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Site History
<br /> 14000 Highway 88 Lockeford,CA
<br /> Time Oil Property No 04-049
<br /> somewhat limited by the lens of clayey silt existing at 30 to 35 feet bgs Deeper contamination (beginning at
<br /> approximately 40 feet to 45 feet bgs) appears to be present to the northeast of the former tank bed Based
<br /> on data collected during field activities, it is estimated that vapor extraction would be very effective in reducing
<br /> hydrocarbons in the areas of highest soil and groundwater concentrations
<br /> Proposed Scope of Work
<br /> In order to evaluate the feasibility of utilizing soil vapor extraction at the subject site, SECOR generated a
<br /> workplan for the completion of the following scope of work
<br /> 1 A permit for a 5-day vapor extraction pilot test will be obtained from the San Joaquin Valley Unified Air
<br /> a
<br /> Pollution Control District
<br /> 2 A 200 cfm positive displacement blower will be used to extract vapors from the various extraction wells
<br /> (W-1 through W-8), while a thermal oxidizer will be utilized for vapor abatement
<br /> 3 Dunng the pilot test, vacuum measurements will be collected periodically to determine the radius-of-
<br /> influence of each extraction well Air flow rates and system performance will also be evaluated
<br /> - 4 Influent concentrations will be periodically monitored with a PID, and a tedlar bag air sample will be
<br /> collected from the extraction point location(s)for laboratory analyses
<br /> 5 A report will be generated which contains the results and conclusions of the pilot test
<br /> A copy of SECOR's "Work Plan for Soil Vapor Extraction Pilot Test" dated June 26, 1997, was forwarded to
<br /> the appropriate regulatory agencies on July 9, 1997 Approval of the workplan was received from the County
<br /> on October 6, 1997 Upon submittal of the pilot study costs for pre-approval, the Cleanup Fund determined
<br /> that a 2-day vapor extraction test would be more appropriate Pre-approval of costs for the 2-day pilot test
<br /> was received from the Cleanup Fund on January 15, 1998
<br /> Second Quarter 1997 Groundwater Sampling Results-April 1997
<br /> On Apnl 16, '1997, samples were collected from each of the groundwater monitoring wells (MW-1 through
<br /> MW-10) Pnor to purging, the depth to water in each well was measured to evaluate elevation, flow direction,
<br /> and gradient Groundwater with a southwesterly flow at a rate of 0 02 ft/ft was encountered in the wells at
<br /> depths of 66 17 feet to 85 05 feet below ground surface Free product was not encountered in any of the
<br /> wells The locations of the wells are identified on Figure 2 of the attached report
<br /> Since the December 1996 sampling event, groundwater elevation increased in MW-1, MW-2, MW-4, MW-6,
<br /> MW-7, MW-8, MW-9, and MW-10 by 0 20 feet to 1 48 feet, and groundwater elevation decreased in wells
<br /> MW-3 and MW-5 by 3 31 feet and 7 07 feet, respectively These changes resulted in an overall average
<br /> decrease in groundwater elevation of 0 31 feet across the site Since the previous sampling event,
<br /> groundwater gradient decreased slightly from 0 08 ft/ft to 0 02 ft/ft Changes in groundwater gradient and
<br /> elevation and are most likely a result of seasonal variation Groundwater flow direction remained unchanged
<br /> from the previous quarter
<br /> Analyses identified elevated concentrations of hydrocarbons to the samples collected from MW-1 (25,200
<br /> ppb gasoline, 1,160 ppb benzene, 6,410 ppb toluene, 852 ppb ethylbenzene, and 4,460 ppb xylenes), and
<br /> MW-3 (2,640 ppb gasoline, 24 6 ppb benzene, and 13 2 ppb xylenes) Lower concentrations of
<br /> hydrocarbons were found in the samples collected from MW-2 (181 ppb gasoline, 3 7 ppb benzene, 1 5 ppb
<br /> toluene, 0 9 ppb ethylbenzene, and 24 7 ppb xylenes), MW-4 (132 ppb gasoline, 1 0 ppb benzene, and 0 6
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