ARCHIVED REPORTS_XR0011586 - Laserfiche WebLink

Home Browse Search

concentrations of total petroleum hydrocarbons as gasoline (TPH-G) and total petroleum hydrocarbons as diesel (TPH-D) detected at the site prior to remedial efforts were 590 and 3,700 parts per million (ppm), respectively. • Onsite hydrocarbon concentrations in soil were excavated to the standing water level in July 1990. More than 6,000 cubic yards of soil were excavated and hauled to appropriate disposal facilities. The excavation was backfilled to grade with approximately 7,300 cubic yards of clean imported fill and compacted. Figure 2 indicates the approximate limits of the area of excavation. • On May 10, 1994, eleven soil borings (SB-1 through SB-11) were drilled to depths ranging from 24 to 34 fbg. Laboratory results for soil Borings SB-1 through SB-5 indicate that hydrocarbons have not impacted soil on the southern half or rear of the property. Adsorbed-phase hydrocarbons are characterized vertically beneath the site(SB- 6 through SB-11). Residual adsorbed-phase hydrocarbons are present from 11.5 to 16.5 fbg. These residual concentrations are adsorbed to clayey soils present below the water table at the base of the 1990 remedial excavation. The adsorbed-phase hydrocarbon concentrations attenuate rapidly with depth and do not appear to be migrating downward. • Eight onsite and 4 offsite ground water monitoring wells are present at the site. • Dissolved-phase hydrocarbons have historically been detected in Monitoring Wells AW-3 and AW-9, along the northern margin of the site. A dissolved-phase concentration of 110 ppb TPH-D was detected in AW-3 on October 6, 1994. No other dissolved-phase TPH- G, TPH-D, or BTEX concentrations were detected in any other wells at the site during the October 6, 1994 sampling event. • No free product has been observed in wells at this site. 4.4 PLANNED SITE ASSESSMENT ACTIVITIES 4.1 PRE-FIELD WORK ACTIVITIES Boring permits, encroachment permits, and property access will be acquired prior to drilling. Underground Service Alert (USA)will be notified approximately 10 days prior to field activities, and a geophysical survey will be performed to mark potential underground utilities at the proposed drilling locations. 4.2 DRILLING AND SOIL SAMPLING Two offsite borings will be drilled to a depth of approximately 20 fbg or 10 feet below the deepest detected hydrocarbon concentrations. See Figure 2 for the approximate boring locations. Borings have been located in the most feasible positions allowed by site conditions to further characterize hydrocarbon concentrations as requested by the San Joaquin County Public i- 3