SITE INFORMATION AND CORRESPONDENCE

Home Browse Search

URS ' Ms. Kathleen Amaru Page 4 Regional Water Quality Control Board—Central Valley Region ' July 31,2009 hammer-drill with a 1-inch-diameter bit was used to install the passive soil gas modules to an average depth of 15 to 18 inches bgs. Drilling depth was restricted due to hard soil conditions.Prior to drilling, the bit and stainless steel insertion rod were cleaned using a three-step decontamination procedure with laboratory-grade detergent and rinsed twice in distilled water. A passive soil gas device attached to a cork with a cord was placed in the hole using the decontaminated stainless steel insertion rod and sealed at the surface with the cork and covered with native soil. Each location was marked with a flag bearing ' the location name,module ID number, insertion date and time. The module ID number was labeled on a map and on the insertion date and timed entered onto the Installation/Retrieval log.Three randomly selected passive soil gas modules remained sealed in the shipment container for trip blanks for the duration of the investigation. The passive soil gas modules installed on April 30 and May 4, 2009, remained in the ground until May 28,2009. Retrieval ' On May 28,2009,URS returned to the site to retrieve the 50 passive soil gas modules.Forty-nine of the 50 modules were able to be retrieved from the site. Module#599024 installed May 4, 2009,was not ' located.During removal,the ID number on the device was verified to ensure that it matched the ID number on the jar.The cord and the cork were removed and the passive soil gas module was placed into the jar and sealed with the lid.A custody seal was affixed to both the jar and the jar lid and care was ' taken to not cover the barcode on the jar. The retrieval date and time was recorded on the histallation/Retrieval log. ' Destruction The shallow borings were backfilled to near surface with bentonite crumbles and hydrated with potable water. Each shallow boring was then covered with surface dirt. Analysis ' The modules were sent via overnight delivery in the original shipping containers to the Screening Modules Laboratory W.L. Gore&Associates, Inc. located in Elkton,Maryland,to be analyzed for VOCs including TCE and PCE,by modified United States Environmental Protection Agency(EPA) ' Methods 8260 and 8270. ANALYTCAL RESULTS Refer to the GORE Surveys Final Report(Attachment C). ' CONCLUSIONS AND RECOMMENDATIONS Soil gas analytical data shown in the Gore figures presents TCE, PCE, and 1,2-DCE impacts focused in the area between monitoring wells MW-5 and MW-6 which have historically reported the highest KAWpmuessU DiDVI-Bum PitMW Panive SGTwsive Soil Gm Survey Rcon.doo