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Additional Site Investigation Reporl Western Stone Products-Tracy,CA Project No.W0195.01 Page 2 the site specific Health and Safety Plan (Attachment 3, 1992 Third Quarter Monitoring Report, August 28, 1992). Attachment 1 contains the monitoring data and field notes collected during site activities. Drill cuttings are stored on site, underlain and covered with plastic, pending a disposal plan. The soil borings were abandoned with neat cement. ANALYTICAL RESULTS Petroleum hydrocarbon analytes were not present at or above method detection limits in either sample collected from boring B2W. Petroleum hydrocarbon analytes were present in the soils collected from B1W at 7.5 feet (3.1 parts per million - ppm diesel), 8.0 feet (23 ppm diesel), 9.25 feet (0.088 ppm toluene, 0.64 ppm ethylbenzene, 0.93 ppm xylenes and 180 ppm diesel). No analytes were detected in the sample collected from BIW at a depth of 6 feet. Benzene was not detected in any sample. The depths at which petroleum hydrocarbon analytes were present indicates residual impact is likely related to fluctuations in groundwater depths that have occurred during the history of the site. Attachment 2 contains the laboratory analytical data. Based on the analytical data collected from this investigation along with the results of previous 4=?=a analyses it is estimated that approximately 1800 cubic feet of soil beneath the structure contains some residual diesel contamination. The affected soil interval lies between 7.0 and 11.0 feet below grade. Analysis of the soil samples previously collected from soil boring B1 (located within the former tank pit) indicate that concentrations are considerably reduced between 8.0 feet (53 ppm diesel) and 11.0 (2.2 ppm diesel) feet below grade. In order to calculate the volume of diesel remaining within the soil the affected area was subdivided laterally into three concentration zones. These are depicted on Figure 3 for the 8 foot depth. The average TPHD concentration for the affected vertical interval from 7.0 to 11.0 feet was estimated by weighted average to be 2.875 times the concentration at 8.0 feet. This "operative concentration" was used to calculate the mass of residual diesel in the affected soils. Table 3 summarizes the calculations. It is estimated that approximately 12 pounds of diesel are contained within approximately 1800 cubic feet (67 cubic yards) of affected soil. CONCLUSIONSIRECOMMENDATIONS The analytical data and the historical groundwater monitoring data indicate that residual petroleum hydrocarbon contamination is confined to the soils located within the capillary fringe and uppermost saturated zone, approximately 7.0 feet to 11.0 feet below grade. The majority of the impacted soil, approximately 375 to 400 cubic yards, has been removed from the site. Removal of the residual impacted soil, estimated to be approximately 67 cubic yards, is impossible without removing the structure located above the area of concern. REP0RT8IR-071293.1-"N L