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850 --. - 8 <br /> 800 --- -----....... ___ ---__--. -------- -- — -- — — ---------- ---- <br /> • • • 78 <br /> 750 - ___. _.---. --.____ • <br /> • • • 7.6 <br /> • <br /> • <br /> _700 .__ ■ <br /> 7.4 <br /> 650 144-AN <br /> ♦ - -_ 7.2 <br /> 600 -_ - ------- -- '� <br /> • 7 <br /> 550 <br /> 6.8 <br /> f.1 <p 8 Epp Epp 1� 1� ppp qp pp O O N N 1'1 O c♦ e /1 1D D 1� 1� <br /> 0 0 0 0 0 0 0 0 0 0 0 0 0 o O o 0 o O O o 0 0 0 0 0 0 0 0 <br /> VIN 28-140 504 —VIN 2A-270 SO4 VIN 2A-270 pH --VIN 2B-140 pH <br /> ---Poly.(VIN 2B-140 SO4)-—Poly.(VIN 2A-270 pH) Poly.(VIN 2B-140 pH) <br /> Figure 35: Sulfate and pH in groundwater from the Vindicator Valley compliance monitoring wells. Third order <br /> polynomial trend lines have been fit to the sulfate data for VIN 26-140,and pH from both wells. The vertical red <br /> line is drawn at 11 March 2008 as an approximation for when backfilling of the pit at the head of Vindicator <br /> Valley began. <br /> The time series data in Figure 35 suggest that recent mining of the Altman pit at the head of Vindicator <br /> Valley may have resulted in stabilization of sulfate concentration in groundwater, and the trend appears to <br /> be towards a gradual decline in sulfate. As shown in Figure 13, manganese concentration has been in <br /> decline since mid-2010. <br /> The historical data support the hypothesis that the elevated concentrations of sulfate and manganese in <br /> the Vindicator Valley monitoring wells are the result of historic mining activity. Prior to being relocated for <br /> processing, the old waste dumps would have been a significant source of soluble species. With each <br /> precipitation event, soluble species would have been dissolved, and a portion of the water that infiltrated <br /> the dumps would have recharged the shallow groundwater, gradually building a chemical load. Recent <br /> open pit mining and reclamation appear to have resulted in improving groundwater quality, although <br /> several constituents still exceed the domestic well standard. <br /> Given that Vindicator Valley and the compliance monitoring points are underlain by the diatreme, in order <br /> for the monitoring wells to have measurable water levels groundwater must be perched in recent <br /> unconsolidated sediments above the diatreme. It is apparent from Figures 30 and 31 that the <br /> groundwater gradient along the north fork of Wilson Creek, which flows southwesterly along the western <br /> side of the town of Goldfield, is fairly moderate. <br /> The surface topography has a gradient of about 230 feet over 3870 feet, from near the monitoring wells to <br /> close to the northeast end of Victor. The groundwater surface generally mimics the topography, so it is <br /> probable that groundwater moves very slowly from Vindicator Valley to the North Fork of Wilson Creek <br /> near Victor. The recharge area in Vindicator Valley is substantially reduced after mining of the two pits <br /> visible in Figure 34 (Altman is the pit that has been backfilled), because the exposed pit walls and backfill <br /> offer ready infiltration into the diatreme. Therefore, the impacted groundwater is likely to have the current <br /> concentrations of dissolved constituents for some time. <br />