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Site History
<br /> . 14000 Highway 88 Lockeford,CA
<br /> Time Oil Property No 04-049
<br /> Since the Third Quarter 1996 sampling event, groundwater elevation decreased in MW-2, MW-4, MW-7 and
<br /> MW-8 by 0 05 feet to 0 53 feet, and groundwater elevation Increased in wells MW-1, MW-3, MW-5, MW-6,
<br /> MW-9, and MW-10 by 0 09 feet to 4 55 feet These changes resulted in an overall average increase in
<br /> groundwater elevation of 0 63 feet across the site and are most likely a result of seasonal variation
<br /> Groundwater flow direction and gradient remained relatively unchanged from the previous quarter
<br /> Analyses identified elevated concentrations of hydrocarbons in the samples collected from MW-1 (21,000
<br /> ppb gasoline, 1,500 ppb benzene, 5,230 ppb toluene, 742 ppb ethylbenzene, and 3,590 ppb xylenes), MW-3
<br /> (3,510 ppb gasoline, 522 ppb benzene, 184 ppb toluene, 191 ppb ethylbenzene, and 349 ppb xylenes), MW-
<br /> 6 (515 ppb gasoline, 45 5 ppb benzene, 45 2 ppb toluene, 7 5 ppb ethylbenzene, and 124 ppb xylenes), and
<br /> MW-9 (2,400 ppb gasoline, 140 ppb benzene, 90 ppb toluene, 88 ppb ethylbenzene, and 173 ppb xylenes)
<br /> Lower concentrations of hydrocarbons were found in the samples collected from MW-2 (175 ppb gasoline,
<br /> 3 7 ppb benzene, 12 ppb toluene, 1 6 ppb ethylbenzene, and 8 3 ppb xylenes), MW-4 (284 ppb gasoline, 4 9
<br /> ppb benzene, 0 6 ppb toluene, and 0 7 ppb xylenes), MW-5 (122 ppb gasoline, 9 6 ppb benzene, 0 9 ppb
<br /> toluene, and 1 5 ppb xylenes), and MW-8 (102 ppb gasoline and 10 1 ppb benzene) Hydrocarbons were not
<br /> present at detectable concentrations in the samples collected from MW-7 or MW-10
<br /> Although the extent of groundwater Impacts is onty truly delineated in the upgradient (northeast) and
<br /> downgradient (southwest) directions, it is generally defined and appears to remain limited to the vicinity of the
<br /> pump islands When compared to the August 1996 sampling event, groundwater concentrations showed
<br /> slight Increases in MW-1, MW-2, MW-3, MW-4, MW-5, and MW-8 A larger increase was noted in MW-9
<br /> (sidegradient) Hydrocarbon concentrations in MW-6 decreased slightly, while concentrations in MW-7 and
<br /> MW-10 remained below detection limits The observed fluctuations in hydrocarbon concentrations might have
<br /> been a result of a changes in groundwater elevation, however, not enough data has been collected to
<br /> evaluate their significance Additional monttonng data will be collected to further evaluate the extent of the
<br /> 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 RCsults-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 prior 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 feet
<br /> 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, MW-4,
<br /> MW-6, MW-7, MW-8, and MW-9 by 0 88 feet to 1 52 feet, and groundwater elevation decreased to wells MW-
<br /> 5 and MW-10 by 1 87 feet to 10 30 feet, respectively These changes resulted in an overall average increase
<br /> in groundwater elevation of 0 75 feet across the site (excluding measurements from MW-10) Since the
<br /> previous sampling event, groundwater gradient increased slightly from 0 02 ft/ft to 0 08 ft/ft Changes in
<br /> groundwater gradient and elevation and are most likely a result of seasonal variation Groundwater flow
<br /> direction remained unchanged from the previous quarter
<br /> Analyses identified elevated concentrations of hydrocarbons in the samples collected from MW-1 (2,740 ppb
<br /> gasoline, 280 ppb benzene, 320 ppb toluene, 68 5 ppb ethylbenzene, and 458 ppb xylenes), MW-3 (2,090
<br /> • ppb gasoline, 136 ppb benzene, 37 4 ppb toluene, 70 ppb ethylbenzene, and 54 3 ppb xylenes), MW-6
<br /> (1,510 ppb gasoline, 93 ppb benzene, 137 ppb toluene, 234 ppb ethylbenzene, and 297 ppb xylenes), and
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