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` f PARSONS 2121 North California Boulevard, Suite 500 •Walnut Creek, California 94596• (925) 941-3700• Fax: (925) 979-9781 •wmv.parsons.com MarRef-ch6, 200 UCENE DD MAR 14 2003 California Regional Water Quality Control Board Central Valley Region ENVilRO NIENT HEALTH 3443 Routier Road, Suite A PERM!?:/SERVICES Sacramento, California 95827-3003 Attention: Mr. Gerald J. Djuth Subject: Soil Vapor Survey Work Plan Vicinity of MW-5R, South of Building 2 Applied Aerospace Structures Corporation Stockton, California Dear Mr. Djuth: On behalf of Group Environmental Management Company (a BP affiliated company), Parsons is pleased to submit this letter which presents a work plan for soil vapor investigation in the vicinity of monitoring well MW-5R. In a recent letter dated 21 January 2003, the Regional Water Quality Control Board (RWQCB) required implementation of a Contingency Plan in response to continuing detections of trichloroethene (TCE) observed at MW-5R, which is located outside the capture zone of site remedial groundwater extraction wells. BP responded with a letter dated 13 February 2003, which proposed a schedule for completion of a work plan by 14 March 2003 and requested a meeting at the site for orientation and discussion of project historical data. During the 26 February site meeting, we discussed the Draft Monitoring and Reporting Program, conducted a site walk, and outlined the soil vapor investigation which is detailed below. Soil Vapor Sampling As shown on Figure 1, soil gas sample borings are planned at 8 locations surrounding MVV-5R. The objective is to obtain samples for delineation of a possible secondary source of contamination in the vicinity of the monitoring well. Three (3) soil gas samples will be collected in each boring at various depths between 15 and 40 feet below ground surface (bgs) for a total of 24 samples. Samples will be collected from approximately 20, 30, and 40 feet bgs as default depths. The actual sampling depths will be selected in the field based on drilling response, indications of adequate air permeability, and field screening information such as PID readings. In addition, a groundwater sample will be collected at four of the borings. On February 10, the depth to the groundwater table depth was measured to be approximately 46 feet bgs at well MW-5R. The Regional Water Quality Control Board has expressed concern that if significant precipitation occurs just prior to sampling, infiltration and percolation of rain water from the surface of the empty lot adjacent to the