and refill the lagoon
           with clean fill

        •  Install a multimedia cap over the lagoon to prevent

        •  Maintain the cap and conduct  post-closure monitoring
           and care


        •  Long-term integrity of the cap and its effectiveness
           in preventing infiltration

        •  Continued source strength of  chemicals/ in or near the
           saturated zone, that are released by ground-water
           through-flow beneath the cap

        •  Extent of long-term monitoring and general
           post-closure care

     Option 2;  Cap/Pump and Treat

     This option includes the cap described in Option 1 plus
pumping and treating the contaminated ground-water plume with a
carbon adsorption system.


     The scope includes the items described for Option 1.   In
addition, the owners would have to:

        •  Conduct an additional hydrogeological study


        •  Install extraction wells and treat the ground water by
           carbon adsorption


     The same uncertainties as in Option 1 exist, with two

        •  Length of time for operating the treatment system

        •  Effectiveness of ground-water extraction system in
           removing contaminated ground water

     Option 3;  Cap with Slurry
     Wall/Pump and Treat

     This option is similar to Options 1 and 2 in that the lagoon
would be capped in the same manner and the ground-water contami-
nation corrected through pumping and a carbon adsorption
treatment system.  However, Option 3 would also include
installation of a soil-bentonite slurry wall at the perimeter of
the lagoon to prevent ground-water through-flow and further limit
the movement of DNC from the saturated zone beneath the lagoon
into the ground water.


     The same uncertainties as in Options 1 and 2 exist, with one

        •  Long-term integrity of the slurry wall as a method of
           isolating both the contamination and the potential for
           future releases of DNC into ground water

     Option 4;  Excavation/Pump and Treat

     Option 4 comes closest to completely eliminating any traces
of DNC from the Electrobotics facility and the surrounding area.
The current ground-water contamination would be corrected by
pumping the ground water and treating it with a carbon adsorption
system.  In addition, the source of contamination would be
controlled by excavating the soil around and under the lagoon.


•  De-water the lagoon and excavate any accumulated
   sludges and liner material

•  Test the underlying soil for chemical contamination
   and remove soil to the water table if DNC
   concentrations are above ground-water contamination

•  Refill the excavation with clean fill and stabilize it
   with grass or other cover material

•  Conduct an additional hydrogeological study

•  Install extraction wells and treat ground water  by
   carbon adsorption

•  Conduct long-term monitoring and general  post-closure

•  Length of time for operating the treatment  system

•  Effectiveness of ground-water extraction system in
   removing contaminated ground-water plume

Issues to Be Considered

1.   What are the key components  of  each option,  and  how do
     the options differ?

2.   What is the nature of the uncertainties  associated
     with each option? Which ones are most critical?

3.   Which aspects of each option do you find most

4.   Are there other options  that you think the Regional
     Administrator should consider?


      Adopting any one  of the  options discussed above  would
require cash  expenditures by  Electrobotics.    A summary  of the
costs  for each option  is presented  in Table 1.
                                       Table 1


       Option 1
         Cap and Associated Costs

       Option 2
         Cap and Associated Costs
         Pump and Treat System


       Option 3
         Cap and Associated Costs
         Slurry Wall
         Pump and Treat System


       Option 4
         Excavation and Associated Costs
         Pump and Treat System

Present Value of Costs1

     $  450,000

     $  600,000
     $  600,000
     $  890,000
     $  600,000


Annualized Costs'
 (costs per year)

   $ 48,000

   $ 64,000
   $ 64,000
    $ 95,000
   $ 64,000


       Mime sequence of costs is  discounted at  10 percent.
       ^Present value of costs is  annualized at  a 10 percent interest rate over
        30 years.

     Electrobotics has a turbulent history and has been close to
bankruptcy several times.  Its recent performance, however,  has
improved, with revenues increasing from $1.5 million in 1980 to
$7.5 million in 1986.  Even so, the company was only marginally
profitable in 1986, with after-tax profits of less than $50,000.
We do not have a good forecast of 1987 revenues, although the
computer industry as a whole has been performing poorly.

     Electrobotics1 owners feel they can,  with great difficulty,
pay the costs of their proposed retrofitting program and costs
estimated for Option 1.  They are adamant, however, that
implementing Options 2, 3, or 4 would force them to declare
bankruptcy; these three options would result in annual costs
substantially greater than the company's 1986 after-tax profits.

     If Electrobotics goes out of business, its 150 employees
would have to find new jobs.  This would worsen an already diffi-
cult situation in the town of Utopia, whose unemployment rate is
among the highest in the country.  In addition, Electrobotics has
paid significant property taxes—about $120,000 in 1986—to  the

     Finally, if the Electrobotics facility were closed because
of bankruptcy, it would have to be considered for addition to the
National Priority List for cleanup as a Superfund site.

Issues About Economic Impacts
to Be Considered

1.  How accurate are the cost and economic impact estimates?
    How does the accuracy of the cost estimates compare  with
    the risk estimates?

2.  What additional information would you want?  Are  any key
    elements missing?

3.  Is it appropriate to consider such factors as costs  of
    the control options and economic impacts  in deciding
    what will be required of Electrobotics1 owners?   Are any
    of the impacts large enough to rule out a particular

4.  If economic considerations are to play a  part in  the
    decision making, should the focus be on the dollar costs
    of each option or on the impact of the option on  the
    continuing viability of Electrobotics and the potential
    loss of jobs?


     Adopting the proposal or any of the alternative options
identified above would reduce individual exposure to DNC and
hence reduce the risk.  However, the options do not reduce the
risk to the same degree or with the same certainty.  In addition,
it is difficult to predict the changes in risk by predicting the
reduction in concentrations resulting from the adoption of each
option.  Even so, your staff and the engineers hired by
Electrobotics1 owners have estimated the reduction in the DNC
concentrations in the ground water and air, and the reduction in
risk for each option.

     A program of retrofitting the lagoon would reduce the risks
associated with contaminated ground water.  No more DNC would
leach into the aquifer (assuming the double liner under the
lagoon does not leak).  The upper-bound estimates of excess
lifetime risks for an individual receiving drinking water from
the Eastern property boundary after the retrofitting program are
presented in Table 2:

     The retrofitting program will not eliminate the air risk
associated with the lagoon.  As a result, the risks to workers
and nearby residents are higher than for the general population.
The ground-water risks confronting the general population are
estimated using an average concentration of DNC in the
ground water over the next 70 years, assuming the retrofitting
has been completed.

     The upper-bound estimates of excess lifetime human risk for
an exposed individual after implementation of one of the
alternative control options are also presented in Table 2.

                                       Table 2

                                                Individual Risks-3

             General  Population
             Nearby Residents

             Control  Options2

             1.  Cap

             2.  Cap/Pump and Treat

             3.  Cap/Slurry Wall/
                 Pump and Treat

             4.  Excavate/Pump
                 and  Treat •
Eastern Property

    1  x 10"5
    3  x ID"4
    4  x 10~4
    1 x  10-5

    1 x  ID'6

    2 x  10~7

    1 x  10~7
Public Well
  2 x  10-7

  2 x  iQ-8

  4 x  ID-9

  2 x  10~9
             iRisks are obtained by multiplying the highest slope factor
              estimate from Table 7 of Part I (0.0897 for ONC) by the
              estimated units of exposure after each option has been
             2A11 four alternative control options eliminate any air risks
              from the lagoon.  The remaining risks are attributable to the
              risks from DNC remaining in the ground water after completion
              of the control option.  As a result, the risks remaining after
              implementation of an option are the same for the general
              population, nearby residents, and workers.
             3The individual risks at the Eastern property boundary and the
              public well field are based on estimated average
              concentrations in the ground water at these points over the
              next 70 years.  Your engineers have estimated that control
              options will reduce the concentrations of DNC in the ground
              water, and the associated risks,  by 98 percent.  Current risks
              at the Eastern property boundary  and the public well field are
       The upper-bound  estimates of  excess cancer cases over a
lifetime after  implementing the  retrofitting  program or one  of
the alternative  options  are presented in Table  3:

                                      Table 3

                           AND CORRECTIVE ACTION OPTIONS1

                     (Cases based on drinking water consumption at
                         •  the Eastern property boundary2)

      . Alternative
     Control Options*

1.  Cap

2.  Cap/Pump and Treat

3.  Cap/Slurry Wall/Pump
     and Treat

4.  Excavate/Pump and


0.0015     0.0008

0.0015     0.00008

0.00003    0.000016

0.000015   0.000008








Reduction in
 of Excess
Cancer Cases




    estimates of excess cancer cases are obtained by multiplying the excess lifetime risk by
 the estimated number of people exposed.
2The cases are estimated assuming exposure at the Eastern property boundary. Estimated cases
 assuming exposure at the public well field would be significantly lower.
'All four alternative options eliminate any air risks from the lagoon.  The estimated excess
 cancer cases for each option are attributable to the DNC remaining in the ground water after
 completion of the control option.
      Electrobotics1 owners are concerned about  the air risks
after  reviewing the material  prepared  for  their Part  B applica-
tion.   In  response, they  have discussed installing a  floating
synthetic  cover over  the  lagoon  to  control  the  air emissions  in
the short  run.   This  would address  some of  the  risks  during the
period of  negotiation of  the  permit requirements.   The cover
would  cost $10,000.

Remarks on Risks

1.  The proposed approach,  retrofitting,  would not eliminate the
    air risks.  All four of the alternative options would
    eliminate the risks from the air route of exposure.

2.  Engineers working for Electrobotics'  owners have argued that
    it is technically impossible to completely eliminate DNC from
    the contaminated ground-water plume.   Your staff generally
    agrees that it is probably not possible to remove all traces
    of DNC, but feels that  the risks could be reduced beyond the
    most stringent option (Option 4) with an extended pump and
    treat system.  Extended pump and treat would involve increas-
    ing the length of time  a pump and treat system is operated.

3.  It is difficult to forecast the effectiveness of the
    retrofitting program, or any closure  and corrective  action

4.  The four alternative options will eliminate volatilization of
    DNC from the lagoon.  Some members of your staff have
    speculated that this could potentially increase the  concen-
    tration of DNC in the wastewater sent to the wastewater
    treatment plant, which  in turn could  lead to concentrations
    of DNC in the treatment plant effluent.

Issues About Changes in Risk

1.  Risk to an individual is:

    Lifetime  = (slope factor) x (Units of Exposure)

    The allowable units of exposure for a given excess
    lifetime risk can thus be  estimated as follows:

              Units of   Excess Lifetime Cancer Risk
              Exposure =        Slope Factor

    If the excess lifetime cancer risk at the point of
    compliance is 1 x 10~6, what is the associated DNC

2.  What effect would installing the synthetic cover  over
    t'he lagoon have on the risks from DNC, assuming the
    cover eliminated the air risks?  What percentage  of the
    estimated current excess cancer.cases would be

3.  What are the key uncertainties associated with estimates
    of risk'under each option?  What additional information
    would you want on the effect of each option on the

4.  In light of the major uncertainties in the risk esti-
    mates, is it valid to compare the different options in
    terms of risk or reduction in risk?

5.  Is it at all appropriate to consider the risk assessment
    results and the associated estimates of the changes in
    risk when evaluating possible options?  Is a less
    quantitative and more qualitative approach preferred?

6.  Should you balance the increased costs of Options 1,  2,
    3, and 4 against the associated benefits (as measured by
    increased reductions in risk)?

7.  What other approaches might be more appropriate?

                        IV.   CONCLUSIONS
     At this point/ you and your working group should decide  what
actions you will require of Electrobotics1  owners.   You have
information on a number of options,  including the one proposed  by
the owners.  You may accept the owners'  proposal, choose one  of
the alternative options, or develop  an alternative you feel is
more appropriate.  In addition, you  may attach any caveats,
qualifications, or modifications you wish.   At the end of this
meeting, you will present your results.

       What do you recommend?

                           APPENDIX A
Overview of Hazardous Waste Treatment
Technologies Available for Use at the
Electrobptics Site

        Installation of a Slurry  Wall

        Ground-Water Extraction/Injection

        Carbon Adsorption

        In-situ Biological Treatment


     After the lagoon has been dewatered and refilled with clean
fill, it must be covered with a secure cap to prevent water
infiltration, which could leach DNC from the fixed sludges in the
fill.  The primary steps in cap construction are layering imper-
meable material over the landfill, revegetation, and regrading
the site.

     Impermeable cover material for landfills can be clay, syn-
thetic membranes or liners, or a combination of clay and syn-
thetics.  Hazardous waste landfills are usually capped with a
sandwich of clay/ synthetic liners, and topsoil for vegetation.
According to the National Center for Ground Water Research's
State-of-the-Art of Aquifer Restoration, synthetic materials
(such as bituminous or Portland cement concrete barriers) or
synthetic membranes (alone or in conjunction with clay barriers)
may be preferable to soil-based systems when protecting high-risk
wastes.  After the chosen impermeable material has been placed on
the site, the area should be covered with topsoil, seeded, and

     Landfill caps, seemingly a good infiltration prevention
measure, actually are subject to a number of problems.  The
problem that often appears first is erosion, which is exacerbated
by the cap's impermeability function.  (Rain hits the cap and,
not being absorbed, carries off the maximum amount of soil.)
Regrading techniques, such as terracing the topsoil and creating
lined waterways and storage basins, help minimize this problem.
Establishing vegetation early will also help control erosion by
decreasing rain and wind impact on the cap.  Grass should be
planted first for a quick cover, and then shrubs and trees should
be cultivated.

     Other factors that affect clay caps in particular are
changes in the fill, such as settling and freeze-thaw/wet-dry
cycles, which can cause cracks.  In the Midwest, these cracks can
reach three to six feet, below commonly practiced cap and cover
depths.  Plants growing in the cracks can widen them further, as
can burrowing animals.  In addition, large plant tap roots can
increase water infiltration in the cap.  Cracks are most likely
to form in systems where the clay has been combined with some
other agents (e.g., lime, Portland cement, fly ash) to increase
impermeability, because the clay and other mixture components do
not settle at the same rate.

     Synthetic membranes, on the other hand,  can be affected by
tearing if they are flexible and cracking if  they are rigid,
especially if differential settlement occurs  in the fill.
Installation of a smooth sand buffer can reduce the chance of
flexible-liner puncture during cap construction.  Concrete
barriers are subject to both cracking and deterioration,
especially in sulfate-rich environments.  However, cracks  in
rigid membranes can be cleaned and sealed (most often with tar)
fairly easily, giving rigid membranes an advantage over the
flexible variety in the long run.

     There is no foolproof method for sealing off a landfill.
Therefore, all literature sources stress good initial planning
and long-term management as the primary factors in maintaining
the integrity of a landfill cap.


     Option 2 calls for the installation of a slurry wall at the
lagoon's perimeter to prevent further movement of DNC by
restricting ground-water movement under the contaminant source.
A slurry wall is a civil engineering technique previously used
primarily in construction; its recent use in Superfund sites has
made it more popular with hazardous waste landfill operators.  By
far the most common slurry wall construction method is the trench

     The first step in building a slurry wall using the trench
method is digging a channel in the selected area.  (Choosing
where to place the wall requires study of the site and ground-
water characteristics.)  Excavation techniques include the
backhoe method/ which is good for shallow depths/ and the
dragline method/ which is used for trenches that will be
30 meters or more deep.  As the trench is dug/ a slurry of 4 to
7 percent bentonite clay is recirculated through to support the
channel walls and form a more impermeable soil structure.
Bentonite is popular because it swells when wet and so restricts
the flow of water through it.  Digging usually proceeds a short
way into the clay or bedrock underlying the aquifer.

     Once the trench has reached the desired depth/ it is solidi-
fied in one of two ways:  backfilling with a mixture of bentonite
and the excavated solid (the soil-bentonite/ or S-B, method)/ or
letting it solidify by itself by mixing cement with the original
slurry (the cement-bentonite/ or C-B/ method).  Choosing a soli-
dification technique requires examination of the pros and cons of
each.  With the C-B method/ there is no worry, over availability
of quality soil for backfilling/ the cement sets quickly/ and the
trench can be constructed in sections.  This method is also
better for limited-access areas.  The S-B method is cheaper
(lower materials costs) and generally less permeable than the
C-B, but it is not as strong as the C-B and requires continuous
trenching in one direction.  S-B trenches are used more often,
primarily because of their low cost and low permeability.

     Possible problems from slurry walls include inadequate con-
struction and stress/strain forces, which can cause structural
damage.  Acids and sulfates in ground water can seriously degrade
C-B trenches, and the permeability of S-B trenches can increase
in the presence of certain organics, calcium, magnesium, heavy
metals, and solutions of high ionic strength.  Even if the walls
do not degrade appreciably, some leakage through slurry walls

is  inevitable;  permeability ranges  from less  than  1x10-8  cm/sec
for an S-B  trench  to  over  1x10-5  cm/sec for a C-B  trench.   A more
complete  list of the  advantages and disadvantages  of  slurry walls
is  provided in  Table  1.
                                        Table 1


          1.  Construction methods are

          2.  Adjacent areas are not affected
              by ground-water drawdown.1

          3.  Bentonite (mineral) will not
              deteriorate with age.1

          4.  leachate-resistant bentonites
              are available.1

          5.  Maintenance requirements are

          6.  Risks from pump breakdowns  or
              power failures are eliminated.2

          7.  Headers and other above-ground
              obstructions are eliminated.2

1.  Shipping bentonite from the
    West is costly.

2.  Some construction procedures
    are patented and require a

3.  In rocky ground, overexcava-
    tion is necessary because of

4.  Bentonite deteriorates when
    exposed to high-ionic-strength
          1Tolroan, et al., "Guidance Manual for Minimizing  Pollution  from
           Waste Disposal Sites," 1978.
          2Ryan, "Slurry Cut-off Walls:   Methods and Applications," 1980.

          Source:  National Center for Ground Water Research, State-of-the-Art of
                  Aquifer Restoration.  1984.


     To treat the contaminated ground water/  extraction and/or
injection wells must be dug.  Carbon adsorption requires extrac-
tion wells; in-situ biodegradation requires both extraction and
injection wells.  The same basic sequence of  steps is used to
install either well type.  The first step, drilling the hole, can
be accomplished by one of several methods, depending on the site
characteristics and economics.  Next, casings and liners are
installed, annular spaces are grouted and sealed, and well
screens and other fittings are put into place.   Finally, above-
ground facilities (pump houses, etc.) are built.

     Some information (e.g., plume size, aquifer characteristics)
is necessary before the wells can be constructed.  The depth
within the aquifer to which each of the wells is drilled is a
function of the plume location, which can stretch through the
entire aquifer or remain close to the upper boundary.  Hydro-
geologists can determine plume dimensions as  well as plume
movement and the hydrogeological characteristics of the aquifer.

     Within the injection and extraction categories, two types of
well systems currently are in use.  The first,  well point
systems, consists of a number of closely spaced, shallow wells
that are connected to a main pipe, or "header."  If water is
being extracted, this header leads to a central suction lift
pump, which draws the water to the surface.  (Injection wells
require a different type of pump to force water from the surface
to the aquifer.)  The main constraint on extraction well point
operation is the suction pump, which cannot raise water more than
25 feet.  Since the aquifer under Electrobotics is 20 feet below
the surface, deeper wells may be needed.  The second type of well
system, deep well, can be used at greater depths than the well
point system.  Unlike well point, in which pumping is done for
groups of wells, in the deep well system each well is individu-
ally pumped.

     After the wells are sunk in the path of  the plume and pump-
ing starts, a number of things happen in the  aquifer.  As water
is removed from the "zone of influence" around  the well, the
water level decreases, causing a change in aquifer flow patterns,
or "drawdown" (see Figure 1).  Wells are designed so that this
drawdown intersects the plume.  As water is pumped to the
surface, plume movement away from the source  stops and eventually
reverses itself.  The rate of extraction must be monitored care-
fully, as it is fairly easy to pump a well dry  if pumping is done
too fast.  For injection wells, essentially the reverse happens:

water  is pumped into the aquifer,  and the water  table rises,
especially around the  point of  injection.  This  pushes  the plume
forward and increases  the rate  of  ground-water flow.
                                   Figura 1

                       Ground-Uaear Pattarna dua to Extraction Wall*
                                  Original Wacar
                                  1  Tabla
        40 ft./day
 Hoe drawn eo acala.


     As reported in the March 1986 edition of Pollution Engineer-
ing, biological methods are usually the chosen treatment for
industrial and municipal waste waters, but "the low concentra-
tions found in ground water . .  .  make air stripping and carbon
adsorption the most widely used ground water treatment methods."
The primary constraint on carbon adsorption is the concentration
of the hazardous constituents.  The concentration must be less
than 1 percent for removal to be effective; at this level the ICF
RCRA Risk-Cost Analysis Model estimates the efficiency of the
process to be 99 percent (i.e.,  99 percent of the contaminants in
the influent are tied up in the carbon after treatment).  Since
DNC concentrations in the ground water are well below 1 percent/
carbon adsorption should work well in removing the contaminants
from the ground water.

     In carbon adsorption, activated carbon granules remove the
organic contaminants from the waste water by attracting and hold-
ing the constituents onto their surface.  Figures 2 and 3 display
two slightly different treatment trains for this option.  The
train selected depends on the amount of carbon used per day:  For
amounts exceeding 400 pounds per day, it is more economical to
recycle the carbon; otherwise, the carbon is placed into con-
tainers and disposed of.

     The basic treatment steps outlined in Figures 2 and 3 are
the same.  Contaminated ground water flows from the storage tank
into a prefilter.  The prefilter removes excess suspended solids,
oil, and grease, which can interfere with the adsorption process
by clogging the surface of the carbon particles.  After this
pretreatment, the waste is directed to the activated carbon tank,
where the organics are transferred to the carbon granules.  The
ICF model has determined that the average carbon adsorption
capacity is 5 pounds of organics per 100 pounds of carbon;
however, this value can vary with the compound being adsorped.
(Adsorptivity increases with decreasing solubility.)

     As mentioned above, the exhausted carbon is then recycled,
or regenerated if over 400 pounds are used per day.  (The ICF
model estimates that only 90 percent of exhausted carbon can be
regenerated; the remaining 10 percent must be made up with fresh
carbon.)  Regeneration can be performed using heat, steam, or
solvents.  Thermal regeneration, the most common method, destroys
the organics on the carbon but leaves a low-concentration, gas-
eous emissions stream.  Figure 3 depicts the equipment necessary
for regeneration (two storage tanks for spent and regenerated

carbon and a multiple-hearth furnace).   The furnace  should
destroy most of the organics.   (The ICF assumes  99.993  percent;
the remaining 0.007 percent will appear in the emissions

     Contaminant releases during the adsorption  process can  occur
through air releases from the furnace as well as from discharge
of the treated effluent,  which contains approximately 1 percent
of the original amount of organics.   In addition,  contaminants
are discharged into the air from vessel failures and/or spills
(estimated in the ICF report to occur at a rate  of 0.000013
releases per year)  and to a lesser degree from pumps, valves, and

                                      Figure 2
                     (carbon consumption leu than 400 pounds per day)
H Multi-Media   L^^f(

 """**    II
(Granular Aattoatad
 CarMfl Column*
Souraa: Th« BCBA
                                    Inc. Marcn 1SW4.
                                                                 from V
                                    Figure 3
                  (carbon consumption greater than 400 pounds per day)

                     Carbon Column*
                                           Multtpta Haarth
                                 ICP Inc.. Maren 19*4.


     Another method of contaminant treatment advanced by Super-
fund is in-situ biodegradation, in which the waste is biodegraded
in the aquifer by indigenous or added microorganisms to produce
carbon dioxide, water, various intermediates, and new cell bio-
mass.  The two main techniques used are modifying the environment
to enhance microbial activity and altering the microbial popula-
tion by seeding with microorganisms that have already been
acclimated to the pollutants to be degraded.  Environmental
modification is currently the more popular and more effective

     Enhancing the indigenous microbial population involves the
addition of nutrients and/or dissolved oxygen.  A number of steps
are involved.  First, the extent of ground-water contamination,
site hydrogeology, and other characteristics is examined.
Various environmental factors control biodegradation, including
pH, temperature, oxidation-reduction potential, salinity, avail-
ability of nutrients, dissolved oxygen level, and concentration
of contaminants.  Next, researchers must determine whether native
microorganisms will degrade the spill.  If biodegradation is
possible, researchers must then find the nutrient/dissolved oxy-
gen levels that will yield maximum cell growth over a set time
period at ground-water temperature.  Possible nutrient choices
are nitrogen, phosphorus, and inorganic salts such as ammonium
sulfate, magnesium sulfate, sodium carbonate, ferrous sulfate,
and calcium chloride.  Nutrients are added at concentrations of
0.005 percent to 0.02 percent by weight; this can result in tons
of nutrients being added before treatment is complete.

     Once the optimal nutrient/dissolved oxygen levels have been
calculated, the well system for injecting the nutrients and
oxygen and recirculating them in the aquifer is designed and
constructed.  Extraction wells are used to draw water for recir-
culation out of the aquifer, while injection wells are used to
force the nutrients, oxygen, and drawn water into the aquifer.
Recycling contaminated water for mixing purposes is recommended,
as it eliminates problems of waste disposal and permits recircu-
lation of unused nutrients.  Wells should be placed at the begin-
ning of the plume so that the nutrients move with the ground
water through the contaminated zone.

     After the equipment has been set up, the nutrients and
oxygen are added.  Nutrients can be supplied using either a batch
or a continuous process.  Generally, the batch process has
yielded better results and is more economical.  Oxygen is added
by forcing air through the wells with diffusers.  The advantages
and disadvantages of microbial enhancement are listed in
Table 2.

                                  Table 2

                           BY MICR08IAL ENHANCEMENT

      1.  Useful for removing low levels
          of organic compounds that are
         "difficult to remove by other

      2.  Environmentally sound (no waste
          products, uses indigenous

      3.  Fast, safe, and generally

      4.  Treatment moves with the
          contaminant plume.

      5.  Good for short-term treatment.

1.  Does not degrade some

2.  Introduction of nutrients could
   adversely affect nearby surface

3.  Residues left in ground water
   may cause taste and/or odor

4.  May be slower than physical
   recovery methods under certain
   conditions (e.g., high
   pollutant concentrations).

5.  Could be expensive if long-term
   oxygen/nutrient injection is
   necessary or if equipment
   maintenance costs are high.

6.  Long-term effects are not

7.  Bacteria can plug soil and
   decrease circulation.
      Source: National Center for Ground Water Research, State-of-the-Art of
             Aquifer Restoration. 1984.
      The second  technique,  adding  microorganisms that have been
acclimated to the pollutants/  is not yet completely successful
but has  good potential for the future.   In  this  procedure,
researchers  test a variety of  microbes  to determine which will
best degrade the contaminants.  The chosen  microbes are used
instead  of  (or  in addition to) the indigenous  population.   It is
also possible to genetically alter microorganisms  to get strains
that will work  even  better; this,  however,  is  still in  the
experimental stage.

     Since in-situ biodegradation  is  so new,  there  is  little
information on its efficiency.   According  to  the National Center
for Ground Water Research's State-of-the-Art  of Aquifer Restora-
tion, in-situ biodegradation of  organic solvents has been "fairly
effective."  More research still needs  to  be  done,  but this tech-
nology has been used with positive results in the past and holds
great promise for the future.

U.S. Environmental Protection Agency
Region 5, Library (PL-12J)
77 West Jackson Boulevard  13th n
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