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Mr. Robert Granberg - 3 - • 25 May 2010 <br /> minimize the potential for groundwater extraction to impact the Herman and Helen's plume, <br /> CDM designed an infiltration trench that will be located between the groundwater plume and <br /> the area to be dewatered. A portion of the dewatered groundwater will be used to fill an <br /> infiltration trench, establishing a hydraulic barrier to groundwater flow between the MTBE <br /> groundwater plume and the dewatering activities in the shallow zone. <br /> The effectiveness of the hydraulic barrier will be monitored using groundwater monitoring <br /> wells. Water will be maintained in the infiltration trench to maintain groundwater gradients as <br /> close to baseline conditions as possible. Due to the distance (approximately 600 feet) <br /> between the dewatering activities and the MTBE groundwater plume, and the hydraulic <br /> barrier that will be created by the infiltration trench, the impact on groundwater conditions <br /> there are expected to be minor. This NOA requires groundwater monitoring whenever <br /> dewatering activities occur within 1,000 feet of the right angle corner of the pipeline (near <br /> Herman and Helen's Marina). <br /> CDM performed an analysis of the potential for dewatering activities in the deep zone to alter <br /> the vertical hydraulic gradient and cause MTBE to migrate downward. The analysis indicted <br /> a downward vertical gradient exists on the west side of the area; and an upward gradient <br /> exists on the eastern portion of the area. Well MW-2, a shallow zone well where the highest <br /> concentration of MTBE is reported, is located where an upward gradient exists. CDM's <br /> groundwater model indicates the magnitude of the upward gradients will be reduced, but the <br /> dewatering activities will not cause a downward vertical gradient at Well MW-2. <br /> Groundwater Dewatering Rate and Quality <br /> The Discharger has supplied calculations to support the estimated groundwater dewatering <br /> flow rates. The flow rates are anticipated to vary from 0.3 million gallons per day (Mgpd) to <br /> 2.3 Mgpd. The variation in flow rate is dependant upon the activities at the time, the depth to <br /> groundwater in the area being dewatered, and the soil conductivity. <br /> Groundwater samples were collected at one location on Empire Tract. The analysis is <br /> summarized in the following table: <br /> Empire Tract WQO WQO <br /> AnalVte Date Units Total Dissolved Dissolved Source <br /> Arsenic 3/11/2009 ug/L 91 -- NA -- <br /> Arsenic 4/16/2009 ug/L -- 59 10 US MCL <br /> Arsenic 4/16/2009 ug/L 80 -- NA <br /> Aluminum 4/16/2009 ug/L -- ND (50) 1,000 CA MCL <br /> Aluminum 4/16/2009 ug/L 11,000 -- NA <br /> Calcium 4/16/2009 ug/L -- 66,000 NAWQG <br /> Calcium 4/16/2009 ug/L 68,000 NA <br /> Chromium 3/11/2009 ug/L 1.3 NA <br /> Chromium 4/16/2009 ug/L -- ND (0.5) 50 CA MCL <br /> Chromium 4/16/2009 ug/L 21 NA <br /> Copper 3/11/2009 ug/L 0.64 -- 20 a AG WQG <br /> Iron 4/16/2009 ug/L -- 29 5,000 AG WQG <br /> Iron 4/16/2009 ug/L 16,000 -- NA <br /> Lead 3/11/2009 ug/L ND (0.5) -- 15 a US MCL <br /> Manganese 4/16/2009 ug/L 590 200 AG WQG <br />