Derivation of Risk-based Cleanup Goals
for PCB-contaminated Soils at the
Winston-Thomas Site
Bloomington, Indiana
To: Consent Decree Parties
From: Dan Hopkins, U.S. EPA
Enclosed with this letter are the clean-up criteria that U.S. EPA has
determined to be protective of human health and the environment at the Winston-Thomas
site. Also enclosed please find the supporting documentation, including
the equations used for calculating the human health based clean-up values
and the factors used in determining the clean-up values.
U.S. EPA's human health based clean-up criteria is based on an analysis
of two probable commercial/industrial future use exposure scenarios. These
scenarios address dermal absorption and ingestion of soils for on-site construction/utility
workers and on-site industrial mainterance workers. The attached document
provides a complete description and calculations of clean-up criteria based
on carcinogenic and non-carcinogenic effects for various exposure durations.
Based on these results U.S. EPA has determined that the a clean-up level
of 15 parts pcr million (ppm) of total PCBs is protective of human health.
This clean-up criteria is considered a not-to-exceed value and applies site
wide.
U.S.EPA has also considered clean-up criteria sufficient to protect the
environment. A formal ecological risk assessment has not been performed
for this site. However, based on clean-upgoals developed for other sites
with similar habitats, a clean-up criteria for total PCBs that is protective
of most ecological receptors likely to be exposed to soils in wet areas
of the site is approximately 1 ppm. Consultation with U.S. Fish and Wildlife
Service resulted in their concurrence with this value of 1 ppm PCB. The
portions of the Winston Thomas site for which the 1 ppm clean-up value applies
is in thc area of the abandoned lagoons and the West Side of Clear Creek
area. U.S. EPA expects that the 1 ppm value in surface soils will be readily
achieved by backfilling excavated areas in the above-mentioned locations
with clean soil.
l suggest that, as soon as possible, the project schedule a meeting to
discuss the parties' concerns and issues related to clean-up criteria for
the Winston Thomas site. It is very important that the parties resolve any
difeferences with respect to clean-up values at the site in thc very near
future, so that clean-up work is not delayed.
If you have any questions regarding this letter or the enclosures please
contact me as soon as possible. I expect that the project managers will
identify issues related to this matter soon, in anticipation of a meeting
to resolve any issues that may exist.
Thank-you in advance for your cooperation.
Dan Hopkins
Senior Remedial Manager
U.S. EPA Region V
Cleanup Criteria
I. Purpose
The purpose of this exercise is to determine risk-based cleanup goals
for PCB-contaminated soils that will be protective of various populations
utilizing the Winston-Thomas site under future use scenarios. The exercise
utilizes U.S.EPA methodology derived from the forward calculation of a baseline
risk assessment to determine risks associated with contaminant concentrations
at a site. This exercise includes supporting documentation which addresses
exposure scenarios and the attendant pathways and assumptions, data gaps
and uncertainties inherent in risk calculations.
II. Background
The Winston-Thomas Facility is a 26-acre waste water treatment plant
which consists of a 17-acre tertiary treatment lagoon, abandoned sludge
lagoons, three sludge drying beds, four digesters, a trickling filter, primary
and secondary clarifiers, grit chambers and associated piping and pumps.
All process units are planned to be remediated, except for the grit chambers
and clarifiers which are not contaminated. The facility discontinued operations
in 1982, however, the process units were not dismantled and the sludges
that were present in the units at the time of facility closure were not
removed due to the presence of PCBs. The City of Bloomington and Westinghouse
Electric Corporation performed interim remedial measures at the site to
ensure that no contaminated materials are released. Site access is limited
by perimeter fencing and the City utilizes the Site for the storage of impounded
vehicles. City employees periodically access the site to perform limited
maintenance or to move vehicles in or out of storage.
In that the Consent Decree Parties have agreed that the Winston-Thomas
site must be remediated, it has not been necessary to develop an extensive
data base to determine exposure point concentrations that would support
a baseline risk assessment. Some sampling, however, has been conducted by
the Parties to determine the nature and extent of contamination.
III. Data Gaps
Sampling at the site occurred in Summer 1996. Sample analysis consisted
of field screening using immunoassay kits. Additionally, ten percent of
these screening samples were laboratory analyzed to compare to results obtained
from the kits in order to verify that the kits provided useful data for
screening purposes. While these screening data indicate ranges of contamination,
the kits are limited by their accuracy and ability to quantify concentrations
above 115 ppm. Further sampling may be necessary during remedial activities
to ensure that contaminated areas exceeding cleanup goals are addressed.
While there are no known connections between the process units and groundwater,
previous groundwater monitoring indicated the presence of PCBs in some wells,
however the source of contamination was not established. &Groundwater
has never been used or considered for future use as a drinking water supply
for this facility. Groundwater monitoring is planned during the implementation
of remedial alternatives.
The process units themselves were sampled' however there is little to
no information regarding concentrations in the areas between the units or
large areas unoccupied by facility units. These areas would need to be sampled
to determine whether and how they will be addressed.
IV. Exposure Pathways
The site is bounded by State Route 37 on the east, Gordon Pike on the
south, a business area to the north, and Clear Creek on the west. Access
roads traverse the site, and the majority of the area surrounding the facility
units is maintained grass and large trees.
The site is currently used and accessed by City of Bloomington personnel
for monitoring the tertiary lagoon levels, mowing and maintenance of the
premises whereby workers would sustain seasonal or longer-term intermittent
exposures. Seasonal trespassers would sustain these exposures as well. Shorter
term intermittant exposures would be sustained by persons accessing the
site for dropping off or picking up impounded vehicles, or routine utilities
inspections. While these types of exposures have occurred in the past and
may continue to occur until the site contamination is addressed, the Parties
have since agreed that this site will be remediated to protect human health
and the environment from unacceptable risks from PCB exposure. It is therefore
more appropriate to develop PCB cleanup goals based on exposures derived
from anticipated future use of the site instead of current exposures. To
assess current exposures, it is more appropriate to calculate a risk (probability)
value, since cleanup goals would be irrelevant.
The sampling conducted at Winston-Thomas facility over the years indicates
that chemicals of potential concern could include volatile and semivolatile
organics (including PCBs), metals, dioxins and furans. The purpose of this
assessment, however, is to assess cleanup goals based solely on total PCBs
as they are by far the chemicals that occur the most frequently and at the
highest concentrations. It is recognized that the presence of additional
contaminants would increase the overall cumulative human health risk, and
that remedial efforts directed at PCBs will remove other soil contaminants
as well. The sampling also indicates that the impacted media at the site
include soils (surface and subsurface) and groundwater. Groundwater is not
considered in the derivation of cleanup goals since it is not used at the
site and the municipal water system which is supplied by the Monroe reservoir
would service this area in the future.
The reasonably anticipated future land use of the site, according to
the City of Bloomington, is for commercial or retail purposes. This could
include such structures as a mall or office building complex/park which
may include landscaped areas, paved parking facilities, commercial warehousing
or any combinations thereof. This assessment considers contamination from
soil exposures which can occur via incidental ingestion, dermal absorption
and inhalation of fugitive dust. While there are a variety of potential
exposure scenarios which can be evaluated for soil cleanup goals, it is
critical to include those scenarios where exposure is expected to be the
greatest. U.S.EPA believes that the following two scenarios will result
in the greatest exposures and amounts of intake and will therefore result
in the most appropriate and protective cleanup.
1. An adult construction worker who is performing soil contact intensive
activities such as excavation, soil moving, surveying, pouring foundations,
etc. Some dust control measures may be implemented such as soil wetting,
however no vegetation would be present at this point. Utility workers are
included in this group as there are trenching activities, laying of cables,
surveying, etc. These exposures are expected to be of a more acute nature
in that high exposures are sustained over a short duration (1-3 years)
2. An adult industrial or site maintenance worker. As with the preceding
scenario, this work is also expected to be contact intensive, but these
persons would sustain a lesser amount of exposure per day because of less
soil disruption and activities would include othernon-soil related activities
as well. These persons, however, would certainly be more exposed than an
indoor office worker, a regular patron, or an occasional visitor to the
facility.
U.S. EPA recognizes that soil/dust inhalation is a common exposure route
in occupational scenarios and is certainly a legitimate exposure pathway
in the above scenarios. In consideration of this, a preliminary assessment
of inhalation-based soil cleanup goals was performed to weigh its contribution
to the risk-based goals from the combined dermal and ingestion pathways.
l The inhalation-based values were found to have negligible impact on the
combined goals. Since the uncertainties in the inhalation assessment calculations
arc much greater, this pathway was not included in the combined pathway
cleanup value.
Risk-based cleanup goal calculations are derived from the standard baseline
risk assessment intake equations as documented in RAGS Volume 1 (U.S.EPA,
1989). The Soil concentration cleanup goals for carcinogens are back-calculated
by solving the standard intake equations for the concentration term and
substitution of a target risk level and cancer slope into the standard intake
and risk calculations presented in RAGS Part B-Preliminary Remediation Goals(U.S.EPA,
1992) . For noncarcinogenic endpoints, the soil cleanup goals are derived
by the same method except the appropriate hazard index and reference dose
are respectively substituted into the standard intake and risk calculations.
The derivations are presented in the individual sections for ingestion and
exposure equations. The target risk levels and hazard indices used are those
deemed acceptable by U.S. EPA as set forth by the NCP and fall between 1
E-04 and 1E-06 for carcinogens and cannot exceed 1 for noncarcinogens. |
