Portland, OR - Deep, DNAPL Remediation Brochure

In 1999, the senior managers of TRS Group, Inc (TRS) while working for a former employer, as a subcontractor to AMEC, provided Electrical Resistance Heating (ERH) for VOC-impacted groundwater at a commercial site in Port-land, Oregon. The remediation was conducted under the Oregon Department of Environmental Quality (DEQ) Volun-tary Cleanup Program. The remedial action objective was to remove DNAPL to protect the drinking water source beneath the contami-nated area, and reduce the contaminant concentrations in groundwater to levels indicating DNAPL was below concen-trations protective of human health and the environment. Contaminant concentrations in monitoring wells were re-duced by 99% meeting all remedial action objectives.Project Manager: Mr. Tom PowellSite Geology and Hydrogeology: Overbank deposits (silts & sands) to 60-ft bgs; groundwater at approx. 8-ft bgsTreatment Area, Volume, and Depth: 5,800 ft2; 20 to 60-ft bgs; 8,592 yd3Beginning Concentrations (averages): cis-DCE = 15,283 µg/l; TCE = 157 µgl/l; VC = 10,031µg/lEnd Concentrations (averages): cis-DCE = 137 µg/l; TCE = 7 µg/l; VC = 5 µg/lRemedial Goal: Prevent migration of DNAPL; reduce contaminant levels to the extent practicalActual Cleanup Achieved: >99% reductionPeriod of Performance: 18 monthsContract Terms: Standard Fixed Price RemediationBackgroundFigure 1. Site overview of electrode layout and ERH equipment compound Areas and Electrode PlacementSite Characteristics & Design ParametersThe target ERH treatment area measured approximately 5,800 ft2 and the extent of treatment was from 20 to 60-ft bgs for a total treatment volume of 8,592 yd3. Figure 1 is a photo showing the treatment area with general configura-tion of the electrodes and ERH equipment.Site geology to a depth of approximately 60-ft bgs consists of fluvial and lacustrine deposits (Overbank Deposits). The upper 15-ft consists predominantly of silts. Underlying the Overbank Deposits is an aquifer consisting of unconsolidated and cemented gravels approximately 175-ft thick. The water table is located in the silts at ap-proximately 8-ft bgs.The primary contaminants of concern were trichloroethene (TCE), cis-1,2-dichloroethene (DCE), and vinyl chloride (VC), as well as other volatile organic compounds (VOCs), including benzene and toluene. Of these, the chlorinated solvents were present as DNAPL.The site was used for agricultural purposes from 1929 until approximately 1960. In 1962, United Medical Laboratory purchased the property, and constructed a mail order clini-cal laboratory. In the early to mid 1970s, ICN Pharmaceuti-cals, Inc. purchased the property and shutdown the lab in 1980. The laboratory building and associated structures were demolished in 1993/94. Deep, DNAPL RemediationPortland, ORProject SummaryTRS Contact InformationMr. David Fleming, (425) 396-4266 dfleming@thermalrs.comwww.thermalrs.comThe ERH system was installed with 73 electrodes, 70 shal-low vapor recovery (VR) points, 13 shallow perimeter vac-uum monitoring points, and 8 temperature monitoring probes that provided more than 50 fixed and portable tem-perature monitoring points. Each electrode was capable of directing power to three zones in the Overbank: 20 to 30-ft bgs, 34 to 44-ft bgs, and 48 to 58-ft bgs. The vapor extrac-tion points were ultimately screened from 5-ft bgs to below the Overbank deposits allowing for steam and vapor recovery below this semi-confining unit. The heating strat-egy consisted of establishing a hot floor, then heating por-tions of the treatment area in stages, moving from the down gradient extent of the groundwater plume back to-ward the source area. The ERH system was fully operational in May 2000. The ERH system operated through mid-November 2001. System Construction and OperationsProject ResultsFollowing ERH operations, the VOC groundwater concentra-tions in the treatment area were reduced by greater than 99%. A pilot-scale in-situ biosparging study, conducted by AMEC, in late 2001, suggested that further reductions of the remaining aerobically degradable VOCs was possible. An exit strategy that used biosparging and remedial goals established by the baseline risk assessment commenced in Fall 2002. Figure 2 presents the average percent reduction in groundwater concentrations of cis-DCE, TCE and VC in the combined Shallow, Deep, and Intermediate subsurface levels as well as below the heated interval. The starting concentrations are from May 2000 and the final sampling period was in March 2002.Figure 2. Average percent reductions in groundwaterµg/L