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I� s • Date April 30, 2003 ARCO QUARTERLY GROUNDWATER MONITORING REPORT Facility No 6100 Address 25775 Patterson Pass Road, Tracy, CA ARCO Environmental Engineer Paul Supple Consulting Co/Contact Person Stratus Environmental, Inc 1 Jay R Johnson, R G Consultant Project No U6100-14-4 Primary Agency/Regulatory ID No Nuel Henderson 1 San Joaquin County Public Health Serivices 1 1708 BRIEF HISTORY Four gasoline UST's, one waste oil UST, and associated product piping were removed in 1987 Between 1991 and 1995 a total of 31 sod borings were drilled to depths between 26 and 115 feet below ground surface (bgs) Twenty vapor extraction wells (VW-1 through VW-20) were installed in selected borings Pinnacle Environmental Solutions, Inc submitted a request for "No Further Action" to the RWQCB on February 1, 2000 The RWQCB denied the request, and requested a groundwater investigation One sod boring (B-32) was drilled at the site to a depth of approximately 200 feet bgs in August 2000 Groundwater monitoring well MW-1 was installed in this boring to a depth of approximately 115 feet bgs Following construction of the well, free product was observed in the well Floating product has been removed manually from the well on a weekly basis since September 2000 During August and September 2001, Delta advanced six onsite mud rotary soil borings (B-33 through B-38) to depths up to 140 feet bgs In each boring, soil samples were collected continuously and an open hole geophysical log completed An air rotary casing hammer rig was used to install a well (B-2 through B-9) adjacent to each of the sod borings The dispensers and product piping were replaced during the first quarter 2002 Delta collected compliance soil samples between January 18 and February 11, 2002 Lateral conveyance piping was installed to selected vapor and monitoring wells for future use in sod vapor extraction Piping was stubbed up in the northwest corner of the property which is the proposed future location of the treatment system compound WORK PERFORMED THIS QUARTER(First 2003) 1 A Stratus technician conducted eleven site visits during first quarter 2003 to measure the thickness and remove floating product from well MW-1 Floating product in VW-4 was also measured and bailed on a frequent basis 2 Stratus monitored all vapor extraction and monitoring wells for the presence of water and free product on March 24, 2003 Groundwater samples were collected from wells MW-2, VW-6, and the domestic well 3 Stratus compiled and evaluated the first quarter 2003 monitoring and sampling data • P 1Bp-Arco for URS161001Quarter1y120031Arco_6100_1Q03 doe 5TRATU3