[en] This conference was held November 7--11, 1994 in Pasco, Washington. The purpose of this conference was to provide a multidisciplinary forum for exchange of state-of-the-art information on current and future technologies for in-situ remedial action. Attention in this conference is focused primarily on nuclear wastes. Individual papers have been processed separately for inclusion in the appropriate data bases

[en] Dual Vacuum Extraction trademark provides a rapid and cost-effective method of remediating soil and ground water contaminated with volatile organic compounds. The system involves the removal of both water and vapors through the same borehole by use of entrainment. This technology provides for the remediation of the vadose zone, capillary fringe, smear zone, and existing water table. The effectiveness of this technology is shown in a case study. A release from an underground storage tank was responsible for a hydrocarbon plume spreading over approximately 50,000 ft². The release produced vadose-zone contamination in the silty and sandy clays from 10 to 30 ft below ground surface (bgs) with total petroleum hydrocarbon (TPH) concentrations up to 1,400 mg/kg. In addition, a layer of free-floating liquid hydrocarbon was present on a shallow aquifer located at 25 ft bgs in thicknesses ranging from 0.5 to 3.0 ft. An in-situ dual-extraction system was installed to remediate the soils and ground water to levels as required by the Los Angeles Regional Water Quality Control Board (RWQCB). The system operated 24 hr a day, with an operating efficiency of over 99%. After 196 days (28 weeks), over 17,000 lb of hydrocarbons had been extracted from the soils. Seven confirmatory soil borings in the area of highest initial hydrocarbon concentrations indicated that TPH and benzene, toluene, ethylbenzene, xylene (BTEX) concentrations had decreased over 99% from initial soil concentrations

[en] An innovative in-situ remediation technology has been developed for solidification and stabilization of hazardous wastes. The system incorporates a specially designed rotary mixing head attached to the boom of a long-reach backhoe or other dirt-moving equipment. A variety of mixing-head configurations are available to treat various types of wastes, ranging from oil sludge to very dry contaminated soils containing significant amounts of large aggregates and gravel. The system has been successfully applied in the field to remediate hazardous petroleum sludge, mine tailings, and steel mill process sediments containing heavy metals (e.g., chromium, arsenic, cadmium, and lead). A very elaborate quality assurance/quality control program was implemented to ensure minimum variation in additive concentration and thorough mixing. The mixing effectiveness and reagent injection capabilities of this unit have resulted in the in-situ treatment of listed hazardous wastes to below delisting thresholds at depths in excess of 15 ft. Applications of this unit are currently being reviewed for incorporating and mixing nutrients in a bioremediation process. The new technology provides a very economical means for treatment, with excellent product quality

[en] Batch adsorption experiments were conducted with three zeolites (clinoptilolite, chabazite, and A-51) to determine their potential applicability as in-situ permeable barriers to ground water strontium migration in the 100-N Area of the Hanford Site. Each of the zeolites was an effective adsorbent for strontium, even in competition with calcium at concentrations typical of Hanford ground water, and the authors determined that clinoptilolite would be the most cost-effective. The strontium adsorption data for calcium-saturated clinoptilolite were fitted to a Langmuir isotherm, which is linear at solution concentrations of less than 10^-5 mol/L. In this region, the adsorption coefficient (K_d) was 956 L/kg. Because strontium concentrations in hanford ground water are typically 3 x 10^-6 mol/L, assuming linear adsorption (K_d = 956 L/kg) for modeling purposes is appropriate. These data were used to design an effective barrier and were incorporated into a transport model to assess its performance. Calculations indicated that a barrier 1.3 m thick would prevent strontium-90 migration to the Columbia river at 100-N Area for over 50 yr. Because of radioactive decay and adsorption, the maximum breakthrough of strontium-90, approximately 5% of the initial input, would occur at 100 yr. Preliminary experimental work was conducted to determine the adsorption kinetics of strontium on clinoptilolite. A comparison of the adsorption rate of strontium with its residence time (within the barrier) indicates that adsorption kinetics are sufficiently fast that the barrier performance will not be significantly affected

[en] Argonne National Laboratory is leading a project for demonstration of in-situ remediation of contaminated ground water utilizing MAG*SEP^SM technology developed by Bradtec. This technology is being considered for eventual application at sites involving groundwater contaminated with heavy metals and/or radionuclides, such as the Savannah River Site (SRS) and Berkeley Pit. The MAG*SEP^SM technology uses specially coated magnetic particles to selectively adsorb contaminants from ground water. Particles are mixed with ground water, contaminants are adsorbed onto the particles, and the particles are removed by magnetic filtration. The technology can recover low levels of radioactive and/or inorganic hazardous contamination (in the ppm range), leaving nonradioactive/nonhazardous species essentially unaffected. The first phase of this project has involved the optimization of MAG*SEP^SM process chemistry for a selected site at SRS. To date this work has identified a candidate adsorber material (the amino form of iminodicarboxylic acid) for selective removal of lead, cadmium, and mercury from this site's ground water. Decontamination factors of 170, 270, and 235, respective, for each contaminant have been achieved. Further process chemistry optimization work for this adsorber material is planned. The project will eventually lead to an in-situ demonstration of the MAG*SEP^SM technology, integrated with the EnviroWall trademark barrier technology developed by Barrier Member Containment Corporation (BMC)

[en] Since plants are known to take up and accumulate ³⁷Cs and ⁹⁰Sr, removal of these radionuclides from contaminated soils by plants would provide a reliable and economical method of remediation. One approach is to use fast-growing, perennial plants combined with specific mycorrhizal fungi to maximize plant accumulation and removal of ¹³⁷Cs and ⁹⁰Sr from contaminated soils. The objective is to find a series of plants that can quickly accumulate and remove radionuclides from soils. Specific mycorrhizal fungi inoculated onto plants should enhance the uptake of ¹³⁷Cs and ⁹⁰Sr. Laboratory studies indicate that certain plants may be able to remove radionuclides, especially ¹³⁷Cs and ⁹⁰Sr, from soil over a period of less than 10 yr. In addition, one could change the physical and chemical properties of the soil to enhance the availability of ¹³⁷Cs and ⁹⁰Sr to plants while decreasing the mobility of these radionuclides in soil. The above-ground portion of perennial plants would be harvested. High-temperature combustion would be used to oxidize plant material, concentrating ¹³⁷Cs and ⁹⁰Sr in ash for disposal. One of the many strengths of this method is its applicability to any terrestrial environment. Transportation of radionuclides from the site could be minimized through plant management, selection of plants that are less palatable to grazing animals, and fencing. Environmental conditions will change with each site; however, radionuclide accumulation could be accomplished by plants that are adapted to a wide spectrum of environmental conditions. There is no other practical and economic method to remove these radionuclides form the vast areas of land that have been contaminated by nuclear testing and nuclear reactor accidents

[en] Vacuum extraction technology has become one of the most widely acclaimed methods for remediating soils contaminated by petroleum hydrocarbons and volatile organic compounds. Removal of the source of contamination in the soil is often the first step in effective control of groundwater contamination. Though originally thought effective only for removal of light-end hydrocarbons from permeable vadose-zone soils, vacuum extraction can now be adapted to address situations of low-permeable soils, heavier-end hydrocarbons and groundwater contamination. This paper reviews four innovative modifications to the vacuum extraction process and how they solve a wide variety of subsurface contamination problems. The modifications, or processes, reviewed include: vacuum-extraction-enhanced bioremediation, groundwater sparging, pneumatic soil fracturing, and soil heating

[en] Geosafe Corporation began commercial application of in-situ vitrification (ISV) during 1993. The first application is at the Parsons Chemical/ETM Enterprises Superfund Site (Parsons Site) in Grand Ledge, Michigan, which contained 4,800 tons of pesticide- and mercury-contaminated soil. The effectiveness of the cleanup and overall performance of the ISV system will be presented. Projects in the US that will follow the Parsons project include: (1) soils associated with a former transformer service facility, which are contaminated with polychlorinated biphenyls; (2) a chemical packaging plant contaminated with dioxin, pesticides, and other chemicals; (3) a contaminated landfill. The status and expected results of these projects is discussed. In Australia, ISV has been selected for in-place treatment of burial pits at the Maralinga Nuclear Weapons Test Site, which contains test debris and plutonium and uranium contamination. In Japan, a 3-yr engineering-scale testing program has been completed, in which the application of ISV for vitrifying a low-level-waste burial vault has been evaluated. This paper provides technical information showing that ISV can successfully remediate various contaminated sites if adequate site characterization and preparation are provided and small-scale ISV testing is utilized to understand the technical obstacles that must be dealt with in the field. The paper identifies the benefits of ISV for hazardous, radioactive and mixed-waste site remediation and criteria pertinent to such applications

[en] This paper describes a new remediation technology that uses foams to treat dense, nonaqueous-phase liquids (DNAPL) in the subsurface. This project is a joint effort involving Argonne National Laboratory and the US Department of Energy Office of Technology Development (under the In-Situ Remediation Integrated Program) and the Gas Research Institute (in collaboration with the Institute of Gas Technology and the Illinois Institute of Technology). Foams are used to release and mobilize NAPL contaminants in the subsurface, thereby making the contaminants bioavailable. Foam is a dispersion of gas bubbles, separated by thin liquid films containing surfactants. Foams are currently used by the oil industry to improve crude oil recovery, resulting in 20 to 50% higher recoveries of oil for some applications. Foams can be designed with different phases (e.g., three-phase foams containing an aqueous foam with an organic pollutant or oil phase), wettabilities, surfactant concentrations, mobilities, and stabilities. Foams can carry different gases, chemicals, bacteria. Foams can also be coupled to and enhance in-situ bioremediation since surfactant concentrations are well below toxicity levels. Furthermore, foams can be designed to enhance bioremediation by carrying nutrients, bacteria, or specific gases

[en] Zero-valent iron (Fe⁰) (metallic iron) is a strong chemical reductant that is capable of degrading several halogenated-hydrocarbon compounds (e.g., trichloroethene and tetrachloroethene) and chemically reducing several highly mobile oxidized oxyanions and oxycations to their immobile forms. A series of studies was undertaken to develop methods of injecting micrometer-sized Fe⁰ colloids into the subsurface environment to form a chemical barrier to these highly mobile contaminants. Forming a barrier by means of this technique may have the distinct advantage over traditional trench-and-fill technologies: it may be safer, more cost-effective, and may be used at greater depths. Several commercially available Fe⁰ colloids were evaluated. One type was selected for further study based on its small size (1 to 2 microm) and the presence of an organic coating. This organic coating was weathered away within 7 days by Hanford ground water (CaCO₃ system, pH 8.1) and exposed the chemically active Fe⁰-colloid surface. Through the use of surfactants in a low ionic strength solution, the length of time that these extremely dense (7.8 g cm^-3) colloids remained in suspension increased as much as 250%. The efficiency of quartz-sand columns to remove surfactant-coated Fe⁰ colloids appeared to be at least partially controlled by injection rate; the filter coefficient values at injection rates of 6, 124, and 248 ml min^-1 were 0.30, 0.05, and 0.02 cm^-1, respectively. Studies are underway to develop further understanding of this relationship and to determine the interactive effect of influent colloid concentration and injection flow rate on colloid placement in aquifer sediments for barrier formation