Manufactured
Gas Plant
Easton, Maryland
The subject Site was originally a privately owned manufactured gas
plant (MGP) that employed coal gasification to produce fuel gas for
public use between 1860 and 1961. Coal tar, a primary by-product of
coal gasification, was found in subsurface soil. Coal tar consists
primarily of polycyclic aromatic hydrocarbons (PAHs). CGS was
contracted by the Maryland Department of Environment, Environmental
Restoration and Redevelopment Program (MDE-ERRP) to provide for
remediation and safe disposition of the Site under the State Superfund
Program.
Investigation activities
included the installation and sampling of soil borings, groundwater
piezometers and monitoring wells, indoor air sampling, and soil
porosity and permeability analysis. Investigation costs were reduced by
using immunoassay and x-ray fluorescence field analyses.
Soil borings revealed that
coarse sand sediments in the subsurface were saturated with black,
oily, liquid coal tar. This zone of saturation occurred below the water
table at depths between 5 and 28 feet below grade. Low permeability
clay sediments were found surrounding the coal tar saturated sands
which limited liquid coal tar and groundwater contaminant
migration.
Shallow soil (0 to 2 feet
deep),covering an area of approximately 1/2 acre, were found to contain
elevated levels of PAHs, arsenic, lead, and manganese that were
attributable to former MGP operations. CGS performed a comprehensive
Risk Assessment that indicated that dermal contact and incidental
ingestion of this shallow soil constituted the primary source of
unacceptable health risk at the Site. Remedial activities were required
to eliminate potential health risks and to make the Site available for
future beneficial use. CGS performed a Feasibility Study to evaluate
potential remedial options. MDE-ERRP approved CGS’s
recommended risk-based remedial approach consisting of removal of
shallow soil, replacing it with clean backfill, and prohibiting all
deep excavations and groundwater withdrawal in the area. This remedial
approach will allow for the redevelopment, planned for the Site, to be
safely implemented.
CGS authored the specification
for a Removal Action that went out to public bid. The Removal Action
was performed in December 2003 and was comprised of the excavation and
removal of contaminated soil to the depth of the static groundwater
level over the area of the former GMP building and the location of the
proposed building. The static groundwater level in December 2003 was
approximately 3 feet below grade. A total of 2,882 tons of soil were
excavated and taken off-site for disposal. CGS provided oversight of
installation of sediment and erosion control requirements, site
demolition, excavation of contaminated soil, and clean backfill
placement, compaction, geotechnical testing, and grading to ensure
compliance with the specification and plans for construction of the
proposed building. CGS installed vapor mitigation measures in the
neighboring building and performed air monitoring during soil
excavation.
Well installation. |
Before soil excavation activities. |
Concrete/asphalt rubble loading. |
Soil excavation. |
Excavation liner and backfilling. |
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ADDITIONAL PROJECT
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