Dames & Moore, 1999 - USDA Forest Service

USEPA's Weight-of-Evidence Carcinogenicity Classification System
Group
A
BI
B2
C
D
E
Description
Humancarcinogen
Probable human carcinogen - limited human data arc available
Robable human carcinogen - sufficient evidence in animals and inadequate or no evidence in humans
Possible human carcinogen
Not classifiable as to human carcinogenicity
Evidence of non-carcinogcnicity for humans
USEPA recommends that the weight-of-evidence classification be presented for each potential carcinogen to
indicate the strength of evidence that it may be a human carcinogen (USEPA, 1986a: USEPA, 1989). Table
7.1-38 summarizes the oral and inhalation CPFs and carcinogen classification for each IHS.
Constituents for Which No Toxicity Values are Available
Neither lead nor total petroleum hydrowbons have toxicity criteria which can be used to calculate site-
specific Method C criteria. Therefore, these constituents are discussed qualitatively in the risk
characteritation.
7.1.4.3 Development of Site-specific Method C Levels
For each exposure pathway, site-specific Method C levels were calculated. The equations for calculating
these cleanup levels are based on the equations presented in MTCA.
Selection of Exposure Parameters
Exposure assumptions utilized in calculation of the site-specific Method C criteria were based on a
reasonable maximum exposure (RME) scenario, and included assumptions regarding the types of exposure
that may occur and the frequency and duration of those exposures. To conduct the site-specific assessment,
assumptions were made such that exposure to these media more closely reflect actual conditions, but still
reflect an RME scenario. The exposure applied in the scfeening level assessment's Method A
and B criteria are conservative with respect to the living habits of potential receptors at the Site and Holden
Village. The Method A and B levels presented in the screening tables (Tables 7.1-6 to 7.1-35) generally
represent risk to a receptor resulting from continuous exposure over a 30-year period. In the site-specific
HHRA, the exposure duration was modified to reflect actual exposure conditions of the Holden Village
residents. The occupants of Holden Village are transient, with a maximum known residence time of 20
years, according to Ms. Janet Grant (Holden Village Director). Therefore, as a conservative measure, the
exposure duration was assumed to be 20 years for adult residential exposures. For those cleanup criteria
based on exposures in a child, the default exposure duration of six years was used. For the USFS personnel,
a maximum exposure duration of three years was assumed based on information provided by the USFS.
Frequency of exposure was also adjusted to reflect the likely seasonal nature of exposures, i.e., the presence
of snow-cover for approximately eight months of the year. The exposure parameters used to calculate
cleanup leve1s;and their sources, are provided in Table 7.1-39.
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17693-005-019Vuly 27.1999;5:16 PMDRAFT FINAL IU REPORT