Metal Contamination in Urban Watersheds - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 337

than its trivalent form—and has greater potential to damage the environment and impact
human health. This is especially significant since hexavalent chromium has a high con-
taminant risk factor, which will be examined in great detail in Chapter 10. Significantly
high contamination ratios were demonstrated by Cr, Cd, and Pb within the watershed's
sand unit, but there were also several metals detected at concentrations exceeding their
MCLs in clay-related soil units, indicating the existence of some mobility within a soil
medium previously considered virtually immobile for metals.
These findings create considerable environmental concern because of the hydraulic con-
nection between the watershed's surface waters and the Great Lakes. Moreover, many
private and public wells use the groundwater within the region for potable water, thus
creating a potential public health risk.
In the next chapter, a model is developed and applied within an urbanized watershed to
help predict the risks posed by specific contaminants to soils, groundwater, and air.
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