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March 2014 Mill MLGW -7 Groundwater Quality Assessment ♦ 5 <br />pH values decreased back to a range of 6.0 to 7.0. Lower pH values have <br />corresponded to winter months following an average or above average precipitation <br />period but have also been recorded in the summer months following snowmelt. <br />• Other monitor wells at the site have exhibited similar pH ranges. For example, <br />reported pH values from MLGW -6, a shallow glacial /alluvial monitor well east of <br />MLGW -7, show the same pH fluctuations over the period of record between 1996 <br />and 2012 (Figure 6) indicating responses to recharge. Additionally, recent pH <br />measurements (2012 -2013) of the background monitor well, MLGW -11 and other <br />Henderson Mill monitor wells, MLGW -10 and MLGW -17 (not influenced by <br />seepage) are shown on Figure 7. These monitor wells appear indicative of <br />background water quality and report pH values that range between 5.8 and 7.5. <br />• Figure 8 is a graph showing pH measurements recorded in MLGW -7 for the seven <br />year period beginning in 2007. As discussed with the historical pH record, pH <br />measurements increase following a drought or a below - average winter as is again <br />evidenced in 2012. The following is a list of pH measurements collected since <br />October 2012. <br />Date <br />pH <br />10/18/2012 <br />6.6 <br />12/13/2012 <br />6.9 <br />4/8/2013 <br />6.7 <br />7/31/2013 <br />6.1 <br />8/14/2013 <br />6.2 <br />9/24/2013 <br />6.5 <br />10/15/2013 <br />6.5 <br />11/20/2013 <br />6.6 <br />12/18/2013 <br />6.4 <br />1/15/2014 <br />6.5 <br />2/05/2014 <br />6.6 <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 />