Contaminant Risk Factors - Urban Watersheds: Geology, Contamination, and Sustainable Development - page 355

TABLE 10.6
Critical Information Obtained from Sites of Environmental Contamination

Category Description

Contaminant General chemical category (e.g., DNAPL)

Type of facility Primary activity at the site (dry cleaning, foundry, etc.)

Geology Composition, stratigraphy, and other information on subsurface units

Remedial technology for
groundwater

Contaminant abatement method (e.g., air sparging, pump and treat, in situ chemical
or biological treatment, natural attenuation)

Remedial technology for
soil

Contaminant abatement method (e.g., excavation, capping, soil vapor extraction,
institutional controls)

Mass (kg) Total mass of contamination at site

Cost Total cost of investigation and remediation from start to finish

Media remediated Soil, water, or other (e.g., building decontamination, demolition)

Extent (m) Measured extent of contamination in each media affected

Cost/kg Cost of investigation and remediation per kilogram of contaminant

Years of operation Number of years the facility had been in operation

Geologic vulnerability Geologic vulnerability rating (see Table 6.1)

Surface risk factor Average surface risk (Section 10.2 and Table 10.1)

CRF GW CRF GW calculated for each contaminant (see Section 10.3, Equation 10.5)

Soil cost Amount of the total remediation cost attributed to soil

Soil cost/kg Cost per kilogram to remediate soil

Groundwater cost Amount of the total remediation cost attributed to groundwater

Groundwater cost/kg Cost per kilogram to remediate groundwater

Groundwater mass (kg) Mass of groundwater remediated at the site

10.4 Soil Contaminant Risk Factor
In most cases, contaminants released to the ground surface migrate downward through
the upper soil layers. Over time, they may or may not contaminate groundwater. Therefore,
evaluating the potential for a chemical to contaminate the soil should also be conducted
whenever there is a potential for it to contaminate groundwater. Development of the Soil
Contaminant Risk Factors (CRF SOIL ) should be a high priority in urban watersheds because
it provides an additional piece for characterizing the total risks posed by contaminants in
the environment.
The migration potential of a contaminant in soil is dependent upon the same physical
and chemical attributes as those found in groundwater: solubility, vapor pressure, den-
sity, chemical stability, persistence, and adsorption potential. There is also a biological
interaction between the contaminant and the soil environment to which the chemical is
released (Schnoor 1996) and, as with the CRF GW , is accounted for within the persistence
factor.
Given the similarities between the two processes, developing the CRF SOIL requires
rather simple modifications to the CRF GW equation. The CRF SOIL is calculated by mul-
tiplying the inverse of a chemical's toxicity (T), by its mobility (M) and persistence (P)
(Equation 10.6). The change in the equation is reflected in the mobility factor, where it