ARCHIVED REPORTS XR0005822 - Laserfiche WebLink

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MW-1 MW-3 MW-2 , 4 & 5 12/96 5/97 12/96 5/97 ND Benzene 9240 2320 101 4 0 ND Toluene 1110 378 6 . 0 ND ND EBenzene 983 351 13 0 1 0 ND Xylene 5180 1740 22 0 1 0 ND THPg 43 , 100 15, 000 550 101 ND NOTE- Units are ug/L The decrease in levels of contamination, and the reduction in the size of the plume indicates the possibility that natural attenua- tion in taking place, although that has not been evident from prior work Three casing volumes were purged from each well prior to sampling, and recharge was quite good Even though the water table is above the screened intervals, the sample results are considered to be accurate PLATES II through VI show the estimated lines of equal concen- tration of benzene, ethylbenzene, toluene, xylene, & TPHg based on the latest test results . They continue to show that the center of the plume is in the vicinity of MW-1, which has been confirmed by prior work. The shape of the plume has not changed significantly since monitoring began, indicating that it has stabilized CONCLUSIONS : 1 . The limits of the soil & water plumes have been fairly well defined in all directions . There is no indication of an offsite source 2 . The groundwater plume has migrated no more than 100 feet to the north and 125 feet to the west of the site of UST' s, which were removed in 1989 The highest levels of BTEX & TPHg have consistently been recorded from MW-1, indicating that there has been very little movement of the groundwater. On October 3 , 1996, WJH submitted a workplan addendum to the San Joaquin County EHD to place seven (7) shallow soil borings or geoprobe holes in an attempt to characterize the amount & volume of contaminated soil that exists beneath the property The work was completed on February 25, 1997, and a report covering the results has been submitted to the San Joaquin Co. EHD The results of that work revealed that soil contamination is confined to the approximate area shown on PLATE VII, within the depth range of 11 ' to 23 ' bgs . The extensive data collected to date . reveals that the soil & water plumes are quite stable, and there 2