Eva L. Davis, Ph.D., US Environmental Protection Agency

Assessment of the applicability of thermal remediation at two wood treater sites is ongoing. The two wood treaters had been operation for 50 to 80 years, and a variety of wood treating chemicals had been employed, including creosote, pentachlorophenol, and various metal preparations. Creosote was commonly spilled to the ground at the completion of the wood treatment process, and waste products were disposed by burial into unlined pits. The first step in assessing the applicability of steam remediation is to determine the extent and distribution of contaminants in the subsurface and the stratigraphy. Using innovative site characterization techniques and a dynamic work plan, the extent of the nonaqueous phase liquids (NAPL) and pentachlorophenol in the subsurface was determined. SCAPS CPT/LIF data provided most of the geologic and creosote and petroleum hydrocarbon distribution information, while geoprobe and rotosonic cores were collected for characterization purposes in areas inaccessible to SCAPS. Creosote NAPL was found to have penetrated through low permeability layers at both sites and are threatening potential drinking water aquifers. Pentachlorophenol and its carriers have also been found at significant depths below the water table. Contaminant distribution found in the field and the results of laboratory tests were used to determine the important transport mechanisms for the various contaminants. Treatability studies for the thermal remediation of these sites have been used to study PAH recovery and the effects of steam injection on metals mobility. Preliminary data indicates that dioxins and furans present in these soils may be dechlorinated under the conditions present during a steam injection. Microcosm studies indicate that some contaminants may be oxidized by biological and/or thermophysical means during and after steam injection. This is an abstract of a proposed presentation and does not necessarily reflect EPA policy.

Ken Borngrebe, B.S., University of California, Riverside, Gary D. Runnells, R.G., R.E.A., B.S., American Integrated Services, Inc., David Herrera, R.E.A., B.S., American Integrated Services, Inc.

This paper describes the clean up of a California Superfund site used as a trench and fill landfill during the 1950s and 1960s for the disposal of experimental waste pesticides, herbicides, laboratory chemicals, and hazardous debris. Much of the waste was disposed directly into the unlined waste pits with unknown liquid and solid product, most of them in their original container. Containers ranged in sizes form 10ml vials to 5 gallon bottles. As a result, the site soils were impacted with a wide range of contaminants including research and experimental herbicides & pesticides, laboratory chemicals, PCBs and PAHs.

The project required methodical excavation and innovative material handling to remove the containers from the waste pits with minimal breakage, while at the same time segregating the impacted soils for later on-site treatment. The project team designed and fabricated a segregation and sorting conveyor specifically for the project to sort and manage the containers and bulk solid chemicals. The chemicals were removed and over 5000 individual tests for chemical properties and compatibility were performed. Some of the specific chemicals removed included pesticides such as temek, aldrin, dieldrin, DDT, DDE, DDD, phorate and chloropicrin. Examples of other chemicals removed included bromine, mercury, chromate and hydrofluoric acid. Each of these chemicals were bulked into compatible hazard categories such as oxidizers, flammables, corrosives and toxics. This field-testing and bulking substantially minimized lab packing of individual containers, saving hundreds of thousands of dollars in incineration costs. Over 20,000 tons of impacted soil was treated on-site using low temperature thermal desorption to project specific clean up goals. Treated soil was backfilled and compacted on site.

The project has been recognized by the California EPA as an innovative and pioneering approach to this complex site, and is considered a model remediation site in Southern California.

Jason B. Bidgood, John R. Hicks, and Bruce M. Henry, Parsons Engineering Science, Inc., and Jerry E. Hansen, Air Force Center for Environmental Excellence

Monitored Natural Attenuation (MNA) is an accepted remedial strategy for groundwater at many sites contaminated with fuel hydrocarbons and/or chlorinated solvents. Often the acceptance of this remedial approach is based on the time to achieve remedial objectives predicted by analytical or numerical fate and transport models. Prediction of the persistence and extent of dissolved contaminant plumes relies on the accurate evaluation of hydrogeologic parameters, natural source weathering rates, dissolved contaminant biodegradation rates, and engineered source reduction determined from site-specific data. In this study, model predictions for fuel hydrocarbon and/or chlorinated solvent plumes at more than 10 Air Force sites are compared to site-specific long-term monitoring data. Discrepancies between estimated and measured plume extent and concentration are evaluated with regards to the estimated source reduction and dissolved contaminant biodegradation rates used in model predictions. In many cases, overly conservative estimates of the rate of natural weathering of the source mass leads to overly conservative predictions of plume persistence and extent. The use of more accurate (i.e., often less conservative) source weathering or biodegradation rates in models can enhance the anticipated performance and acceptance of MNA.

Chenju Liang and Clifford J. Bruell, University of Massachusetts Lowell, Michael C. Marley and Ken Sperry, Xpert Design and Diagnostics (XDD)

Under thermally activated conditions (i.e., temperatures of 40 ~ 99^o C), there is considerable evidence that the persulfate anion (S₂O₈^2-) can be converted to a powerful oxidant known as the sulfate free radical (SO₄^-· ) which could be used in situ to destroy groundwater contaminants. In a field application Na₂S₂O₈ could be dosed using injection wells and activated via radio frequency (RF) heating. In this laboratory treatability study aqueous samples were prepared containing 50 - 70 mg/L of TCE or TCA and dosed with Na₂S₂O₈ at an oxidant/contaminant molar ratio of 10/1 in a series of sealed bottles. After various reaction times, in a heated shaker bath, bottles were sacrificed and analyzed via GC/FID. Little TCE degradation was observed at 20^oC. TCE is rapidly oxidized at 40^o, 50^o, and 60^oC as a result of thermally activated persulfate oxidation. At 40^oC, 80% TCE removal was seen after 3 hours. At 50^oC, 100% TCE removal was achieved after 3 hours. At 60^o C, 100% TCE removal was achieved after only 1 hour. No TCA degradation was observed at 20^o C and little was observed at 40^oC. However, at 50^o and 60^oC, TCA removal efficiencies roughly reached 40% and 100%, respectively, after a 6-hour time period. An examination of the data reveals that the pseudo-first-order reaction rate constants increase with temperature. Activation energies for the TCE and TCA oxidation were determined to be 97.74 ± 3.04 kJ/ mole and 163.86 ± 1.38 kJ/mole respectively. Preliminary soil slurry tests reveals that higher temperatures and longer treatment times will be required for effective treatment of target contaminants in soil systems vs. aqueous systems. These studies demonstrated that persulfate compounds have the ability to degrade TCE and TCA under thermally activated conditions. Kinetic data clearly illustrates that oxidation rate is increased at increased system temperature.

Falk Doering and Niels Doering, ElectroChemical Processes L.L.C., Joe L. Iovenitti, Don G. Hill, and William A. McIlvride, Weiss Associates

ElectroChemical Remediation Technologies (ECRTs) are phenomena related to colloid electrochemistry and belong to the class of Direct Current Technologies (DCTs) where DC electricity is passed between two electrodes. The primary distinctions between ECRTs and traditional electrokinetics are the (1) operative mechanisms, (2) energy input, (3) nature of the direct current, and (4) resulting outcome. Employing low-energy, proprietary AC/DC current, ECRTs generate reduction-oxidation (redox) reactions at the pore scale, mineralizing organic contaminants through the ElectroChemical GeoOxidation (ECGO) process, and complexing metals, migrating and depositing them onto the electrodes through the Induced Complexation (IC) process. ECRTs are patented in the United States and Europe.

ECRTs use a proprietary AC/DC current passed through soil between electrode pairs to create an induced polarization field. In the presence of this field, individual soil particles behave as capacitors, accepting and discharging electricity many times per second. The electrical discharges create redox reactions that can mineralize organic molecules to their inorganic components. Neither pumping nor chemical additives are used in either the ECGO or IC processes. The reaction rates are inversely proportional to grain size, such that ECRTs remediate faster in clays and silts than in sands and gravels.

ECRTs are successful both in-situ and ex-situ. Among the contaminants remediated to below regulatory standards are VOCs, CVOCs, SVOCs, PAHs, PCBs, phenols, fuels, other hydrocarbons, explosives, mercury, cadmium and lead. In many of the more than 50 successful projects, multiple contaminants have been removed with a single system, including combinations of metals and organics. ECRT projects are documented, ISO 9001-certified and insurable. ECRTs work rapidly, on the order of months, at costs well below excavation and disposal. Site data are presented.

Scott D. Hartsough, Parsons Engineering Science, Inc., Cincinnati, Ohio

The remedial action for one site in Ohio recommended not one technology but five, in a combination that represented the most cost-effective and reasonable approach to remediation of the site. The site is a gasoline service station in southwest Ohio, located in a designated sensitive area. Soils consist of unconsolidated glacial deposits with fill material near the surface. Saturated sand and gravel occur from approximately 12 feet to 20 feet below grade. The depth to water was approximately 12 feet below grade. BTEX exceeded action levels in the center of the site and throughout a plume that extended 300 feet. Free product was encountered. SVE was run simultaneously with the groundwater pumping. Vapors contain benzene (25.85 ppm), toluene (3.39 ppm), ethylbenzene (2.95 ppm), xylenes (6.8 ppm) and total petroleum hydrocarbons (TPH) (1,258 ppm). Parsons designed a system using six combined SVE/groundwater recovery wells in the native soils and one groundwater recovery/SVE well in the former UST excavation. Water was pumped to a treatment building with a gravity style oil/water separator. Vapor extraction was facilitated with a 7.5 HP regenerative blower. The exhaust of the blower was piped to the inlet of a catalyic oxidizer. Operation of the remediation system began in July 1998. Vapors were destroyed using the Catox unit, with a destruction efficiency of over 99%. Vapor concentrations declined within 18 months to the point that the Catox unit was taken off-line, and vapors were discharged directly into the atmosphere. Monitored natural attenuation was selected to evaluate if BTEX concentrations are decreasing naturally in the off-site wells. Six wells were selected for additional analytical parameters in June 2000. Offsite impacts have been completed remediated, and the concentration of BTEX has decreased almost everywhere on site.

Hani Al-Zalzala, Ph.D., Shabbir A. Shahid, Ph.D. and Ghulam Shabbir, M.Sc Hons, Kuwait Institute for Scientific Research

Phytoremediation uses green plants and their associated biota, soil amendments, agronomic techniques to remove, contain or render environmental contaminants. Iraqi invasion and occupation of Kuwait resulted into fire of more than 732 oil wells and refineries, which is one of the world’s worst environmental disaster. The oilfields and the surrounding productive areas had turned into pools of oil lakes, tarmat, and soot which eventually turned into black soil and degraded it for further users. Kuwait Institute for Scientific Research has successfully developed bioremediation technology to clean oil lake beds, and resulted into bioremediated soil to be used for other purposes. The bioremediated soil is used to develop a park at Ahmadi and a number of plants (grasses, ground covers, shrubs and trees) used at the site. Same plants are also used in a parallel experiment on a good agricultural soil (control) for a comparison. Irrigation was accomplished with fresh water. Soil characteristics such as EC, pH, CaCO₃ and properties (bulk density, porosity, penetation resistance) are evaluated at zero and final stage of the experiment. The results show that the bioremediated soil has shown better response in improving physical soil properties compared to agricultural soil under a variety of plant species. In this paper the soil properties developed with respect to different plant types as a part of phytoremediation, and the suitability of bioremediated soil to be used for establishing park will be presented and discussed.