Dense Nonaqueous Phase Liquids (DNAPLs)

Thermal Processes: In Situ

Conductive Heating

Halogenated Alkenes

General Resources

In Situ Thermal Treatment of Chlorinated Solvents: Fundamentals and Field Applications
U.S. EPA. EPA 542-R-04-010, 145 pp, 2004

Contains information about the use of in situ thermal treatment technologies to treat chlorinated solvents in source zones containing free-phase contamination or high concentrations of contaminants that are either sorbed to soil or dissolved in groundwater in the saturated or unsaturated zone.

Case Studies: Chlorinated Solvents

Combining Thermal Treatment with MNA at a Brownfield DNAPL Site
Heron, G., J. LaChance, J. Bierschenk, K. Parker, S. Vinci, R. Woodmansee, and J. Schneider.
Remediation of Chlorinated and Recalcitrant Compounds: Proceedings of the Seventh International Conference on Remediation of Chlorinated and Recalcitrant Compounds (Monterey, CA; May 2010). Paper 384, 2010

A heavily contaminated brownfield site in New York was remediated and redeveloped using a combination of in situ thermal desorption (ISTD) and monitored natural attenuation (NA). Four chlorinated VOC (PCE and TCE) source areas were addressed by the thermal technology, and NA of VOCs in the site groundwater is being monitored. About 86,000 lbs of volatile organics were extracted and treated on site. All the thermally treated areas met the negotiated cleanup standard. Based on current trends, all the wells likely will meet the cleanup goals within 5 or 10 years.

Dense Non Aqueous Phase Liquid (DNAPL) Removal from Fractured Rock Using Thermal Conductive Heating (TCH)
Lebron, C.A., D. Phelan, G. Heron, J. LaChance, S.G. Nielsen, B. Kueper, D. Rodriguez, A. Wemp, D. Baston, P. Lacombe, and F.H. Chapelle.
Contract Report CR-NAVFAC ESC-EV-1202, ESTCP Project ER-200715, 427 pp, Aug 2012

This project conducted (1) treatability studies to ascertain a treatment strategy (duration and temperature) for several rock types, (2) modeling to perform screening calculations and carry out mass estimates, and (3) field application of TCH at Naval Air Warfare Center Trenton, a fractured bedrock site. Treatability study results indicate that heating duration had a greater effect on the degree of PCE and TCE mass removal than heating temperature. In 97 days of continuous heating in the field, the average reduction in TCE concentrations was 41-69%; however, the rock matrix did not achieve the targeted temperature in all locations, due mostly to contaminated groundwater influx thru existing fractures. Additional information: ESTCP Cost and Performance Report

In Situ Conductive Heating at a Confidential Chemical Manufacturing Facility, Portland, Indiana
Federal Remediation Technology Roundtable Cost and Performance Database, 2003

The site of a 16-acre chemical manufacturing facility has been used since 1886 for a variety of operations, initially as a lumberyard, then for wheel manufacturing, followed by the manufacture of hard rubber products used in automobiles. The most recent use was for the manufacture of plastic exterior automobile parts. Chlorinated solvents (PCE, TCE, and 1,1-DCE) were detected in the unsaturated zone, with the elevated concentration of PCE suggesting the presence of DNAPL. VOCs were not found above the cleanup goals in groundwater after treatment. The in situ conductive heating system began operation in July 1997 to treat the contaminated soil in two source areas. A total of 130 heater/vacuum wells were installed on a 7.5-foot triangular spacing in the first area to a depth of 19 feet. The second area had 15 heater/vacuum wells on a 7.5-foot triangular spacing to depths of 12 feet. These wells were used to heat (1,400 - 1,600°F) the subsurface and to extract soil gas. Offgases were treated with a flameless thermal oxidizer and were cooled by a heat exchanger, then passed through a carbon adsorption bed. Offgases were monitored for hydrogen chloride, which was used as an indicator of the decomposition of chlorinated solvents. Results of confirmation sampling after treatment showed that PCE and TCE concentrations were below the cleanup goals.

Thermal DNAPL Source Zone Treatment Impact on a CVOC Plume
Heron, G., J. Bierschenk, R. Swift, R. Watson, and M. Kominek.
Groundwater Monitoring & Remediation 36(1):26-37(2016)

The dissolved-phase PCE plume emanating from the source zone at a site in Endicott, NY, was commingled with a petroleum hydrocarbon plume from an upgradient source of fuel oil. Implementation of in situ thermal desorption in the source area removed ~1,406 kg of PCE and 4,082 kg of commingled petroleum-related compounds. The treatment reduced the PCE mass discharge into the plume from an estimated 57 kg/yr to 0.07 kg/yr, essentially removing the source term. Five years following ISTD completion in early 2010, the PCE plume had collapsed and degradation products concentration in the PCE-series plume area declined by 2 to 3 orders of magnitude. Based on post-ISTD groundwater monitoring data, the hydraulic containment system was downsized in 2014 and discontinued in early 2015.

Thermal Treatment of Thick Peat Layers: DNAPL Removal and Shrinkage
Nielsen, S.G., G. Heron, P.J. Jensen, C. Riis, T. Heron, P. Johansen, N. Ploug, and J. Holm.
CONSOIL 2010, 22-24 September, Salzburg, Austria.

A PCE DNAPL source zone in a wetland area in Denmark was treated using thermal conduction heating combined with multi-phase extraction. Based on the results of a 2006 pilot test of In-Situ Thermal Desorption (ISTD), the source area was hydraulically isolated by installation of metal sheet piles for more effective heating and remediation. The DNAPL source zone was treated thermally at 100 degrees C using ISTD. Thick peat layers contaminated with PCE DNAPL were remediated to average soil PCE concentrations of 0.17 mg/kg (99.6% reduction compared to starting levels) in 83 days of heating.