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� J r <br /> w <br /> Former Chase Chevrolet Facility <br /> 423 Madison 424 Van Buren <br /> Stockton, CA 95201 <br /> Page 2 <br /> quarterly sampling of sentinel downgradient monitoring wells at 423 Madison. Selected <br /> drowned wells at 424 Van Buren should also be sampled quarterly as groundwater is <br /> expected to drop in the coming months. (See Table 2) <br /> Table 2: Sampling Schedule <br /> 423 Madison 424 Van Buren <br /> Annual Sampling 3rd Quarter) All wells All Wells <br /> Semi-annual Sampling (15` and 3`d MW-2, MW-4, MW-5,MW- MW-3, MW-6, <br /> Quarter): Wells with stabilizing or 19A,MW-19B,MW-20A, MW-9, MW-10, <br /> reducin contaminant concentrations MW-20B,MW-21A, MW-21B MW-22 <br /> Quarterly Sampling: Sentinel Wells MW-2,MW-4,MW-5 MW-3,MW-6, <br /> down-gradient of critical groundwater MW-9,MW-10, <br /> MW-22 <br /> flow ath <br /> Additional remediation technology such as ozone sparging to supplement the existing <br /> remediation system has been approved but has not been implemented. Sampling schedule <br /> should be re-adjusted after implementation of the additional remediation activity. <br /> Three sets of nested monitoring wells MW-19A and B,MW-20A and B,and MW-21A and B <br /> were installed in the area of underground storage tank (UST) #8 area in August 1998 . <br /> Concentrations of TPH-g and TPH-d have declined in most of the wells except MW-20A <br /> and MW-21A (See Table 3 below). <br /> Table 3. Ma 20024AAnalltic"al results of UST Area #8 <br /> MW-19 -20A MW-21A MW-19B MW-20B MW-21B <br /> Screen 11-31'b2'bs 12-32'bs 48.5-53.5'bs 50-55'bs 48-53' bs <br /> TPH- <50 7,300 <50 <50 750 <br /> TPH-d <50 8,100 <50 <50 260 <br /> Results in pg/l. TPH-d =Total Petroleum Hydrocarbon as diesel <br /> Data from 2°d 2002 Quarterly Report dated June 26, 2002 prepared by AGE. <br /> EHD and AGE agreed that the lateral extent of the contamination in groundwater has not <br /> been defined to the west and east of UST#8. Submit a work plan to EHD that will define <br /> the lateral extent of the ground water plume by October 25,2002. <br /> Addendum to Ret sed Corrective Action Plan dated September 30, 1997 prepared by AGE <br /> evaluated multiple remediation alternatives and recommended excavation of the <br /> contaminated soil in the area of UST #8 followed by monitoring of natural attenuation. <br /> Subsequent investigation revealed that the vertical extent of the contamination in <br /> groundwater to be deeper than initially anticipated. Excavation was subsequently dropped <br />