Resolution - #91-04-088 - 04/23/1991

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23. 24. 25. 26. 27. Detectable levels of VOCs at the water table are restricted to within approximately 800 feet of the landfill boundaries. Total VOC concentrations detected at the water table range from about 28 ug/I to near 1000 ug/I with the highest concentrations occurring in wells east of the landfill (MW-8, MW- 16A, MW-IAR). Aromatic and ether compounds were only detected in the area east of the landfill at the water table, while the halogenated compounds were present in all samples collected from water table wells in which VOCs were detected. Ether compounds were present in significantly higher concentrations than the aromatic compounds and were detected within a larger area than the aromatics. The aromatic compounds are generally associated with petroleum products or paint solvents. Aromatics are Iow molecular weight, highly volatile compounds that are moderately soluble in water from an environmental chemistry definition. These compounds also possess specific gravities less than a value of one which indicates the compounds are less dense than water. Ether compounds such as ethyl ether and tetrahydrofuran are normally associated with industrial solvents, particularly solvents for PVC products. Tetrahydrofuran can also be found in Iow levels in food packaging. Ether compounds are lighter than water compounds and are highly volatile and extremely soluble in water (Remedial Investigation). Halogenated VOCs include chlorinated alkanes and alkenes and fluoroalkanes. Chlorinated compounds are generally associated with industrial and household solvents. Fluoroalkanes, more commonly known as freon, are associated with aerosol spray cans, polyurethane foam and refrigerants. Halogenated compounds are more dense than water, with the exception of chloroethane and vinyl chloride, and are highly to extremely volatile. These compounds range in aqueous solubilities from slight to highly soluble (Remedial Investigation). Trace heavy metals have only been detected sporadically at downgradient well locations nearest to the landfill. Concentrations have not been significantly greater than those detected at ambient locations. Metals detected, with the exception of zinc, have had concentrations less than 10 ug/land in most cases, concentrations have been nearer to the detection limit of 1 ug/l. Zinc ranged in concentrations up to about 40 ug/I at impacted downgradient wells. However, upgradient concentrations for zinc were significantly higher than those zinc concentrations detected downgradient. Metals do not appear to be migrating from the landfill in the groundwater because of the neutral or slightly basic pH conditions of the aquifer. The high bicarbonate content (alkalinity) of the neutral groundwater buffers the acidic leachate generated at the landfill to keep the pH of the groundwater near neutral, thereby immobilizing metals.