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1 <br /> HydroGeo Consultants <br /> ' 1 .0 INTRODUCTION <br />' On behalf of Thrifty Oil Co (Thrifty), H droGeo Consultants has prepared this report to <br /> fulfill the requirements of the San Joaquin County Public Health Services, Environmental <br />' Health Division (PHS-EHD), which required Thrifty to perform an aquifer test and <br /> prepare an Aquifer Testing Report and Remedial Action Plan Report for Thrifty Station <br /> No 171 located at 1250 Wilson Way in Stockton, California ("the Site", Figure 1) The <br />' requirements of this work were set forth in the PHS-EHD's letter to Thrifty which <br /> approved performing a 24-hour groundwater pump test on monitoring well MW-5 as a <br />' result of the rising/elevated levels of Methyl Tertiary-Butyl Ether(MTBE) in this well in <br /> accordance with the proposed scope of work set forth in Thrifty's 3`d Quarter 2 00 1, <br /> Status Report As stated in the 3`d Quarter 2001, Status Report, if the groundwater <br />' extraction test shows it is feasible to remove hydrocarbon impacted groundwater, Thrifty <br /> will then submit a remediation design for groundwater extraction from well MW-5 This <br /> report fulfills these requirements <br /> 2.0 SITE DESCRIPTION <br />' The Site is owned by Thrifty and is currently leased and operated as a self-service <br /> gasoline sales facility by ARCO Products Company It is located on the southeast coiner <br /> of Wilson Way and Harding Way in Stockton, California(Figure 1) The Site is <br /> generally square and about 12,300 square feet in size The Site features a cashier's booth, <br /> three product dispenser islands, and three double-walled fiberglass underground tanks <br />' (Figure 2) These tanks were installed in November 1994 and are Iocated near the <br /> northeastern corner of the Site The newer tanks replaced five steel USTs that were <br /> located in the southwest portion of the Site There is an equipment enclosure located in <br />' the southeast corner of the Site which currently houses the thermal oxidizer being used at <br /> the Site to perform ongoing soil remediation through vapor extraction The Site has been <br /> operated as a service station for at least the last 30 years and there are no plans for <br />' alternate use <br />' 3.0 SITE CHARACTERIZATION DATA <br /> 3.1 Geology/ Hydrogeology <br /> 1 <br /> The Site is located in the San Joaquin Valley of the Central Valley geomorphic province <br />' Recently Published geologic maps indicate that Holocene age flood-basin deposits extend <br /> from ground surface to a maximum depth of approximately 100 feet below grade <br /> Oligocene to Holocene age alluvial deposits lie below the younger flood-basin deposits to <br />' a maximum depth of approximately 3,500 feet below ground surface Continental and <br /> marine rocks of pre-Tertiary to Oligocene age underlie the alluvial deposits, and are <br /> comprised of shale, sandstone, and conglomerate Crystalline bedrock underlies the <br /> sedimentary formations <br />' Thrifty Od TOC#171 Aquifer Test and RAP Rpt Page l <br />