ARCHIVED REPORTS XR0008209 - Laserfiche WebLink

Home Browse Search

s I • specifically, where excavating had succeeded in removing the s contaminated soil. PHASE II IN--SITU VAPOR RECOVERY Two areas of soil contamination remained in the pump island areas, the southern end of the excavation of the western pump island (P3) i and the northern end of the eastern pump island area (P1) . These - = two areas were then deepended with a backhoe to the 26 foot depth and then backfilled with 1/4" rounded clean pea gravel to the 10 foot depth. The tank field excavation (EX) was also backfilled with 1/4" pea gravel to the 10 foot depth, then "Typar" matting was placed over the pea gravel and a 6" layer of AS gravel was used to hold the "Typar" in place. The remaing excavated areas where then backfilled with the clean aerated native soil in two i foot lifts and compacted to surface grade. Figure 3A indicates • areas of contaminated soil from the 25 foot depth to the 40 foot # i depth. d r On October 8 and 9, 1990, the P1, P3 and EX areas where drilled to the 40 foot depth using 10" hollow steam augers and 2" PVC extraction wells were installed, see Figures 3B and 4D. A pilot test for vapor extraction was conducted from December 10, 1990 to January 4, 1991, see Table 3A. After evaluating the pilot fest results an application for Authority to Construct for vapor extraction was proposed and received by San Joaquin County Air f Quality (SJCAQ) on April 26, 1991. SJCAQ were unable to review the application for at least 90 days so a variance with public comment was initiated by WEGE. The public hearing was presented by Mr. Jack Napper of WEGE on Wicklands behalf on May 9, 1991. An Interium Variance was granted for vapor extraction prior to the hearing on March 29, 1991. Vapor extraction commenced on April 26, 3991 (see Update Status Report 6, Appendix A, dated July 26, 1991) . Vapor extraction concentrated on the vadose zone (10 foot depth to 40 foot depth) but also effected the ground water beneath the site, see Vapor extraction Tables 3A, 3B, 3C and Ground Water ry Monitoring Data Table 2. As of October 3, 1991 11,910 pounds of gasoline range hydrocarbons have been removed from the soil and ground water at this site. Of this, approximately 626 pounds from the soil around the vapor extraction wells P1, P3 and EX and 11,284 pounds from the soil and ground water near monitor wells MWI and MW5. Monitoring at ~his site has shown a dramatic decline in vapor recovery at P3 from �-5 pounds per day to 0.3 pounds per day and at EX from 2-3 pounds per day to 0.03 pounds per day, P1 never produced significant hydrocarbons and has been used as an ambient air injection well and vapor influence monitor well, see Figure 3C. Figures 5A through 50 show the indicated vacuum influence created by the vacuum extraction system at this site, and compared to the areas of known soil contamination, Figure 3A, indicators that the vacuuum extraction has successfully lowered and/or removed the hydrocarbon contamination that existed between the 25-40 foot page 2 i