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- e <br /> Mr. John Welty <br /> April 10, 1990 <br /> Page 14 <br /> Conclusions <br /> The data reviewed indicates the following conclusions: <br /> 1. Groundwater beneath TGA's property has been affected by dissolved gasoline <br /> constituents, in all likelihood coming from the 7-Eleven site. <br /> 2. The groundwater remediation system now operating at the site does not capture <br /> contaminated groundwater that has moved off site. It also may not restrict further <br /> migration of contaminated groundwater from beneath the 7-Eleven site. The original <br /> capture zone map developed by GTI indicates that a pumping rate of less than 10 gpm <br /> at the 7-Eleven site will not capture groundwater at the TGA property. Since no effort <br /> has been made to replace Well 12 on the TGA property and the pump rate at the site <br /> is less than 2.5 gpm, it appears that Southland does not plan to recover the plume or <br /> to continue the monitoring of hydrocarbons downgradient of the site. <br /> 3. T'he cluster wells were not individually sampled to determine how contamination <br /> differed in concentration at different depth zones. in addition, because the perforated <br /> zones were not adequately separated between each well, the data developed by these <br /> wells may have limited value, as stated in the letter by the RWQCB. <br /> 4. The soil-vent system appears to be working as designed and should reduce <br /> hydrocarbons from the soil immediately around each vapor point. The area affected <br /> by each vapor point can not be determined without further soil testing on the 7-Eleven <br /> site. The expansion of the vapor system to include the dry on-site wells should act <br /> to clean up the deeper zones of contamination in the soil that were previously under <br /> the water table. It can not be determined whether the soil-vapor system is working <br /> to reduce hydrocarbons in the groundwater around the vapor points. <br /> 5. To date, Southland and their consultant have continued to address the contamination <br /> problem at the site by continuing to sample the groundwater, submitting update <br /> reports, and operating and maintaining the remediation systems. <br /> Recommendations <br /> 1. We recommend that TGA request a letter from Southland stating Southland's <br /> commitment to remediate the contamination resulting from the 7-Eleven site. <br /> 2. We recommend that TGA make a request to the County and to Southland that <br /> Southland replace Well 10 and 12 and continue to monitor the downgradient shallow <br /> and deep groundwater beneath TGA's property. <br /> Brown and Caldwell <br />