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R NOMA 1992 Third Quarter Report,Site Code 1178 City of Stockton,Police Facility October 14, 1992 Page 4 To characterize the stockpiled soil at the Service Center, RESNA personnel collected three 2:1 composite samples on July 31, 1992 under the guidance of Ms. Meays. Laboratory results are summarized in Table 2. Laboratory Analyses Collected soil samples were placed on ice and transported under chain-of-custody protocol to State-certified Sequoia Analytical Laboratory in Redwood City, California. All samples were analyzed for benzene, toluene, ethylbenzene, xylenes (BTEX) and total petroleum hydrocarbons as gasoline (TPHG) utilizing EPA methodologies 8020 and modified 8015, respectively. Laboratory results are summarized in Table 2. Laboratory reports and chain-of-custody documentation are contained in Attachment 2. Analytical results indicate hydrocarbon impacted soils remain in place along the northern wall of the excavation, apparently extending some distance beneath the existing structure. In addition, the soils under the concrete-encased electrical lines (the central wall) contain hydrocarbon constituents at very low levels (Table 2). The electrical lines apparently acted as a conduit for a small volume of liquid hydrocarbons to move laterally from the leak location. The degree of lateral migration appeared to be limited and at concentrations three orders of magnitude less than those near the leak locations; spreading along the electrical lines is considered negligible. The volume of impacted soils remaining in-place beneath the building can be estimated based upon the analytical results of soil samples collected during the excavation. The highest concentration of gasoline hydrocarbons (1900 ppm) was recorded in sample NW-5.5W, collected at 5.5 feet below grade near the product line leak. Based upon the non-detected results of samples collected nearby, it is estimated that soil impaction is limited to a semicircle with a radius of approximately 12 feet, extending north of the leak location. The vertical extent of contamination is limited from 2 feet below grade (depth of product line) to approximately 8 feet_ below grade. - d t`t` `' x a 1: rTim= ,a mainnium fin- ae,gntaitiin a rQ'X im_a e n f It should be noted that these are estimated maximum Pumes.WAsoils and typical conical spreading, the actual volume of impacted soil could be a little as one-third of the estimated maximum (approximately 17 yd ). Groundwater Sampling On August 20, 1992, RESNA conducted confirmation groundwater monitoring/sampling from the site monitoring well (MW1). Groundwater currently exists at a depth of approximately 46.5 QRTLYRP \QR090292.FNL