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Draft RI/FS Amendments -2- 12 April 1993 DDRW, Tracy summarized by Woodward-Clyde. The CoE indicated that Montgomery Watson will review these data prior to beginning the field investigation program. Soil Sample Analysis for Soluble Concentrations. In response to the Boards 9 April 1992 comments Woodward-Clyde stated in Section 3.1.2.5.4 of the Comprehensive RI/FS Work Plan that soluble concentrations would be analyzed on selected samples. Montgomery Watson has not incorporated analyses for soluble concentrations in soil into the Work Plan Amendments. This omission was pointed out in the 23 March 1993 meeting. DDRW, Tracy agreed to analyze for soluble concentrations on a minimum of 20 percent of selected soil samples so that a ratio of soluble to total concentrations may be established. Soluble concentrations are necessary to determine whether the residual wastes, if left in-place, will continue to degrade groundwater quality. Soil cleanup levels for many of the contaminants should be based on soluble concentrations rather than total concentrations. A soil cleanup level of hazardous concentrations or slightly less may not be acceptable. Soluble analyses must be performed on samples that have known elevated total concentrations (above background concentrations) . We would like to discuss the criteria by which the samples for soluble concentrations are chosen before the Phase I field investigation begins. Background Investigation. Establishing background concentration values for soil and groundwater is one the most important objectives of the Phase I RI . The general strategy described in the Work Plan is acceptable. The criteria for collecting acceptable soils data to determine background inorganic concentrations were discussed in the 23 March 1993 meeting and are discussed in more detail below. ► For soil samples collected exclusively for background determination, analyzing for pesticides and volatile organic compounds (VOCs) is unnecessary. These compounds are not naturally occurring, therefore, background soil sampling should be conducted for inorganics only. The Board considers non-detect values to be representative of background concentrations for these constituents. ► Background soil samples should be collected onsite and in unaffected areas where disposal activities have not occurred. ► Soil samples must be collected and analyzed for background concentrations. Background soluble concentrations are necessary to conduct a Water Quality Site Assessment on UST and Solid Waste Management Units (SWMUs) . ► A significant number of soil samples should be collected from each of the major soil types identified at this site (ie: clays, sands, silts, and gravels) . Soil samples for background determination should be collected throughout the unsaturated zone. Multiple soil samples are needed to determine a representative range of inorganic background concentrations throughout DDRW, Tracy.