ARCHIVED REPORTS_XR0006136 - Laserfiche WebLink

Home Browse Search

Cardock Gasoline Station,4555 North Pershing Avenue ' The Cardock gasoline station, located east of the Shell service station, was investigated for diesel contamination and received no-further action status in December 1997 ' During a file review conducted by ETIC personnel at the SJCEHD, ETIC received a copy of a memo dated 12 November 1996 summarizing efforts by Ms Elizabeth A Thayer of the Regional Water Quality Control Board (RWQCB) to assess the relationship of hydrocarbon-impacted ' groundwater at the ExxonMobil, Shell, and 7-Eleven sites This memo is included as Appendix F Based on the isoconcentration contour map prepared by Ms Thayer, the hydrocarbon- impacted groundwater from the Shell site was commingled downgradient with the hydrocarbon- impacted groundwater from the ExxonMobil site in 1996 ' 2.7 SUMMARY OF PREVIOUS REMEDIAL ACTIONS In October 1990, EA proposed a groundwater extraction, treatment, and reinfection system for former Exxon RS 7-3942, and installed the required wells for this remedial approach Due to problems in securing the permit for reinjection of treated groundwater, this remedial option was not implemented ' From 1992 to 2000, three remedial approaches were implemented to address petroleum hydrocarbons detected in soil and water The initial remedial approach was LPH removal using passive skimmers in wells RW3 and V1 The second remedial effort was a soil vapor extraction/air sparging (SVE/AS) system, which operated from May 1994 to November 1996 and recovered petroleum hydrocarbon vapors from wells MW2, MW3, MW5, and MW6 ' (screened from 10 to 30 feet bgs), wells V1 and V2 (screened from 20 to 40 feet bgs), and well V4 (screened from 25 to 40 feet bgs) in conjunction with air sparging wells A total of approximately 14,500 pounds of petroleum hydrocarbons was removed from the vadose zone by the SVE/AS system (EA 1997) The SVE influent concentration and the cumulative estimated pounds of TPH-g removed became asymptotic over time As presented in Figure 10 the groundwater elevations across the site had risen approximately 2 5 feet by October 1995, indicating that the decline in influent concentrations and the associated pounds removed is attributable to the success of the SVE rather than rising groundwater conditions, which can submerge the screened portion of the vapor extraction system The third remedial effort consisted of the installation of a vacuum vaporizer well system, known as UVB, for groundwater remediation at the site beginning in November 1996 The installation of the UVB system consisted of overdrillmg existing groundwater recovery well RW3 to install the dual-screen UVB well for groundwater extraction-infection, and the installation of adjacent monitoring wells UVB-MW1 and UVB-MW2 to monitor system performance (EA 1997) Between 6 February 1997 and 22 September 2000, a total of 1,890 pounds of petroleum hydrocarbons as gasoline (TPH-g) was removed from groundwater by the UVB system based on laboratory analytical results, and 821 pounds based on field measurements (ETIC 2000a) Figure 11 presents the pounds removed based on both laboratory and field data over time The Iower value of 821 pounds is viewed as more representative of the actual pounds removed by this remedial system as the field values are consistent and not dependent on a single high value ' G1Projects1739421MASTERNWPiWM3031WPtx 6x