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October 2015 MLGW-ACR GW Quality Memo♦5 <br /> • The sample yielded a low level of dissolved mineral content. <br /> • The sample yielded a high re-suspended iron concentration. A high re-suspended iron <br /> concentration can indicate the presence of IRB as well as the entrapment and <br /> accumulation of iron oxide in biomass present within the well. <br /> • The total organic carbon (TOC) was elevated. At elevated levels carbon can provide <br /> a food source and stimulates the growth of microorganisms. <br /> • Biological analysis of the sample confirmed a large population of IRB. The dominant <br /> organisms identified within the sample were species of Flavobacterium and the iron <br /> oxidizing bacteria Gallionella. No SRB or E. coli were present in the sample. <br /> In summary, the confirmation of a large population of IRB in MLGW-ACR supports the <br /> interpretation that localized effects associated with biological activity in the well are a primary <br /> cause of dissolved iron (and likely dissolved manganese) present in water quality samples. <br /> 2.4 WATER QUALITY DATA <br /> Four additional triannual samples (third quarter 2014, fourth quarter 2014, second quarter <br /> 2015, and third quarter 2015) have been collected from MLGW-ACR since the Baseline <br /> Parameters Report. Figures 2 and 3 present the dissolved iron and manganese concentrations <br /> in the well since fourth quarter 2012. As shown in these figures, a third dissolved iron and <br /> manganese exceedance of the CBSG Table 2 standards occurred in third quarter 2014(August <br /> 2014). The concentrations for dissolved iron and manganese in this third quarter 2014 sample <br /> were 338 µg/L and 59.8 µg/L,respectively. Concentrations currently are below standards and <br /> have decreased during the past three triannual sample events. <br />