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Site History
<br /> 14000 Highway 88,E_ockeford,CA
<br /> Time Oil Property No 04-049
<br /> east of the former tank bed Hydrocarbon concentrations decreased in the perimeter wells (MW-2, MW-3,
<br /> and MW-4), and increased in MW-1, however, not enough data existed to evaluate the significance of these
<br /> variations Groundwater levels decreased somewhat across the site (most likely a result of seasonal
<br /> variation) since the previous sampling event, although flow direction remained 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 through
<br /> MW-4) 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 at a
<br /> rate of 0 15 ft/ft was encountered in the wells at depths of 77 21 feet to 85 88 feet below ground surface
<br /> Since the previous sampling event, groundwater elevation increased in each well by 0 62 feet to 9 41 feet, or
<br /> an overall average increase of 3 27 feet across the site The rise in groundwater elevation is most likely due
<br /> to seasonal variation Groundwater flow direction and gradient remained consistent with previously collected
<br /> 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 collected
<br /> from MW-3, located to the southeast of the former tank bed (sidegradient), contained 8,000 ppb gasoline,
<br /> 560 ppb benzene, 1,400 ppb toluene, 360 ppb ethylbenzene, and 1,900 ppb xylenes The sample collected
<br /> from MW-4, located to the southwest of the former tank bed (sidegradient), contained 180 ppb gasoline, 47
<br /> 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 BTEX
<br /> concentrations have increased somewhat in each of the wells Additionally, concentrations of gasoline and
<br /> BTEX increased in MW-3 by two orders of magnitude The observed increases of hydrocarbon constituents
<br /> in each were thought to be a result of seasonal variation in groundwater levels, however, not enough data
<br /> had been collected to evaluate the significance of these variations
<br /> SECOR's"Quarterly Status Report and Work Plan for Additional Environmental Investigation" dated January
<br /> 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 each
<br /> well was measured to evaluate elevation, flow direction, and gradient Groundwater with a southeasterly flow
<br /> at a rate of 0 001 ft/ft was encountered in the wells at depths of 73 42 feet to 85 19 feet below ground
<br /> surface
<br /> Since the previous sampling event, groundwater elevation increased in MW-1, MW-3, and MW-4 by 0 40 feet
<br /> to 0 69 feet, while it fell in MW-2 by 3 3 feet The changes in groundwater levels resulted in an overall
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