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Dames & Moore, 1999 - USDA Forest Service

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Selection of.Target Risk and Hazard Index<br />

As specified in MTCA, a target risk level of 1 x 10" and a target hazard quotient of one were selected for<br />

development of the'Method C levels (WAC 173-340-700[j][c]). Cumulative risk is also evaluated in the<br />

risk characterization section. MTCA specifies that the curnularive cancer risk must not exceed 1 x 10" and<br />

the cumulative hazard index for each toxic effect endpoint must not exceed one.<br />

Development of Method C Levels<br />

Method C levels are summarized in Table 7.1-40. The following equations were utilized for calculating<br />

site-specific Method C criteria:<br />

Ingestion of Soil and Sediment<br />

Screening criteria cleanup levels based on ingestion of soil in a residential setting are developed assuming a<br />

child's exposure. Screening criteria for the maintenance area and USFS guard station were developed<br />

assuming adult exposures. Equations for this pathway are as follows:<br />

Carcinogens:<br />

RISK x ABW 1 x LIFE x UCF<br />

Screening Criteria (mgkg) =<br />

CPFxSIRx ABlx DURlx FOCI<br />

Noncarcinogens:<br />

where:<br />

Screening Criteria (mgkg) = RfDxABWlxUCFxHQ<br />

SIR x ABI x FOCI<br />

RISK = Acceptable cancer risk level (unitless)<br />

ABW 1 = Average body weight over period of exposure (kg)<br />

LIFE = Lifetime (years)<br />

UCF = Unit conversion factor (1,000,000 mgtkg)<br />

CPF = Cancer potency factor (kg-daylmg)<br />

IUD = Reference dose (mgkg-day)<br />

SIR = Soil ingestion rate (mglday)<br />

ABl = Gastrointestinal absorption rate (unitless)<br />

DURl = Duration of exposure (years)<br />

FOC l = Frequency of contact (unitless)<br />

C:\~pdrtlUWIS\rrponrUloldm-2\ri\74~doc 7-27<br />

17693405419Uuly 27. <strong>1999</strong>5: 16 PMDRAFT FINAL RI REPORT

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