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Mr. Verrill Norwood i - 2 - In 2 -In the future, All Pure should consider the comments in the following three paragraphs in evaluating the potential impact of leachable soil contaminants to ground water quality. MCLs are not necessarily the appropriate water quality goals to determine potential impact to ground water quality. The lowest applicable water quality goal should be used in this determination. The lowest applicable water quality goals for chloride, zinc, and copper are the agricultural water quality goals, not MCLs. It also is not appropriate to compare soluble concentrations of VOCs or inorganics in soil directly to MCLs in evaluating the potential threat to ground water. The attenuation due to the soil and contaminant characteristics and the dilution used to derive the soluble extract must be considered in this evaluation. Board staff use the designated level methodology to evaluate the potential impact of contaminants in soil to ground water. The soluble concentration of a contaminant in soil is determined to be a potential threat to ground water if it exceeds the product of the lowest applicable water quality goal, the attenuation factor, and the reciprocal of the dilution factor of the extraction method used. VOCs in Soil Vapor All Pure has tried to show in two ways that the concentrations of chloroform and carbon tetrachloride detected in the soil vapor are due to volatilization from the shallow ground water rather than from a source area within Fire Pond 2. All Pure first evaluated the concentrations of VOCs detected in soil gas using the soil/soil vapor partitioning methodology applied in the Remedial Investigation/Feasibility Study for the Tracy Army Depot. All Pure calculated the total concentrations of VOCs expected in soil based on VOC concentrations in soil gas, the physical properties of the site, and the chemical properties of the VOCs present. All Pure states that since the predicted total concentrations in soil equate to soluble concentrations of chloroform and carbon tetrachloride (within the model's range of accuracy), the VOC concentrations in soil vapor are consistent with a hypothesis of vapor transport from ground water rather than a soil source pathway. Ignoring the accuracy of All Pure's calculations, it does not make sense to conclude the VOCs in soil vapor are derived from vapor transport from ground water due to a predicted soil concentration which is based on detected vapor and soluble concentrations of VOCs. The approach does not identify the source of VOCs present in the soil vapor. All Pure's second evaluation to show that chloroform and carbon tetrachloride in the soil vapor are due to volatilization from ground water compared measured soil vapor concentrations to predicted soil vapor concentrations based on measured ground water concentrations and liquid-gas partitioning of VOCs using Henry's Law. All Pure has compared the predicted vapor phase to ground water quality in MW-2. The comparison should be made to MW-3, since MW-3 is much closer to Fire Pond 2 than is MW-2. The predicted soil vapor concentrations of chloroform from the water quality of MW-3 is 1.0 x 10-5 mg/ml while the detected soil vapor concentrations was 1.23 x 10-4 mg/ml. The differences in these concentrations do not appear to be significant, indicating that a significant portion of the chloroform may be due to volatilization from ground water. I therefore agree that the soil in Fire Pond 2 is not a source of VOCs to ground water. IRecycled Paper Our mission is to preserve and enhance the quality of California's water resources,and ensure their proper allocation and efficient use for the benefit of present and future generations.