Contaminant Risk Factors - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 350

TABLE 10.2
CRF GW for Common VOC LNAPLs
LNAPL Compound

Soil Type CRF GW

Benzene Clay 3.64

Silty clay 14.50

Sand silty clay 15.40

Sand 19.40

Toluene Clay 0.63

Silty clay 4.10

Sand silty clay 4.53

Sand 7.53

Ethyl benzene Clay 0.27

Silty clay 2.10

Sand silty clay 2.40

Sand 4.80

Xylenes Clay 1.10

Silty clay 7.80

Sand silty clay 8.10

Sand 13.90

Mean LNAPL CRF GW Clay 1.41

Silty clay 7.12

Sand silty clay 7.60

Sand 11.40

Table 10.3 lists the CRF GW for common VOCs from the DNAPL group (Kaufman et al.
2005; Rogers et al. 2007a).
Examination of the CRF GW for DNAPL compounds indicates they are much greater than
those of the LNAPL compounds listed in Table 10.2. The comparatively higher CRF GW
of DNAPLs stems not from their relative toxicity, but from their higher persistence and
mobility in groundwater compared to the LNAPL compounds (Rogers et al. 2007a).
Table 10.4 lists the CRF GW for common PAHs.
The CRF GW for PAH compounds are significantly lower than the CRF GW for DNAPL and
LNAPL VOCs. This difference occurs because PAHs strongly sorb to soil particles and are
much less soluble in water compared to the VOCs examined (Rogers et al. 2007a).
Table 10.5 contains a summary of CRF GW for the LNAPL and DNAPL VOCs, PAHs, and
includes the CRF GW for total PCBs, the pesticide chlordane, and the heavy metals chro-
mium VI, lead, mercury, and arsenic.
The contaminant with the highest CRF GW is chromium VI, followed by DNAPL VOCs,
LNAPL VOCs, mercury, and lead, with their CRF GW ranging from 100 to 10,000 times less
than chromium VI. Contaminants with the lowest CRF GW include chlordane, PAHs, and
the PCBs having a CRF GW more than a billion times lower than chromium VI.
The distributions of CRF GW are shown in Figure 10.5.
Examination of the CRF GW values in Figure 10.5 reveals a grouping of contaminants
into three distinct levels. Chlordane, PCBs, and PAHs form the group with low CRF GW ;
lead, mercury, and LNAPLs constitute the moderate range; and Chromium VI and DNAPL
compounds appear on the top of the figure with the highest CRF GW . Chlordane, PCBs, and
PAHs are very toxic and persistent contaminants in the environment, but they strongly