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No clear relationship between precipitation and manganese and zinc is apparent, so precipitation was not <br /> included in Figure 9, although since early 2011 both metals appear to vary inversely to precipitation. <br /> 12 0.45 <br /> 0.4 <br /> SO —____. .. <br /> 0.35 <br /> 0.3 <br /> 0.25 <br /> 6 <br /> 0.2 <br /> � � I <br /> 4 0.15 <br /> x <br /> z <br /> 0.1 <br /> x <br /> 0.05 <br /> II \ <br /> m <br /> .. .. .. .. :. .. :. . .. .. .. .. .. .. .. .. .. .. .. ., .. <br /> —CRMW 3A-35 Mn CRMW 3B-63 Mn —CRMW 3A-35 Zn —CRMW 3B-63 Zn <br /> Figure 9: Manganese and zinc data from Arequa Gulch. <br /> Figure 10 presents the pH and quarterly total precipitation data as measured at the Rigi meteorological <br /> station. Field pH in the two Arequa Gulch monitoring wells varied substantially until late 1999, after which <br /> the sample to sample variability diminished substantially. Figure 10 indicates that pH has been slowly <br /> increasing since achieving low values in late 2001 (CRMW 3A-35) and early 2005 (CRMW 313-63). Over <br /> the period for which precipitation data are available, it is evident that pH rises and falls with precipitation, <br /> suggesting rapid recharge of groundwater. The very low pH recorded in CRMW 3A-35 in mid-2008 is <br /> considered to be an erroneous measurement because it is significantly outside the range of the rest of the <br /> data from this well. <br /> The lack of elevated pH or WAD CN in the Arequa Gulch monitoring wells is solid evidence that process <br /> solution is not escaping from the Arequa Gulch valley leach facility (VLF1). Therefore, construction of the <br /> VLF1 did not create a new or increased source of sulfate, manganese, or zinc in Arequa Gulch. Instead, <br /> as described in Section 6.2 below, historical sources put in place well before January 31, 1994 are the <br /> likely explanation for groundwater concentrations of sulfate, manganese, and zinc. <br />