Contaminant Risk Factors - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 351

TABLE 10.3
CRF GW for Common VOC DNAPLs
LNAPL Compound

Soil Type CRF GW

Tetrachloroethene (PCE) Clay 98.0

Silty clay 601.0

Sand silty clay 657.0

Sand 1048.0

Trichloroethene (TCE) Clay 148.0

Silty clay 933.0

Sand silty clay 1018.0

Sand 1647.0

cis -1,2-Dichloroethene Clay 228.0

Silty clay 702.0

Sand silty clay 730.0

Sand 851.0

trans -1,2-Dichloroethene Clay 131.0

Silty clay 495.0

Sand silty clay 520.0

Sand 647.0

Vinyl chloride Clay 860.0

Silty clay 1911.0

Sand silty clay 1962.0

Sand 2132.0

1,1,1-Trichloroethane (1,1,1-TCA) Clay 2.1

Silty clay 11.0

Sand silty clay 12.0

Sand 17.3

Mean DNAPL CRF GW for degradation
sequence from PCE to vinyl chloride a
(Figure 7.4)

Clay 333.0

Silty clay 773.0

Sand silty clay 1091.0

Sand 1274.0

a Represents cumulative risk.

sorb to soil and are not very soluble in water. As a result, they have very low CRF GW com-
pared to the other contaminants listed.
The middle grouping has moderate CRF GW resulting from a combination of factors
unique to each contaminant. LNAPLs have moderate mobility and the ability to degrade in
the environment. Mercury is not very mobile but may become transformed in the environ-
ment to methyl mercury, a change allowing it to be adsorbed by organisms that increases
its environmental risk. Lead has low solubility in water but is very persistent. Arsenic has
a much higher CRF GW compared to lead because it is more soluble and toxic.
The group consisting of chromium VI and DNAPL compounds has the highest CRF GW
values. Some of these values may be more than a million times greater than the contami-
nants in the lowest group. This magnitude of difference occurs because chromium VI
and DNAPL compounds have relatively high toxicity, mobility, and persistence in the
environment.