2014-04-17_REPORT - M1977004 - Laserfiche WebLink

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Pitch Reclamation Project Colorado Mined Land Reclamation Board — 2013 Annual Reclamation Report 4.3.3 Pinnacle Adit Flow The flow rate from the Pinnacle adit at PP -01 has been monitored since November 1993. The flow from the adit generally consists of a seasonal pattern of high flows during the short period of spring melt in late May or early June and stable flows of less than 10 gallons per minute (gpm) throughout the year. The spike in flows observed at PP -01 each spring are likely a result of snowmelt and runoff from surrounding sources originating between the Pinnacle plug and the PP -01 monitoring point. Once the snowmelt period is over, the flow rate at PP -01 decreases and stabilizes at normal levels. The adit discharge is a direct reflection to the snow pack each year. This is shown clearly on the hydrograph of the Pinnacle adit flow at PP -01 provided as Figure 5. In 2013, the snow pack was back to a normal range compared to 2012 when the snow pack was significantly reduced and there was no spike in adit discharge. The peak flow in 2013 was 20.0 gpm in June compared to 6.0 gpm in 2012 and 28.5 gpm in 2011 and 22.6 gpm in 2010. Dissolved radium 226 and total uranium have been monitored at PP -01 since March 1994. After construction of the Pinnacle adit plug in September 1995, both the dissolved radium 226 and total uranium concentrations have stabilized at reduced concentrations. A graph of the radium and uranium concentrations at PP -01 is provided as Figure 6. During 2013, total uranium and dissolved radium 226 levels remained at the reduced concentrations observed over the preceding seventeen -year period. 4.4 Sediment Control Embankment The safety and efficiency of the sediment embankment is monitored with a network of surface and subsurface systems. There are five permanent survey monuments where any physical movement of the embankment can be measured and nine piezometers have been installed to monitor the phreatic surface within the embankment. Five of the nine piezometers were installed during the initial construction in 1980, and four of the piezometers were completed in the core of the embankment in 2001. The 2013 monument survey was performed on July 23 and results indicate the amount of vertical movement is minimal and within the range of survey instrument error. No significant vertical displacement has occurred since the initial settlement following construction. The pond level was maintained at 9,884 ft amsl during 2013, except during the May reading, when the pond elevation had reached 9885 ft amsl. . This was below the clay blanket repair top elevation of 9,885.5 ft. As a result, the water levels in the piezometers showed little response to water stored in the impoundment in 2013. Because piezometer P4 is in close proximity to the seepage area noted in 2000, it is monitored closely. From 2005 to 2009 the water level in P4 was not falling back as rapidly as the other piezometers. It was noted that when the probe was pulled out of both P4 and P5 it was covered with silt. The silt build up had not allowed the pipes to drain sufficiently to accurately reflect the phreatic surface in the embankment. In July 2009 both piezometers P4 and P5 were flushed with high pressure water in an attempt to minimize the silt and other debris that had built up in the standpipes. The high pressure flushing resulted in the water levels in both piezometers falling back to normal levels within a few days over the past two years, with the average water level in P4 dropping by more than 4ft. Piezometer P5 also fell back rapidly after being flushed. Based upon the monitoring data and embankment inspections since 2001, it appears that the cutoff trench and clay blanket reconstruction performed in 2001 have addressed the previous localized perched zone and related seepage through the embankment core, thus, allowing the embankment to function as designed. Pitch 2013 Reclamation Report 14Apri12014.Docx 23