2017-04-14_REPORT - M1977004 - Laserfiche WebLink

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Pitch Reclamation Project Colorado Mined Land Reclamation Board — 2016 Annual Reclamation Report The following additional observations have been noted since the adit plug was installed in 1995: • Baseflow water levels in piezometer P-7 have stabilized at just under 10,385 ft amsl. This value has not changed substantially since 2002, indicating that water levels behind the Pinnacle adit plug have stabilized. • Water levels in P-4 and P-5,which are in direct hydraulic connection with the underground mine workings, have been very similar since 1997. Since their installation in 2015, water levels in P-11 and P-12 are also comparable to each other and comparable to P-4/13-5. These results demonstrate that, despite backfilling and/or collapse of void space, there is minimal hydraulic resistance between the northern and southern ends of the underground mine workings. • Piezometers in hydraulic connection with the underground mine workings(P-4, P-5, P-11, and P- 12) show a stronger sensitivity to seasonal snowmelt(i.e., greater water level rise)compared to P-8, P-9, and P-10, suggesting more connection with infiltrating water. This is consistent with the fact that the underground mine workings are overlain by unconsolidated backfill in the South Mine area,which likely allows for more snowmelt infiltration than the undisturbed bedrock. Seasonal response in P-7 is generally greater than P-8 and P-9, but less than observed in P4, P-5, P-11 and P-12, suggesting an intermediate level of hydraulic connection with snowmelt infiltration. • Baseflow water levels in P-4 and P-5 have been generally stable since 1997. P-8 has consistently displayed the lowest water level in the mine vicinity although it has increased approximately 15 ft since 1997. P-8 is located where the workings once day-lighted in the south wall of the North Pit. One possibility for the slow rise in water level near this piezometer is the continued collapse and compression of mine workings, disturbed bedrock, and material backfilled into the opened workings following mine activities,which has caused a decreased hydraulic conductivity and resulting head rise in this area. 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 4).The flow from CFS has been measured since fall 1999 and has ranged from 0.1 to 7.2 gallons per minute(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. Between the October 21, 2015 and November 4, 2015 monitoring events, water levels in both P-5 and P- 12 exhibited a consistent drop of approximately 10.5 ft(Figure 5 and Figure 6). The reason for this water level drop is unknown (the rapid and uniform nature of the drop suggests that it may have been due to a systematic field measurement error). Regardless, baseflow measurements in P-5 and P-12 collected in 2016 were again consistent with water levels in P4 and P-11. In the summer of 2016, water levels in P-4 and P-5 temporarily decreased due to extraction/reinjection activities as part of uranium load reduction phosphate injection pilot testing (Section 4.7). Specifically, activities in 2016 included extraction of water from P-4 with reinjection into P-11, and extraction from P-5 with reinjection into P-12.The water level decrease in P-4 was less than in P-5,which is believed to be due to the greater permeability of the P-4 piezometer screen and potential clogging of the P-5 screen. Pumping tests in P-5 resulted in substantial water level decreases of up to 70 ft, but this drop is believed to reflect the level in the piezometer itself, not in the surrounding formation (i.e., rapid pumping dewatered the piezometer, with slow water movement across the piezometer screen). A temporary water level decrease in P-11 was also observed in August 2016,which was associated with extraction of 2,000 gallons from this well as part of a push-pull test for evaluating phosphate injection performance(Figure 6). 4.3.4 Pinnacle Adit Flow and Water Quality The flow rate from the Pinnacle adit at PP-01 has been monitored since November 1993. The flow 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 gpm throughout the year(Figure 7). The spike in flows observed at PP-01 21