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Site History
<br /> 14000 Highway 88 Lockeford,CA
<br /> Time Oil Property No 04-049
<br /> MW-3 indicated 430 ppb TPH, 18 ppb benzene, 48 ppb toluene, 13 ppb ethylbenzene, and 70 ppb xylenes
<br /> Analyses identified 100 ppb TPH, 2 3 ppb benzene, and 0 6 ppb xylenes in the sample collected from MW-4
<br /> At this time, it appears as though there may be two areas of soil contamination at the subject site one
<br /> shallow and one deep it appears that the extent of shallow soil contamination has been defined and does
<br /> not appear to extend much beyond the limits of the former tank bed The vertical migration of shallow soil
<br /> contamination may be limited by the lens of clayey silt existing at 30 to 35 feet bgs Deeper contamination
<br /> (beginning at approximately 40 feet to 45 feet bgs) appears to be present at highest concentration to the
<br /> northeast of the former tank bed The extent of deeper soil contamination is fairly well defined to the
<br /> northeast, southeast, and west by the samples collected during the additional site investigation, however, it
<br /> may need to be further investigated to the north and south Time's records do not indicate any potential
<br /> sources for the deep sod contamination noted in the vicinity of MW-1 Since this deeper contamination is
<br /> some distance from the former tank bed, we believe that it may be due to an offsite hydrocarbon source
<br /> The extent of groundwater contamination has not been defined in any direction and appears to extend offsite
<br /> to the north, south, and east The elevated concentrations of hydrocarbons in MW-1 and MW-2 (both
<br /> sidegradient of the former tanks), suggest that an offsite source of hydrocarbons may be impacting the
<br /> subject site
<br /> Time has reviewed several reports concerning the Beacon Station located immediately to the north of the
<br /> subject site It is Time's understanding that a "dry well" was once present on the southeast corner of the
<br /> Beacon Station property This dry well, located immediately upgradient of MW-1 and MW-2, could be a
<br /> potential source of contamination to deeper soils Investigation performed near a second dry well, located on
<br /> the southwest portion of the Beacon property, revealed significant groundwater contamination which has not
<br /> yet been defined in the downgradient direction
<br /> A copy of SECOR's "Environmental Investigation Report" dated May 4, 1995, was forwarded to the
<br /> appropriate regulatory agencies on May 18, 1995
<br /> Groundwater Monitoring Report and Quarterly Status Report for- and Quarter 1995
<br /> Based on the results of the investigation, Time Oil implemented quarterly status reporting and quarterly
<br /> groundwater monitoring
<br /> On May 23, 1995, samples were collected from each of the monitoring wells at the subject site Prior to
<br /> purging, the depth to groundwater in each well was measured by a representative of SECOR to assist in
<br /> evaluating changes in elevation, flow direction, and gradient Groundwater was encountered at 75 40 feet to
<br /> 86 62 feet below ground surface Although groundwater levels rose in some wells and fell in others since the
<br /> previous sampling event, groundwater elevation decreased across the site by an average of 2 17 feet
<br /> Consistent with previous findings, groundwater flow remained to the southeast with a gradient of 0 15 ft/ft
<br /> Analyses identified gasoline and its constituents in groundwater samples collected from each of the
<br /> monitoring wells MW-1, located nearest the existing pump islands was found to contain 9,200 ppb gasoline,
<br /> 440 ppb benzene, 1,900 ppb toluene, 280 ppb ethylbenzene, and 1,100 ppb xylenes Perimeter wells MW-2,
<br /> MW-3, and MW-4, located sidegradient and downgradient of the former tanks were found to contain 55 ppb
<br /> to 320 ppb gasoline, 0 7 to 13 ppb benzene, as well as low concentrations of toluene, ethylbenzene, and
<br /> xylenes
<br /> Results of the quarterly monitoring event indicated that the extent of hydrocarbon-impacted groundwater at
<br /> the site had been relatively well defined to the west, however, it remained undefined to the north, south and
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