Environmental Engineering Reference
In-Depth Information
TABLE 10.8
CRF SOIL Values for Common LNAPL VOCs
LNAPL Compound
CRF SOIL
Soil Type
Benzene
Clay
10.00
Silty clay
2.50
Sand silty clay
2.30
Sand
1.90
Toluene
Clay
12.76
Silty clay
1.97
Sand silty clay
1.79
Sand
1.07
Ethyl benzene
Clay
74.80
Silty clay
9.60
Sand silty clay
8.40
Sand
4.20
Xylenes
Clay
23.13
Silty clay
3.43
Sand silty clay
3.10
Sand
1.80
Mean LNAPL CRF SOIL
Clay
30.17
Silty clay
4.37
Sand silty clay
3.89
Sand
2.24
The CRF SOIL values for PAH compounds are significantly higher than the CRF SOIL for
LNAPL VOCs, because PAHs strongly sorb to soil particles and are much less soluble in
water (Kaufman et al. 2009).
Table 10.11 summarizes the CRF SOIL for the LNAPL and DNAPL VOCs, PAHs, and lists
the CRF SOIL for total PCBs, the pesticide chlordane, and the heavy metals chromium VI,
lead, mercury, and arsenic (Rogers et al. 2007b; Kaufman et al. 2009).
Contaminants with the highest CRF SOIL are mercury, chlordane, PCBs, arsenic, and
PAHs, respectively. These contaminants strongly sorb to soil particles and tend not to be
very soluble in water. DNAPL compounds also have rather elevated CRF SOIL , especially in
soil composed of clay because they also strongly sorb to fine-grained soils. LNAPL VOCs
and chromium VI had the lowest CRF SOIL . LNAPL VOCs have rather short half-lives in soil
and chromium VI does not strongly sorb to soil grains and is rather soluble.
When the data in Table 10.11 are graphed, it becomes clear that the highest CRF SOIL in
each group occurs in soils composed of clay. Clay soils have the lowest permeability and
have more surface area available for contaminants with high sorptive potential. Therefore,
contaminants with low water solubility and high relative sorptive potentials will have
high CRF SOIL values in clay-rich soils (Figure 10.6).
Figure 10.6 indicates mercury has the highest CRF SOIL and chromium VI has the lowest.
Chromium VI's low CRF SOIL results from its high relative water solubility and low sorptive
potential. On the other hand, mercury has a high sorptive potential and low water solubil-
ity, and checks in with a high CRF SOIL . It should also be noted that for every contaminant
the CRF SOIL value is the highest in clay, a consequence of this soil texture acting to impede
the migration of contaminants.
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