Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 67
4
The California Site Mitigation
Decision Tree Process:
Solving the "How Clean Should
Clean Be?" Dilemma
DAVID J. LEU AND PAUL W. HADLEY
One of the greatest environmental issues facing our nation dur-
ing this decade is expressed by the cliche "How Clean Should Clean
Be?" This cliche refers to the complex problems associated with
the mitigation of soils and waters contaminated by chemicals that
are produced and used by our modern society. Different federal
and state agencies, together with other research and consulting
groups, have developed various approaches to this issue. One real-
istic approach to answering the question "How Clean Should Clean
Be?" has been developed by the California Department of Health
Services (DHS). This process is contained in a technical guidance
document entitled The California Site Mitigation Decision Tree
Manual (DHS, 1986~.
At. . . . . .
This decision tree manual (also referred to as the decision
tree process) was created to fulfill four basic functions. First,
it establishes a realistic approach to answering the question of
"How Clean Should Clean Be?" Second, it identifies the key
The authors of this paper would like to recognize those individuals who
made the development of The California Sit c Mitigation Decuon lFcc Marshal
possible. The coauthors of the manual include Michael Kiado; William
Quan; Stanford Lau; James Polisini, Ph.D., California Department of Fish
and Game; Stephen Reynolds; Richard Sedman, Ph.D.; Judith Tracy; and
Caryn Woodhouse. At the same time the authors of this paper especially
wish to acknowledge the contribution of Susan Solarz, also a coauthor of the
decision tree manual, to the arsenic-contaminated site case study.
67
OCR for page 68
68
HAZARDOUS WASTE SITE MANAGEMENT
decision points needed to set cleanup criteria. Third, it establishes
a technical basis for each major decision. Last, it standardizes the
decisionmaking process so that it can be applied consistently to
all sites.
Fundamental to the decision tree process is a series of dis-
tinctive aspects. One such aspect is that the process specifies
a multimedia approach to site characterization activities and to
establishing cleanup criteria. Specifically, the decision tree pro-
cess requires one to address analytically the significance of the
air, water, soil, and biotic exposure pathways for each site. It
also identifies the specific parameters for which such data must
be collected. This type of approach promotes a well-focused site
characterization effort and minimizes the need for costly revisita-
tions to collect data. Another unique aspect of the decision tree
process is that it identifies preferred data gathering, handling, and
analytical techniques that should be used to ensure high-quality
environmental data.
A critical aspect of the decision tree process is that it quickly
sets statewide, health-based criteria called applied action levels
(AAI`s). AAI,s are specific to substances, media, and biologic re-
ceptors. They define exposure levels at which no observed adverse
effect would be found.
The decision tree process also allows one to set different
cleanup levels for a particular site that reflect the different degrees
of effectiveness of various remedial action combinations. Thus, the
project manager is in a position to select the final cleanup solution
that best suits the conditions of a particular site.
The purpose of this paper is to discuss briefly the basic con-
cepts affiliated with the decision tree process. The paper will con-
clude with two case studies that illustrate how this process works
quickly to reach a cleanup level that has a strong technical and
scientific basis. Because this paper is an overview of the decision
tree process, the reader is referred to the California site mitigation
manual noted earlier (DHS, 1986) for a detailed presentation of
the complete approach.
COMPONENTS OF THE DECISION T1lEE PROCESS
The decision tree process consists of five basic components:
(1) preliminary site appraisal, (2) site assessment, (3) risk ap-
praisal (4) environmental fate and risk determination, and (5)
OCR for page 69
DECISION TREE PROCESS
69
development of site mitigation strategies and selection of remedial
action.
Each component is made up of several steps, procedures, and
decision points. To minimize the time needed to finish a cleanup,
the components are designed to be highly interactive and the last
four components run concurrently.
Preliniinary Site Appraisal
The purpose of this component is to quickly assess a site's
potential for environmental and/or public health damage. Sites
that are potentially contarn~nated with hazardous substances are
qualitatively assessed using conventional procedures developed for
the U.S. Environmental Protection Agency. Based on the charac-
teristics of the wastes that are present and the features of the site
itself, the site may be determined to be sufficiently hazardous to
be placed on either the National Priority List (for the federal Su-
perfund) and/or dealt with through the state Superfund program.
This scoring process, which is referenced in the decision tree, is
based on the Mitre model approach developed for EPA and used
throughout the nation. The advantage of this approach is that it
quickly establishes a priority list of sites based on qualitative data
obtained from each site.
Newly enacted statutes within the state of California also as-
sist DHS in establishing its priorities for state-managed cleanups.
These statutes create three categories of sites. Each category
reflects the degree of willingness and active involvement by the
responsible party in addressing the problems that exist. The cate-
gories range from proactive participation by the responsible party
(thus requiring minimal oversight by the state) to total recalci-
trance and strong state participation. (For more details on these
priority categories, the reader is referred to the California Health
and Safety Code, Division 20, Chapter 6.8, Article 5, Section
25356.)
Site Assessment
After a site has been identified, a detailed quantitative assess-
ment is then conducted by activating the site assessment compo-
nent. The function of this component is threefold. First, it defines
OCR for page 70
70
HAZARD O US WA S TE SI TE MANA GEMEINT
the thought process and procedures used to adequately character-
ize a site. Second, it defines the parameters for which data must
be collected. Finally, it identifies the preferred data collection,
handling, and analytical techniques needed to ensure high-quality
environmental information. This is accomplished through the use
of a series of decision branches and data checklists. Through the
use of these tools, the project manager is able quickly to identify
the pathways of concern, the chemical contaminants of concern,
and the biologic receptors of concern. The assessment also provides
the project manager with site data needed in other components to
determine the short-term and long-term health threat of the site.
It should be noted that all of the branches presented in this
component need not be used on all sites. In fact, the branching
process has been designed to address certain core questions first,
a method that allows one to close down a particular branch of
analysis before it is pursued very far. For example, if a site only
has relatively small amounts of surficial contamination, one may
be able to justify not opening up the ground water pathway branch
and thus save tremendous time and the costs associated with fully
characterizing that medium. Furthermore, this process allows one
to document the basis for a particular decision. Thus, if later
questioned either through public scrutiny or in the courts, one
wouIc] have a documented, technical basis for not pursuing that
particular branch.
Representations of transport pathways are referred to as mod-
ules and are developed from data collected during this component.
Each module may consist of observations, deductions, calcula-
tions, numerical models, and professional judgments that allow
the project manager to make scientifically and technically de-
fensible statements and conclusions regarding the behavior and
transport of chemical contaminants at the site. The focus of site
characterization and the development of environmental modules
is ascertaining what the concentrations of toxic chemicals will be
at the points of exposure to biologic receptors of concern.
Risk Appraisal
Risk appraisal, the next component, begins while the site as-
sessment process is still going on. Here the purpose is to assess
quickly whether any immediate corrective action should be consid-
ered to mitigate the short-term risk to the public. This assessment
OCR for page 71
DECISION TREE PROCESS
, ~Prevailing Wind Direction
I AAL waver
-a. ~ ~
~ Expose
I ~ ~
~ ,,,, Point ~
71
\
Direct AAL son
>~Contact ~
BY At_
\t,_!1!~!1~!~!;~l ~
~ ~ ~ A
FIGURE 4-1 Illustration of the applied action level (AAL) concept and
point of application.
is done using three simple risk appraisal tests. By using these tests
the project manager quickly compares the amount of contaminants
reaching a biologic receptor to the statewide health-based criterion
known as the AAL.
As previously mentioned, the AAL is a substance-medium-
biologic receptor-specific value. It defines the maximum exposure
value in which no observable adverse effect would be detected.
It is viewed as a statewide health-based criterion in that it does
not matter where in the state the biologic receptor is located;
if he is exposed above this level, he is at risk. AAL values are
derived using conventional toxicologic principles and are published
by DHS. Figure 4-1 illustrates the AAL concept and how it is
applied at the location of the biologic receptor instead of at the
site of initial contamination.
The project manager can quickly assess whether or not a
biologic receptor is currently at risk through the use of three
simple tests contained in the decision tree process. The three tests
taken together make up the risk appraisal mechanism.
The first test evaluates whether a biologic receptor receives
an excessive exposure to any toxic substance through contact with
OCR for page 72
72
HAZARDOUS WASTE SITE MANAGEMENT
each contaminated medium (e.g., air, water, soil, biota). The test
compares the level of exposure for a substance In the medium
(Cmedium) with a safe exposure level delineated by the AAI, crite-
rion. Test 1 is written as follows:
if Cme~ium/AALme~ium > 1, then
a biologic receptor of concern is considered to be at risk to an
adverse impact, the test fails, and a risk management process
should be initiated.
The second test determines whether a biologic receptor re-
ceives an excessive exposure to any toxic substances through con-
tact with all substantially contaminated media. The exposures by
various media are assumed to be cumulative.
Excessive exposure is determined by the cumulation of expo-
sure in various media normalized to the AAL standard developed
for that medium. Test 2 is written as follows:
n
med ium= 1
Cmedium/AALmedium > 1, then
a biologic receptor of concern is considered to be at risk to an
adverse impact, the test fails, and a risk management process
should be initiated.
The third test in the risk appraisal process determines whether
a biologic receptor may receive excess exposure to an aggregate of
substances that produces toxic manifestations. This test assumes
additivity of such exposures across all media. The test can be
modified to account for different types of interactions between
toxic substances if shown to exist. Test 3 is written as follows:
z ~
~ Cmedium, sub > 1 then
sub=i medium=! AALmedium, sub ~
a biologic receptor of concern is considered to be at risk to an
adverse ~rnpact, the test fails, and a risk management process
should be initiated.
It should be noted that additional criteria may be used in lieu
of AAL values. For example, if worker exposure and risk appraisal
were to be assessed, it might be appropriate to use worker safety
standards providing they are health based in their derivation.
OCR for page 73
DECISION TREE PROCESS
Environmental Fate and Risk Determination
73
As with the previous component, the environmental fate and
risk determination component begins soon after the initiation of
the site assessment component. Whereas the risk appraisal com-
ponent evaluates whether a biologic receptor is currently at risk,
this subsequent component assesses how the contaminants will be-
have through time and then evaluates if the receptor will be at
risk in the future. The environmental fate and risk determination
component establishes methods and procedures to assess the en-
vironmental fate of chemicals and their potential to move across
media. Conservative projections are then made as to what the
concentrations of a substance will be in the future at the exposure
point for a biologic receptor.
The process contained in this component allows one to make
two critical determinations. First, it allows the project manager
to establish the maximum contaminant concentration in each
medium that will not pose a health risk (i.e., a health-based
cleanup criterion). Second, the process allows one to project the
relative efficiencies of different remedial actions and determine
whether they will meet the health-based cleanup criterion just
established. Because these two actions are the strength of the
decision tree process, two case studies are presented later in this
chapter to demonstrate each action. The first case illustrates how
the decision tree process quickly establishes the cleanup criteria.
The second case demonstrates how the decision tree process al-
lows the project manager to evaluate the effectiveness of different
remedial actions.
It should be noted that the risk determination process used to
establish the cleanup criteria is composed of the three simple tests
that make up the risk appraisal mechanism. The difference is that
now the concentration values used in each test are those derived
through the environmental fate assessment.
A dynamic aspect of the risk determination process is that
it allows the transformation of various concentrations of contam-
inants at a particular location into a single risk value. As shown
by Figure 4-2, such a transformation greatly simplifies the evalua-
tion of risk and males it easier for the project manager to convey
this concept to the public. The risk values that are plotted out
in Figure 4-2 are defined as risk index scores (RIS). Case study 2
graphically illustrates how risk index scores can be used.
OCR for page 74
74
Concentration, mg/l
A N = 0.02 C N = 0.01 E N = ND
X= 1.2 X=0.80 X=0.21
B N = 0.001 D N = 0.005
X = 0.45 X = 0.60
HAZARDOUS WASTE SITE A~4NAGEMENT
Naphthalene= ~ /
Rlsk Index Scores
ARIS = 3 0 CRIS = 1.84 ERIS = 0.34
BRIS = 0.78 DRIS = 1.25
FIGURE 4-2 A comparison between contours of ground water contamina-
tion concentrations and risk index scores. The AAL values for naphthalene
and xylene are 0.018 mg/1 and 0.62 mg/1, respectively.
Development of a Mitigation Strategy and the
Selection of Remedial Action
If it is determined, either through the risk appraisal process or
the risk determination process, that a biologic receptor of concern
is or will be at risk, mitigation of that risk should be investigated.
The development, evaluation, and selection of such remedial ac-
tions are presented as elements of the last component of the deci-
sion tree process. Discussing these activities in the latter portion
of this section, however, does not mean that these activities begin
late in the decisionmaking process. Rather, they begin during site
assessment and run concurrently with the remaining components.
The selection of the remedial action for a project is based on
the specific site characteristics (Component 2), the existing toxic
concentrations at the location of the biologic receptor (Compo-
nent 3), and the ability of the contaminants to move across and
within media to reach biologic receptors in the future (Component
4~. Thus, by initiating the screening process concurrent with site
assessment activity, the impractical remedial actions are quickly
discarded. Detailed analyses of feasible alternatives can be con-
ducted along with the rest of the investigations to yield a timely
solution.
_
. .
_ _.
OCR for page 75
DECISION TREE PROCESS
75
Alternative site mitigation measures are identified and eval-
uated in the feasibility study component of the development of a
remedial action plan. A decision process for the development and
evaluation of appropriate alternative remedial actions for a given
site is contained in the EPA Guidance on Feasibility Studies Under
CERCLA (U.S. EPA, 1985~. The discussion presented here has
been adapted from the discussion presented in that more detailed
document. The process for the development and evaluation of ap-
propriate alternative remedial actions for a given site is shown in
Figure 4-3.
An example of how this component can be used to define and
evaluate the various alternatives Is contained in the second case
study. The reader is also referred to The California Site Mitigation
Decision Tree Manual (1986) for a more detailed description of this
component.
APPI~G To DECISION T=E PROCESS:
TWO CASE STUDIES
Two case studies are presented below. The first study illus-
trates how the decision tree process is used to set cleanup criteria
quickly. The second study demonstrates how various remeclial
actions are evaluated so that the best option is selected.
Case Study 1: An Arsenic-Contam~nated Site
In this first example, the preliminary site appraisal identified
the site as a pesticide-formulating plant that had been in operation
for more than 40 years. The facility covered over 10 acres and
was located adjacent to a saltwater marsh. Samples showed that
extremely high levels of arsenic compounds (up to 10,000 parts
per million [ppm] total arsenic) were contained in soils underlying
former waste disposal impoundments and storage areas, as well as
along former loading and handling areas. Elevated levels of arsenic
(up to 100 mg/~) were also observed in samples of the shallow
ground water underlying the site. Although the site was located
in an industrial zone, a residential neighborhood was less than
one-half mile away.
Site assessment activities were undertaken for a better def-
inition of the characteristics of the site and neighboring areas.
First, the shallow (~12 feet) ground water was determined to be
OCR for page 76
76
HAZARDOUS WASTE SITE MANAGEMENT
~ .
Characterize Problem
and Identify
General Response
Actions
rem
Develop
Alternative Specific
Technalacilen
~ _ _
!
Technical creeping
of Specific
Technolonles
I~
Formulate Broad
Alternative Remedial
A~tl~nQ
Environ rental,
Pubilc Health, and
Institutlonal
Screening
Cost Screening
Identity Surviving
Alternative
Remedial Actions
Phase 1:
Phase 11:
Project Scoping
Identification of Specific
Technologies
Phase 111: Screening of Alternatives
Technical Institutlonal Cost
An:llVals Analysis Ana veils
Statutory
Environmental
Impact
Analysis
Phase IV: Detailed
Analyses of
Surviving
Alternatives
Summ;rizatlon
of
Alternatives
.
Final
Feasibillty
Report
I
FIGURE 4-3 Feasibility study process.
Phase V: Summarization
Phase Vl: Preparation of Feasibility Report
OCR for page 77
DECISION TREE PROCESS
77
nearly stagnant and highly saline (about 25,000 ppm total dis-
solved solids). This aquifer was shown to reside above a drinking
water aquifer found at a depth of approximately 200 feet. Do-
mestic wells were so located that they used this deeper aquifer,
but they were hydraulically upgradient and located a considerable
distance from the site. The drinking water aquifer was separated
from the contaminated, shallower aquifer by approximately 100
feet of low-permeability deposits.
The surface and near surface (0-12 feet) soils consisted primar-
ily of silty sands. There were large areas of arsenic contamination
as a result of surface transport of the contaminant by seasonal
flooding and manufacturing activities. The soil concentration val-
ues ranged as high as 10,000 ppm total arsenic for a few "hot spots"
but were more typically confined to the I,00~ to 5,00~ppm range.
In addition to soil and water data, meteorological information
and marsh flora/fauna data were collected. The California De-
partment of Fish and Game analyzed tissue samples from aquatic
species living in the marsh and conducted a vegetation assessment.
While site assessment activities were under way, a risk am
praisal was conducted to assess any existing health threats. It was
determined that by limiting access to the site the public would
be adequately protected. To preclude any surface contamination
reaching the marsh and endangering aquatic species, a berm was
constructed along the marsh boundary. This barrier eliminated
seasonal flooding and surface water runoff into the marsh.
To set a health-based cleanup criterion for the site, the envi-
ronmental fate and risk determination component was activated.
To project what the future concentrations of arsenic compounds
would be at the location of the biologic receptors, two conservative
scenarios were created. For the first scenario the future site condi-
tions were defined as an undistributed site with all buildings and
structures removed; no soil cap or vegetative cover were present,
and dry soil conditions existed. The biologic receptor of concern
was identified as the general public, and the predominant exposure
pathway (medium) was the air. It was assumed that residential
development had encroached up to the site boundary. The pri-
mary health concern for this first scenario was based on long-term
chronic exposure to arsenic compounds.
In the second scenario the site conditions were once again
defined as all buildings and structures removed, no soil cap or
vegetative cover present, and extant dry soil conditions. In this
OCR for page 87
DECISION TREE PROCESS
r source ~
I Area ~
-1,
87
-1
~ 'I
,~ ~ ~
~ _ . -
it.
. -
din
-
~-
5- ~1
~ 1
Agricultural Wed
rem
b~ .
_~
ll
City
Well
~ . ~
. ~
l
l
.-, _
no_
RIS> 1
Private
Ne11
River ~
1
FIGURE 4-8 Environmental fate and risk determination: potential future
conditions if the city well is closed.
ground water. The private well is located in the path of the con-
taminated ground water plume and typically would have such a
small capture zone as to preclude at-the-welIhead dilution. The
continuing operation of the agricultural and municipal wells to
harvest contaminated ground water and thereby work to protect
the private well cannot be assumed without formal commitments
from the farmer and water purveyor. Therefore, the level of chIo-
roform at the private well would be expected to exceed the AAL
in the future; test 1 of the risk appraisal mechanism fails; and a
risk management process should be considered to protect those
biologic receptors demonstrated to be at risk in the future.
In addition to the existing downgradient biologic receptors,
human beings who in the future may wish to use the ground water
resource downgradient of the site would be considered at risk. As
illustrated in Figure 4~9, this is equivalent to evaluating the site
by identifying the biologic receptor of concern as a human being
exploiting the ground water just downgradient of the contam~na-
tion source. Thus, a second biologic receptor has been identified
as being at risk, although this second receptor currently does not
exploit the ground} water and, in reality, may not have been born
yet.
OCR for page 88
88
Area ~
_ ~
HAZARDOUS WASTE SITE MANAGEMENT
. I
>~U~_
~-
r,
4~
Private ~ 7
WeI'
River
FIGURE 4-9 Environmental fate and risk determination: future beneficial
uses of ground water.
As shown also in Figure 4-9, the flux of contaminated ground
water that could eventually enter the river in this problem has
been determined to be small with respect to the flow of the river.
This condition would provide sufficient dilution and result in non-
detectable levels of chloroform in the bulk flow of the river. Based
on this analysis the aquatic species identified as the biologic recep-
tors of concern would not be considered at significant risk in the
future, and a risk management process would not be warranted to
protect them.
Development of a Mitigation Strategy and
Selection of Remedial Action
At this point in the case study the problems to be solved
through remedial action have been identified and defined by in-
vestigation and analysis. Specifically, the potential risks of future
adverse impacts on biologic receptors of concern have been eval-
uated and defined through the risk appraisal mechanism. Those
risks deterrn~ned to be significant have been identified as media
specific, receptor specific, chemical specific, and site specific. The
mitigation strategy to be used must address the defined problems.
OCR for page 89
DECISION TREE PROCESS
89
In this case, the mitigation strategy must preclude adverse health
effects associated with the exposure of humans to chloroform in
ground water.
In the fifth component of the decision tree process, the project
manager has the opportunity to evaluate various remedial alterna-
tives. The effect of each alternative in reducing the risks associated
with remedial actions is evaluated through the decision tree pro-
cess, again employing the environmental fate modules and the risk
appraisal mechanism. Both technical and nontechnical considera-
tions are evaluated by the site manager before proposing plausible
remedial alternatives. In this example, four remedial alternatives
are evaluated.
Alternative 1- No Action. The no-action remedial alternative
would not alleviate or reduce the risk posed to downgradient water
users, nor would it protect future human biologic receptors wishing
to use the ground water resource as a drinking water supply.
Although humans would be at risk here, the nonhuman bi-
ologic receptors of concern, the fish in the nearby river, are not
considered to be at significant risk. For this case the no-action al-
ternative would be acceptable with respect to the aquatic species.
Alternative 2 Aquifer Remediation. A second alternative,
aquifer remediation, would intend to restore all contaminated
ground water to a condition in which the AAL for chloroform
is not exceeded anywhere (Figure 4-10~. At this particular site,
such an alternative protects all biologic receptors of concern but
has an associated cost that is extremely high.
Alternative ~ Alternate Water Supply. This third remedial
alternative (Figure 4-11) would protect the biologic receptors of
concern that have been identified as being at risk, but it would
limit the availability of the ground water resource. As shown in
Figure 4-11, the alternate source of water would be the existing
municipal supply well.
Potential problems in implementing this alternative might
arise from a reluctance on the part of the water purveyor either to
operate this well in a regime that provides the necessary dilution
at the welThead or to operate such a well at all. At this point it
might be appropriate for the risk manager, the water purveyor,
and the public to consider the risks associated with other sources
OCR for page 90
go
Source
Area _
RIS ~ 1
)1
FIGURE 4-10 Remedial alternative: aquifer remediation.
Capture _
Radlus ~
Source
Area
1
r~
W! ~
l ~
!
Cultural ~ el ~ I
d:
RIS<1 _
~-
_,
-
FIGURE 4-11 Remedial alternative: alternate water supply.
HAZARDOUS WASTE SITE MANAGEMENT
~ Hi_
~ 9 :
.
~ ~3 ~ ',
River
River
l
OCR for page 91
DECISION TREE PROCESS
Capture
Radlus
-
=m
Source
Area
d' ,
Ha,
A'
91
.~-~
_ ~ _
. _ ~ _
alit
~ r
~ _~ ~
-~
1
C12
1 1
! 1 .
RIS > ~
'1
RIS ~ 1
River
1
FIGURE 4-12 Risk index scores for surface water supply and ground water
supply.
of water, such as chlorinated surface water, and compare the
risk index scores associated with both sources of water. Figure
4-12 illustrates the relative risks associated with the water supply
alternatives of concern. As can be seen in this figure, exposure to
by-products of chlorination, including chloroform, would often be
expected to place human biologic receptors at greater risk than
they would be from the delivery of untreated ground water.
Alternative 4 Plume Monitoring and Maintenance. A fourth
alternative that might be subtitled the "don't go near the water"
alternative is shown in Figure 4-13. As the figure illustrates, re-
stricting the use of portions of the ground water system would
preclude the exposure of humans to ground water containing chIo-
roform above the AAI.. Controlling the pumping of the municipal
well would protect downgradient ground water users. This alter-
native also protects those biologic receptors identified as being at
risk and, like other remedial alternatives, has associated costs and
problems in implementation.
The four remedial alternatives considered in this example are
compared in summary form in Table 4-1. Only one alternative,
the no-action alternative, fails to protect the biologic receptors of
OCR for page 92
92
Capture _
Radius
Source
Area U
HAZARDO US WASTE SITE MANAGEMENT
r
'A
.1
> _ `~.~
=
Subcultural Shells
Em- ~
~-
- 7~
~_~
d_
mar
City
W 811
L, ] l
RIS c 1 ll
RIS < 1
- ^
w~
Private
We11
.
4
~ River
. ,
_ _
FIGURE 4-13 Remedial alternative: plume monitoring and maintenance.
concern, as discussed above. The aquifer remediation alternative is
acceptable under all categories of evaluation but has a cost that is
far in excess of the other alternatives. The availability of financial
resources to remediate all sites to the standard implied in Alterna-
tive 2 is a serious consideration for project managers. Alternatives
3 and 4 rely on administrative and resource management practices
rather than the traditional soil removal/ground water treatment
program; yet, if rigorously enacted, they would also meet the
criterion of protecting the biologic receptors of concern.
It should be noted that the traditional evaluation of "How
clean is clean?" for soil contamination is applicable to only one
of the four alternatives considered here. It should also be noted
that such an evaluation is technically defensible only following
a site assessment. As illustrated in Figure 4-14, such an evalu-
ation would rely on the characterization of the soils system as
represented by the unsaturated zone module. The construction
of such a representation requires the input of several disciplines,
as indicated in Figure 4-14. In fact, the multidisciplinary team
approach to evaluating hazardous waste sites is an explicit recom-
mendation made throughout the decision tree manual, but it is
perhaps most important when evaluating the subsurface behavior
of contaminants.
OCR for page 93
DECISION TREE PROCESS
TABLE 4-1 Remedial Alternative Analysis
93
Remedial Public
Alternative Cost Technical Health
Aquatic
Species
Concerns
Public
Input
No action None Unacceptable Unacceptable
Aquifer
restoration
with source
control
t500X Acceptable Acceptable
Alternate $50X Acceptable Acceptable Acceptable
water supply
Plume $20X Acceptable Acceptable Acceptable
monitoring
maintenance
Acceptable Unacceptable
Acceptable Acceptable
Water agency
reluctant
Water agency
reluctant
of *meteorology
Hydrology
COMA
Inflltratlon
. i~ ~
' Jl
Rate
Kd a'
Containment Flux ~ |
Hi;
Chemistry
> Son Science
.3~
FIGURE 4-14 Unsaturated zone module.
An)
'''~'
Geology
-
OCR for page 94
94
HAZARDOUS WASTE SITE MANAGEMENT
In summary, the project manager who must make the final
recommendations regarding this case has been provided with an
analysis of the various remedial alternatives considered plausible
to implement. The technical basis for each alternative has been
constructed through the decision tree process, and the strengths,
weaknesses, and costs associated with each alternative have been
compared. At this point, it becomes the state decisionmaker's job
to select the alternative that is considered the "best" for this par-
ticular site. He or she must balance concerns over implementability
and public acceptance with the very real-worId constraint of cost.
The role of the decision tree process is to provide that decision-
maker with the strongest possible technical basis for making such
a decision, in part with the goal of making the decision defensible
in the event of a challenge in a public or legal forum.
CONCLUSION
The California Site Mitigation Decision Tree Manual has been
created as a technical guidance document to assist project man-
agers in making decisions that have a strong analytical basis and
technical merit. The process specified in the document was de-
signed to be flexible in application. The decision-branching format
allows one to quickly identify the pathways of exposure that must
be characterized for each site. Simple sites generally require sim-
ple approaches; complex sites require more detailed multipathway
analyses.
To facilitate a scientifically based decision process the decision
tree incorporates a series of unique aspects. First, it requires a mul-
timedia approach to site characterization and the establishment
of cleanup criteria. Second, it identifies the specific parameters
for which data must be collected. Third, it identifies the preferred
data gathering, handling, and analytical techniques that should be
used. Fourth, it establishes statewide, health-based criteria called
applied action levels that are specific to particular substances, me-
dia, and biologic receptors. They define an exposure level in which
no observed adverse effect would be found. Fifth, the decision
tree process also allows one to set different cleanup levels for a
particular site, a capability that reflects the different degrees of
effectiveness of various remedial action combinations. Using the
process the project manager is in a position to select the final
OCR for page 95
DECISION TREE PROCESS
95
cleanup solution that best suits the condition of the particular
site.
Finally, it should be noted that DHS views the decision tree
manual as a dynamic document; as new field techniques and an-
alytical procedures are developed, the document will be updated
accordingly. The intent is to have a process that yields decisions
with the strongest technical basis.
REFE1lENCES
California Department of Health Services, Toxic Substances Control Division.
1986. The California Site Mitigation Decision Tree Manual. Sacramento,
California.
Cooper, W. C., J. Murchio, and W. Popendorf. 1979. Chryotile asbestos in
a California recreation area. Science 206: 685-688.
Cowherd, C. M., G. E. Muleski, P. J. Englehart, and D. A. Gillette. 1984.
Rapid Assessment of Exposure to Particulate Emissions From Surface
Contamination Sites. Kansas City, Mo.: Midwest Research Institute.
U.S. EPA. 1985. Guidance On Feasibility Studies Under CERCLA. Prepared
for Hazard Waste Engineering Research Laboratory, Cincinnati, Ohio,
and Office of Emergency and Remedial Response and Office of Waste
Programs Enforcement, Washington, D.C.
PROVOCATEUR'S COMMENTS
Joan Berkowitz
The California decision tree process, which is outlined in the
report that David was kind enough to send to me, is really a "how-
to" manual for conducting a remedial investigation/feasibility
study (RI/FS). The document presents a series of flowcharts on
what data to obtain and a text on how to obtain them. The mate-
rial is basically an amplification of the requirements of the national
contingency plan. If the directions in the manual were followed,
believe that both the R! and the FS would be of high quality
and that they would be linked together. This linkage has not al-
ways been achieved with RI/FS studies in the past, as Hirschhorn
(1987) points out.
Although the California decision tree manual provides excel-
lent guidance on fact finding, the manual does not provide the last
word on how those facts should be used to come to a decision on
remedial action. It cannot be emphasized too strongly that facts
OCR for page 96
96
HAZARDOUS WASTE SITE MANAGEMENT
are fundamental. Without a good factual base, reasonable and
defensible conclusions cannot be drawn.
The decisionmaking guidelines in the California mode! center
around AALs (applied action levels). These action levels are set
at the point at which contaminants in air, surface water, ground
water, and soils impinge on target organisms. The decision it-
self is based on a comparison between the concentrations (either
measured or estimated through a model) at the points of expo-
sure and theoretically derived, health-based AALs. Specifically,
the concentration of a chemical in a medium (Cc,m) is compared
to an AAL for the same chemical in the same medium. If the
ratio, Cc,m/(AAL)c,m, is greater than one, there is a potential
risk. Conceptually, this is very nice. However, uncertainties in the
measured or modeled concentrations, as well as in the AALs, are
both reflected in even greater uncertainties in the ratio. A recent
book by Wood et al. (1984), for example, shows that measured
concentrations in ground water can vary by an order of magnitude
in a given location over relatively short periods. This means that
there will be large error bounds on the numerator (environmental
concentrations). There will also be large error bounds on the de-
nominator (AAL) because of uncertainty in the data that go into
calculating the AAL. The uncertainties are still greater in the sum
of the ratios of Cc,m/(AAL)c,m over all chemicals and all media
used to reflect overall risks. Therefore, the final answer, taking
into account error bounds of the input data, might range from
something below one to something above one.
The case example that David gave highlights an additional
problem with the AALs. The contaminant selected in the example
was chloroform; the AAL was set at 4.3 ppb on the basis of
potential carcinogenic effects. Yet the drinking water standard for
total trihalomethanes (primarily chloroform) is 100 ppb. Based
on conventional dose-response extrapolations, 100 ppb happens to
correspond to an increased cancer risk of about 10-4. Admittedly,
the drinking water standards are technology based and not health
based. In fact, however, the drinking water standards trade off the
uncertain risk of cancer as a result of the presence of chloroform
against the certain risk of pathogenic diseases if the water were not
chlorinated. Chloroform is a byproduct of chlorine disinfection. A
dual standard 4.3 ppb for cleanup and 100 ppb for drinking
water- may be appropriate. Nonetheless, there is clearly some
subjective judgment involved in setting the AALs.
OCR for page 97
DECISION TREE PROCESS
97
Finally, the California decision tree process and this entire
workshop are based on the premise that priority attention must
be paid to protecting human health and the environment from
hazardous waste sites. After the RI/FS has been completed and a
decision has been made to spend, let us say, $20 million on a site,
the question is never asked, "If $20 million were made available to
this particular community to protect and enhance public health
and the environment, what would it be spent on to achieve the
maximum overall benefits?" Over the next 5 years, more than
$20 billion is likely to be spent in the United States for inactive
waste site cleanup; the question is never asked, "If that same $20
billion were to be put into a program to improve public welfare
in the United States would it all be put into waste sites?" In an
even broader context, the question is never asked, "If $20 billion
were to be invested in a global public health program, would
it be spent on cleaning up hazardous waste sites in the United
States?" ~ am not suggesting that these questions be addressed
here; we have a full agenda focused on issues of major national
interest. ~ am suggesting that current national priorities may not
be directly proportional to current health and environmental risks
in the United States, much less worldwide.
REFERENCES
Hirschhorn, J. S. 1987. Superfund: A Scientifically Sound Strategy Needed.
Ground Water Journal, Jan.-Feb.: pp. 3-11.
Wood, E. S., R. A. Ferrara, W. G. Gray, and G. F. Pinder. 1984. Ground
Water Contamination from Hazardous Waste. Englewood Cliffs, N.J.:
Prentice-Hall.
Representative terms from entire chapter:
ground water
