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• Monitoring Well Installation and VET Report—Former Unocal Station#2859,Stockton,CA <br /> MY 30,2001 <br /> 4 In Zone B wells, dissolved hydrocarbons were only detected in well MW-12, with trace benzene in <br /> well NP-1 Because groundwater flow in Zone B appears to be to the southeast, Zone B is not <br /> delineated southeast of well MW-12 <br /> 5 Based on the VE test results, it is estimated that less than one pound per day of hydrocarbons can be <br /> extracted at test conditions using the vapor extraction wells This would be expected to decrease over <br /> time. The expected radius of influence would be less than 45 feet Vapor extraction would have little or <br /> no effect at this site <br /> RECOMMENDATIONS <br /> Based on the above site conceptual model,additional delineation is needed in Zone A to the north of well <br /> MW-15, and in Zone B southeast of well MW-12 GR recommends the installation of two groundwater <br /> monitoring wells as shown on Figure 6 one well screened in Zone A near the northwest corner of West <br /> Walnut Street and Pacific Avenue in order to complete delineation of that zone, and one well screened in <br /> Zone B adjacent to well MW-9 in order to assess the extent of dissolved hydrocarbon migration in that <br /> direction <br /> To limit further migration of hydrocarbons from the site in the downgradient directions, GR recommends <br /> . the installation of ozone-microsparging{C-Sparge} wells along the eastern boundary of the site as shown <br /> on Figure 6 Each C-Sparge well location shown on Figure 6 will consist of multiple wells set at various <br /> depths The two southern most locations shown on Figure 6 will consist of three wells set at <br /> approximately 30, 60,and 90 feet bgs The northern most C-Sparge location will consist of two wells set <br /> at approximately 30 and 60 feet bgs This placement of wells should be effective at remediating the <br /> majority of dissolved hydrocarbons remaining beneath the site <br /> The newly installed groundwater monitoring wells have been integrated into the ongoing quarterly <br /> monitoring program for the subject site <br /> Vapor extraction is not recommended as a viable treatment option for this site <br /> 24007204-1 8 <br />