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1805 Harbor, Stockton <br /> Page 2 <br /> • Procedures to advance the two deep soil borings in the area of the former UST beyond the . <br /> proposed 35 feet bsg if needed to determine the vertical extent of the soil and groundwater <br /> contamination. <br /> The deepest soil boring to date has been SB-12 to 50 feet b§g;.however, since SB-12 <br /> was advanced approximately 35 feet from SB-1 and M%V-2, the suspected source area <br /> of the release,the results may not reflect the actual bottom of the soil contamination. <br /> EHD recommends converting at least one of the deeper borings to a monitoring well <br /> to address the vertical extent of the groundwater contamination in the deeper aquifer. <br /> EHD recommends reviewing existing soil boring Iog data to determine the most <br /> appropriate depth to set the screen section for this deeper well. <br /> 0 An installation plan for additional soil borings that will adequately,define the lateral extent of <br /> the soil and groundwater contamination north of the former UST area and north of MW-4 <br /> and M%V-3. <br /> Analytical results of the grab water sample from S13-4,located approximately 150 feet <br /> north of the UST,were 200.µg/l of diesel. EHD recommends strategically placing <br /> the 5 soil borings proposed for this area,as well as any additional borings,in an <br /> expanded grid pattern between the tank area,NIV-1,and SB-4, to clearly define the <br /> lateral extent of the soil.and groundwater contamination north of the UST area. Also, <br /> since the soil samples as well as groundwater samples of both MW4 and MW-3 have <br /> contained detectable contaminants in soil,additional sampling points are required to <br /> address the area north of these wells. <br /> EHD recommends resurvey of the monitoring wells and recalculation of the groundwater flow <br /> direction. The previously determined groundwater flow direction was toward the south and <br /> southwest. However,based on the presence and distribution of contamination in groundwater, <br /> be an eastern component to the flow. <br /> there appears to p <br /> REASONS FOR DISAPPROVAL OF THE WORKPLAN (H&S 25299.37, subd.(C)(3).); <br /> None <br /> Jeffrey Wong,effre W ,Senior REHS Nuel C. Henderson,Jr.,RG <br /> LOP/Site Mitigation Unit IV LOP/Site Mitigation Unit N <br /> c; RWQCB, Central Valley Region—James Barton <br /> c: Haley&Aldrich—James T.Wells <br /> E <br />