DC Electro Thermal Soil Remediation - the integration of DC electrical resistive heating, electroosmosis and in-situ zero-valent iron reductive technologies for the clean up clays and glacial tills contaminated with chlorinated solvents

DC Electro-thermal Remediation is the integration of electrical (DC) heating and in-situ treatment developed specifically designed to treat chlorinated solvent contamination in low permeability soils totally below grade.

The DC electricity provides two primary functions. The first is heating the soil to about 90°C helping to disperse residual DNAPL pools or ganglia and creating vapor phase transport or lower temperatures to assist in biodegradation. The second function is to induce electroosmotic flow. Electroosmosis is the directional movement of pore water in soil, from anode to cathode, providing a flushing action even in the tightest clays. This electroosmotic flow is the proven advantage of using DC electricity over AC (including 6-phase resistive heating) or steam and allows the addition of in-situ reactive treatment zones (or curtains) perpendicular to the electroosmotic flow.  In-situ destruction means no extraction or above ground treatment is necessary keeping O&M to a minimum.  The treatment zones for cholrinated solvents typically consist of zero-valent iron suspended in kaolin clay spaced about 5-10 feet apart.  For biodegradation based systems, the treatment zones can be a source of electron donors or acceptors including organic carbon, sulfate, ferous or lactate.

Electro-thermal remediation has been used to treat clays and glacial tills contaminated with solvent such as trichloroethylene (TCE) perchloroethylene (PCE), vinyl chloride, cis-1,2-dichloroethylene (cis-DCE), 1,1-dichloroethylene (DCE), 1,1,1-trichloroethane (TCA), 1,1-dichloroethane (1,1-DCA) and others. When applied to the source zones, 99% or more removals are achieved. Even DNAPL areas can be treated to levels well below 1 mg/kg for about one third, or less, the cost of excavation and disposal. This technology can be applied above (vadose zone) or below the water table (saturated zone). 

Lasagna^TM is the patented and trademarked name for this integration of DC electricity and in-situ treatment and was developed by a consortium of scientists from DuPont, General Electric and Monsanto along with the USEPA and DOE.

Typically, a series of planar electrodes are emplaced at the outer edge of a source zone with a spread of between 20 and 100 ft apart. Treatment zones, consisting of iron filings suspended in a clay slurry, or some other desired treatment material, are emplaced between and parallel to the electrode zones. When the power is on, the whole soil mass is heated and pore water travels from the anode to the cathode uniformly and predictably.  Alternative treatment materials may be used for other contaminants.  The pore water that collects at the cathode is recycled to the anode by gravity. 

Although there are many possible configurations and electrode arrangements, a two segment approach is typically taken.  The two segments approach consists of two outer anodes and one central common cathode and results in minimal stray voltage and current.  In urban settings, it is important to eliminate corrosion impacts on local utilities.   Stray voltage and current testing at the latest urban site indicates Lasagna can be operated without negative impacts to buried gas and water lines nearby.

Lasagna^TM is a registered trademark of Pfizer (from Monsanto, though acquisition of Pharmacia) and Patented.

PGDP - Paducah

Lasagna was extremely successful in reducing trichloroethylene (TCE) contamination at a DOE facility in Paducah, KY from levels indicative of DNAPL to well below the Record of Decision (ROD) mandated level with no increase in cis-DCE or vinyl chloride.   Pictures of the Paducah installation are below.

Installing electrodes at Paducah	Installing electrodes  at Paducah	Electrode Wiring	Completed Lasagna  site at Paducah

Quicfrez - Wisconsin

Lasagna was also used at the abandoned Quicfrez industrial site in Fond du Lac, Wisconsin to remove high levels of TCE from the site and under a near-by river (pictures below).  The soil at the site consisted of saturated clay and silt with very high levels of TCE (much of the site contained DNAPL levels of TCE).  The project lasted a little over 2 years, when funding was pulled due to economic conditions.  Two anodes (north, south) were used with a single center cathode.  Installation of the electrodes and treatment zones lasted only 3 weeks with the electrical and recycle plumbing taking another 2 weeks to complete.  Little or no stray current was found at nearby utility lines.  The system was fed by 208 volt, 3-phase line power rated for 600 amps.  The initial DC output measuring 190 volts and 500 amps.  Once the system reached operating temperature (70-80°C), the power was reduced to about 110 volts and 450 amps.

Quicfrez site with river terrace	Installing electrodes at Quicfrez site	Installing treatment zones in front of rectifier building	Using cement truck and Nilex rig for treatment zone materials installation
Quicfrez site finish grade and rectifier shed	Quicfrez power pole (208 3-phase)	Quicfrez site from across the river	Completed Quicfrez site and river terrace

The figure below shows the Quicfrez soil TCE concentration prior to Lasagna.  The “shell” image encases TCE concentrations above soil pore water solubility (DNAPL) with the red color showing concentrations above 1000 mg/kg.  The red portion is at the river’s edge and under the river. Yellow color indicates concentrations above 200 mg/kg and green indicates concentrations above 100 mg/kg.
 

Quicfrez Soil TCE Concentrations Prior to Lasagna Application. Blue labels are pre-Lasagna boring locations, black dots are sample collection locations

The next figure shows the soil TCE concentrations after Lasagna.  Again, the “shell” encases soil with TCE exceeding the pore water solubility (DNAPL).  The color scale is the same as the previous image.  Notice the red shading has disappeared and the “shell” volume has been significantly reduced.   Given more time, the area could have been treated to the clean up target.  Unfortunately, the project funding was limited due to budget cuts at the Wisconsin DNR.   Although there were hopes of a better result, over 2/3 of the TCE mass was removed.  However, the iron filings remain in place and will continue to treat any TCE migrating due to convection or diffusion.

Quicfrez Soil TCE Concentrations After Lasagna Application. Blue labels are pre-Lasagna boring locations, black dots are sample collection locations

Cambridge - Ohio

The latest installations where installed in October 2008 at an operating facility in Cambridge, Ohio.  Two separate installations are currently being operated to treat TCE contamination in saturated clay soil.  The facility currently manufactures window seals.  The Lasagna systems were installed under parking lots without interfering with the facility’s production or distribution.   

Area-1 measured 160 feet by 70 feet to a depth of 20 feet.  It was located under abandoned buildings that became parking lots.  During concrete surface and footer removal that there were remnants of an old ceramics facility including slaker pits and materials storage bunkers that required removal for Lasagna to operate correctly.  Area-2 measured 50 feet by 50 feet to a depth of 20 feet and was located adjacent to a building used for production.  Area-2 was also located under a parking lot area.  The removed concrete materials did not leave the site but were crushed and reused as a rock working surface to minimize issues of working on wet clay.  

The soils were primarily contaminated with TCE to near DNAPL levels and the breakdown products cis-DCE and vinyl chloride.  Area-2 was a chemical drum storage pad and also contained some TCA, 1,1-DCE and methylene chloride along with non-chlorinated VOCs like acetone, methyl-ethyl ketone and xylenes.  The soil was mostly saturated with the groundwater surface at 3-5 feet below grade.  The Lasagna materials installation lasted 10 weeks and did not interrupt plant operations.  Routes to the loading docks were available at all times.  Like the Quicfrez project, a full stray voltage and current survey was performed to assure no impact of the DC field on local utilities.  The impacts to nearby buried utilities can be minimized by employing a properly designed system.
 

Removing old building floors turned parking lots, and footers and buried bunkers	Crushing removed concrete to use as working surface	Making Electrodes – Wickdrains fastened to steel plates	Using cement truck and Nilex rig for treatment zone materials installation
Cathode buss wire connections	Area-1 finished grade	Area-2 finished grade	Rectifier in shed

Lasagna Videos

Lasagna electrode installation movie (AVI, 82 MB)	Lasagna treatment zone installation movie (AVI, 40 MB)	Lasagna animation video (WMV, 0.5 MB)

How much does it cost?

A Lasagna system typically costs around $100 per ton of soil treated. Very deep sources (>40 ft) and very small sites (<0.1 acres) usually cost more whereas larger, shallower sites cost less. Call Chris Athmer at Terran (937-320-3601) for a cost estimate for your site.

DC Electro-Thermal Remediation (Lasagna) advantages:

• Most thorough in-situ remediation process (every soil pore and all pore water is affected),
• System is emplaced using sheet pile techniques resulting in NO WASTE to dispose of,
• Completely installed and operated below ground,
• Not constrained by vapor or hydraulic permeabilities,
• No extraction equipment to operate,
• Reductive in nature - compatible with most naturally occurring reductive dechlorination processes (MNA),
• In-Situ Treatment materials are left in place and will continue to polish the site for years after the power is turned off,
• Extremely low O&M requirements.

How does it work?

Electroosmosis has been known since the 1930s as an efficient means of dewatering clays and silts for soil stability. It can also be used to move pore water and contaminants through all types of soils. This attribute, plus the resistive soil heating that occurs makes it a useful tool for reclaiming solvent contaminated soils.

When a DC electric field is applied to soil, cations begin to move toward the cathode and anions move toward the anode. Since soil typically has a negative surface charge there are more cations than anions in the pore water (conservation of charge). These extra cations, lined up along the pore walls and moving toward the cathode, drag the pore water along causing a net pore water flow to the cathode that is uniform and predictable. In low permeable soils (clays and silts), this process is much more efficient and thorough than conventional hydraulic based processes. The directional movement through the soil allows for the effective use of in-situ capture and/or reduction zones.  The application of DC energy also results in the heating of the soil, which is a bonus when dealing with VOC contamination. The soil heating can be harnessed to assist in the efficient mobilization of DNAPL pools and residuals much like a thermal technology. The combination of heat and pore water movement (flushing) gives EK a powerful one-two punch dealing with VOC contamination in low permeable soils. 

Example Application

Lasagna was developed by a consortium of industrial partners (Monsanto, DuPont and General Electric) and the USEPA in the mid 1990s to specifically treat low permeable soils contaminated with chlorinated solvents. Terran Engineer, Chris Athmer was a member of the development team at Monsanto and participated as the field engineer and principal designer of the first Lasagna site at DOE's Paducah Gaseous Diffusion Plant (PGDP) for the in-situ treatment of TCE in clay using electroosmosis and zero valent iron treatment. Electroosmosis-induced pore water flow and elevated temperatures have been proven effective in the treatment of TCE in clay soils in a most cost efficient manner. At Paducah, the process reduced the soil concentrations from an average of 84 mg/kg (with a high of 1,500) to an average of 0.38 mg/kg (with a high of 4.5) in two years of operation. The project was highlighted in a recent "Technology News and Trends" newsletter (EPA, TIO). The Final RA Report for Paducah (DOE, 2002) shows the details of the installation and verification soil sampling.

Contact

Chris Athmer by phone at 937-320-3601 or email at cjathmer@terrancorp.com 

News links

Technology News and Trends

Cooking Up Solutions, Cleaning Up With Lasagna^TM, United States Environmental Protection Agency, Solid Waste and Emergency Response, EPA505-F-99-004, April 1999. Cooking up Solutions.

Technical Articles

Record of Decision (ROD) for Paducah Site Specifying Lasagna

GWRTAC Technology Overview Report - Electrokinetics

Rapid Commercialization Initiative Verification Statement for Lasagna^TM, March 2, 1998.  This statement shows the agencies that recognize Lasagna as an acceptable remediation technology.

The Lasagna Technology for In Situ Soil Remediation. 1. Small Field Test, Sa V. Ho , Christopher Athmer, P. Wayne Sheridan, B. Mason Hughes, Robert Orth, David Mckenzie, Philip H. Brodsky, Andrew Shapiro, Roy Thornton, Josepy Salvo, Dale Schultz, Richard Landis, Ron Griffith and Steve Shoemaker, Environmental Science & Technology, 33, 7, 1086-1091, 1999.

The Lasagna Technology for In Situ Soil Remediation. 2. Large Field Test, Sa V. Ho , Christopher Athmer, P. Wayne Sheridan, B. Mason Hughes, Robert Orth, David Mckenzie, Philip H. Brodsky, Andrew Shapiro, Roy Thornton, Josepy Salvo, Dale Schultz, Richard Landis, Ron Griffith and Steve Shoemaker, Environmental Science & Technology, 33, 7, 1092-1099, 1999.

Lasagna^TM/RTDF Technical Documents, Lasagna Remediation Technology, The Remediation Technologies Development Forum (RTDF).

Copyright © 2006 by Terran Corporation, Beavercreek, Ohio U.S.A.
Phone: 937-320-3601, Fax: 937-320-3620

www.terrancorp.com, This page edited June 15, 2010
Send mail to webmaster@terrancorp.com with questions or comments about this web site.