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Work Plan Addendum Attachment -4- 21 September 1992 <br /> DDRW, Sharpe <br /> c. Compare the base-wide and site extracted concentrations. If the <br /> constituent's extractable concentration for the site is less than <br /> or equal to background, then it is assumed groundwater will not be <br /> impacted if the contaminant concentrations are left in-place in <br /> the unsaturated zone. <br /> d. If the extractable concentrations for the site are greater than <br /> background, then the potential leachate concentration for the site <br /> must be compared with both the base-wide background groundwater <br /> and the water quality goal concentrations. <br /> e. If the leachate concentration for the site is less than the <br /> smaller of the water quality goal or background groundwater <br /> concentrations, then the concentration in the site soils should <br /> not impact groundwater. <br /> f. If the leachate concentration for the site is greater than the <br /> smaller of the two concentrations, then a determination of the <br /> required site attenuation must be made. The required site <br /> attenuation factor may be determined by dividing the smaller of <br /> the background or water quality goal concentrations into the <br /> leachate concentration. <br /> g. Based upon the physical features of the site and the constituent <br /> characteristics, a determination is made as to whether the site <br /> subsoils have the ability to provide the required attenuation. If <br /> the site subsoils have the required attenuation, then the <br /> contaminant or constituent will not have to be remediated. If the <br /> site subsoils do not have the required attenuation, then the <br /> contaminant could impact groundwater and would require <br /> remediation. <br /> 3. Rationale and supporting analyses must be included for each site and <br /> constituent specific attenuation factors. <br /> 4. If necessary, the project managers and the necessary contractor <br /> personnel should meet as soon as possible to clear any <br /> misunderstandings of these comments. <br /> MHM:CKW <br />