2015-04-17_REPORT - M1977004 (2)

Home Browse Search

Pitch Reclamation Project Colorado Mined Land Reclamation Board — 2014 Annual Reclamation Report snow packs at the site since 2005. The flow in IC-4 and all springs decrease rapidly during the early summer months to a point where there is little to no flow in the fall. 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 plugi 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 and /or in immediate hydraulic connection of the Pinnacle workings include P-4 and P -5. Piezometers located outside of the Pinnacle workings include P -7, P -8, P -9, and P -10, with P -7 located immediately upgradient of the adit plug. i Piezometers that monitor water levels in the underground mine workings (P-4 and P -5) have behaved very similarly 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, the water levels in the Pinnacle piezometers in 2014 reflected heavier snow pack compared to a reduced snow pack in 2012 and 2013. Piezometer P -9, located to the west of the main extent of the workings, exhibits a similar trend to P-4 and P -5. In particular, although the peak water level during high -flow is consistently lower in P -9, the low -flow water level has been similar to P-4 and P -5 since 1997, also exhibiting no apparent increasing trend. Planned activities in 2015 may include the installation of two additional piezometers into the underground workings (located between P-4 and P -5 and /or immediately north of P-4) for the purpose of reagent injection and monitoring. These piezometers would also be used to understand water level changes within the workings. ` Piezometer P -7 is designed to monitor bedrock water levels upgradient of 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 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, as well as the underground workings which 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. As shown on Figure 4, the heavier snow pack in 2014 was noted by a spike following the spring snow melt compared with the previous three years with a reduced to average snow pack. Piezometer P -8 lies just to the north of the Pinnacle workings and was also constructed to monitor bedrock water levels upgradient of the Pinnacle adit plug. This is also 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 Pitch 2014 Reclamation Report 16Apri12015_Cw.Docc 24