ARCHIVED REPORTS XR0001515 - Laserfiche WebLink

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EXECUTIVE SUMMARY The objectives of this phase of environmental corrective action were to evaluate if the plume of impacted groundwater threatens any nearby sensitive receptors, to define the lateral extent of ' impacted soil and groundwater, and to expand the groundwater monitoring capability at the site To achieve these project objectives, Ramage Environmental, surveyed sensitive receptors within 2,000-feet of the site, supervised the installation of four off-site groundwater monitoring wells, ' and monitored and sample the expanded groundwater monitoring well network No sensitive receptors located within the site vicinity appear to be threatened by the gasoline hydrocarbons in soil and groundwater, originating from the former UST system at the site For ' the site vicinity, one well completion report was on file at DWR Three additional well completion reports were identified immediately outside of the 2,000-foot site vicinity radius The nearest water supply well (approximately 800 feet west of the site) is the California Water ' Service Company Well #50, which has been out of service for several years, but remains open for potential future use The nearest active water well is the San Joaquin County Fairgrounds well, approximately 2,100 feet southeast of the site No schools, hospitals, day care centers or ' other possible sensitive receptors were observed in the site vicinity The nearest surface water body to the site is the Mormon Slough, which crosses the site vicinity approximately 1,000 feet north of the site ' All of the soil and groundwater samples collected from the four new wells were free of detectable concentrations of gasoline compounds As such, the lateral extents of impacted soil and groundwater appear to be defined Based on the cumulative soil sample analytical data, impacts to vadose zone soil appear to be limited to the footprint of the former UST system On-site, the groundwater samples collected from MW-2 and MW-3 continued to contain ' concentrations of TPH-as-gasoline, BTEX and 1,2-DCA The sample from MW-2 contained 210,000 µg11 of TPH-as-gasoline, 4,600 µg/l of benzene, 37,000 µg11 of toluene, 4,700 µg/l of ethylbenzene, 29,000 µg/I of xylenes, and 500 µg/l of 1,2-DCA The groundwater sample ' collected from MW-3 contained 1,400 µgll of TPH-as-gasoline, 0 61 µg11 of benzene, 59 µg/l of TBA, and 250 µg11 of 1,2-DCA The groundwater sample collected from MW-1 did not contain detectable concentrations of gasoline hydrocarbons MTBE was not detected in groundwater ' beneath the site The expanded groundwater monitoring well network indicates that groundwater flow may be 1 more toward the east-southeast Based on the groundwater analytical and monitoring results, the plume of impacted groundwater probably extends from the vicinity of the former UST system to the southeast beneath the East Charter Way right-of-way Ramage Environmental recommends the following course of environmental corrective action 1 Complete two additional CPT borings and collect additional discrete groundwater samples, 2 Complete a geophysical survey of the former UST excavation area, and 3 Continue to monitor and sample groundwater on a quarterly basis 1 r� ' 4 I 1