SITE INFORMATION AND CORRESPONDENCE

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Water Quality Site Assessment• -5- • 3W75 November 1992 a. Site Soil Leachate Concentration = 10 x (Site WET Extract Concentration) b. When an assessment site soil leachate concentration is less than or equal to the background ground water concentration,regardless of whether background is greater than or less than the numerical water quality limit, the soil constituent does not threaten water quality. No further action is required for that con- stituent in that lithology, provided that the concentration does not present a risk to human health. 4. When the background ground water concentration is less than the numerical water quality limit for a constituent, the assessment site soil leachate concentration is com- pared to the numerical water quality limit to determine the threat to beneficial uses, and is compared to the background ground water level to determine the threat of ground water degradation. a. If an assessment site soil leachate concentration is greater than the numerical water quality limit (and also background in this case), the constituent not only threatens to degrade ground water, but poses a threat to beneficial uses,as well. Then, the degree of attenuation that would be necessary to protect benefi- cial uses is determined by dividing the numerical water quality limit into the assessment site soil leachate concentration. i. If the calculated degree of attenuation is available between the base of the contaminated soil and the highest level of ground water, the soil con- stituent does not threaten beneficial uses,but may threaten to degrade ground water. Further assessment is required for that constituent in that lithology per Section 4.b. below. ii. If the calculated degree of attenuation is not available between the base of the contaminated soil and highest ground water, the soil constituent threatens beneficial uses (pollution) in addition to threatening ground water quality (degradation). Then,the constituent must be remediated to below the beneficial use protective level, and to the lowest level that is technologically and economically achievable. iii. If the same contaminant is present both ground water and in overlying soils, contaminant breakthrough has occurred and no attenuative capacity is available for that constituent within overlying soils. b. If an assessment site soil leachate concentration is greater than background,the soil constituent may threaten to degrade ground water. Then, the degree of at- tenuation necessary to protect ground water quality is determined by dividing the background ground water concentration into the assessment site soil leachate concentration.