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7 <br /> East Bay MUD - 3 - 10 March 1995 <br /> Memo #1 <br /> MW8 at 19,000 ppb gasoline and 160 ppb benzene. No ground water contamination was <br /> detected in MW2, MW3, MW4, MW6, and MW9. MW5 and MW7 were not sampled. Ground <br /> water contamination was detected in HP1, HP4, and HP5 with up to 45,000 ppb gasoline and <br /> 1300 ppb benzene in HP4. <br /> Ground water samples collected in December 1993 and February, May, August, and November <br /> 1994 continue to show significant contamination in MW 1 and MW8, and occasional low level <br /> contamination in MW9. MW2 through MW4 and MW6 have not been sampled since December <br /> 1993, when they were ND. MW5 and MW7 have not been sampled since March 1993, when they <br /> were ND for gasoline; no BTEX analyses were conducted. <br /> BV conducted slug tests in February 1994 to determine aquifer characteristics. Both rising and <br /> falling head tests were conducted on MW1, MW8, and MW9. Hydraulic conductivities were <br /> estimated by the Hvorslev method. Based on their calculations, the aquifer is capable of <br /> sustaining an extraction rate of 10 gpm, the drawdown will be less than 50% (based on saturated <br /> thickness of about 12 feet), and the radius of influence will be 30 feet. <br /> In the Additional Site Assessment and Remedial Options Report, dated December 1993, a number <br /> of remedial methods were discussed. In the Addendum No. I to the Additional Site Assessment <br /> and Remedial Options Report; Remedial Action Plan, dated September 1994, which contains slug <br /> test data and the RWD, they have chosen in-situ bioremediation as their cleanup method. They <br /> propose to extract ground water from MW8 and reinject treated ground water into MWl and two <br /> new injection wells, MW10 and MW11. The proposed system is a "closed loop", in which ground <br /> water is extracted; injected with oxygen, enzymes, surfactants, and amino acids; mixed; and <br /> reinjected. The extraction and injection rates will be the same. <br /> A bench scale test was conducted in January 1995. Ground water samples were collected from <br /> MW8 and an unspecified upgradient well. The sample from MW8 was "exposed to the enzyme <br /> complex and a sample was collected from the effluent". The upgradient sample was not treated. <br /> The MW8 sample was submitted to Hughes Analytical Lab and the upgradient sample was <br /> submitted to Curtis & Tompkin. Both samples were analyzed for nitrate, nitrite, ammonia, and <br /> Total Kjeldahl Nitrogen (TKN). BV reported that ammonia and TKN were higher in the treated <br /> sample than the untreated sample. Nitrate and nitrite were not detected in either sample, <br /> however, the detection limit used on the bench scale sample was higher than that of the <br /> upgradient sample. <br /> Nussmg Repoift copies mast be mdxrx ted to the Regional Bowd <br /> A. In file documents, references were found to the following reports, which are not in our file: <br /> 1. Final Report, Removal of Fuel Storage Tanks, dated 14 December 1987, by Universal <br /> Engineering <br /> 2. Final Report Data, Underground Tank Closure at EBMUD Yard..., dated 27 January <br /> 1988, by Universal Engineering <br /> 3. A work plan, dated 11 May 1988, by Kleinfelder <br /> 4. A report regarding the September 1989 tank removal <br /> 5. A work plan, dated February 1991, by Weston <br />