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13 .October 2003 <br /> AGE-NC Project No. 95.-0106 <br /> Page-3 of 4 <br /> _ y <br /> 4.0. SUMMARY AND CONCLUSIONS <br /> The following conclusions were drawn,from the results of the site investigation: . <br /> •.' ` The ground water flow direction was generally northward on 20 June 2003, and gradients <br /> were calculated to range from 0.005 feet/feet toward the.north-northwest to 0.004 feet/feet <br /> towatd,the northeast. <br />! •. Dissolved petroleum hydrocarbons were detected in groundwater samples from monitoring <br /> well MW-4, located down-gradient off-site from-the former UST excavation, and MW-1 <br /> located just north of the former UST area. <br /> • BTEX-cornpounds were.detected in the water samples collected from MW-1 and MW-4. The -. <br /> concentrations of benzene in the samples. exceeded the State of California maximum <br /> contaminant level (MCL) of 1 µg/l for drinking water. <br /> • Analytical data from monitoring wells MW-2 an,d'MW-7 limits the horizontal extent of <br />' dissolved hydrocarbons south and.east of the site,,respectively. Analytical data from wells <br /> MW-3 .and MW-6 limits the extent of dissolved hydrocarbons northeastward of the site. <br /> Analytical data from monitoring well MW-5 limits the extent of dissolved hydrocarbons <br /> northwestward of the site. The extent-of dissolved hydrocarbons to the west or well MW-4 <br /> is not completely,defined at this time. <br />' Continued detection of TPH-g and BTE&X in ground water samples collected from the off- <br /> site well MW4 indicates that the plume of impacted groundwater has migrated off-site <br /> towards the north, however, the general lack of detection of hydrocarbons in the MW-7, <br />' MW ab, MW-5; and MW-3 wells shows that the plume is not wide-spread and has not <br /> migrated northeast of MW-4 or northwest of the former UST excavation. ; <br /> • The extent of the plume around MW-4 is constrained by data from MW-6 toward the north- <br />' ,northeast, MW-5 toward.the southwest and MW=7 toward the east relative to MW-4. The . <br /> northwestem,extent�bfthe plume from.MW-4 is not well defined. ; <br /> 5.0:, RECOMMENDATIONS <br /> Based on'this:and previous.site investigations, AGE recommends continued quarterly monitoring <br /> wwas <br /> : . <br />' of the ell network',The next monitoring event was`performed'int September 2003. <br /> Advanced GeoEnvironmentai'Inc. <br /> ii <br />