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AZURE <br /> ENVIRONMENTAL <br /> May 8, 2008 <br /> Harlin Knoll [�V�LUQ <br /> D <br /> San Joaquin County Environmental Health Dept. <br /> L� k� <br /> 304 E. Weber Avenue, Third Floor <br /> Stockton; CA 95202-2708 MAY 1 2 2008 <br /> ENVIRONMENT HEALTH <br /> RE:.. Workplan for Off.-Site Confirmation Ground- ater Sampling PERMIT/SERVICES <br /> Tesoro Site#67080, 2448 West Kettleman Lan , Lodi, CA, SJCEHD Case No. 1948 <br /> Dear Mr. Knoll: = <br /> Y This Workplan for Off-Site'Confirmation Ground-Wat r Sampling ("Workplan") is submitted on <br /> behalf of Tesoro Environmental Resource Company(Tesoro) for the Tesoro Site #67080 (former <br /> Beacon Station 43696)at 2448 West Kettleman Lane in Lodi, California(."the Site"; Figure 1). <br /> The Workplan is submitted in accordance with the San Joaquin County Environmental Health <br /> Department (SJCEHD)_email to Azure Environmental and Tesoro dated May 8, 2008. <br /> Regulatory and technical guidance documents used to prepare this Workplan include the <br /> California Regional Water Quality Control Board=Central Valley Region (RWQCB) guidance <br /> _documents for site investigation'work plans. <br /> Included in this Workplan is the description of a scope of work to assess the lateral extent of <br /> petroleum hydrocarbons'in shall`ow'and deeper ground water in the'off--site area downgradierit <br /> (southwest and southeast) of monitoring well MW-1 and the Site USTs (Figure 1). Most recent <br /> monitoring results collected from well MW=1 in May 2007 show only.a low concentration of <br /> MTBE,(2.1 ug/1) was reported. Grab ground-water samples are proposed to be collected at three. <br /> boring locations (HP-1, HP-2 and HP-3)to assess the lateral and vertical extent of petroleum <br /> hydrocarbons in the area within approximately 60-feet from well MW-1 (Figure 1). In addition, <br /> quarterly ground-water monitoring will be performed on,the date the grab ground-water samples <br /> are collected. Results from the ground-water investigations will be evaluated to update the <br /> w. Conceptual Site Model,(CSM) and supplement case clo sure'data presented in Azure ' v <br /> Environmental's.Case Closure Summary Report and. o Further Action Request dated <br /> December 3, 2007 ("Closure Report"). <br /> Ground-Water Investigation Methods and Procedures <br /> Additional grab ground-water sampling is proposed to confirm the lateral extent of MTBE in <br /> shallow ground water at depths of approximately 40-feet below grade, and the vertical extent of <br /> MTBE in deeper-ground water at a depth below 60 fee . Shallow ground-water sampling is <br /> proposed at two downgradient locations toward the so `thwest(HP-1) and southeast (HP=2), and <br /> deeper sampling is proposed., oneaoeation south (HP 3) of the USTs andw611 MW4 <br /> (Figure l). One CPT pilot boring will be`advanced ad acent to sample location HP-3 to <br /> characterize the lithology to a�deptli of approximately 0-feet, prior to collecting grab ground-' _ <br /> water samples from an adjacent.step-out boring. <br /> 769 Center Boulevard,#123, Fairfax; CA 94930 1 415/488-1738 Fax 415/488-1708 <br />