Dames & Moore, 1999 - USDA Forest Service

corresponding grouping. The Method B levels listed in the screening tables have been adjusted in this
manner.
Method B Criteria for Manganese
The CLARC fl Method B levels for manganese for soil and water are based on an oral reference dose (RfD)
developed by USEPA. The Rfl) was derived 6om data on total dietary intake of manganese. USEPA
(IRIS, 1998) and MTCA (Ecology, 1996) recommend that a modifying factor of three be applied to the IUD
if it is used for assessments involving nondietary exposures. Since exposure to manganese at the Site would
primarily be nondietary, the IUD, and thus the cleanup criteria listed in CLARC 11, have been adjusted
downward by a factor of three. This adjustment is reflected in the cleanup levels shown in Table 7.1-3.
Soil to Air Pathway
For the soil to air pathway (i.e., padculate emissions h m soil), soil cleanup criteria were calculated using
the methodology in Soil Screening Guidrmce: Technical Background Document (USEPA, 1996). The
MTCA Method B levels for air were considered to be the acceptable air concentration. A particulate
emission factor (PEF) was then calculated that relates the concentration of compound of concern in soil to
the concentration of dust particles in air. The PEF represents an annual average emission rate based on wind
erosion that can be compared with chronic health criteria. The equation for calculating the PEF is as
follows:
PEF (m3/kg) =Q/C x
where:
3600
0.036 x (1 - V) x (U , / u , )' x F(x)
PEF = Particulate emission factor (m3/kg)
QIC = Inverse of mean concentration at center of source (g/m2-s per
kg/m3) = 42.86
V = Fraction of vegetative cover = 0.5
Um = Mean annual windspeed (mls) = 4.69
Ut = Equivalent threshold value of windspeed at 7 m (rnls) =
1 1.32
F(x) = Function dependent on Um/Ut = 0.194
QIC was selected from the Soil Screening Guidance for the closest geographical area (Seattle) and the
largest source size (30 acre). Default values given in the Soil Screening Guidance were used for all other
variables. Based on this equation, the calculated PEF for the site was 6.21 x 10' m3/kg. The acceptable air
concentration (Method B level for air) was multiplied by the PEF.to derive the Method B levels for soil
based on protection of air. The Method B levels for soil based on protection of air are listed in Table 7.1-3.
G:\wpdrmW)~\hoIQn-2\n~7-o.doe
17693-005419Wuly 27.1999;5:16 PMDRAIT FINAL R1 REPORT