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May 2013 Groundwater POC Memorandum ♦ 8 <br />3.0 1 -DAM POC WELL EVALUATION <br />3.1 EAST OF 1 -DAM <br />Monitor well MLGW -15, northeast of 1 -Dam, was drilled and installed in September 2012 <br />and is paired with existing monitor well MLGW -7 (Figure 2). The objective of installing <br />MLGW -15 was: <br />• to investigate vertical hydraulic gradients and vertical variations in water chemistry <br />east of 1 -Dam. <br />• to evaluate the necessity of a deep aquifer POC monitor well at this location. <br />MLGW -15 was drilled to a total depth of 184 feet bgs. Generalized subsurface conditions <br />consisted of moist to wet poorly sorted gravels with sand and clays. These sediments <br />included subangular to rounded cobbles and boulders of granitic and gneissic composition. <br />Increased water in the sediments was noted at 27.5 feet bgs. Precambrian bedrock (Xg) <br />consisting of gneiss and schist was encountered at approximately 178 feet bgs. The gneiss <br />was weathered in the upper few feet but competent and non -water bearing. <br />Monitor well MGW -15 was screened between 148 and 168 feet bgs and the depth to water is <br />approximately 24 feet bgs (water elev. of 8515.14 feet above mean sea level [amsl] in <br />December 2012). For comparison, shallow monitor well MGLW -7 is screened in glacial <br />sediments between 30 and 40 feet bgs and the depth to water is 22 feet bgs (water elev. of <br />8519.2 feet amsl in December 2012). <br />A potentiometric surface map of the 1 -Dam area was developed using recent groundwater <br />elevation data (Figure 7). The map shows that groundwater flows east - northeast from 1- <br />Dam towards well pairs MLGW- 7 /MLGW -15 and towards the Williams Fork River. <br />Outside the influence of the 1 -Dam extraction wellfield, hydraulic gradients are fairly <br />consistent and range between 0.02 and 0.04 ft /ft. Vertical hydraulic gradients were also <br />analyzed. The vertical gradient between MLGW -7 and MGLW -15 was 0.03 ft /ft. Other <br />AJAX Ltd ♦ 28828 Cedar Circle ♦ Evergreen, CO 80439 ♦ (303) 241 -2057 <br />Clear Creek Associates* 6155 E. Indian School Rd. ♦ Scottsdale, AZ 85251 ♦ (480) 659 -7131 <br />