|
Site History
<br /> 14000 Highway 88, Lockeford,CA
<br /> Time Oil Property No.04049
<br /> and 70 ppb xylenes. Analyses identified 100 ppb TPH, 2.3 ppb benzene, and 0.6 ppb xylenes in the
<br /> 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
<br /> does not appear to extend much beyond the limits of the former tank bed. The vertical migration of
<br /> shallow soil contamination may be limited by the lens of clayey silt existing at 30 to 35 feet bgs. Deeper
<br /> contamination (beginning at approximately 40 feet to 45 feet bgs) appears to be present at highest
<br /> concentration to the northeast of the former tank bed. The extent of deeper soil contamination is fairly
<br /> well defined to the northeast, southeast, and west by the samples collected during the additional site
<br /> investigation; however, it may need to be further investigated to the north and south. Time's records do
<br /> not indicate any potential sources for the deep soil contamination noted in the vicinity of MW-1. Since
<br /> this deeper contamination is some distance from the former tank bed, we believe that it may be due to
<br /> an offsite hydrocarbon source.
<br /> The extent of groundwater contamination has not been defined in any direction and appears to extend
<br /> offsite to the north, south, and east. The elevated concentrations of hydrocarbons in MW-1 and MW-2
<br /> (both sidegradient of the former tanks), suggest that an offsite source of hydrocarbons may be impacting
<br /> the subject site.
<br /> Time has reviewed several reports concerning the Beacon Station located immediately to the north of
<br /> the subject site. It is Time's understanding that a "dry well" was once present on the southeast corner of
<br /> the Beacon Station property. This dry well, located immediately upgradient of MW-1 and MW-2, could
<br /> be a potential source of contamination to deeper soils. Investigation performed near a second dry well,
<br /> located on the southwest portion of the Beacon property, revealed significant groundwater contamination
<br /> .. which has not 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 Re ort and Quarterly Status Report for- Second 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
<br /> feet to 86,62 feet below ground surface. Although groundwater levels rose in some wells and fell in
<br /> others since the previous sampling event, groundwater elevation decreased across the site by an
<br /> average of 2.17 feet. Consistent with previous findings, groundwater flow remained to the southeast with
<br /> 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
<br /> gasoline, 440 ppb benzene, 1,900 ppb toluene, 280 ppb ethylbenzene, and 1,100 ppb xylenes.
<br /> Perimeter wells MW-2, MW-3, and MW-4, located sidegradient and downgradient of the former tanks
<br /> were found to contain 55 ppb to 320 ppb gasoline, 0.7 to 13 ppb benzene, as well as low concentrations
<br /> of toluene, ethylbenzene, and xylenes.
<br /> Results of the quarterly monitoring event indicated that the extent of hydrocarbon-impacted groundwater
<br /> at the site had been relatively well defined to the west; however, it remained undefined to the north,
<br /> south and east of the former tank bed. Hydrocarbon concentrations decreased in the perimeter wells
<br /> 5
<br />
|