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1 <br /> ' May 2014 Groundwater POC Update Memorandum♦5 <br /> ' 4.1 3-DAM MONITORING NETWORK <br /> The 3-Dam groundwater monitoring network consists of five monitor wells (MLGW-16 <br /> tthrough MLGW-20) that were installed and developed in the Fall of 2012 (see Figure 3). A <br /> hydrogeologic cross-section through selected monitor wells is presented in Figure 5. The <br /> ' monitor wells are constructed to depths ranging from 25 to 135 feet bgs. Each well was <br /> constructed with 20-foot screened intervals. Monitor wells MLGW-16, MLGW-17, and <br /> MLGW-19 are screened near the base of the glacial drift and outwash sediments (Qd), just <br /> above the bedrock contact. Monitor well MLGW-20 was constructed adjacent to MLGW- <br /> ' 17, but is screened at an intermediate depth (lithologic logs included in the POC <br /> Memorandum [AJAX and Clear Creek, 2013]. Monitor well MLGW-18 is also screened at <br /> ' intermediate depths within the Qd sediments. Only two of the wells, MLGW-17 and <br /> MLGW-18, had measureable water during the initial December 2012 water level monitoring <br /> ' event. The other three wells were dry. <br /> 4.2 WATER LEVEL MONITORING <br /> Periodic internal water level monitoring has been conducted at 3-Dam since the wells were <br /> installed in 2012. Water levels recorded during these monitoring events are presented in <br /> Table 1 and results are summarized below. Depth-to-water hydrographs for 3-Dam monitor <br /> ' wells are presented in Figures 6 and 7. Groundwater elevation hydrographs for 3-Dam <br /> monitor wells are presented in Figures 8 and 9. <br /> ' Water level results show that seasonal responses occur in the Qd sediments east of 3-Dam <br /> (Figures 6 to 9). The seasonal response ranges from a gradual rise observed in MLGW-17 to <br /> ' an abrupt appearance of water in MLGW-19 and MLGW-20. Monitor well MLGW-18 <br /> varies significantly, likely in response to direct precipitation/recharge events. Gradual water <br /> ' level decreases are observed in MLGW-17, MLGW-19, and MLGW-20 during the Fall and <br /> Winter months. With the exception of one measurement Quly 2013), when 0.20 feet of <br /> ' water was recorded at the bottom of the well,MLGW-16 has been dry since installation. <br />