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lit) <br /> �91k <br /> Item Evaluation Criteria Comments/Discussion <br /> vertical/extent of MTBE in groundwater defined by <br /> the CPT borings No other fuel oxygenates have <br /> been- detected in groundwater beneath the site <br /> /-igure = presents MTBE concentrations- <br /> p Groun water data tables are included in <br /> �h ?SSU Attachment 2 and MTBE isoconcentration maps are <br /> } (t r included in Attachment 3 <br /> 2 7 Oxygenate Plume Stability and MTBE concentrations appear to have started <br /> Concentration Trends increasing in early 2003 in wells MW-8 and MW-9, <br /> but have since peaked and are currently declining s' <br /> MTBE concentrations have steadily declined over the <br /> last year as shown in the graphs in Attachment 4 <br /> Maximum MTBE concentrations are observed in <br /> well MW-8 Based on the concentration reductions <br /> mentioned above, MTBE concentrations in MW-9 <br /> (which is located downgradient of MW-8) should be <br /> near or below water quality objectives within the next <br /> few years Estimated times to reach water quality <br /> objectives in MW-9 are included in Attachment 4 <br /> 2 8 Groundwater Flow Direction, Although there is some variation, the predominant <br /> Depth Trends and Gradient groundwater flow direction is north to northeast and <br /> there is often a hydraulic mound near well MW-2 <br /> From August 1999 through May 2004, the gradient <br /> ranged from about 0 01 to 0 05 In the past five years, <br /> dept—to water has ranged�froin 15"89-to 20`94;fbg <br /> Groundwater began rising in about 1995 and <br /> stabilized at current depths in about 1998 The water <br /> table rose about 15 ft during this time Groundwater <br /> depths are presented on the well concentrations table <br /> (Attachment 2) <br /> The second quarter 2004 groundwater contour map is <br /> inlcuded in Attachment 2 <br /> 2 9 Stratigraphy and Hydrogeology Soils at the site consist primarily of fine grained soils, <br /> such as silts (ML) and clays (CL) with thin sandy <br /> zones While there do not appear to be any <br /> continuous sands that extend over the entire site, <br /> many of the borings contain silty sand (SM) and/or <br /> sand (SP) zones from approximately 25 to 35 fbg and <br /> 72 to 88 fbg Available boring logs, including <br /> continuous CPT logs, are presented in Attachment 5 <br /> Cross sections are presented in Attachment 6 <br /> 0778 3 <br />