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f . .ir <br /> \1 Vio <br /> 6 J 1* <br /> Figure 34: Aerial images of Vindicator Valley in 1991(left)and 2013(right),with the compliance monitoring <br /> point shown with a red dot labeled VIN 2. The Precambrian-diatreme contact is the red dashed line in the lower <br /> right portion of both images. <br /> Mining of the Altman pit removed significant quantities of historic mine waste, and the backfill in the pit <br /> has significantly high vertical permeability, which allows for rapid infiltration of precipitation into the <br /> diatreme. <br /> Figure 35 shows sulfate and pH data for the Vindicator Valley monitoring wells. The vertical red line is <br /> drawn at 11 March 2008 as an approximation of when backfilling of the Altman pit at the head of <br /> Vindicator Valley began (no reliable data of the exact end of mining or the beginning of backfilling was <br /> available, but aerial photographs from 2007 and 2008 constrain the timeframe for these two events). <br /> Third order polynomial trend lines have been fit to the data for VIN 213-140 to clarify the trends. The <br /> geometric mean sulfate concentration for the period 30 June 2004 through 11 March 2008 is 673 mg/L <br /> with a standard deviation of 53 mg/L, and after 11 March 2008 the geometric mean is 746 mg/L with a <br /> standard deviation of 36. The two geometric means are within one standard deviation of one another, <br /> indicating that there is no significant difference between them. <br />