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I
<br /> Site History
<br /> 14000 Highway 88, Lockeford, CA
<br /> >f Time Oil Properly No.04-049
<br /> (MW-2, MW-3, and MW-4), and increased in MW-1; however, not enough data existed to evaluate the
<br /> significance of these variations. Groundwater levels decreased somewhat across the site (most likely a
<br /> result of seasonal variation) since the previous sampling event, although flow direction remained
<br /> consistent.
<br /> SECOR's "Quarterly Monitoring Report, April - June 1995" dated July 13, 1995 was forwarded to the
<br /> appropriate regulatory agencies on July 31, 1995.
<br /> Third Quarter 1995 Groundwater Sampling Results - October 1995
<br /> On October 4, 1995, samples were collected from each of the groundwater monitoring wells (MW-1
<br /> through MW-4) 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 /> southeasterly flow at a rate of 0.15 ft./ft. was encountered in the wells at depths of 77.21 feet to 85.88
<br /> feet below ground surface.
<br /> Since the previous sampling event, groundwater elevation increased in each well by 0.62 feet to 9.41
<br /> feet, or an overall average increase of 3.27 feel across the site. The rise in groundwater elevation is
<br /> most likely due to seasonal variation. Groundwater flow direction and gradient remained consistent with
<br /> previously collected data.
<br /> Analyses identified gasoline and its constituents in groundwater samples collected from each of the
<br /> monitoring wells. MW-1, located nearest to the existing pump islands, was found to contain 8,200 ppb
<br /> gasoline, 500 ppb benzene, 2,400 ppb toluene, 300 ppb ethylbenzene, and 1,400 ppb xylenes. MW-2,
<br /> located on the northeast corner of the property and upgradient of the former tank bed, contained 320 ppb
<br /> gasoline, 9 ppb benzene, 35 ppb toluene, 5 ppb ethylbenzene, and 92 ppb xylenes. The sample
<br /> collected from MW-3, located to the southeast of the former tank bed (sidegradient), contained 8,000
<br /> ppb gasoline, 560 ppb benzene, 1,400 ppb toluene, 360 ppb ethylbenzene, and 1,900 ppb xylenes. The
<br /> sample collected from MW-4, located to the southwest of the former tank bed (sidegradient), contained
<br /> 180 ppb gasoline, 47 ppb benzene, 8.5 ppb toluene, 6 ppb ethylbenzene, and 15 ppb xylenes.
<br /> The extent of groundwater impacts have not been defined in any direction. Since the previous sampling
<br /> event, gasoline concentrations in MW-1, MW-2, and MW-4 remained relatively unchanged, although
<br /> BTEX concentrations have increased somewhat in each of the wells. Additionally, concentrations of
<br /> gasoline and BTEX increased in MW-3 by two orders of magnitude. The observed increases of
<br /> hydrocarbon constituents in each were thought to be a result of seasonal variation in groundwater levels;
<br /> however, not enough data had been collected to evaluate the significance of these variations.
<br /> SECOR's "Quarterly Status Report and Work Plan for Additional Environmental Investigation" dated
<br /> January 9, 1996 was forwarded to the appropriate regulatory agencies on January 25, 1996.
<br /> Fourth Quarter 1995 Groundwater Sampling Results- December 1995
<br /> On December 19, 1995, samples were collected from each of the groundwater monitoring wells (MW-1
<br /> through MW-4) 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 /> southeasterly flow at a rate of 0.001 ft./ft. was encountered in the wells at depths of 73.42 feet to 85.19
<br /> feet below ground surface.
<br /> Since the previous sampling event, groundwater elevation increased in MW-1, MW-3, and MW-4 by 0.40
<br /> feet to 0.69 feet, while it fell in MW-2 by 3.3 feet. The changes in groundwater levels resulted in an
<br /> overall average decrease in groundwater elevation of 0.44 feet across the site. Groundwater flow
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