PROJECT A-4
In Situ Sub-Surface Soil and Groundwater Treatment
Automobile Dealership, Danvers, MA
PROBLEM:
Hydrocarbon contaminated soils and groundwater present after underground storage tank
removal
A release of petroleum hydrocarbons to the environment was discovered
upon the removal of four under-ground storage tanks (two gasoline and
two waste oil) at a car dealership. During the removal process, total
organic vapor readings exceeded 100 ppm, thus triggering the 72-hour
notification requirement according to the clean-up regulations in
Massachusetts. The Massachusetts DEP gave authorization to conduct an
Immedi-ate Response Action (IRA) for the site. Upon removal of the
tanks, visible holes were identified in all of them. Also, soil
samples taken from each of the tank excavations indicated petroleum
hydrocarbons in excess of reportable concentrations.
SOLUTION:
In situ application of MicroSorb® SC and MicroSorb® Biocatalyst
To determine the extent of the release, four monitoring wells were
installed in and around (both upgradient and downgradient) the
excavations. (Little or no contamination was found in the soils or
groundwater at these locations.) Because of the number of buried
utilities in the area, additional soil removal from the former tank
locations was not a viable solution to the contamination problem. The
in situ application of MicroSorb microbial products was determined to
be the most cost effective and timely solution as a remedial IRA. An
infiltration system of slotted pipe was installed at the top of the
contaminated zone in both former tank excavations. At grade, a
1,000-gallon bioreactor tank was set up and supplied with 20 pounds of
MicroSorb® SC (Super Concentrate),
MicroSorb® Nutrients, water, and 220 gallons of
MicroSorb® Biocatalyst. The bioreactor discharged to
the injection piping bathing the contaminated areas with microbes,
nutri-ents, and biocatalyst (source of oxygen). This liquid stream was
collected downgradient at the groundwater table by means of a recovery
well that would then pump the recovered (treated) groundwater back
into the bioreactor tank for recirculation to the injection
trenches. A second application of microbes, nutrient, and biocatalyst
was applied after 30 days.
RESULTS:
After three months, non-detect levels of EPH, VPH, and targeted VOCs
After three months of operation, groundwater was sampled from the
system with non-detect levels of EPH, VPH, and targeted
VOCs. Confirmatory drilling indicated all groundwater samples and soil
samples (except one minor EPH aliphatic soil sample violation) met
risk characterization standards for closure. A Class A-2 Response
Action Outcome (closure) was submitted for the site.
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