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Site History
<br /> • 14000 Highway 88 Lockeford, CA
<br /> Time Oil Property No 04-049
<br /> collected from MW-2 (175 ppb gasoline, 3 7 ppb benzene, 1 2 ppb toluene, 1 6 ppb ethylbenzene, and
<br /> 8 3 ppb xylenes), MW-4 (284 ppb gasoline, 4 9 ppb benzene, 0 6 ppb toluene, and 0 7 ppb xylenes),
<br /> MW-5 (122 ppb gasoline, 9 6 ppb benzene, 0 9 ppb toluene, and 1 5 ppb xylenes), and MW-8 (102 ppb
<br /> gasoline and 10 1 ppb benzene) Hydrocarbons were not present at detectable concentrations in the
<br /> samples collected from MW-7 or MW-10
<br /> Although the extent of groundwater impacts is only truly delineated in the upgradient (northeast) and
<br /> downgradient (southwest) directions, it is generally defined and appears to remain limited to the vicinity
<br /> of the pump islands When compared to the August 1996 sampling event, groundwater concentrations
<br /> showed slight increases in MW-1, MW-2, MW-3, MW-4, MW-5, and MW-8 A larger increase was noted
<br /> in MW-9 (sidegradient) Hydrocarbon concentrations in MW-6 decreased slightly, while concentrations in
<br /> MW-7 and MW-10 remained below detection limits The observed fluctuations in hydrocarbon
<br /> concentrations might have been a result of a changes in groundwater elevation, however, not enough
<br /> data has been collected to evaluate their significance Additional monitoring data will be collected to
<br /> further evaluate the extent of the dissolved hydrocarbon plume
<br /> A copy of SECOR's "Quarterly Monitoring Report, October - December" dated February 28, 1997, was
<br /> forwarded to the appropriate regulatory agencies on March 12, 1997
<br /> First Quarter 1997 Groundwater Sampling Results- March 1997
<br /> On February 26, 1997, samples were collected from each of the groundwater monitoring wells (MW-1
<br /> through MW-10) at the subject site by a representative of SECOR Pnor to purging, the depth to water in
<br /> each well was measured to evaluate elevation, flow direction, and gradient Groundwater with a
<br /> southwesterly flow at a rate of 0 08 ft/ft was encountered in the wells at depths of 67 65 feet to 78 92
<br /> feet below ground surface Free product was not encountered in any of the wells
<br /> Since the December 1996 sampling event, groundwater elevation increased in MW-1, MW-2, MW-3,
<br /> MVV 4, MW-6, MW-7, MW-8, and MW-9 by 0 88 feet to 1 52 feet, and groundwater elevation decreased
<br /> in wells MW-5 and MW-10 by 1 87 feet to 10 30 feet, respectively These changes resulted in an overall
<br /> average increase in groundwater elevation of 0 75 feet across the site (excluding measurements from
<br /> MW-10) Since the previous sampling event, groundwater gradient increased slightly from 0 02 ft/ft to
<br /> 0 08 ft/ft Changes in groundwater gradient and elevation and are most likely a result of seasonal
<br /> variation Groundwater flow direction remained unchanged from the previous quarter
<br /> Analyses identified elevated concentrations of hydrocarbons in the samples collected from MW-1 (2,740
<br /> ppb gasoline, 280 ppb benzene, 320 ppb toluene, 68 5 ppb ethylbenzene, and 458 ppb xylenes), MW-3
<br /> (2,090 ppb gasoline, 136 ppb benzene, 37 4 ppb toluene, 70 ppb ethylbenzene, and 54 3 ppb xylenes),
<br /> MW-6 (1,510 ppb gasoline, 93 ppb benzene, 137 ppb toluene, 23 4 ppb ethylbenzene, and 297 ppb
<br /> xylenes), and MW-9 (1,570 ppb gasoline, 119 ppb benzene, 67 4 ppb toluene, 47 ppb ethylbenzene, and
<br /> 248 ppb xylenes) Lower concentrations of hydrocarbons were found in the samples collected from MW-
<br /> 2 (190 ppb gasoline, 4 1 ppb benzene, 1 4 ppb toluene, 0 9 ppb ethylbenzene, and 6 9 ppb xylenes),
<br /> MW-4 (390 ppb gasoline, 4 6 ppb benzene, 1 0 ppb toluene, 0 9 ppb ethylbenzene, and 1 4 ppb xylenes),
<br /> MW-5 (184 ppb gasoline, 7 8 ppb benzene, 1 0 ppb toluene, 1 0 ppb ethylbenzene, and 2 8 ppb xylenes),
<br /> MW-7 ( 64 ppb gasoline, 1 9 ppb toluene, 0 7 ppb ethylbenzene, and 2 7 ppb xylenes, MW-8 (97 ppb
<br /> gasoline and 4 5 ppb benzene, and 0 7 ppb xylenes), and MW-10 (256 ppb gasoline, 3 6 ppb benzene,
<br /> 2 8 ppb toluene, 0 8 ppb ethylbenzene, and 3 6 ppb xylenes) Per the County's request, samples
<br /> collected from MW-1 and MW-10 were analyzed for the presence of MTBE by EPA Method 8020
<br /> Analyses identified 7 9 ppb MTBE in the groundwater sample collected from MW-10, however, MTBE
<br /> was not detected in the sample collected from MW-1
<br />. Although the extent of groundwater impacts is not truly defined, the highest concentrations of
<br /> hydrocarbons appear to remain onsite in the vicinity of the pump islands (MW-1, MW-3 and MW-9)
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