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Site Hcstory
<br /> • 14000 Highway 88 Lockeford CA
<br /> Time Oil Property No 04-049
<br /> A copy of SECOR's"Quarterly Monitoring Report-September 1997"dated October 13, 1997, was forwarded
<br /> to the appropriate regulatory agencies on October 16, 1997
<br /> Fourth Quarter 1997 Groundwater Sampling Results-October 1997
<br /> On October 13, 1997, 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 which appeared to converge
<br /> in the center of the site was encountered in the wells at depths of 66 40 feet to 81 81 feet below ground
<br /> surface Free product was not encountered in any of the wells
<br /> Since the July 1997 sampling event, groundwater elevation decreased in MW-1 and MW-4 through MW-9 by
<br /> 0 34 feet to 1 14 feet, and groundwater elevation increased in MW-2, MW-3, MW-10 by 0 25 feet, 0 42 feet,
<br /> and 0 03 feet, respectively These changes resulted in an overall average decrease in groundwater elevation
<br /> of 0 42 feet across the site Groundwater flow direction has typically been to the southwest on the subject
<br /> site, however, a convergence in groundwater flow was indicated in the October sampling event Changes in
<br /> flow direction and gradient are most likely a result of seasonal variation
<br /> Analyses identified elevated concentrations of hydrocarbons in the samples collected from MW-1 (35,500
<br /> ppb gasoline, 921 ppb benzene, 5,410 ppb toluene, 1,400 ppb ethylbenzene, and 5,820 ppb xylenes), MW-2
<br /> (675 ppb gasoline, 114 ppb benzene, 16 6 ppb toluene, 2 8 ppb ethylbenzene, and 150 ppb xylenes), MW-3
<br /> (2,820 ppb gasoline, 246 ppb benzene, 72 ppb toluene, 107 ppb ethylbenzene, and 133 ppb xylenes), MW-5
<br /> (2,010 ppb gasoline, 138 ppb benzene, 221 ppb toluene, 28 4 ppb ethylbenzene, and 291 ppb xylenes), and
<br /> MW-6 (247 ppb gasoline, 26 ppb benzene, 3 4 ppb toluene, 2 9 ppb ethylbenzene, and 46 1 ppb xylenes)
<br /> Lower concentrations of hydrocarbons were found in the samples collected from MW-4 (225 ppb gasoline,
<br /> 3 7 ppb benzene, and 0 8 ppb xylenes), MW-7 (73 ppb gasoline), MW-8 (52 ppb gasoline and 2 ppb
<br /> benzene), and MW-9 (103 ppb gasoline and 2 5 ppb benzene) Hydrocarbons were not detected in the
<br /> samples collected from MW-10 MTBE was detected in the sample collected from MW-4 at 10 9 ppb,
<br /> however, it was not detected in any of the other samples
<br /> The highest concentrations of hydrocarbons appear to remain onsite in the vicinity of the pump islands (MW-
<br /> 1 and MW-3) When compared to the July 1997 sampling event, groundwater concentrations decreased in
<br /> MW-1 and MW-5, while they remained relatively unchanged in the remainder of the wells
<br /> A copy of SECOR's"Quarterly Monitoring Report- December 1997" dated January 28, 1998, was forwarded
<br /> to the appropriate regulatory agencies on February 2, 1998
<br /> First Quarter 1998 Groundwater Sampling Results-January 1998
<br /> On January 27, 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 southeasterly flow
<br /> direction at a hydraulic gradient of 0 02 ft/ft was encountered in the wells at depths of 67 88 feet to 62 18
<br /> feet below ground surface Free product was not encountered in any of the wells
<br /> Since the October 1997 sampling event, groundwater elevation increased in MW-2 and MW-5 by 0 96 feet
<br /> and 5 26 feet, respectively, while groundwater elevation decreased in MW-1, MW-3, MW-4, and MW-5
<br /> through MW-1 0 by 0 27 feet to 1 54 feet Changes in groundwater depth, flow direction, and gradient are
<br /> most likely a result of seasonal variation
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