Proposed Westinghouse Work
Plan to Develop HBCGs for
the Winston Thomas Facility
by Alceon Corporation
6 February 1997
Mr. John Langley
City of Bloomington
Utilities Department
1969 South Henderson Street
PO Box 1216
Bloomington, IN 47402
Dear John:
We have reviewed the proposed Westinghouse Work Plan to Develop Health-Based
PCB Cleanup Goals for the Winston Thomas Facility (Westinghouse, 1996) and
your draft comments on this plan. In this letter, we offer comments on the
plan from a risk assessment perspective. In addition, we have estimated
Health-Based Cleanup Goals (HBCGs) based on the three scenarios discussed
in the Westinghouse proposal. The risk tables for these calculations and
a short discussion are included as an attachment to this letter.
Alceon and the City of Bloomington Utilities (CBU) have independently
arrived at many similar conclusions about the HBCG Work Plan. In this letter,
we have repeated the comments which concern risk assessment methodology
and those which require special emphasis.
Our general impression of the HBCG Work Plan is that it attempts to accomplish
much more than it actually does. Westinghouse declares that the plan covers
the entire Winston Thomas Facility, but the text does not include the east
side of the entrance road or the west side of Ciear Creek; the plan purports
to address both ecological and human health concerns, but the cleanup goals
only consider human receptors; and the cleanup goals are presented to cover
all current and future uses, yet they do not consider potential recreational
or residential receptors or a rationale for eliminating them. The net effect
of the plan, as presented, is to produce extremely high cleanup goals while
compromising the future use and economic value of the Winston Thomas site
by dismissing several key future use scenarios.
This work plan blurs the distinction between risk assessment and risk
management by limiting exposure options prior to an adequate discussion
of future use. The risk assessment should fairly consider a broad range
of use options and the risk management which follows should evaluate the
various options and then, only if necessary, limit the acceptable future
uses.
The risk-based corrective action approach can contribute to useful, health-protective,
and cost-efficient remedies for contaminated sites. However this Work Plan,
though "exploratory" and a first draft, is inadequate for addressing
human health and ecological risks for all current and reasonable future
uses of the entire Winston Thomas site.
Specific Comments on the proposed Westinghouse Work Plan
We have included the following comments, referenced by page number and
paragraph.
Comment 1: Cover Page, second paragraph
"One approach...is to develop a health based cleanup goal...thereby
having a remedy which will be protective of human health and the environment."
A health-based cleanup goal is not necessarily protective of the environment.
This claim from the cover page is not supported in the proposed Work Plan,
nor are environmental impacts discussed at length. This is both a risk assessment
and risk communication issue. For the risk assessment, the inclusion or
elimination of environmental exposure pathways must be supported. As a public
document, the risk assessment report must clearly communicate why HBCGs
are protective of both human health and the environment.
Comment 2: Cover Page, third paragraph
The cover page and report assume that HBCGs will be based on existing
surface soil only, without any discussion of future exposures to deep soil.
Given that the site is likely to be developed, exposure to deep soil is
a significant pathway and cannot be dismissed in the calculation of a remedial
goal.
Also, the text does not support the claim made in the second sentence
of this paragraph regarding ecological threats and pathways of concern.
The assumptions concerning ecological risk in this Work Plan are not discussed
and remain to be demonstrated.
Comment 3: Page 1-1, second paragraph
The text needs to explain what comprises "buffer zone material."
Comment 4: Page 1-1, third paragraph
What is meant by technically adequate? The text needs to clarify the
distinction, if any, between this and technically "feasible."
Comment 5: Site Map following Page 1-2
Neither the map nor the text appear to include property to the east side
of the entrance road or on the west side of Clear Creek as part of the Winston
Thomas site. In future versions of the Work Plan and HBCG report, these
should be included in the site descriptions and considered in the derivation
of cleanup standards.
Comment 6: Page 2-1, first paragraph
Does the CBU agree that the clarifiers and grit chambers are not contaminated?
Comment 7: General Comment, Section 2.0
This section is titled "Site Characterization" yet it does
not discuss in detail the efforts to characterize the extent of contamination
at the site or their results. In future drafts of this work plan and/or
calculation of cleanup goals, this section should be revised to include
detailed discussion of sampling efforts and results including specific reference
to contaminant concentrations in both surface and deep soil.
Comment 8: Page 3-1, second paragraph
"Nevertheless, this work plan proposes to evaluate the unlikely
potential for human exposures resulting from contact with on-site soil."
What is "unlikely" about the potential for exposure? The Winston
Thomas site has several current uses and is likely to be developed for future
use involving excavation and a variety of potential use options. The word
"unlikely'' has no place in this sentence.
Comment 9: Page 3-1, third paragraph
The presentation of current and future receptors at the site does not
discuss all current or potential future uses. The text should discuss all
current users and explain the rationale for selecting a subset of these
receptors for calculating HBCGs. Likewise, these steps should be taken when
including or eliminating potential future receptors. Currently, the proposed
scenarios for evaluating HBCGs severely restrict the potential future uses
of the property. The text must include discussion of the potential for excavations,
recreational, and residential future uses of the site. If any of these receptors
are ruled out, the rationale must be clearly stated.
Comment 10: Page 3-1, fifth paragraph
The rationale provided here for dismissing the separate evaluation of
sub-surface exposures for HBCGs makes no sense. In the calculation of HBCGs,
no site specific information is necessary to determine the exposure point
concentrations (EPCs) which would result in unacceptable risk. One need
only to estimate the exposure parameters, postulate a risk threshold, and
calculate the EPC. If specific information concerning the nature and extent
of contamination is necessary for taking the remedial action, then it should
be obtained. The assumption in the third sentence of this paragraph does
not consider utility and excavation exposures which are more intense and
of shorter duration. This exposure must be evaluated by a separate scenario.
Subsurface soil may also become surface soil in a future development of
the site. Therefore, the HBCGs for current subsurface soil must be developed
considering all future surface and subsurface exposure scenarios.
Comment 11: Page 3-2, second paragraph
Based on our observation of ground cover during a September 1996 site
visit, there appears to be enough exposed soil that fugitive dust can be
a significant exposure pathway. In this report it is dismissed without a
rationale.
Comment 12: Page 3-2, third and fourth paragraphs
As discussed in previous comments, the scenarios to be evaluated for
future use do not adequately represent the potential future use of the Winston
Thomas site. Any remedial goals based only on these scenarios would severely
restrict the future use and economic value of the property.
Comment 13: General Comment, Sections 3.3 and 3.4
In the two sections titled "Equations for Calculating HBCGs"
and "Exposure Assumptions," all of the information necessary to
calculate the HBCGs for the proposed scenarios are presented, yet the HBCGs
are not. We believe that it is somewhat disingenuous to offer equations
and assumptions which completely determine these results without presenting
the final values, which are the ultimate goal of the report.
The attached tables include the calculations that are specified, but
not presented in the Work Plan. The accompanying text presents the HBCGs
and discusses the various significant variables in their calculation.
Comment 14: Page 3-9, third paragraph
This paragraph provides no explanation for the application of a range
of RfDs for non- carcinogenic exposures, other than to state that this approach
was approved by US EPA for carcinogenic exposures. If there is further justification
behind this approach, other than the inductive reasoning provided, it should
be included in the text. Please include the appropriate references for these
non-carcinogenic toxicity values. In the last sentence of this paragraph,
strike "through the food web."
Comment 15: Page 3-9, fourth paragraph
To adequately represent the range of carcinogenic threshold levels considered
by US EPA, HBCGs corresponding to risks equal to 1 E-04, 1 E-05, and 1 E-06
should be presented. A graph displaying the range of HBCGs as a continuous
function over this interval would be additionally useful.
To say that 1 E-05 is the midpoint between 1 E-06 and 1 E-04 is somewhat
misleading. It is only the midpoint on a logarithmic scale, not an arithmetic
scale. It should be noted in documents for the public what this means: i.e.,
an HBCG based on a 1 E-05 risk is ten times higher than the analogous HBCG
for a 1 E-06 risk, an HBCG based on 1 E-04 is one hundred times higher than
the HBCG for 1 E-06, etc.
Conclusion
Please note that there are two major issues presented by this Work Plan.
They should be made distinct in the discussions to follow this round of
comments. The first concerns acceptable exposure assumptions for specific
scenarios (i.e., "Is the exposure frequency for Maintenance Workers
equal to 32 cl/y or 64 d/y?", "Aren't trespassers exposed to fugitive
dust?", etc.). The second, and more fundamental, issue concerns the
exposure scenarios considered in the calculation of cleanup goals. As currently
proposed, the Work Plan does not include residential and recreational exposures.
This second issue should be resolved first, and should not be obscured by
discussions concerning the minutiae of the calculations and exposure assumptions.
If you have any further questions regarding these comments and the attached
tables, please contact me. I may be reached by phone at (617) 864-4300 x233
and by e-mail at amw @ alceon.com
Sincerely,
Andrew M. Wilson
Senior Associate
Attachment
References
Westinghouse, 1 996
Westinghouse and McLaren/Hart-ChemRisk, Inc. Work Plan to Develop Health-Based
PCB Cleanup Goals for Winston Thomas Facility, Bloomington, Indiana. 19
December 1996.
Attachment
Risk Calculations for Three Scenarios Outlined in the Westinghouse
Work Plan to Develop HBCGs for the Winston Thomas Facility
Tables 1, 2, and 3 of this attachment present health-based cleanup goals
(HBCGs) based on the three scenarios detailed in the Westinghouse Work Plan
to Develop HBCGs for the Winston Thomas Facility. For each scenario, we
have used the equations and the exposure assumptions provided in the Westinghouse
Work Plan to estimate the risks associated with PCB contamination in soil
at the Winston Thomas site. The Work Plan has provided all of the quantitative
information necessary to make these estimates.
Each table presents a baseline risk calculation, beginning with the exposure
point concentration (EPC) and ending with the hazard and risk estimates
which results from the EPC and exposure factors. This is known as a "forward
calculation." HBCGs are "back-calculated"; they combine the
exposure and toxicity factors with a target risk threshold to arrive at
an EPC which represents the maximum concentration protective of human health.
Therefore, in Tables 1, 2, and 3, the HBCG is given by the EPC at the beginning
of each table.
The HBCGs estimated for each scenario are as follows:
Exposure Scenario Age Group Exposure HBCG (mg/kg) Driver
Maintenance Worker Adult CurrenVFuture 67.93 Carcinogenic
Trespasser Teenage Current 178.65 Carcinogenic
Visiting Child Child Future 89.22 Carcinogenic
Note that the HBCG estimated for each scenario is greater than the limit
of 50 ppm for total PCBs specified in the regulations for the Toxic Substances
Control Act (TSCA; 40 CFR 761). At this time, Alceon is unaware that Winston
Thomas has any exemption from the TSCA statute.
Additionally, note that these HBCGs are based on a target cancer risk
level of 1 E-05. Cleanup standards based on the most health protective end
of US EPA's acceptable risk range would be 10 times lower than presented
in this table.
Any discussion concerning the development of these HBCGs should bear
in mind the following points:
- The exposure scenarios used for the calculations have the greatest
effect on the final goal and therefore should be settled first. At Winston
Thomas, we recommend that the issues concerning residential, recreational,
and other future receptors be settled before any discussions are made regarding
exposure pathways and assumptions.
- The exposure pathways should be settled following agreement on the
exposure scenarios. An example for this site is the issue of fugitive dust
exposure for trespassers.
- The exposure assumptions should be settled following agreement on the
scenarios and pathways. Exposure assumptions are very important in the
development of HBCGs. However, it is important to postpone discussion of
these assumptions until after the scenarios and pathways are set, so that
smaller issues do not obscure larger ones.
As a result of these points, we do not offer a detailed analysis of the
exposure factors which contribute to the HBCGs in the table above. These
issues can be resolved after an agreement is reached between Westinghouse
and the government parties regarding the exposure scenarios to be included
in this Work Plan. |
