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Site History
<br /> 14000 Highway 88,i_ockeford CA
<br /> Time Oil Property No 04-049
<br /> direction, and gradient could have been a result of additional data points provided by the new wells, or they
<br /> could have been due to seasonal variation
<br /> Analyses identified elevated concentrations of hydrocarbons in the samples collected from MW-1 (13,600
<br /> ppb gasoline, 1,130 ppb benzene, 4,100 ppb toluene, 482 ppb ethylbenzene, and 2,710 ppb xylenes), MW-3
<br /> (2,700 ppb gasoline, 288 ppb benzene, 242 ppb toluene, 133 ppb ethylbenzene, and 280 ppb xylenes), and
<br /> MW-6 (1,370 ppb gasoline, 142 ppb benzene, 292 ppb toluene, 81 ppb ethylbenzene, and 495 ppb xylenes)
<br /> Trace concentrations of hydrocarbons were found in the samples collected from MW-4 (83 5 ppb gasoline,
<br /> and 1 4 ppb benzene), MW-5 (54 ppb gasoline, 15 3 ppb benzene, 0 7 ppb toluene, 2 5 ppb ethylbenzene,
<br /> and 14 ppb xylenes), MW-8 (5 8 ppb benzene and 1 0 ppb xylenes), and MW-9 (1 4 ppb benzene)
<br /> Hydrocarbons were not present at detectable concentrations in the samples collected from MW-2, MW-7,
<br /> and MW-10
<br /> Based on the results of the site investigation it appears as though sod impacts remain limited to the
<br /> immediate vicinity of the former tank system Although low concentrations of hydrocarbons appear to be
<br /> migrating offsite to the east (MW-8, sidegradient) and west (MW-5, sidegradient), groundwater impacts
<br /> appear to be fairly well defined in except to the northwest(MW-6, upgradient)
<br /> Since the May 1996 quarterly sampling event hydrocarbon concentrations decreased in MW-2 and MW-4
<br /> and increased in MW-1 and MW-3, however, the changes were not very great in any of the wells The
<br /> observed fluctuations in hydrocarbon concentrations may be a result of a changes in groundwater elevation,
<br /> however, not enough data has been collected to evaluate their significance Additional groundwater data will
<br /> be collected to further evaluate the extent of the dissolved hydrocarbon plume
<br /> The results of the most recent site investigation suggest that the extent of impacted soil has been defined In
<br /> all directions, and that the extent of groundwater Impacts is fairly well defined except to the northeast
<br /> (upgradient) of the former tank system Because the extent of impacts is nearly defined, and it may be
<br /> difficult to obtain access to Install additional upgradient monitoring wells, Time proposed that efforts be
<br /> focused on interim remediation rather than further investigation
<br /> Time believes that the installation and operation of an interim remediation system, such as a vapor extraction
<br /> system, may mitigate the need for additional investigation in the upgradient direction, as well as prevent
<br /> additional groundwater impacts During the operation of the interim remediation system, groundwater
<br /> monitoring would be continued to confirm that additional contaminant migration is not occurring, to monitor
<br /> remediation efforts, and to assist in identifying source areas which may require the implementation of
<br /> additional remediation technologies
<br /> Time requested the PHSIEHD's concurrence that additional investigative efforts will not be required at this
<br /> time and that interim remediation efforts would be appropriate A copy of SECOR's "Environmental
<br /> Investigation and Quarterly Summary Report" dated October 9, 1996 was forwarded to the approporate
<br /> agencies on October 21, 1996
<br /> Fourth Quarter 1996 Groundwater SampLng Results- December 1996
<br /> On December 19, 1996, 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 02 ft/ft was encountered in the wells at depths of 66 90 feet to 79 92 feet
<br /> below ground surface Free product was not encountered in any of the wells
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