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March 2014 Mill MLGW -7 Groundwater Quality Assessment ♦ 8 <br />4.0 SUMMARY AND RECOMMENDATIONS <br />The results of the historical internal monitoring and recent triannual groundwater <br />monitoring were used to develop the following AJAX /Clear Creek recommendations for <br />further monitoring and evaluation of groundwater downgradient of the Mill. <br />• MLGW -7 pH measurements do not strongly correlate with higher concentrations of <br />TDS, sulfate or other metals in the monitor well and do not suggest that low pH <br />values are an indication of seepage impacts. <br />• The data suggest that pH measurements in MLGW -7 and other Henderson Mill Site <br />monitor wells naturally fluctuate below a pH of 5.5 and above a pH of 8 likely as a <br />result of recharge and drought conditions. As such, it is recommended that <br />Henderson work to establish pH NPLs at MLGW -7 and other POC wells that <br />appropriately bracket naturally occurring conditions. It is recommended that these <br />NPLs be established using statistical methods consistent with those utilized in the <br />development of past ambient NPLs. <br />• Triannual sampling at MLGW -7 for the GWMP triannual indicator parameters listed <br />in Table 1 is recommended at this POC well location. <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 />