PROJECT A-5
In Situ Sub-Surface Soil and Groundwater Treatment
University, Boston, MA
PROBLEM:
Hydrocarbon contaminated soils around underground storage tank
A historical release of petroleum hydrocarbons (fuel oil) was
discovered around a 10,000 gallon capacity underground storage tank
(UST) located between a building and a sidewalk at a major university
in Boston. Initial response actions performed at the site included
removal of two USTs, and excavation and removal of contaminated
soil. However, excavation activities were terminated due to structural
concerns for the adjacent building and sidewalk, as well as safety
concerns for the university population and general public. The
excavation was back filled following installation of a replacement
UST. Results of a follow-up subsurface investigation indicated that a
significant amount of contaminated soil remained in the (groundwater)
saturated zone at depths between 12 and 20 feet. Concentrations of
Extractable Petroleum Hydrocarbon (EPH) fractions exceeded
Massachusetts Contingency Plan (MCP) risk characterization (cleanup)
standards. The highest EPH concentrations in the soil were between
2,300 ppm and 3,540 ppm. EPH fractions were not detected in the
groundwater.
SOLUTION:
In situ bioremediation to reduce petroleum hydrocarbon concentrations
In situ bioremediation was the selected response action
utilized to reduce the petroleum hydrocarbon concen-trations. The
Massachusetts Department of Environmental Protection (MADEP) approved
the Release Abatement Measure (RAM) Plan for the in situ
bioremediation. Seven bioinjection wells were strategically installed
within the area of concern, and a blend of MicroSorb®
SC (Super Concentrate), MicroSorb® Nutrients, and
MicroSorb® Biocatalyst were introduced into the
subsurface via low pressure injection pumping through the bioinjection
wells.
RESULTS:
Concentrations of hydrocarbons reduced to levels below applicable MCP risk characterization
standards
Groundwater monitoring performed in March, 1998, indicated that
petroleum hydrocarbons were virtually nondetected in the ground
water. Confirmatory soil sampling nine months following initial
injection of the subsurface as well as analytical test data indicated
that concentrations of EPH fractions in the soils had been reduced
between 90 -98%. Average EPH concentration was well below risk
characterization (cleanup) standards. The results of the monitoring
and confirmatory testing programs indicated that concentrations of
petroleum hydrocarbons in the subsurface (soil and groundwater) media
had been successfully reduced to levels below applicable MCP risk
characterization standards. The Massachusetts DEP audited the site
remediation and concluded the remediation met all standards.
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