In June 2005, TerraTherm completed a novel MGP site cleanup
under a performance-based contract with National Grid at their
facility in North Adams, MA. The site was a former Manufactured
Gas Plant (MGP) facility operated by the North Adams Gas Light
Company in the late 1800s and early 1900s. A 62-ft diameter by
18-ft deep gasholder tank, located entirely below grade, contained
soil, debris, and coal tar, but National Grid had not been able to
recover significant quantities of the coal tar and needed to clean
the tank to state standards. The usual approach for such sites is
to dig them up and dispose of the soil and waste off-site;
however, National Grid selected TerraTherm's ISTD technology as
less expensive and much greener than excavation. TerraTherm
demonstrated that their choice was well justified!
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After dewatering the gasholder, TerraTherm applied ISTD to
eliminate the dense non-aqueous phase liquid (DNAPL) coal tar and
proceeded to remediate the gasholder using a tailored heating
approach, thereby achieving soil cleanup standards protective of
groundwater, all without excavation.
We first installed 25 thermal wells and employed gentle heating
(~80°C) for thermally enhanced DNAPL recovery, producing over
16,000 gallons of coal tar/emulsion. This was significant, as the
client had expected us to be able to recover several hundred
gallons at the most. We then raised the heating temperatures to
attain the project goals, which a risk assessment had determined
to be distinctly different above versus below 15 ft depth (the
limit of construction worker exposure). Within the mid-section
(above 15 ft depth), we achieved temperatures of 615°F to
volatilize, boil, pyrolyze and oxidize the Polycyclic Aromatic
Hydrocarbons (PAHs). This is our classic ISTD approach. Within the
bottom portion of the gasholder (15-18 ft depth), we attained more
moderate temperatures of 212°F (the boiling point of water) to
remove the DNAPL. In the process we vaporized the benzene and
naphthalene from the entire gasholder. Overall the extracted vapor
contained 165,000 lb expressed as naphthalene, which we treated in
an aboveground thermal oxidizer to meet the required air emissions
standards.
Within the mid-section of the gasholder, elevated heating
produced the following significant reductions in soil
concentrations (mg/kg) that more than met the required standards
at the site: benzene - 2068 to 0.35; naphthalene - 679 to 5.7; and
benzo(a)pyrene - 20 to 0.33. Within the lower portion, more
moderate heating was sufficient to remove all the DNAPL, as
required. In fact the residual material looked much like asphalt -
it was dry, brittle, and the benzene and naphthalene
concentrations were reduced by over 99.5%! National Grid judged
the turnkey cost ($850,000 for ISTD) to be less than the
excavation alternative. TerraTherm conducted the project under a
guaranteed performance contract, meeting all the remedial goals.
We will co-present these results with our National Grid client at
the upcoming MGP2006 Conference in Reading, UK in April 2006, and
at the Battelle Monterey Conference in May
2006. Please contact us
to see how we can apply our tailored heating approach to your MGP
site!
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