SITE INFORMATION AND CORRESPONDENCE_3

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Mr. Mike J. Infurna Jr. Del Mode Foods—Former Disco Site December 19, 2008 Page 2 of 4 Stockton, California Sparging ozone into these points is no longer warranted because: 1. Groundwater flow has changed directions since the ozone points were installed and the sparge curtain is no longer located downgradient of the Site. The ozone sparge curtain is located south of the Site. As reported in routine groundwater monitoring and sampling reports, groundwater has been flowing from the source area toward the east/northeast or east/southeast since June of 2007. 2. Groundwater concentrations in the vicinity of the ozone sparge curtain are extremely low and current concentrations do not pose a significant risk to human health or the environment. Table 1 presents historical and current groundwater concentrations detected in monitoring wells south of the Site. The only constituent that has been detected above Water Quality Objectives (WQOs) in monitoring wells south of the Site has been 1,2-DCA. The highest 1,2-DCA concentration located south of the Site based on the most recent sampling event (October, 2008) is in well MW-11S at a concentration of 26 ug/I. Although this concentration is higher than the MCL for 1,2- DCA of 0.5 ug/L, there are no water supply wells within 2,000 feet of the Site (Corrective Action Plan, dated January 9, 2003). Concentrations of 1,2-DCA in all monitoring wells located south of the Site (MW-DIS-11S, MW-DIS-14S, MW-DIS-15, MW-DIS-12, and MW-DIS-13), have never been detected above RWQCB Groundwater Screening Levels for Soil Vapor Intrusion Concerns for 1,2-DCA (200 pg/L). 3. Based on analytical results from the ozone sparge curtain monitoring wells (MW-11 and MW-14), 1,2-DCA concentrations have reached an asymptote. Figure 3 shows the 1,2-DCA concentrations of monitoring wells MW-11S and MW-14S over time. As shown, concentrations in these wells have reached an asymptote and are currently at levels that are near MCLs and well below vapor intrusion screening levels. Active remediation in this offsite area is not warranted and the ozone sparge curtain may not be having any significant effect on groundwater concentrations. Shutdown and monitoring of groundwater concentrations in this area will determine whether concentrations rebound and additional treatment is necessary. In summary, SGI proposes to shutdown the offsite ozone sparge system, as groundwater is no longer flowing from the source area in the direction of the sparge curtain and residual concentrations of 1,2-DCA in groundwater south of the Site do not pose a significant threat to human health or the environment. SGI will continue to monitor concentrations in the vicinity of the ozone sparge curtain. The ozone generator, conveyance piping, and ozone sparge wells will remain in place. Should groundwater concentrations rebound following ozone system is shutdown, SGI will consider restarting the ozone system or implementing another treatment technology south of the Site. The Source Group,Inc.