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District is currently remediating the sludge lagoons which is scheduled to be complete in late spring of
1997.
II. Summary of Remedy
The selected remedy consists of treatment of certain contaminants in-place and excavation and disposal of
all contaminated materials off-site at permitted off-site landfills. Ori-site wastes and soils are to be
remediated to the cleanup levels specified in the ROD.
The soil cleanup levels established in the ROD for specified contaminants were based on calculations
performed as part of the 1992 Health Risk Assessment (HRA) which utilized toxicity data in. effect at that
time. This risk assessment was performed as part of the Remedial Investigation for the Site. The cleanup
criteria established in the ROD has allowed for unrestricted future use of the property once the cleanup is
complete.
III. Explanation of Significant Difference
As mentioned above; the cleanup levels established in the ROD for on-site wastes and soils were
calculated as part of the 1992 Health Risk Assessment, conducted as part of the Remedial Investigation
for the Site. The calculated levels were based on toxicity criteria in effect at that time or on background
concentrations available for the site. This BSD will establish soil cleanup levels for six carcinogenic
polyaromatic hydrocarbons (cPAHs), revise the cleanup level for one cPAH and revise the background
concentration and thus the soil cleanup level for beryllium.
A. With regard to the cPAHs, the risk evaluation was based on toxicity data which was available for only
one of the cPAHS - benzo(a)pyrene, which had an oral potency slope factor value of 12 (mg/kg/day)'
when the ROD was signed. The oral slope factor is EPA's terminology for describing how potent a
compound may be in causing cancer, based on studies conducted in animals and human studies when
available. The risk evaluation and the cleanup value specified in the ROD for all cPAHs [1.2 parts per
million (ppm)] were based on the assumption that all cPAHs were of equal potency as benzo(a)pyrene.
Since that time, EPA has revised the oral potency factor for benzo(a)pyrene to its current value of 7.3
(mg/kg/day)'1 (EPA 1997) rendering benzo(a)pyrene less potent than it was believed when the ROD was
written.: EPA has also published (EPA 1993) an interim recommendation for addressing the
carcinogenic potential of the other six cP AHs. This is known as the relative potency factor approach.
Using the relative potency factor approach, the oral slope factor for benzo(a)pyrene can be multiplied by a
relative potency factor for each of the six cPAHs to derive relative oral slope factors for each cPAH. Five
of the six cP AHs identified have resulting oral cancer slope factors one to three orders of magnitude less
than the oral slope factor for benzo(a)pyrene. Through this ESD, EPA will be establishing cleanup levels
for each of the seven cPAHs based on the availability of a new oral slope factor for benzo(a)pyrene and
the adoption of the relative potency factor approach for cP AHs.
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Please note, however, that the original acceptable risk level of 6.7 xlO"6 which was used to determine a
cleanup level in the ROD for the combined effects of cPAHs remains unchanged (as do all assumptions
regarding the nature and intensity of exposure). The incremental cancer risk level assigned to each of the
seven cPAHs in this ESD is 9.5 xlO'7>or one-seventh of 6.7 xlO"6. The resulting soil cleanup levels are
presented in the following table.
COMPOUND SOIL CANCER
CLEANUP LEVEL, ppm RISK
Benzo(a)anthracene 2.7 9.5 x 10'7
Chrysene 266.7 9.5 x 10"7
Benzo(b)fluoranthene 2.7 9.5 x 10'7
Benzo(k)fluoranthene 26.7 9.5 x 10'7
Benzo(a)pyrene 0.3 9.5 xlO'7
Indeno(l,2,3-cd)pyrene 2.7 9.5 x 10'7
Dibenz(a,h)anthracene 0.3 9.5 x IP'7
Total cPAH risk = 6.7 xlO'6
In summary, the only thing that has changed is the associated cleanup concentrations of the cPAHS. The
risk-based protectiveness of 6.7 x 10~6 established in the ROD remains the same. The result of cleaning up
cPAHS to these new concentrations will allow for the same protectiveness that was sought as a remedial
action goal under the ROD. The Site, once cleaned, will allow for unrestricted future use.
In addition to the ESD, EPA is taking this opportunity to articulate how compliance with all cleanup
levels identified for soils at the Salem Acres Superfund Site will be determined. Consistent with Risk
Assessment Guidance for Superfund (RAGS), Part A (EPA 1989) which calls for assessment of the
reasonable maximum exposure, and Supplemental Guidance to RAGS: Calculating the Concentration
Term (EPA 1992) which articulates that a 95% upper confidence limit on the arithmetic mean of
contaminant concentrations is to be used when computing exposure, EPA Region I will use the 95% upper
confidence limit on the arithmetic mean concentration of each compound of concern in soils at the Site
and compare it to the appropriate cleanup level specified in the ROD as amended today by this ESD.
EPA recognizes that data obtained from sampling and analysis are never fully representative of actual
human exposure. To account for the uncertainty in the data, EPA Region I has opted to use the 95 percent
upper confidence limit for Superfund Sites (RAGS, EPA 1989) as embodied in the Supplemental
Guidance to RAGS (EPA 1992). The 95% UCL provides reasonable confidence that the true site average
of concentrations of compounds remaining in the soils are less than the cleanup levels established for the
Site.
If the 95% upper confidence limit on the arithmetic mean concentration for any compound exceeds the
cleanup limit, the Site is still considered above the cleanup level for the compound. On the other hand, if
the 95% upper confidence limit on the arithmetic mean concentration for any compound is below the
cleanup level, the Site is considered below the cleanup level for that particular compound (i.e., no further
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excavation will be necessary based on that compound of concern).
B. With regard to beryllium, the soil cleanup level established in the ROD was based on a very limited
(two samples) characterization of site background. The lower of the two background concentrations
(0.42 ppm of beryllium) was used as the cleanup level.
In an effort to better characterize naturally occurring levels of beryllium, twelve representative
background samples were taken at various depths from undisturbed areas in close proximity to the site.
The results show that beryllium is naturally present in the soils in concentrations that range from 0.50
ppm to 1.50 ppm, with an average concentration of 0.83 ppm (Memorandum dated April 4,1997). The
95% upper confidence limit calculated for the arithmetic mean of 0.83 ppm is 1 ppm.
Given the variability in the data set, it is consistent with EPA practices to use the 95% upper confidence
limit on the arithmetic mean (1 ppm) as representative of naturally occurring (background) beryllium
concentrations. Thus through this ESD, EPA is redefining the background concentration of beryllium in
soils as 1 ppm. EPA is replacing the former cleanup level for beryllium of 0.42 ppm with 1 ppm for
compliance purposes. The excess lifetime cancer risk resulting from exposure to 1 ppm beryllium in soils
given the exposure -scenario and assumptions specified in the HRA is 2 xlO"6 which is consistent with
EPA's goal for remedial actions (clean up to within the acceptable risk range of 1 xlO"4 to 1 xlO'6).
As a consequence of this change, there may be a potential estimated cost savings of approximately
$680,000 in remedial costs.
IV. Support Agency Comments
The Massachusetts Department of Environmental Protection has reviewed this ESD and has concurred
with EPA in its issuance.
V. Affirmation of Statutory Determinations
Considering the new toxicity information for cPAHs that has been developed and the continued use of the
original risk based cleanup goal of 6.7 x 10~6 for cPAHs, and the revision to the background value for
beryllium based on more extensive data than was previously available, EPA believes the remedy as
amended by this ESD remains protective of human health and the environment, complies with Federal
and State requirements that are applicable or relevant and appropriate to this remedial action, and is cost-
effective. In addition, this remedy reflects EPA's commitment to utilize the most up-to-date scientific
information and methodology available.
VI. Public Participation Activities
This ESD and supporting information are available for public review at the locations and times identified
in the Introduction to this document. In addition, a notice of availability and brief description of the ESD
will be provided to a local newspaper of general circulation, the Salem Evening News.
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VII. Declaration
For the foregoing reasons, by my signature, EPA is issuing this Explanation of Significant Difference for
the Salem Acres Superfund Site in Salem, Massachusetts.
//. / 947
Date / Linda M. Murphy, Director
Office of Remediation and Restoration
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References
U.S. EPA 1989. Risk Assessment Guidance for Superfund. Volume I, Human Health Evaluation Manual
(Part A). Office of Emergency and Remedial Response, Washington, D.C. EPA/540/1-89/002.
U.S. EPA 1992. Supplemental Guidance to RAGS: Calculating the Concentration Term. Office of Solid
Waste and Emergency Response, Washington, D.C. Publication 9285.7-081, May 1992.
U.S. EPA 1993. Provisional Guidance for Quantitative Risk Assessment of Polycyclic Aromatic
Hydrocarbons. Office of Research and Development, Washington, D.C. EPA/600/R-93/089.
U.S. EPA 1997. Integrated Risk Information System (IRIS). Online database. National Center for
Exposure Assessment, Cincinnati, OH.
Memorandum from Dharmarajan Iyer, URS Greiner, Inc. to Elaine Stanley, EPA dated April 4, 1997
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