Martinsville Closed Landfill In Situ Thermal Desorption
ISTD Remediation Achieves an Average 96% Reduction of VOC Concentrations in Landfill Solvent Pit Soils
The Martinsville Sanitary Landfill is a closed, unlined, municipal solid waste facility owned and maintained by the City of Martinsville, Virginia. Starting in the early 1970s and into the early 1980s, there were two solvent pits located upgradient of the landfill that were designated for disposal of liquid chemical wastes, primarily used paints, varnishes, and solvents produced by the local furniture and textile industries. These were unlined open pits into which the local industries would dump their used chemicals, usually several drums at a time. Periodically, the landfill staff would set fire to the liquids in the pits and let them burn.
A plume of groundwater contamination containing numerous volatile organic chemicals (VOCs) extends under the landfill from the two solvent pits. The facility has been under a groundwater Corrective Action Program involving monitored natural attenuation since 2005; however, the soil contamination in the solvent pits was a continuing source feeding the groundwater plume, so the contaminant concentrations were not generally decreasing as hoped and some were increasing over time.
In 2016, at the request of the Virginia Department of Environmental Quality (VDEQ), LaBella conducted further assessment of the solvent pits and investigated remedial alternatives. Soil sampling found total VOCs as high as 12,675 mg/kg (parts per million) and indicated that there were over 105 tons of VOCs in the soil within the two solvent pits.
LaBella evaluated several potential remedial technologies for the solvent pits for applicability, effectiveness, time required, and cost. The evaluated technologies included excavation and ex situ incineration in an on-site soil burner, enhanced bioremediation using injection of chemicals to accelerate natural biodegradation of the contaminants by bacteria in the soil, air sparging and soil vapor extraction, and in situ thermal desorption (ISTD).
We concluded that ISTD would be the most appropriate technology for this site based on the site geology, the size and depth of the pits, and the types and concentrations of contaminants. ISTD was expected to be the fastest as well as the most cost-effective way to remediate the solvent pit soils. ISTD involves heating the subsurface to temperatures around the boiling point of the contaminants, thus fully releasing the volatile compounds in the soil and groundwater to be drawn off as steam and vapor through a vapor collection system. The vapors are then treated to remove most of the VOCs before being released to the atmosphere.
We submitted an Interim Measures Work Plan proposing ISTD, which was approved by VDEQ in October 2016. Next, we prepared design specifications and a Request for Proposals to solicit bids for turn-key implementation of the ISTD remedy for the two solvent pits. The winning proposal was from Good Earthkeeping Organization for an ISTD system using natural gas thermal conductive heating.
Installation of the ISTD system began in February 2019, and the system commenced operation in May 2019. The ISTD system operated for a total of 165 days and was shut down in November 2019. More than 141.5 tons of VOCs were removed as vapors from the two solvent pits during the ISTD project. This does not include the 32,100 gallons of condensate that were also recovered. Confirmatory soil sampling after the ISTD remediation indicated an average 96% reduction of VOC concentrations in the soils in the two pits.
The majority of the VOC vapors extracted were fed back into the heater wells as supplemental fuel, effectively destroying those VOCs while increasing the efficiency of the system. The off-gas treatment system achieved greater than 95% removal efficiency during the entire project.
We consider this ISTD project to have been extremely successful and the concentrations of VOCs in the two solvent pits have been greatly reduced. As these solvent pits were the primary source of groundwater contamination at the Martinsville Landfill facility, we expect to see a reduction in the VOC concentrations in the groundwater over time.
Case Study: In Situ Thermal Remediation at the Martinsville Landfill