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S This section presents abstracts of 10 of the papers given at the March 1984 meeting in Tucson; the papers are given in their entirety further on. The first three are overviews of pertinent literature on several topics relevant to the Toxic-Waste Program; the last seven are research summaries that describe the application of information from earth-science disciplines to problems in toxic-waste contamination of ground water. The role of geochemical processes in hazardous-waste studies: by Francis H. Chapelle. Predicting the mobility of waste derivatives in hazardous-waste studies requires an understanding of the geochemical processes that affect waste materials. This paper describes how geochemical techniques such as mass-balance, chemical-equilibria, and chemical-kinetic calculations, can be applied to waste-mobility problems. The paper demonstrates the difficulties in quantitatively treating geochemical processes and discusses the application of solute transport and geochemical principles to the study of specific problems. To this end it presents several examples of how geochemical principles can be applied. An overview of organic compounds in ground water: by Anne C. Sigleo. The transport and fate of organic pollutants in ground water are influenced by the processes of dispersion, chemical hydrolysis, sorption/desorption, and biological degradation. This paper describes the hydrologic, geochemical, and microbiological processes that influence the fate of both biological and synthetic organic compounds. The role of earth-science criteria in the selection of hazardous-waste disposal sites: by Albert M. La Sala, Jr. The selection of suitable sites for disposal systems of hazardous-waste material should involve the use of earth-science information in combination with engineering, economic, social, and environmental-impact considerations. This paper describes a stepwise process that can lead to identification of sites potentially suitable for waste-disposal. Factors of geology, hydrology, and geochemistry pertinent to the long-term safety of disposal sites need to be investigated to develop a rational, objective basis for siting disposal facilities for hazardous waste. Capacities and mechanisms of sorption of organic compounds by watersaturated and unsaturated soils: by Gary T. Chiou. Mobility of a chemical in hydrologic and geologic environments is determined to a large extent by its sorptive interaction with soil constituents. This research paper discusses characteristics of soil sorption of nonionic organic compounds that vary with respect to soil composition, moisture content, and solvent medium from which the solutes are sorbed. In aqueous systems, the controlling sorptive mechanism is considered to be solute partition into the soil-humic phase. When soils are fully hydrated, adsorption of the organic solutes by soil minerals becomes relatively insignificant. By contrast, the soil uptake of these compounds on dry soils is effected mainly through mineral adsorption. Use of detrended correspondence analysis to identify factors that affect the structure of aquatic communities: by Harry V. Leland and James L. Carter. Detrended correspondence analysis is shown in this paper to be an effective method for analyzing biological-monitoring data and displaying major factors that control the spatial distribution of periphyton and benthic macroinvertebrates. The method proved highly sensitive to differences among samples and consistently provided ecologically meaningful species ordination. Modeling sorptive processes in laboratory columns: by David B. Grove. A common type of chemical reaction that occurs during the movement of solutes in porous media is sorption of the solute onto the solid surface through a physical attraction or an exchange process. This paper describes sorption isotherms, discusses the shapes and significance of different slopes, and describes equations used to evaluate the slopes of isotherms. Computer codes can be used to compute concentrations of the effluent from a laboratory column and the concentration profile within the column. Microbial populations and nutrient concentrations in a jet-fuel-contaminated shallow aquifer at Tustin. California: by Carry G. Ehrlich, Roy A. Schroeder, and Peter Martin. Jet-fuel leakage from unlined earthen pits has contaminated a shallow aquifer of low permeability; hence, conventional cleanup operations are relatively ineffective. This paper discusses a remedial strategy for cleanup that involves use of indigenous hydrocarbon-degrading bacteria, which are shown to be present in the aquifer. Laboratory studies found that nutrient enrichment of jet-fuel and ground-water mixtures stimulated growth of hydrocarbon-degrading bacteria and resulted in the production of hydrocarbon emulsifiers that might promote dispersion of pockets of trapped fuel in the aquifer. Injection of inorganic nitrogen, phosphrous, and oxygen, in conjunction with operation of a conventional depression-pump and oil-scavenger recovery system, could enhance restoration of the site. Adsorption and desorption of hexavalent chromium in an alluvial aquifer near Telluride. Colorado: by Kenneth G. Stollenwerk. An evaluation of reactions between alluvium and hexavalent chromium Cr(VI) was conducted to determine the mechanisms responsible for these reactions. This paper discusses results of a laboratory investigation. One significant result indicates that desorption of Cr(VI) from alluvium occurs after the contaminated plume has passed. Initial desorption of Cr(VI) is rapid; followed by a steady decrease. Adsorption, it was found, of Cr(VI) is by specific and nonspecific mechanisms. Cr(VI) absorbed by nonspecific processes is desorbed by chromium-free ground water. Stronger bonds formed between Cr(VI) and alluvium during specific adsorption result in slow release of this fraction; thus, adsorbed Cr(VI) will serve as a secondary source of contamination long after the original plume has passed. Effects of pentachlorophenol 'on the methanogenic fermentation of phenol: by Edward M. Godsy, Donald F. Goerlitz, and Carry G. Ehrlich. Pentachlorophenol (PCP) and creosote, two widely used pesticides, contribute potential contaminants to ground-water resources. This paper describes a study to investigate the interactions of PCP and phenol compounds on creosote in anaerobic laboratory digesters. PCP was found to be inhibitory to the methanogenic fermentation of phenol. The inhibition could be relieved when the PCP concentration was low enough to undergo biodegradation. The role of complexation and adsorption processes in toxic metal transport: by James A. Davis and Christopher'C. Fuller. The transport of toxic metals in ground-water systems has become an important water-quality issue. This research paper describes a detailed laboratory study of cadmium uptake into a calcareous, sandy aquifer material. A strong complexing agent (EDTA) was used to increase mobility of cadmium (II) while being present at very low concentrations.

Program overview and selected papers from the Toxic-Waste Program Technical Meeting: Tucson, Arizona, March 20-22, 1984