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Status Report, Robinson Seep Investigation Climax Molybdenum Company <br />This hypothesis was supported by a decrease in dissolved iron during August and September; <br />as water levels in the well decrease, oxygen levels would increase and microbial reduction of <br />iron would decrease. However, a resumed increase in the October and November 2013 <br />dissolved iron concentration in EVMW -1 S was not supported by a corresponding increase in <br />indicators of microbial byproducts (alkalinity, sulfate and total dissolved solids; Table 2.1). This <br />would suggest that microbial activity may not be solely responsible for the observed increase in <br />dissolved iron concentrations, although iron related bacteria has been detected in well EVMW- <br />1S. The proximity of the Eh and pH of water from this well to the stability line of ferrous <br />iron/ferrihydrite may indicate that the saturated nature of the sediments immediately <br />downgradient of the cut -off wall may be producing enough of a reducing environment to create <br />dissolved iron. However, this may not fully explain why dissolved iron continues to increase in <br />this well at a relatively steady and consistent manner. This was investigated further during the <br />additional investigation program discussed in Section 3.0. <br />Table 2.1: Microbial Activity Indicator Parameters - EVMW -1S <br />Date <br />Dissolved <br />Iron <br />(mg/L) <br />Total <br />Alkalinity <br />(mg/L) <br />Sulfate <br />(Mg/0 <br />Total <br />Dissolved <br />Solids <br />(mg/L) <br />10/5/2011 <br />0.10 <br />207 <br />470 <br />880 <br />11/15/2011 <br />0.42 <br />222 <br />410 <br />810 <br />3/27/2012 <br />0.90 <br />226 <br />430 <br />808 <br />6/19/2012 <br />1.57 <br />231 <br />430 <br />813 <br />9/25/2012 <br />1.63 <br />229 <br />430 <br />826 <br />12/19/2012 <br />1.90 <br />224 <br />500 <br />950 <br />3/12/2013 <br />2.15 <br />209 <br />600 <br />1050 <br />4/26/2013 <br />2.26 <br />205 <br />650 <br />1100 <br />5/24/2013 <br />2.11 <br />201 <br />530 <br />1010 <br />6/28/2013 <br />2.41 <br />208 <br />580 <br />1070 <br />7/23/2013 <br />2.43 <br />220 <br />583 <br />1110 <br />8/19/2013 <br />2.28 <br />224 <br />485 <br />1040 <br />9/10/2013 <br />1.92 <br />225 <br />558 <br />1040 <br />10/8/2013 <br />2.98 <br />281 <br />497 <br />998 <br />Tetra Tech, Inc. November 2013 13 <br />