World's Largest In Situ Thermal Desorption Project: Challenges and Solutions

Abstract

This paper presents the largest In Situ Thermal Desorption (ISTD) project completed to date. The redevelopment of a former aerospace manufacturing facility adjacent to a commercial airport was the main driver, requiring relatively rapid reduction of several chlorinated volatile organic compounds (CVOC) in a 3.2‐acre source zone. The source zone was divided into four quadrants with differing treatment depths, 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. Prior to implementation, a risk and optimization study led to placement of a vertical sheet‐pile wall around the treatment zone to minimize groundwater flow, and a pilot test of a novel direct‐drive method for installation of the heater casings. Because of a shallow water table, a layer of clean fill was placed over the treatment zone, and partial dewatering was necessary prior to heating. A network of vertical multiphase extraction wells and horizontal vapor extraction wells was used to establish hydraulic and pneumatic control and to capture the contaminants. The site was split into four decision units, each with a rigorous soil sampling program which included collecting a total of 270 confirmatory soil samples from locations with the highest pretreatment CVOC concentrations requiring reduction to below 1 mg/kg for each contaminant. Temperature monitoring and mass removal trends were used to trigger the sampling events. Eventually, 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. The total energy usage for heating and treating the source area was 23 million kWh—slightly lower than the estimated 26.5 million kWh. Actual energy losses and the energy removal associated with the extracted steam were lower than anticipated. An estimated 13,400 kg (29,800 lbs) of CVOC mass was removed, and all soil goals were met. This paper presents the challenges associated with a project of this scale and describes the solutions to successfully complete the ISTD remedy.

Strategies for Managing Risk due to Back Diffusion

“…Most applications as described in the peer‐reviewed literature have focused on treatment of primary source zones (e.g., NAPL contamination) rather than secondary source zones associated with back diffusion (Beyke and Fleming 2005; Davis et al 2005; Heron et al 2005, 2009, 2013, 2015; Smart 2005; Powell et al 2007; Truex et al 2009; Beyke et al 2014). Assessments of thermal treatment as a DNAPL primary source zone remediation technology based on performance at multiple sites can be found in several papers (McGuire et al 2006; Triplett Kingston et al 2010, 2012; Baker et al 2016).…”

Independent Review of Elemental Phosphorus Remediation at the Eastern Michaud Flats FMC Operable Unit near Pocatello, Idaho

“…In this situation, heating to a temperature of 100°C drives off the VOCs effectively. For example, in the largest in situ thermal desorption project undertaken to date (Heron et al 2015), a 3.2-acre site was remediated by using more than 900 thermal conduction heater wells targeting multiple depths. Such heater borings and their casings can be installed by vibratory push or by augering.…”

Experimental and Simulation Studies on the Capture of Chlorinated Volatile Organic Compounds by Ionic Liquids

“…26 Moreover, the desorption process often comes with high temperature, high energy consumption, and absorbent volatilization, causing serious secondary pollution. 27 In recent years, ionic liquids (ILs) have been favored by researchers as ideal green solvents due to their near-zero vapor pressure, nontoxicity, low viscosity, high thermal stability, and designability, which is beneficial for reducing the absorbent volatile loss and thermal decomposition loss. 28−32 Therefore, the adoption of ILs for the capture of CVOCs is a promising approach.…”