Contaminant Risk Factors - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 374

For all the sites tested, those contaminated with chromium VI and DNAPL compounds
located within a geological setting of sand exhibited the highest extent of contamination
and cost of remediation per kilogram of contaminant recovered.
There still is much work needed on risk scores. Contaminant risk factors of other con-
taminants such as ozone, sulfur dioxide, greenhouse gases, viruses, bacteria, acids and
bases, and fertilizers have not yet been calculated. The main reasons for this are (1) there
is a lack of data required to calculate a CRF, (2) some uncertainties exist in assessing risk
for certain contaminants such as bacteria and carbon dioxide, and (3) the appropriateness
and scientific justification for the use of weighting factors in calculating CRFs for these
compounds are still unknown.
10.7 Summary and Conclusion
CRFs for air, groundwater, and soil provide a powerful tool for assessing risks posed by
contaminants anywhere in the environment. They are derived by combining the three
physical/chemical attributes of toxicity, mobility, and persistence. CRF analysis has dem-
onstrated why some contaminants prefer certain locations or sinks. For instance, CRF
analysis has shown why PCBs and mercury prefer soil or sediments instead of being pres-
ent as dissolved constituents in groundwater.
Combining geological vulnerability analysis with CRF analysis can reveal and explain
potential synergistic effects. Examples of synergy occur when DNAPLs and chromium
VI are released in a vulnerable geologic setting, such as one with a sandy soil, shallow
groundwater, and current use as a potable source of water. Under these conditions, the
potential for adverse human health and ecological impact greatly increases, and is unfor-
tunately often realized. With CRF and geological vulnerability analysis now in hand, these
situations can be avoided in the future with proper urban planning.
CRF analysis employing the risks posed by surface releases, added to the risk factors for
groundwater, soil, and air also has predictive power for evaluating and assessing future
cleanup costs for sites of contamination. This ability has major implications for the rede-
velopment of urban areas, and we explore this in later chapters.
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Eckhardt, D.A.V. and P.E. Stackelberg. 1995. Relation of groundwater quality to land use on Long
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Howard, H.H., R.S. Boethling, W.F. Jarvis et al. 1991. Handbook of Environmental Degradation Rates .
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