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Remedial Action Objective -- Prevent the migration of contamination from the source
area that would result in degradation of site-wide groundwater or surface water to levels
in excess of state or federal standards or that pose a threat to human health or the
environment.
How Alternative will meet RAO -- The removal of free product NAPL, as well as those soils
containing contamination in concentrations contributing to groundwater contamination in excess
of ARARs will be excavated and treated. Following the LTTD, the leachate containment
system will extract remaining leachate contamination until ARARs are met at the GMZ
boundary.
AREA 7
Alternatives SCS-7E (Soil Vapor Extraction and Air Sparging) and SCL-7B (Multi-phase Extraction
with Leachate Containment and Treatment) are the preferred alternatives for Area 7. These alternatives
are recommended because they would achieve substantial risk reduction in consideration of cost.
Alternatives SCS-7E and SCL-7B reduce risks substantially by treating the source materials constituting
principal threats at the site.
Under these alternatives, the in situ technologies soil vapor extraction, air sparging, and multi-phase
extraction would work in concert to treat contaminants in unsaturated and saturated soil and leachate in
Source Area 7. The SVE system would extract vapors from suspected hot spots through sixteen
vacuum extraction wells. Wells would be constructed to a depth of up to 25 feet and screened in the
vadose zone, where they will extract volatile contaminants from the unsaturated zone, as well as some
leachate contaminants that are able to volatilize from the surface of the water table. The estimated flow
rate for the SVE system is 1200 scfm.
An air sparging system would be constructed to volatilize VOCs from saturated soils and leachate
through the injection of air. VOCs would be collected through the SVE system from contaminated soil.
A total of 53 air-sparging wells would be constructed to a depth of 50 feet bgs. CDM has assumed a
radius of influence of 25 feet for the air sparging wells. Two air compressors would be used to inject air
to the subsurface, each at a rate of 400 scfm, for a total of 800 scfm.
A MPE system would focus on the hot spot areas where either highly contaminated soils or NAPL
exists. The MPE system would extract a combination of the following phases: NAPLs; groundwater
(leachate); and soil vapor. Ten MPE wells would be installed into the hot spots to a depth of
approximately 25 feet.
Lastly, a leachate containment system consisting of eight leachate extraction wells, a central pump
station, an air-stripping unit, piping and controls would be installed. A containment system would focus
on contaminated leachate along the down-gradient side of the GMZ. Leachate would be collected in
the extraction wells and pumped to the air-stripping unit at a rate of 10 gpm.
