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Lawrence Liver0bre National Laboratory <br /> August 3, 1994 <br /> Ms. Diane Hinson <br /> San Joaquin County Public Health Services <br /> P.O. Box 2009 <br /> Stockton, CA 95201 <br /> RE: Soil Vapor Monitor Point Ins tion at the Building 834 Complex, <br /> Lawrence Livermore National Laboratory(LLNL)Site 300 <br /> Dear Ms. Hinson: <br /> On July 27, 1994, LLNL excavated and removed a 1,000 gallon, steel diesel <br /> fuel tank (834-D1U1) at the Building 834 Complex at LLNL Site 300. The tank was <br /> excavated to a maximum depth of 9 ft below ground surface (bgs), and soil sample <br /> trenches were dug to a depth of 13 ft bgs on the west and east side of the tank. The <br /> excavation remains open pending your decision on this proposal. <br /> To assist our ongoing CERCLA monitoring and remediation activities at the <br /> Building 834 Complex, LLNL is proposing to install three soil vapor monitoring <br /> points in the excavation sampling trenches. Specifically, the monitoring points <br /> will be installed to a total depth of 13 feet, below the base of the former diesel tank, <br /> in the east and west soil excavation trenches. Each of the soil vapor monitor <br /> points will be constructed with 4.5 inch O.D. standard PVC well casing. The <br /> vapor monitor points will be completed with a pre-packed screened interval of 5 ft <br /> (at a depth of 13 to 8 ft bgs). They will be installed in the soil sample excavation <br /> trenches, and blank PVC well casing will extend to the ground surface. Pea <br /> gravel will be placed around each well screen in the excavation sampling <br /> trenches to enhance soil vapor collection. The remainder of the excavation will be <br /> backfilled and compacted to 95% in 6-in. lifts of clayey soil. The clayey soil backfill <br /> will prevent surface water from preferentially infiltrating into the former <br /> excavation site. The excavation will also be capped with asphalt pavement to seal <br /> the surface. The soil vapor monitor points will be installed under the guidance of <br /> a California State Registered Geologist in LLNL's Environmental Restoration <br /> Division (ERD). ERD operates under an existing San Joaquin County Public <br /> Health Services blanket well installation permit, Permit #00251, issued on <br /> March 22, 1994. <br /> 94-8/075:ERD:rtd <br /> -;n E4uai 0000rruroryE coyer•university of Cafiforrua•P 0 Box 808 Lwernmrs a iforrua 94550•Tefeonone(415)422-1100•r,,,A <br />