ARCHIVED REPORTS_XR0007102 - Laserfiche WebLink

Home Browse Search

IL d Site History - 14000 Highway 88,Lockeford,CA Time Oil Property No 04-049 and 70 ppb xylenes Analyses identified 100 ppb TPH, 2 3 ppb benzene, and 0 6 ppb xylenes in the sample collected from MW-4 At this time, it appears as though there may be two areas of soil contamination at the subject site one shallow and one deep It appears that the extent of shallow sod contamination has been defined and does not appear to extend much beyond the limits of the former tank bed The vertical migration of shallow sod contamination may be limited by the lens of clayey silt existing at 30 to 35 feet bgs Deeper contamination (beginning at approximately 40 feet to 45 feet bgs) appears to be present at highest concentration to the northeast of the former tank bed The extent of deeper soil contamination is fairly well defined to the northeast, southeast, and west by the samples collected during the additional site investigation, however, it may need to be further investigated to the north and south Time's records do not indicate any potential sources for the deep sod contamination noted in the vicinity of MW-1 Since this deeper contamination is some distance from the former tank bed, we believe that it may be due to an offsite hydrocarbon source The extent of groundwater contamination has not been defined in any direction and appears to extend offsite to the north, south, and east The elevated concentrations of hydrocarbons in MW-1 and MW-2 (both sidegradient of the former tanks), suggest that an offsite source of hydrocarbons may be impacting the subject site Time has reviewed several reports concerning the Beacon Station located immediately to the north of the subject site It is Time's understanding that a "dry well"was once present on the southeast corner of the Beacon Station property This dry well, located immediately upgradient of MWA and MW-2, could be a potential source of contamination to deeper soils Investigation performed near a second dry well, • located on the southwest portion of the Beacon property, revealed significant groundwater contamination which has not yet been defined in the downgradient direction A copy of SECOR's "Environmental Investigation Report" dated May 4, 1995, was forwarded to the approoirate requaltory agencies onf May 18, 1995 Groundwater Monitoring Report and Quarterly Status Report for_ Second Quarter 1995 Based on the results of the investigation, Time Oil implemented quarterly status reporting and quarterly groundwater monitoring On May 23, 1995, samples were collected from each of the monitoring wells at the subject site Prior to purging, the depth to groundwater in each well was measured by a representative of SECOR to assist in evaluating changes in elevation, flow direction, and gradient Groundwater was encountered at 75 40 feet to 86 62 feet below ground surface Although groundwater levels rose in some wells and fell in others since the previous sampling event, groundwater elevation decreased across the site by an average of 2 17 feet Consistent with previous findings, groundwater flow remained to the southeast with a gradient of 0 15 ft/ft Analyses identified gasoline and its constituents in groundwater samples collected from each of the monitoring wells MW-1, located nearest the existing pump islands was found to contain 9,200 ppb gasoline, 440 ppb benzene, 1,900 ppb toluene, 280 ppb ethylbenzene, and 1,100 ppb xylenes Perimeter wells MW-2, MW-3, and MW-4, located sidegradient and downgradient of the former tanks were found to contain 55 ppb to 320 ppb gasoline, 0 7 to 13 ppb benzene, as well as low concentrations Of toluene, ethylbenzene, and xylenes Results of the quarterly monitoring event Indicated that the extent of hydrocarbon-impacted groundwater at the site had been relatively well defined to the west, however, it remained undefined to the north, south and east of the former tank bed Hydrocarbon concentrations decreased in the perimeter wells 5