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/d �Rvvwwsecoccom R INTERNATIONAL SC L C O R INCORPORATED 3017 Kilgore Road,Suile 100 Rancho Cordova,CA 95670 916-861-0400 TEL 916-861-0430 Fm O y y August 29, 2005 1^R1Z y' Ms. Mary Serra Regional Water Quality Control Board-Central Valley Region 11020 Sun Center Drive, #200 Rancho Cordova, CA 95670 a-+fl Re: Schedule of Soil Vapor Extraction System Monitoring Activities at Parcel 2AZ 6:Y- St Weber Avenue, Stockton, San Joaquin County L&M Operable Unit Stockton Parcel 2A West Weber Avenue and North Lincoln Street Stockton, California Dear Ms. Serra: This letter, prepared by SECOR International Incorporated (SECOR) on behalf of the L&M Operable Unit Group (L&M OU), is in response to a Regional Water Quality Control Board (RWQCB) request for submittal of a schedule for operation, sampling and reporting on the soil vapor extraction (SVE)system. The SVE system was started on August 18, 2005. For safety reasons each of the individual SVE wells was opened in sequence, monitored with a flame ionization detector (FID), and sampled for: total petroleum hydrocarbons as gasoline (TPHg), benzene, toluene, ethyl benzene, and total xylenes (BTEX), and methyl tert-butyl ether (MtBE). Induced vacuum pressures were measured in wells ASVE-1 through ASVE-6, and system operating parameters recorded. Induced vacuum pressures were not measured in wells SVE-1 through SVE-11 due to high FID concentrations. The high FID readings did not permit the operator time to develop full vacuum in wells SVE-1 through SVE-11 because the high influent fuel content caused the oxidizer to rapidly approach unsafe operating temperatures and conditions. On departure wells ASVE-1, ASVE-2, ASVE-3, and ASVE-6 were left in operation in conjunction with dual phase wells DPE-4, DPE-8, and DPE-11. On August 23, 2005 SECOR sampled wells ASVE-1, ASVE-2, ASVE-3, and ASVE-6 for: FID, TPHg, BTEX, MtBE, and system operating parameters were recorded. Induced vacuum pressures were not recorded as that information was previously collected on August 18, 2005. On departure wells ASVE-1, ASVE-2,ASVE-3, and ASVE-6 were left in operation. It is not possible to run the current soil vapor extraction and oxidation system on all of the soil vapor extraction wells (ASVE-1 through ASVE-6 and SVE-1 through SVE-11) concurrently until vapor concentrations are reduced. Therefore, SECOR will implement, as conditions allow, the following schedule to maintain compliance with the work plan approved by the RWQCB: • Continue to run ASVE-1 through ASVE-3 and ASVE-6 and sample them individually for FID, TPHg, BTEX, and MtBE twice more, during the weeks of August 29 and September 5. • During the week of September 5, 2005 open wells ASVE-4 and ASVE-5, and one SVE well. Sample the added ASVE wells that week and during the following two weeks. Induced vacuum readings will be taken on the SVE well by the third week from its opening. During this period any of the wells ASVE-1 through ASVE-3 and ASVE-6 may be shut off to maintain safe SVE oxidation system running parameters.