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Pitch Reclamation Project <br />Colorado Mined Land <br />Reclamation Board <br />is 2009 Annual <br />Reclamation Report <br />4.4 Sediment Control Embankment <br />The safety and efficiency of the sediment embankment is monitored with a network of <br />surface and subsurface systems. There are five permanent survey monuments where <br />any physical movement of the embankment can be measured and nine piezometers <br />have been installed to monitor the phreatic surface within the embankment. Five of the <br />piezometers were installed during the initial construction in 1980, and four of the <br />piezometers were completed in the core of the embankment in 2001. The 2009 <br />monument survey was performed on October 23 and results indicate the amount of <br />vertical movement is minimal and within the range of survey instrument error. No <br />significant vertical displacement has occurred since the initial settlement following <br />construction. <br />As shown in Table 2, because of the increase in the snow pack coupled with an earlier <br />melt, and a higher runoff volume in 2009, the piezometers in the embankment were <br />monitored more frequently during the peak snow melt in May through July of 2009. <br />The water level in Piezometer 131 in the upstream face of the embankment fluctuated <br />with the increase in the pond level, increasing in early May, and failing back to normal <br />levels as the pond water level decreased by mid-June. In response to the higher water <br />levels in the pond from 2004 through 2009, the maximum water level in Piezometer P3 <br />increased from 9867.0 to 9871.5 ft. amsl and the minimum water level increased from <br />9861.5 to 9861.9 ft. amsl. Similarly, through mid-2009, in Piezometer P4 the maximum <br />level had also increased from 9831.1 to 9839.3 ft. amsl, with the minimum level <br />increased from 9829.3 to 9833.8 ft. amsl. Because P4 is in close proximity to the <br />seepage area noted in 2000, it is monitored closely. Over the past couple of years it <br />was observed that the water level in P4 was not falling back as rapidly as the other <br />piezometers. It was noted that when the probe was pulled out of the P4 and P5 they <br />were covered with silt. The silt build up didn't allow the pipes to drain sufficiently to <br />monitor the phreatic surface in the embankment. In an attempt to remedy the problem, <br />in July 2009 both piezometers P4 and P5 were filled with high pressure water in an <br />attempt to flush out the silt and other debris that had built up in the standpipes. The <br />high pressure flushing resulted in the water levels in both piezometers failing back to <br />normal levels within a few days with the average water level in P4 dropping by more <br />than 3 feet. Piezometer P5 also fell back rapidly to normal levels, but the yearly <br />average difference from 2008 to 2009 was less notable. The 2009 water levels in the <br />embankment piezometers P6 through P9 also increased from historic levels over the <br />past four years, but returned quickly to historic levels after the spring snow melt. <br /> <br />12