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Site History
<br /> • 14000 Highway 88, Lockeford CA
<br /> Time Od Property No 04-049
<br /> direction remained consistent with previously collected data, however, gradient decreased somewhat
<br /> The variations in groundwater elevation and gradient were most likely due to seasonal variation
<br /> Analyses Identified 3,400 ppb gasoline, 200 ppb benzene, 850 ppb toluene, 120 ppb ethylbenzene, and
<br /> 560 ppb xylenes in the sample collected from MW-1(located nearest to the existing pump islands) The
<br /> sample collected from MW-3, located to the southeast of the former tank bed (downgradient), contained
<br /> 1,800 ppb gasoline, 140 ppb benzene, 180 ppb toluene, 78 ppb ethylbenzene, and 260 ppb xylenes, and
<br /> the sample collected from MW-4, located to the southwest of the former tank bed (sidegradient),
<br /> contained 410 ppb gasoline, 65 ppb benzene, 3 6 ppb toluene, 28 ppb ethylbenzene, and 4 1 ppb
<br /> xylenes The sample collected from MW-2, located to the east of the former tank bed (side gradient),
<br /> was not found to contain detectable concentrations of gasoline or Its constituents
<br /> Based on this data, the extent of groundwater Impacts had not been defined in any direction Between
<br /> the Third and Fourth Quarters of 1995, gasoline and BTEX concentrations Increased slightly in MW-4,
<br /> however, they decreased in MW-1 MW-2, and MW-3 The observed fluctuations in hydrocarbon
<br /> concentrations were likely a result of seasonal variation in groundwater levels and/or a result of
<br /> bioattenuation, however, not enough data had been collected to evaluate their significance
<br /> SECOR's "Quarterly Monitoring Report - December 1996" dated February 5, 1996 was forwarded to the
<br /> appropriate regulatory agencies on February 13, 1996
<br /> Workplan for Additional Soil and Groundwater Investigation -Janua 1996
<br />• Based on the results of the previous investigation, a workplan was prepared for the installation of six
<br /> additional groundwater monitoring wells to define the extent of soil and groundwater impacts associated
<br /> with the former underground storage tanks at the subject site On January 25, 1996, SECOR's
<br /> "Quarterly Status Report and Work Plan for Additional Environmental investigation" was forwarded to
<br /> the appropriate regulatory agencies Briefly, proposed site activities consist of the following
<br /> 1 Six bonngs would be advanced to approximately 100 feet below ground surface (or to 10 feet below
<br /> first encountered groundwater)
<br /> 2 Soil samples would be collected from each boring at 5-foot intervals and submitted for gasoline and
<br /> BTEX analyses based on visual observation and field Instrumentation readings A minimum of three
<br /> samples would be submitted from each boring
<br /> 3 Two-inch diameter groundwater monitoring wells would be installed in each of the borings Each of
<br /> the wells would be screened from 5 feet above to at least 10 feet below the first encountered
<br /> groundwater
<br /> 4 The completed wells would be developed, surveyed, and sampled
<br /> Should the results of the additional investigation indicate that the extent of soil and groundwater
<br /> contamination is been defined, a Problem Assessment Report would be generated Otherwise, a report
<br /> containing details of the additional field activities, well construction details, and analytical results would
<br /> be prepared
<br /> The PHS/EHD approved this workplan in correspondence dated March 6, 1996
<br /> First Quarter 1996 Groundwater Sampling Results- February 1996
<br /> On February 28, 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
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