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Subsurface Investigation and Well Installation Report ARCO FacilityNo 6100 Tracy, California . Page 3 A status report was submitted on November 13, 2001, documenting monitoring activities conducted during the third quarter 2001 In addition to MW-1, selected onsite vapor extraction wells containing measurable amounts of water were included in the monitoring events On two events, vapor extraction well VW-4 had floating product present on the water surface Floating product was measured in well MW-1 throughout the quarter at thicknesses between 0 5 and 0 7 feet SITE INVESTIGATION ACTIVITIES The object>ves of the subsurface investigation were to • Further assess the subsurface conditions beneath the site, including detailed logging of the subsurface stratigraphy and identification of hydraulically transmissive material, • Assess the extent of free phase petroleum hydrocarbons in the subsurface, and • Assess the vertical and lateral extent of total petroleum hydrocarbons and MTBE To accomplish the objectives of the investigation, Delta implemented the following work activities • Advanced six onsite soil borings (B-33 through B-38) to depths ranging from approximately 135 to 140 feet bgs using the mud rotary drilling method The soil borings were continuously sampled • Conducted open-hole wireline geophysical logging within the boreholes of soil borings B-33 through B-38 • Advanced eight soil borings (two each adjacent to borings B-33 through B-36) using an air-rotary casing-hammer drill ng The soil borings were converted to 4-inch diameter groundwater monitoring wells MW-2 through MW-9 • Developed, sampled, and surveyed the newly installed and select existing wells Prior to implementation of field activities, a drilling permit was obtained from SJCPHS Underground Service Alert (USA) was notified 48 hours prior to work activities and a subsurface utility locator cleared the drilling locations SJCPHS and CRWQCB were subsequently notified of the work schedule All work was performed under the direction of a California Registered Geologist Information detailing field practices and procedures performed by Delta is presented in Appendix A Delta modified some of the activities proposed in the May 22, 2001 work plan As requested, offsite subsurface assessment activities were not conducted at this time Information gathered from this investigation should be used to aid in developing a scope of work for offsite assessment In addition, all exploratory soil borings advanced for the P IARC0161 WREPORTS16140-well install report doc