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October 2015 MLGW-ACR GW Quality Memo♦6 <br /> 3.0 SUMMARY AND RECOMMENDATIONS <br /> The results of recent bacteriological investigations and groundwater monitoring at MLGW- <br /> ACR were used to develop the following conclusions and recommendations. <br /> • There are no discernable increasing or decreasing concentration trends or seasonal <br /> patterns to the dissolved iron and manganese concentrations since fourth quarter 2012 <br /> other than the exceedances for both analytes occurred at the same time. <br /> • Iron and manganese exceedances of Table 2 CBSG standards appear to be the result <br /> of the microbiological activity (e.g., IRB) occurring in the well and possibly the <br /> formation. This microbiological activity is a common natural occurrence that is <br /> unrelated to mining or milling activities. Since conditions in the well casing are not <br /> anticipated to change, future dissolved iron and manganese exceedances are likely to <br /> occur in the future. <br /> • Due to the microbiological activity that is occurring in the well, ambient NPLs for <br /> dissolved iron and manganese currently cannot be established for MLGW-ACR. <br /> • Henderson should explore alternatives (e.g.,well replacement) prior to collecting data <br /> for the establishment of NPLs. <br />