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Site History
<br /> . 14000 Highway 88 Lockeford,CA
<br /> Time Oil Property No 04-049
<br /> MW-9 (1,570 ppb gasoline, 119 ppb benzene, 67 4 ppb toluene, 47 ppb ethylbenzene, and 248 ppb xylenes)
<br /> Lower concentrations of hydrocarbons were found in the samples collected from MW-2 (190 ppb gasoline,
<br /> 4 1 ppb benzene, 14 ppb toluene, 0 9 ppb ethylbenzene, and 6 9 ppb xylenes), MW-4 (390 ppb gasoline, 4 6
<br /> ppb benzene, 1 0 ppb toluene, 0 9 ppb ethylbenzene, and 14 ppb xylenes), MW-5 (184 ppb gasoline, 7 8
<br /> ppb benzene, 1 0 ppb toluene, 1 0 ppb ethylbenzene, and 2 8 ppb xylenes), MW-7 ( 64 ppb gasoline, 1 9 ppb
<br /> toluene, 0 7 ppb ethylbenzene, and 2 7 ppb xylenes, MW-8 (97 ppb gasoline and 4 5 ppb benzene, and 0 7
<br /> ppb xylenes), and MW-10 (256 ppb gasoline, 3 6 ppb benzene, 2 8 ppb toluene, 0 8 ppb ethylbenzene, and
<br /> 3 6 ppb xylenes) Per the County's request, samples collected from MW-1 and MW-10 were analyzed for the
<br /> presence of MTBE by EPA Method 8020 Analyses identified 7 9 ppb MTBE in the groundwater sample
<br /> collected from MW-10, however, MTBE was not detected in the sample collected from MW1
<br /> Although the extent of groundwater impacts is not truly defined, the highest concentrations of hydrocarbons
<br /> appear to remain onsite in the vicinity of the pump islands (MW-1, MW-3 and MW-9) When compared to the
<br /> December 1996 sampling event, groundwater concentrations increased slightly in MW-6, MW-7, and MWA 0,
<br /> while slight decreases in hydrocarbon concentrations were observed in MW-1, MW-3, MW-4, MW-5, and
<br /> MW-9 Hydrocarbon concentrations in MW-2 and MW-8 remained relatively unchanged With the exclusion
<br /> of MW-10, which contained hydrocarbons for the first time since monitoring began, the range of
<br /> hydrocarbons observed is consistent with previously collected data Changes in hydrocarbon concentrations
<br /> may be a result of a changes in groundwater elevation, however, not enough data has been collected to
<br /> evaluate their significance Additional monitoring data will be collected to further evaluate the extent of the
<br /> dissolved hydrocarbon plume
<br /> A copy of SECOR's "Quarterly Monitoring Report - March1997" dated May 6, 1997, was forwarded to the
<br /> appropriate regulatory agencies on May 19, 1997
<br /> Submittal of Vapor Extraction Pilot Tesi Workplan -July 1997
<br /> Selection of Appropriate Remediation Technology
<br /> Prior to generating the vapor extraction pilot test workplan, SECOR performed an evaluation of to assist in
<br /> determining the most appropriate remediation technology for addressing hydrocarbon-range contaminants
<br /> associated with the subject property After comparing 1) soil excavation combined with onsite aeration,
<br /> offsite aeration and landfarming treatment options, 2) soil vapor extraction, 3) in-situ (enhanced)
<br /> biodegradation, and 4) physical or chemical neutralization, SECOR determined that the most appropriate and
<br /> cost-effective remediation technology for the subject site is vapor extraction Advantages to using vapor
<br /> extraction over other remediation techniques include
<br /> 1 The system can be easily maintained and installed
<br /> 2 Vapor emissions can be reduced prior to discharge
<br /> 3 The cost of installation is low compared to other technologies
<br /> 4 Because treatment is in-situ, public exposure to health risks is minimal
<br /> 5 Vapor extraction can be effective in reducing hydrocarbon concentrations in groundwater
<br /> Purpose and Objectives of Proposed Site Work
<br /> The purpose of the proposed pilot test is to evaluate the feasibility of utilizing vapor extraction to remediate
<br /> hydrocarbon impacted soils associated with the subject site and reduce hydrocarbon concentrations in
<br /> groundwater Data collected during the pilot test will be appropriate for remediation system design
<br /> it appears as though there may be two areas of soil contamination at the subject site one shallow and one
<br /> deep The extent of shallow soil contamination has been defined and does not appear to extend much
<br /> beyond the limits of the former tank bed The vertical migration of shallow soil contamination may be
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