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U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

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Alternative Treatment for PAH and PCP

From Tech Trends November 1995

Alternative Treatment for PAH and PCP

By Teri Richardson, EPA National Risk Management Research Laboratory

The DARAMEND bioremediation technology is an effective alternative to soil washing, incineration or landfilling soils containing high levels of polynuclear aromatic hydrocarbons (PAHs) and chlorinated phenols, including pentachlorophenol (PCP). These contaminants are typically considered too toxic for bioremediation and are found at approximately 400 industrial wood treatment facilities in the United States and an additional 200 sites in Canada. The patented DARAMEND technology, applicable to both in-situ and ex-situ remediation of soils, was developed by GRACE Dearborn Inc.'s Environmental Consulting Group in Mississauga, Ontario, Canada. A full-scale demonstration of the ex-situ application was conducted at the Domtar Wood Preserving Facility in Trenton, Ontario, by the EPA's Superfund Innovative Technology Evaluation (SITE) Program. The SITE evaluation built upon previous evaluations of bench and pilot scale testing by the Developer under Canada's Development and Demonstration of Site Remediation Technology (DSERT) Program. The technology provides shortand long-term protection because it provides irreversible treatment of PAHs and total chlorinated phenols (TCPs) by eliminating these contaminants from the soil, thus preventing further ground water contamination and pollutant migration.

An important operating parameter of the technology is an understanding the specific physical and chemical properties of the contaminated soil that could limit the effectiveness of bioremediation. Once an evaluation of various soil properties is completed, the developer selects an organic amendment formulation with the specific particle size distribution and nutrient profile to create ideal soil microbiological conditions. The organic amendments enable the soil matrix to supply biologically available water and nutrients to contaminant-degrading microorganisms, transiently binding pollutants to reduce the acute toxicity of the soil's aqueous phase. This allows the microorganisms to survive in soils containing very high concentrations of toxicants.

The technology is a relatively simple soil remediation system, both in design and implementation. It consists of three integrated treatment components: (1) addition of the appropriate specially formulated solid-phase organic soil amendments to the target matrix; (2) distribution of the soil amendments through the target matrix and the homogenization and aeration of the target matrix using specialized tilling equipment; and (3) soil moisture control using a specialized system to maintain moisture content within a specified range, to facilitate rapid growth of an active microbial population and prevent the generation of leachate. The process involves a certain amount of materials handling -- the ex-situ application more so than the in-situ application.

For in-situ applications, soil is initially broken up with excavation equipment to a depth of 0.6 meters, which is the limit for the specialized tilling equipment,. For ex-situ applications, contaminated soil is excavated and screened to 10 cm to remove debris that might interfere with the incorporation of organic amendments. Screened soil is spread uniformly in the constructed treatment plots to a depth of 0.5 meters. The plots are lined with a high-density polyethylene liner (impermeable to the target compounds), underlain with 10 cm of screened sand to prevent structural damage. Another 15-cm thick sand layer and a 4mm-thick fiber-pad are spread on top of the liner to minimize the potential for direct contact between the liner material and tillage equipment. The SITE treatment area covered an area of 2,300 sq. meters and allowed treatment of approximately 1,500 tons of soil.

The treatment plots may also be contained within a temporary waterproof structure to produce a warmer environment in northern latitudes, and to aid in the retention of soil moisture. The waterproof structure consists of an aluminum frame covered by a shell of polyethylene sheeting and is left open at each end to allow for equipment access.

The SITE evaluation consisted of two plots, a Treatment Plot and a No-Treatment Plot, both containing excavated contaminated soil from the same source on-site. The plots were constructed identically, with the exception that the No-Treatment Plot was only 2 meters x 6 meters, while the Treatment Plot was a 6 meter x 36 meter area. The No-Treatment Plot was left idle over the course of the demonstration and was isolated. After 254 days of treatment, the DARAMEND bioremediation treatment process achieved an overall approximate 94% removal of PAHs and an overall 88% reduction of chlorinated phenols in the Treatment Plot. Total PAHs were reduced from an average of 1,710 milligrams per kilogram (mg/kg) to 98 mg/kg and TCPs were re reduced from an average of 352 mg/kg to 43 mg/kg. At the end of the treatment process, the treatment plot soil sample was considered non-toxic. The earthworms exhibited a 0% mean mortality rate compared to a 100% mean mortality rate prior to treatment.

Lettuce and radish seeds exhibited a 100% to 52% mean inhibition of germination rate before treatment and a 33% and 0% rate respectively post treatment. No significant reduction occurred in the No-Treatment Plot during the demonstration. A full-scale cleanup of this site using this technology would cost between $640.00 for an in-situ plot with an attendant unit cost of $133/cubic m ($100/cubic yard), and $480,000 for an ex-situ plot with an attendant unit cost of $420/ cubic m. ($320/sq. yard).

For more information, call Teri Richardson of EPA's National Risk Management Research Laboratory, Cincinnati, Ohio at 513-569-7949. To get on the mailing list for a SITE Capsule Report and Innovative Technology Evaluation Report, send a FAX (513-569-7105) to Teri Richardson


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