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ARCADIS GERAGHTY& TRO&'FINVED _ <br /> MAY 2 8 1998 ARCADIS Geraghty&Miller,Inc, <br /> ENVIRONMENTAL_ HEALTH 3700 State Street <br /> Ms. Donna Heran PERMIT / SERVICES Suite 350 <br /> Santa Barbara <br /> San Joaquin County California 93105 <br /> Environmental Health Division, Public Health Services Tel 805 687 7559 <br /> 304 E. Weber Ave., Third Floor Fax 805 687 0838 <br /> Stockton, CA 95201-0388 <br /> ENVIRONMENTAL <br /> Subject: <br /> Vertical Fuel Hydrocarbon PIume Delineation H dro unch— <br /> Y p <br /> Investigation/Piezometer Installation Former UNOCAL Gas Station No. <br /> 2859, 1665 Pacific Ave., Stockton California <br /> Santa Barbara, <br /> Dear Ms. Heran: 26 May 1998 <br /> ARCADIS Geraghty & Miller, Inc., (ARCADIS Geraghty & Miller) has Contact: <br /> prepared this workplan on behalf of UNOCAL of California (UNOCAL) for a limited Dr. Stephen Cullen <br /> subsurface investigation at the subject site. This workplan was prepared in response to <br /> a request by the San Joaquin Public Health Service (SJCPHS) to vertically delineate <br /> the dissolved-phase petroleum hydrocarbon plume at the subject site. <br /> Extension: <br /> 805 6877559 <br /> PURPOSE <br /> The investigation proposed herein is designed to complete the site <br /> investigation activities necessary to provide data which will serve as the fundamental <br /> basis for the design of a corrective action plan which will result in the protection or <br /> restoration of the waters of the State of California as defined and described in Title 23. <br /> It is the understanding of ARCADIS Geraghty & Miller that the SJCPHS is <br /> concerned that rising groundwater elevations from a reported historic low of 70 feet <br /> below ground surface(bgs)to the present-day levels of approximately 27 feet bgs may <br /> have submerged the dissolved-phase hydrocarbons below the existing groundwater <br /> monitoring well network. Data collected at the Site between 1993 and 1998 indicate <br /> that the maximum depth to groundwater was observed at monitoring well MW-7. <br /> Maximum depth-to-water in this well has been reported to be 49.36 feet below the top <br /> of the well casing (btoc) in March of 1993; the minimum depth to water in this well <br /> was reported to be 28.32 feet btoc in March, 1998. UNOCAL or its consultants have <br /> not received, reviewed, or reported data that provides substantiation of reports of the <br /> former historic low groundwater levels. However, it is noted that reports of the <br /> historic low groundwater level are incorporated as an assumption for the purposes of <br /> development of this work plan. <br /> Our ref.: <br /> lIGM_SANTA_BARBARAVATAIAPRO_SBOWNOCALIC_VALLE'AWPS_REVIPACWKP2A.DOC <br /> i <br /> r <br /> 3' <br />