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'I r✓ <br /> Tins <br /> APR28 � <br /> April 24, 2003 �Ul RM�YISER�1CF �1 <br /> PE <br /> Mr Harlin Knoll 02093 <br /> San Joaquin County Environmental Health Department 06 a4 <br /> 304 East Weber Street,Third Floor <br /> Stockton, California 95202 <br /> Re: Vertical Flow Assessment Workplan <br /> ARCO Service Station No.2093 <br /> 3425 Tracy Boulevard,Tracy, California <br /> Dear Mr Knoll <br /> URS Corporation Americas(URS), has prepared this workplan on behalf of Atlantic Richfield Company <br /> (ARCO) in response to discussions with the State Water Resources Control Board (SWRCB) regarding <br /> the potential for vertical flow within groundwater monitoring and/or current or former site remediation <br /> wells This workplan is intended to determine if ARCO wells, at the station referenced above, are <br /> acting as vertical conduits for contaminant migration See Figure 1 and 2 for Site Location and a Site <br /> Map, respectively The focus of the investigation is on wells with screen lengths of 30 feet or greater <br /> Well TEX-1 at this site meets the screen length criteria To gain a more complete understanding of <br /> potential downward vertical flow (from potential perched water bearing zones) at the site and to assess <br /> the condition of well screens and casing, three additional monitoring wells screened over different depth <br /> intervals will also be studied The three additional wells selected for this study, ATR-2, ATR-7, and <br /> ATR-S, have well screens less than 30 feet in length <br /> URS will perform a depth-discrete F1oVlsionTM survey of wells ATR-2 and TEX-1 URS will perform <br /> down-hole camera surveys of wells ATR-7 and ATR-8 This workplan includes a site description, a <br /> discussion of the procedures to be used in the proposed investigation, and a tentative schedule for <br /> conducting the proposed work <br /> SITE DESCRIPTION <br /> Currently, the site is operated as an ARCO service station with an AM/PM mini-mart The site is <br /> bounded by commercial property to the west and north, Tract Boulevard to the east, and Clover Road to <br /> the South The majority of the site is paved <br /> Site structures include double-walled fiberglass gasoline underground storage tanks (USTs), two pump <br /> islands, and the AM/PM mini-mart During previous site work, twelve groundwater monitoring wells <br /> (ATR-1 through ATR-12), seven soil vapor extraction wells (VES-1 through VES-7), three air sparging <br /> (AS) wells (S-1 through S-3), one groundwater monitoring/AS well (SMW-1), and one groundwater <br /> URS Corporation <br /> Crown Corporate Center <br /> 2870 Gateway Oaks Drive Suite 300 <br /> Sacramento CA 95833 <br /> Tel 916 679 2000 <br /> Fax 916 679 2900 K V5 BP ARM020931Vertical Flow Study\2093 Vgradient WorKplan doc <br />