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Site History
<br /> • 14000 Highway 88,Lockeford,CA
<br /> Time Oil Property No 04049
<br /> Quarter 199L8 Groundwater Sampling 6ugust 1998
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<br /> On August 13, 1998, samples were collected from each of the groundwater monitoring wells (MW-1 through
<br /> MW-10) at the subject site by a representative of SECOR Prior to purging, the depth to water in each well
<br /> was measured to evaluate elevation, flow direction, and gradient Groundwater with a southerly flow
<br /> direction and a gradient of 0 04 ft/ft was encountered in the wells at depths of 64 32 feet to 76 85 feet below
<br /> ground surface Free product was not encountered in any of the wells
<br /> Since the April 1998 sampling event, groundwater elevation Increased in each well by 0 81 feet to 9 54 feet,
<br /> resulting in an overall Increase in groundwater elevation of 2 81 feet across the site Groundwater flow
<br /> direction also changed from southwest to south Changes In groundwater depth and flow direction are most
<br /> likely a result of seasonal variation Groundwater gradient was consistent with previously collected data
<br /> Analyses identified elevated concentrations of hydrocarbons in the samples collected from MW-1 (15,700
<br /> ppb gasoline, 380 ppb benzene, 2,500 ppb toluene, 1,130 ppb ethylbenzene, 2,480 ppb xylenes), MW-2 (250
<br /> ppb gasoline, 6 4 ppb benzene, 0 9 ppb toluene, 0 50 ppb ethylbenzene, and 51 1 ppb xylenes), MW-3 (572
<br /> ppb gasoline, 113 ppb benzene, 25 6 ppb toluene, 45 6 ppb ethylbenzene, and 60 4 ppb xylenes), MW-4 (
<br /> 229 ppb gasoline, 12 4 ppb benzene, 2 2 ppb ethylbenzene, 0 7 ppb xylenes), MW-5 (4,760 ppb gasoline,
<br /> 488 ppb benzene, 852 ppb toluene, 207 ppb ethylbenzene, and 1,050 ppb xylenes), and MW-6 (328 ppb
<br /> gasoline, 20 5 ppb benzene, 1 5 ppb toluene, 3 5 ppb ethylbenzene, 32 1 ppb xylenes) Lower
<br /> concentrations of hydrocarbons were found in the samples collected from MW-7 (0 7 ppb xylenes), MW-8
<br /> (1 3 ppb benzene), and MW-9 (82 5 ppb hydrocarbons and 13 ppb benzene) Hydrocarbons were not
<br /> detected in the sample collected from MW-10 Low concentrations of MTBE were detected in the
<br /> groundwater samples collected from MW-4 (8 3 ppb), however, it was not detected in any of the other
<br /> • samples
<br /> The highest concentrations of hydrocarbons appear to remain onsite in the vicinity of the pump islands (MW-
<br /> 1) and sidegradient of the former tank bed (MW-5) The groundwater plume does not appear to be migrating
<br /> to any great extent When compared to the April 1998 sampling event, hydrocarbon concentrations
<br /> decreased in MW-11, MVV 2, MW-3, and MW-8, while they remained relatively unchanged in the remainder of
<br /> the wells Changes in hydrocarbon concentrations are most likely a result of changes in groundwater
<br /> elevation Additional monitoring data will be collected to further evaluate the extent of the dissolved
<br /> hydrocarbon plume
<br /> A copy of SECOR's "Quarterly Monitoring Report, July - September 1998" dated October 16, 1998, was
<br /> forwarded to the appropriate regulatory agencies on October 20, 1998
<br /> f=ourth Quarter 1998 Groundwater Sampling Results-October 1998
<br /> On October 26, 1998, samples were collected from each of the groundwater monitoring wells (MW-1 through
<br /> MW-110) at the subject site by a representative of SECOR Prior to purging, the depth to water in each well
<br /> was measured to evaluate elevation, flow direction, and gradient Groundwater with a southerly flow
<br /> direction and a gradient of 0 03 ft/ft was encountered In the wells at depths of 64 14 feet to 76 93 feet below
<br /> ground surface Free product was not encountered in any of the wells
<br /> Since the August 1998 sampling event, groundwater elevation decreased In MW-8 by 0 30 feet and In MW-
<br /> 10 by 848 feet, while it increased In the remaining wells by 0 17 feet to 357 These changes resulted in an
<br /> overall decrease In groundwater elevation of 0 18 feet across the site Changes in groundwater elevation are
<br /> most likely a result of seasonal variation Groundwater gradient and flow direction remained consistent with
<br /> previously collected data
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