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Site History
<br /> 14000 Highway 88, Lockeford,CA
<br /> Time Oil Property No 04-049
<br /> 2 Soil samples would be collected from each boring at 5-foot intervals and submitted for analyses
<br /> based on visual observation and field instrumentation readings A minimum of three samples
<br /> would be submitted from each boring
<br /> 3 In the event that groundwater is encountered, the boring to be placed near W-8 would be
<br /> installed as a 2-inch diameter groundwater monitoring well If needed, up to three additional
<br /> groundwater monitoring wells might be installed to assist in determining the extent of impacted
<br /> groundwater All wells would be properly developed and purged prior to the collection of
<br /> groundwater samples
<br /> Additional Environmental Investigation - December 1994
<br /> While conducting field activities during the weeks of December 20 and 27, 1994, hydrocarbon-impacted
<br /> groundwater was encountered while attempting to define the vertical extent of soil contamination
<br /> Therefore, four groundwater monitoring wells (MW-1 through MW-4) were installed and one soil boring
<br /> (SB-11) was advanced in an attempt to define the extent of contamination in both media
<br /> As in previous site activities, soils encountered during drilling consisted of fine silty sands to
<br /> approximately 15 feet below ground surface (bgs), this strata was underlain by fine to coarse sands to
<br /> approximately 30 feet bgs Clayey silt was generally encountered at 30 feet to 35 feet while fine to
<br /> coarse sands and gravelly sands were encountered to 70 feet bgs Silty clay with sandy and gravelly
<br /> stringers was encountered from 70 feet bgs to the extent of each boring Groundwater was first
<br /> encountered at depth 85 feet bgs
<br />. MW-1 was installed to the northeast of the currently operating pump islands, MW-2 was installed to the
<br /> east of MW-1, MW-3 was installed to the southeast of the former tank bed, and MW-4 was installed to
<br /> the southwest of the former tank bed (presumably downgradient) Each of the wells was constructed of
<br /> 2-inch diameter PVC and screened from a depth of 65 feet bgs to 100 feet bgs Soil boring SB-11,
<br /> placed to the west of the former tank bed, could only be advanced to a depth of 78 feet bgs due to
<br /> difficult drilling conditions
<br /> Because the extent of shallow soil contamination was defined during earlier investigative activities, soil
<br /> samples were collected only from depths of 25 feet and greater Based on field instrumentation
<br /> readings, four to five soil samples from each drilling location were submitted to a laboratory and
<br /> analyzed for total petroleum hydrocarbons as gasoline (TPH) and also for benzene, toluene,
<br /> ethylbenzene, and xylenes (BTEX) Gasoline was found in the samples collected from MW-1 at 35 feet
<br /> (3 4 ppm), 45 feet (680 ppm), 83 feet (3 2 ppm), and 100 feet (1 6 ppm), varying concentrations of BTEX
<br /> were also found in these samples Trace concentrations of benzene, ethylbenzene, and xylenes (none
<br /> exceeding 0 01 ppm) were also found in the samples collected from MW-2 at 45 feet, 55 feet, and 60
<br /> feet, and in the sample collected from MW-5 at 71 feet Hydrocarbons were not identified in any of the
<br /> remaining samples
<br /> On January 19, 1995, the groundwater monitoring wells were purged and sampled Prior to purging,
<br /> measurements were collected from each well to evaluate groundwater elevation, flow direction, and
<br /> gradient During field activities, groundwater with a southeasterly flow and a hydraulic gradient of 0 13
<br /> ft Ift was encountered at 75 96 feet bgs to 86 80 feet bgs
<br /> Hydrocarbons were found in groundwater samples collected from each of the monitoring wells The
<br /> sample collected from MW-1 contained 5,200 ppb TPH, 200 ppb benzene, 1,100 ppb toluene, 160 ppb
<br /> ethylbenzene, and 620 ppb xylenes The sample collected from MW-2 was found to contain 460 ppb
<br /> TPH, 30 ppb benzene, 48 ppb toluene, 5 ppb ethylbenzene, and 30 ppb xylenes Analysis of the sample
<br /> collected from MW-3 indicated 430 ppb TPH, 18 ppb benzene, 48 ppb toluene, 13 ppb ethylbenzene,
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