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10 May 2002 <br /> • AGE-NC Project No 96-0229 <br /> Page 4 of 5 <br />' • Monitoring wells MW-1 and MW-10B are "drowned", and yield samples representative of <br /> deeper ground water conditions Deeper ground water in the area of MW-1 (48 to 53 feet bsg) <br /> is Impacted by significant TPH-g, BTEX, MTBE, DIPE and 1,2-DCA, deeper ground water <br /> in the area of downgradient well MW-1OB is Impacted by minor MTBE and 1,2-DCA <br /> • Significant MTBE and 1,2-DCA concentrations were detected in the sample collected from <br /> well MW-1 (screened 48 to 53 feet bsg) in deeper ground water, however only minor MTBE <br /> and 1,2-DCA concentrations were detected in the samples collected from shallow water <br /> on-site wells MW-2 (located 5 feet from MW-1) and MW-3, Implying that an undelineated <br /> MTBE and possibly 1,2-DCA-Impact may be present crossgradient to downgradlent of the <br /> site at deeper depths (Figure 5) <br /> • The greatest concentrations of off-site dissolved MTBE were detected in downgradlent wells <br /> MW-6 and MW-7, low concentrations of dissolved MTBE were detected at wells MW-8, <br /> MW-9,MW-1OA and MW-1 OB, a trend of increasing off-site MTBE concentrations has been <br /> noted since March 2001 <br /> • Increasing TPH-g, BTEX and MTBE were reported in water samples collected from MW-9, <br /> suggesting that the plume of petroleum-impacted ground water may have shifted towards the <br /> lieeast <br /> • The elevated concentrations of petroleum hydrocarbons detected in samples collected from <br /> wells MW-1, MW-2, MW-3, MW-6 and MW-7 Indicate that these wells are within or near <br /> the dissolved petroleum hydrocarbon "core area" of the plume (Figure 4) <br /> 50. RECOMMENDATIONS <br /> Based upon data collected during December 2001, AGE recommends <br /> • Preparation of a problem assessment report (PAR), the PAR should Include results of any <br /> feasibility studies to determine appropriate remediation alternatives for the site <br /> • Performance of a receptor survey to locate potential receptors within 2,000 feet of the site, <br /> results of the receptor survey should be Included in the CAP <br /> • Continued utilization of wells MWA through MW-10 for quarterly ground water monitoring <br /> and sampling <br /> • Ground water monitoring events should be performed concurrently at the Pacific Car Wash <br /> site and the former Arco Mini-Mart (Pacific Mini-Mart), located at 4511 Pacific Avenue, <br /> - - - - -Pacific Mini-Mart-ground water monitoring wells could be utilized-to-assess-the northern- - — <br /> extent of the dissolved petroleum hydrocarbon plume <br />! Advanced GeoEnvironmental,Inc <br /> I <br />