Dames & Moore, 1999 - USDA Forest Service

No Method A levels are available for air, or home-grown produce. For home-grown produce it was
assumed that if the maximum concentration of the constituent was below the Method A level for soil. then
ingestion of produce grown in that soil would not present a significant risk. Table 7.1-2 lists the Method A
level used for each constituent along with its source. Because of the conservatism used in deriving Method
A levels, no adjustments to the cleanup levels to account for exposure to multiple constituents were
performed.
Method B Levels
If the maximum concentration of a constituent was less than the relevant MTCA Method B level. it was
considered to contribute a small percentage of the overall risk and was eliminated as an IHS. Method B
levels are developed using standard equations and were obtained from hide1 Toxics Conrrol.4cr Cleanup
Levels and Risk Calculations (CLARC I4 Update (Ecology, 1996). Similar media-specific cleanup levels as
discussed above (Section J-3.1.2.4) were used for each exposure medium. MTCA Method B levels for air
were also utilized. When a cleanup level was not available for a constituent detected at the Site, it was
calculated using equations and standard exposure parameters provided by MTCA if toxicity criteria were
available. In addition, all Method B levels for air were calculated because the 1996 CLARC I1 tables do not
include air cleanup levels. Table 7.1-3 lists the Method B criteria used for each constituent along with its
source. Table 7.1-4 details the toxicity criteria and bioconcentration factors used in calculating cleanup
criteria for non-published constituents. Toxicity criteria are discussed in more detail in the site-specific
HHRA.
Adiustment for Total Risk and Hazard Index
The total risk associated with a site must not exceed 1 x 10" and the hazard index for each target organ must
not exceed one (WAC 173-340-708[5]). Therefore, Method B criteria were reduced to account for the
number of constituents in each group potentially found at the site. Table 7.1-5 lists the carcinogen
classification and toxic effects endpoints, where available, for the constituents detected at the site.
Based on the carcinogen classifications, the following constituents are considered carcinogens by MTCA:
arsenic, beryllium, cadmium, chromium VI, lead, nickel (refinery dust), and PCBs. For each constituent, the
acceptable risk level on which the Method B level is based (and thus the resulting screening level) was
divided by the number of carcinogens at the site (seven constituents) to assurk that the aggregate risk does
not exceed 1 x 10":The Method B levels listed in the screening tables reflect this adjustment.
For non-cancer effects, the analytes can be grouped together by toxic effects endpoints as follow:
Hemotoxicity: antimony, zinc (2 constituents)
Skin toxicity: arsenic, silver (2 constituents)
Nephrotoxicity: cadmium, mercury, molybdenum. uranium (4 constituents)
Neurotoxicity: lead, manganese, mercury, cyanide (4 constituents)
Weight effects: nickel, uranium, cyanide, Aroclor 101 6 (4 constituents)
For each constituent,'the acceptable hazard index on which the Method B level is based (e.g., acceptable
hazard index of one), and thus the resulting screening level, was divided by the number of chemicals in the
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