2014-04-17_REPORT - M1977004 - Laserfiche WebLink

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Pitch Reclamation Proiect Colorado Mined Land Reclamation Board — 2013 Annual Reclamation 4.3.2 Groundwater Levels Seven piezometers were installed in the area of the Pinnacle underground mine workings to monitor the piezometric surface within the area behind the adit plug. The piezometers are identified as P4 through P10. Piezometer P7 was installed as a replacement for P6, which was lost during plug grouting /construction. The locations of these piezometers are provided in Figure 3. All six piezometers fluctuate seasonally with the highest levels in late May or early June sympathetic with snowmelt. A hydrograph of the piezometer water levels is provided as Figure 4. Piezometers located within the Pinnacle workings include P -4 and P -5. P -9 is located downgradient of the Pinnacle workings and also monitors water levels within the workings. Piezometers located upgradient of the Pinnacle workings (and Pinnacle Adit plug) include P -7, P -8, and P -10; these piezometers are not within the workings. Piezometers that monitor water levels in the underground mine workings (P -4, P -5, and P -9) behave very similar since 1997. Spring and summertime water levels may vary from year to year due to the magnitude and timing of snowmelt and heavy summer precipitation event; however, water levels during low -flow conditions since 1997 (i.e., over - the - winter) have consistently been between 10,391 to 10,397 ft- amsl. Water levels during low -flow conditions should be considered when assessing trends and indicate that there is no increasing trend for the Pinnacle workings. Based on the available data since 1997, the water level in the workings has essentially reached steady state. As noted on Figure 4, due to reduced snow pack the past two years, the rise in the water levels rise in all piezometers was reduced from prior years. Piezometer P -7 is designed to monitor bedrock water levels upgradient of in the Pinnacle adit plug. As shown on Figure 4, the water levels in P -7 are approximately 10 to 15 feet below the level in the Pinnacle workings and follow the same seasonal water level patterns as the piezometers that are within the workings, suggesting that P -7 is somewhat hydraulically connected to with the workings. The slightly lower water level is due to the complex geology and hydrogeology at the Pitch site. Groundwater is compartmentalized, as documented in early hydrogeology reports by Dr. David Snow (Leeds, Hill, and Jewett, Inc. 1979), which is a result of cross cutting faults and the underground workings add another level of compartmentalization. Review of the water levels in P -7 reveals that the low -flow levels have been relatively consistent since 2001, varying over a very small range from 10,381 to 10,383 feet. Therefore, we believe that the water level in P -7 is not increasing and has reached steady state similar to the water level within the Pinnacle workings. The lack of a significant spike following the spring snow melt was notable the past two years due to reduced snow pack. Piezometer P -8 lies just to the north of the Pinnacle workings and was constructed to monitor bedrock water levels upgradient of the Pinnacle adit plug, and is the closest piezometer to the Chester Fault Zone. P -8 was converted to a dual - purpose inclinometer in 1999 by installing inclinometer casing inside the piezometer casing. P -8 has consistently displayed the lowest water level in the mine vicinity although it has increased approximately 15 feet since 1997, or 1.3 feet per year on average. P -8 is located where the workings once day - lighted in the south wall of the North Pit. Springs occur in this area (CFS and CFS -2) and perhaps the water is slowly filling the secondary porosity in the bedrock resulting in increased water levels in the piezometer. The fractured nature of the rock within the fault zone may also enhance infiltration of water from the springs. Therefore, water in the Pinnacle workings does not appear to be the cause of the slightly increasing water level in P -8 over the past seven years. Flow from the Chester Fault Zone into the North Pit Lake is measured at CFS and CFS -2, which are springs located on the south wall of the North Pit (Figure 3). The flow from CFS has been measured since fall 1999 and has ranged from 0.1 to 7.2 gpm. The flow from CFS -2 has been measured since fall 2002 and has a similar range from 0.4 to 4.4 gpm. Review of the flow measurements reveals that there is no apparent increase in the flow rate from these springs into the North Pit Lake. Pitch 2013 Reclamation Report 14April2014.Docx 22