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20 May 1999 <br /> AGE-NC Project No 95-0142 <br /> Page 4 of 4 <br /> • The highest concentration of dissolved petroleum hydrocarbons continues to be in the area <br />' of the documented release (vapor well VW-1), located immediately adjacent to the former <br /> TKI-90 UST <br />' • Significant concentrations of TPH-g and benzene were detected in the samples from the <br /> deeply screened monitoring well MW-6 (screened 70 to 80 feet bsg) <br /> • MTBE was detected in four ground water samples collected from the site, with detected <br />' concentrations ranging from 2 8 µg/l to 560 µg11 The MTBE comprises a small portion of <br /> the released fuel mass,but locally exceeds the California secondary Maximum Contaminant <br />' Level (MCL) of 5 µg11 and the California Action Level of 13 µg/1 <br />' 5.0. RECOMMENDATIONS <br /> Based upon the data collected to date, AGE recommends <br /> • Continued quarterly momtorxng, the next quarterly ground water sampling and monitoring ' <br /> • event should be scheduled for lune 1999 <br /> • Installation of two additional deep aquifer zone ground water monitoring wells, with depth- <br /> discrete well screens Grab water samples should be collected at a depth of approximately <br /> 40 feet to 45 feet bsg from these borings advanced for the well installations to aid in <br /> definition of the apparent down-gradient extent of shallow dissolved hydrocarbons These <br /> samples should be analyzed for the same constituents as the proposed ground water <br />' monitoring well network <br /> • Installation of additional soil vapor extraction and/or in-situ air sparging wells needed for <br /> active remediation at the site <br /> 1 6.0. LIMITATIONS <br /> Our professional services were performed using that degree of care and skill ordinarily exercised by <br />' environmental consultants practicing in this or similar localities The findings were based upon <br /> analytical results provided by an independent laboratory Evaluations of the geologic/hydro geologic <br />' conditions at the site for the purpose of this investigation were made from a limited number of data <br /> points (i a monitoring-well ground water samples) and subsurface conditions may vary away from <br /> these data points No other warranty, expressed or implied, is made as to the professional <br /> recommendations contained in this report <br /> Advanced GeoEnvironmental,Inc <br /> 1 <br />