ARCHIVED REPORTS_XR0012231 - Laserfiche WebLink

Home Browse Search

• Ozone Microsparge System Annual Status Report—Former Tosco(76)Station No 6981,Stockton,California March 3 2003 In April 2000, the service station building and all related facilities were removed from the site, including two 12,000-gallon double-wall steel gasoline USTs Soil samples were collected from beneath the USTs, product lines, and dispenser islands Any potentially impacted soil was overexcavated A total of approximately 200 cubic yards of potentially impacted soil was excavated from beneath the northwest and southeast dispenser islands and product lines immediately north of the west UST In addition, the UST pit was excavated to a depth of 21 feet bgs Ozone Micro Sparging The ozone sparge system, manufactured by KVA, was placed into operation on December 19, 2001, and is designed to cycle the ozone/oxygen injection between the 10-points A typical infection schedule through each point is 18 times a day, for between 5 and 15 minutes per point per cycle In order to evaluate system effectiveness, periodic sampling of selected groundwater monitoring wells has been performed at the site Wells MW-7, MW-16, and VW-7 were selected for sampling, and MW-16 has been sampled on a monthly basis since the system was placed into operation . Monitoring well MW-7 was sampled monthly until July 2002 From July 2002 until the present, VW-7 was utilized for the monthly sampling rather than MW-7 Groundwater samples from the three wells were analyzed for TPHg by either EPA Method 8015 modified or Method 8260, benzene, toluene, ethylbenzene, total xylenes (BTEX) and MtBE by EPA Method 8021 or 8260 Groundwater analytical results for the three wells are presented in Table 1 Charts of groundwater concentrations over time for wells MW-7, MW-16, and VW-7 are presented on Figures 3,4, and 5 If an analyte was reported as not detected, a value of one half the detection limit was utilized during chart preparation Laboratory analytical reports for the monthly sampling events are attached in Appendix B OBSERVATIONS Groundwater Sampling Results GR collected monthly groundwater samples from wells MW-7, MW-16, and VW-7 to monitor the progress of the system ' Wells MW-7, MW-16, and VW-7 are all located downgradient of the underground storage tanks (USTs) They are all within the treatment area and the zone of influence of one or more sparge points MW-16 was chosen as the primary point for evaluation of the remedial system effectiveness 140124 08 2