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Pitch Reclamation Project <br />Colorado Mined Land <br />Reclamation Board <br />2016 Annual <br />Reclamation Report <br />remained at the reduced concentrations observed over the preceding fourteen -year <br />period. <br />4.4 Sediment Control Embankment <br />The safety and efficiency of the sediment embankment is monitored with a network <br />of surface and subsurface systems. There are five permanent survey monuments <br />where any physical movement of the embankment can be measured and nine <br />piezometers have been installed to monitor the phreatic surface within the <br />embankment. Five of the piezometers were installed during the initial construction in <br />1980, and four of the piezometers were completed in the core of the embankment in <br />2001. The 2010 monument survey was performed on September 12 and results <br />indicate the amount of vertical movement is minimal and within the range of survey <br />instrument error. No significant vertical displacement has occurred since the initial <br />settlement following construction. <br />In 2010, the highest water level in the pond of 9885.0 amsl occurred in May and was <br />maintained at the 9884.0 elevation for the remainder of the year. This was below the <br />clay blanket top elevation of 9885.5 amsl. As a result, the water levels in the <br />_ piezometers showed little response to water stored in the impoundment in 2010. The <br />water level in Piezometer 131 in the upstream face rose by 4.11 feet compared with <br />15.45 feet in 2009. In response to the higher water levels in the pond from 2004 <br />through 2009, the maximum water level in Piezometer P3 increased from 9867.0 to <br />9871.5 ft. amsl. In 2010, the water level P3 increased by 2.51 feet. Similarly, from <br />2004 through 2009, the maximum water level in Piezometer P4 increased from <br />9831.1 to 9839.3 ft. amsl. In 2010, the water level in P4 increased by 0.75 feet. <br />Because P4 is in close proximity to the seepage area noted in 2000, it is monitored <br />closely. Over the previous five years it was observed that the water level in P4 was <br />not falling back as rapidly as the other piezometers. It was noted that when the <br />probe was pulled out of the P4 and P5 they were covered with silt. The silt build up <br />didn't allow the pipes to drain sufficiently to show the phreatic surface in the <br />embankment. In an attempt to remedy the problem, in July 2009 both piezometers <br />P4 and P5 were flushed with high pressure water in an attempt to minimize the silt <br />and other debris that had built up in the standpipes. The high pressure flushing <br />resulted in the water levels in both piezometers falling back to normal levels within a <br />few days in 2009, with the average water level in P4 dropping by more than 3 feet. <br />Piezometer P5 also fell back rapidly after being flushed. In 2010, the maximum <br />water elevation in P5 was 2.46 feet, below the maximum elevation of 6.7 feet in <br />I 2009. The 2010 maximum water levels in the embankment piezometers P6, P8 and <br />23