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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