PROJECT A-7
In Situ Sub-Surface Soil and Groundwater Treatment
Machine Shop, Whitman, MA
PROBLEM:
Groundwater contaminated by solvents; concentrations exceeded MA drinking water stan-dards
At a machine shop groundwater was contaminated with perchloroethylene,
trichloroethylene, and other industrial solvents. This was caused by a
surface release of used industrial degreasers. Both overburden and
bedrock aquifers were impacted. Assessment of the site indicated that
the two are in hydraulic continuity. Eight years and over 5 million
gallons of traditional pump and treat remediation had not reduced site
contami-nant concentrations to the Massachusetts drinking water
standards.
SOLUTION:
Inject MicroSorb® DC, MicroSorb® Nutrients, and MicroSorb® Biocatalyst into bedrock surface
In 1997, a program of in situ bioremediation was initiated. Thirty-two
inoculation points were driven to the bedrock surface and set with 1/2
inch diameter PVC well screen. The points were arranged in a grid
pattern from upgradient of the known extent of contamination to the
property boundaries. MicroSorb®DC (De-Chlorinator
Product) was mixed with MicroSorb® Nutrients and
MicroSorb® Biocatalyst and injected into the points and
impacted monitoring wells. Groundwater samples were collected prior to
the first inoculation in April, 1997. A second inoculation round was
implemented in September, 1997. The goal was to achieve PCE
concentrations of 5 mg/L throughout the site.
RESULTS:
PCE concentrations are reduced and continue to decline
PCE concentrations declined at an average rate of 50% each quarter. In
the most contaminated area, concen-trations were reduced from 120 to
28 mg/L in six months. In a less contaminated area, concentrations
de-clined from 77 to 11 mg/L. Site closure is anticipated within 12 to
18 months. The table indicates PCE levels in three bedrock wells:
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