ARCHIVED REPORTS XR0007844 - Laserfiche WebLink

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Ms Lon Duncan • Apn14, 2002 Page 2 of 4 groundwater in the immediate vicinity of the former UST The vertical extent of soil contamination has been defined at the source (boring SB3) No contaminants were detected deeper than 31 feet below ground surface (bgs) The lateral extent of soil contamination was also largely defined in previous investigations Soil contammation in the vadose zone appears to be limited to a small area in the immediate vicinity of the former UST, and soil contamination in the capillary fringe zone appears to extend no more than 25 feet north, 20 feet west, 10 feet south, and 5 feet east of the former UST On December 13 and 14, 2000, four groundwater monitoring wells were installed to further investigate the extent of soil and groundwater contamination at the site Analytical results indicated that petroleum hydrocarbons yj soil were limited to a small area in the immediate vicinity of the former UST, and that the extentetroleum hydrocarbon contamination in the groundwater does not extend more than approximately 40 feet downgradient from the source Various chlorinated solvents were also detected in all site wells, and free product was noted in well MW3 Subsequent quarterly groundwater Famphng at the site confirmed that the lateral extent of petroleum hydrocarbon contamination is within close proximity to the former UST The presence of free product and groundwater analytical results indicate that petroleum hydrocarbon contamination is present in groundwater in the immediate vicinity of the former UST but does not extend to perimeter wells Various chlorinated solvents continue to be detected at low levels, however, only PCE continues to exceed its Maximum Contaminant Level (MCL) of 5 0 ppb The measurable product thickness in well MW3 has been steadily declining since regular product bailing was initiated WORKPLAN To further investigate the lateral extent of chlorinated solvents in groundwater beneath the site Ground Zero proposes the following scope of work Drilling, Well Construction and Soil Sampling Three momtonng wells will be installed at the site at the approximate locations shown on Figure 2 Actual locations may be modified as needed depending upon the feasibility of obtaining encroachment permits from the City of Stockton A dulling contractor with a C-57 drilling hcense will advance soil bonngs using a drill ng equipped with 8" diameter hollow stem augers The wells will be completed to depths of approximately 34 feet below ground surface (bgs) and will be constructed of 2-mch diameter, Schedule 40 PVC casing and 0 010-inch slotted screen The wells will be screened from approximately 19 feet to 34 feet bgs The filter pack will consist of No 3 Monterey sand from the bottom of the wells to approximately 2 feet above the top of the screens The remaining annulus will be completed with 2 feet of hydrated bentonite overlain by neat cement grout Each well will be fitted at the ground surface • with a locking cap and watertight, traffic-rated well box G\Data\GROUNDZH\GABBARD\Workplmsl3_add_MW WORKPLAN doe