TerraTherm and its In Situ Thermal Desorption (ISTD) sublicense holders have cleaned close to 50 sites, but what happens when we are presented with one that is remarkably large with more than 100,000 cubic yards (76,500 m3) of PCE and TCE rich soils to a depth of over 40 feet (12 m)? The site in particular that was presented to TerraTherm was a former aerospace manufacturing facility and had to be remediated in less than a year.
Successfully completed by TerraTherm, this site in Teterboro, New Jersey is now the largest ISTD project to date.
The redevelopment of this former aerospace manufacturing facility adjacent to a commercial airport was the main driver, requiring relatively rapid reduction of several chlorinated volatile organic compounds (CVOCs) in a 3.2-acre (1.3 ha) source zone. ISTD was chosen over excavation and Electrical Resistance Heating (ERH) due to its proven effectiveness and lower price.
The source zone was divided into four quadrants with differing treatment depths, and heated simultaneously using a total of 907 thermal conduction heater wells. Five different depths were selected across the area, according to the depth of contaminant impact. In this way, the total volume for treatment was minimized.
Had traditional drilling been used, the many heater borings would have meant a drilling cost of over $1 million. Instead, a novel direct-drive method for installation of the heater casings was developed, pilot tested, and deployed to install the heaters much more quickly, without drill cuttings for disposal, and at close to half the cost.
Due to the sheer size of the site, the utility company provided four separate power drops and transformers – one for the process gear and three for the wellfield. This was the most economical method for distributing power to the large area.
The site had really shallow groundwater, sometimes pooling in small ponds on top of the ground. A risk and optimization study led to placement of a vertical sheet-pile wall around the treatment zone to minimize groundwater flow. Due to a shallow water table a layer of clean fill was placed over the treatment zone, and partial dewatering was necessary prior to heating. Horizontal wells were placed in the fill layer to help with vapor extraction and dewatering. In addition, vertical multi-phase extraction wells were placed around the treatment area and used to lower the water table prior to heating.
Again due to its size, the site was split into four decision units, each with a rigorous soil verification program requiring reduction to below 1 mg/kg for each contaminant. This included collecting a total of 270 confirmatory soil samples from locations with the highest pretreatment CVOC concentrations. Temperature monitoring and mass removal trends were used to trigger the sampling events. A small area near the center of the site required the installation of four additional heaters before the soil goals were reached after 238 days of heating. At this time, all samples were below 1 mg/kg for all contaminants of concern.
Large sites may contain a lot of chemical mass. In this case, a robust and large thermal oxidizer was used to treat the 3,000 scfm stream of extracted steam and vapors. An estimated 29,800 lbs (13,400 kg) of CVOC mass was removed, including a substantial amount of CFC-113. Since CFC-113 cannot be treated using carbon filtration, the hydrofluoric acid generated during its destruction in the oxidizer was removed with a scrubber.
For more information on this site, read Ken Parker’s blog post, “Teterboro, NJ – The Biggest In Situ Thermal Desorption (ISTD) Site in the World – Remediation Completed!“, or the TerraTherm Case Study, “Teterboro Landing Brownfield Redevelopment – World’s Largest In Situ Thermal Desorption Site“.