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EarthTech Ms. Violeta Mislang A Tyco International Ltd.Company September 30, 2005 Page 2 of 4 Pre-Field Activities The following activities will be completed prior to conducting the soil gas and additional groundwater sampling described herein: all A site-specific Health and Safety Plan (HASP), compliant with Title 8 of the California Code of Regulations (CCR), Chapter 4, and prepared in accordance with DTSC guidance documents, was submitted with the Work Plan and approved by DTSC. For the additional planned investigation activities, an addendum to the HASP has been prepared and is included as an attachment to this Work Plan addendum (see Attachment 1). A copy of the HASP addendum will be kept onsite during field activities along with the HASP. 41, At least 48 hours prior to conducting fieldwork, Earth Tech will notify Underground Service Alert (USA) of the proposed drilling activities. Earth Tech will also employ the services of a private utility locator to attempt to determine existence and location of potential underground utilities or obstructions in the vicinity of proposed locations. • Applicable exploratory boring permits will be obtained from the San Joaquin County Department of Public Health. • Site access for the field activities will be coordinated with the Property Owner. Soil Gas Sampling for VOCs and Naphthalene A total of four borings (SV-1 through SV-4) will be advanced in the former drill room at 1856 Field Avenue by a direct-push technology (DPT) drill rig. As shown on Figure 1, one boring (SV-1) will be placed adjacent to the location former soil boring SB 17, while the remaining three borings will be placed within a radius of 15 feet around the location of SB17. Soil gas samples will be collected using the "post-run tubing" (PRT) sampling method. This method consists of advancing a drive rod to the required depth and then withdrawing the tip of the probe several inches to expose the surrounding soils. A 3/8-inch PRT, located inside the drive rod, forms a vacuum-tight seal near the probe tip. The PRT is then purged at a known rate using a vacuum pump at the surface. The sampling canisters are then attached to the PRT, and soil vapor samples are collected. Soil gas samples will be collected in general accordance with the guidelines provided within the document Advisory-Active Soil Gas Investigations developed by DTSC and the Los Angeles RWQCB (DTSC/RWQCB, 2003). Soil gas samples will be collected at a depth of approximately 5 feet below ground surface (bgs) in each boring. During installation of the probe, hydrated bentonite will be used to seal around the drive rod at ground surface to prevent ambient air intrusion from occurring. To ensure a representative sample, a vacuum pump will be used to extract three purge volumes of vapor at a flow rate between 100 to 200 (mUmin) prior to soil gas sampling in order to rid the tubing of ambient air and allow subsurface soil gas to enter. A laboratory-supplied 6-liter pre-evacuated stainless steel Summa canister with a 30-minute flow controller will be used to collect soil vapor samples at a flow rate between 100 to 200 milliliters per minutes (mUmin).