ARCHIVED REPORTS_XR0006746 CASE 1

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EXECUTIVE SUMMARY To evaluate the horizontal and vertical extent of impacted soil and groundwater, establish a groundwater table monitoring capability at the site, and to determine if nearby domestic water wells had been impacted by gasoline hydrocarbons, cone penetration testing (CPT) and discrete soil and groundwater sampling were conducted at four on-site locations, four on-site groundwater table monitoring wells were installed, and the existing water well survey was expanded to include door-to-door inquiries and the sampling of 11 off-site domestic water wells Subsurface sods encountered during drilling consisted of discontinuous sand and silty sand intervals interbedded with finer-grained soils to a depth of approximately 65 feet Between 65 and 90 feet, more massive sand and gravel intervals are continuous across the site The static depth to the groundwater table, as measured in the four groundwater monitoring wells, ranged from 20 69 to 21 79 feet bgs The groundwater surface appears as a plane dipping to the northeast at a gradient of approximately 0 00825 foottfoot Groundwater zones beneath the groundwater table were identified and sampled at approximately 58 feet, 66 feet, and 78 feet In the seven sod samples collected using the CPT rig, only the samples from 40 and 50 feet from CPT-4 contained detectable concentrations of gasoline constituent compounds The sample collected at 40 feet only contained 0 0089 mg/kg of MTBE, and the sample collected at 50 feet only contained 0 04 mg/kg of MTBE At two of the CPT locations, MTBE was detected in groundwater-bearing zones beneath the groundwater table At CPT-4, the groundwater sample collected at 66 feet contained 86 µg/l of . MTBE, and the groundwater sample collected at 78 feet contained 1,100 µg11 of MTBE and 34 µg11 of TBA The groundwater samples collected from all four of the groundwater table monitoring wells contained detectable concentrations of gasoline constituent compounds The groundwater sample collected from MW-2 contained 330 µg/I of TPH-as-gasoline, 0 84 µg/l of benzene, 0 66 µg11 of toluene, 1 3 µg11 of ethylbenzene, 2 8 µg/l of xylenes, 160 µgll of MTBE and 19 µg/l of TBA At MW-4, only MTBE (2,800 µg/l) and TAME (3 2 µg/1) were detected The groundwater sample collected from MW-1 only contained 0 9 µg11 of benzene, and the sample collected from MW-3 only contained 3 8 µg/1 of MTBE A total of 56 domestic water wells were identified along Raylow Avenue and Mylnar Avenue, between East Yosemite Avenue to the south and North Street to the north Of the 56 parcels with water wells, only 12 are also connected to city water service A water sample was collected from the on-site domestic well and from the 11 residential wells within 500 feet of the site Concentrations of gasoline constituent compounds were not detected in any of the domestic wells sampled Based on the results of samples collected during this investigation, the horizontal and vertical extent of MTBE in soil and groundwater is not defined in the northeast part of the site, and although not impacted, the nearby domestic wells are threatened by the plume of impacted groundwater i3 � i 1