Contaminant Risk Factors - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 354

10,000

1,000

100

10

Chromium VI
DNAPL
Arsenic
LNAPL
Hg
Lead
PAHs
Chlordane
PCBs

1

0.1

0.01

0.001

0.0001

0.00001

0.000001

Clay Silty clay Sand and

silty clay

Sand

FIGURE 10.5
Distribution of CRF GW .

CRF GW should be detected in groundwater at greater distances from their source than
contaminants with low CRF GW . Specifically, sites contaminated with chromium VI and
VOC DNAPLs should exhibit greater contamination extents than sites contaminated by
the other chemical compounds evaluated.
To test this hypothesis, 83 contaminated sites within the Rouge River watershed and
127 additional sites located outside the Rouge River watershed were evaluated. The
Rouge sites were located on different types of geological units, and the external sites
were located in areas of varied subsurface geology and contaminant type (Kaufman et
al. 2005). Of the 127 sites located outside the Rouge River watershed, 117 were distributed
among 32 different states, with the remaining 10 sites located in other countries includ-
ing Canada, Italy, England, France, Belgium, South Africa, and Australia. All 210 sites
were located in urban areas with varying geology composed of unconsolidated sedi-
ments originating from lacustrine, fluvial, or glacial processes. The critical information
gathered from each of the 210 sites is described in Table 10.6 (Kaufman et al. 2005; Rogers
et al. 2007a,b). A summary of the data is listed in Table 10.7 (Kaufman et al. 2005; Rogers
et al. 2007a,b).
A scan down the rightmost column (average extent from source) of Table 10.7 strongly
validates the hypothesis: sites contaminated with chromium VI and VOC DNAPLs do
exhibit greater contamination extents than sites contaminated by the other chemical com-
pounds. The top 4 average extents are 2200 m (eight world sites, chromium in sand), 1012 m
(eight Rouge watershed sites, DNAPL in sand), 975 m (15 world sites, DNAPL in sand),
and 625 m (four Rouge watershed sites, DNAPL in moraine). The next ranked average
extent is almost twice as small (328 m) found in eight LNAPL sand sites within the Rouge
watershed. Strong empirical evidence indicates a positive association between a chemical's
CRF GW and its likelihood to migrate.
Since contamination affects other media such as soil and air, we must also develop
Contaminant Risk Factors for those media.