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Homestake Mining Company 2018 Geotechnical Observations Pitch Reclamation Project Indian and Tie Camp Rock Dumps ' Homestake Pitch Reclamation Project Annual Geotechnical Report(M-1977-004HR) ' 2018 Geotechnical Observations Indian and Tie Camp Rock Dumps 1. Indian Rock Dump The following summary provides a description of the Indian Rock Dump water levels for ' 2018. The Indian Rock Dump is a generally south-facing, graded and reclaimed rock dump that can be separated into bench levels corresponding to ground surface elevation. The Indian Rock Dump was regraded in 1994 following procedures approved by the Division under Technical Revision #1 in February 1994. In 1995, several minor, localized areas of slope instability were noted, corrected, and reported in the 1995 Annual Geotechnical Report(HMC 1996). In 2018, no significant changes in surface ground conditions were noted. Subsurface water is monitored in piezometers at the levels described below(Figure 2). "10100 —10300" Level iSite Description: Identical to that of past reports for 1996 through 2017. 2018 Observations: Field observations indicate that the repairs performed in 1995 were successful and no new areas of surficial instability have been observed from 1996 through 2018. Piezometer 1030OR is in the central portion of the Indian Rock Dump and monitors subsurface water levels (Figure 2). Piezometer IC1030OR appears to intersect the east branch of Indian drainage (under the Indian Rock Dump)just north of the confluence with the west branch. In 2018, the water level in Piezometer 1030OR decreased during the high- flow sampling event by 7.3 feet compared to 2017 measurements. The water level rise is within historical minimum and maximum measurements at this location. Water levels during 2018 low-flow monitoring were consistent with 2017 measurements. The 1030OR well is in an area affected by the 2018 in situ source zone treatment program. As such, short-term water levels fluctuated in response to these activities, but returned to steady-state levels later in the fall (Figure 5). Phosphate and tracer amended water was injected and recirculated within the Indian Rock Dump as part of the 2018 in situ source zone treatment program. From mid-June through the end of September, approximately 1,241,300 gallons of water were recirculated within the Indian Rock Dump, using all but one piezometer in the area. Extraction occurred from RD- 01, RD-02, RD-03, and RD-05 at the 10000 level, and injection occurred into RD-06, RD-07, ' RD-08, RD-09, and IC1030OR at the 10300 level. Water levels in piezometers used for extraction fluctuated 10 to 15 feet(Figure 6). Water ' levels in piezometers used for injection fluctuated within a range of approximately 10 - 100 feet during active injection period (Figure 5). The short-term water level variations reflect rapid water level changes during injection activities, and when the injection system was ' stopped for monitoring and maintenance activities. Mounding of subsurface water near injection piezometers dissipated soon after termination of injection, and extraction of water appeared to have little influence on the overall subsurface water level. Pitch Reclamation Project Page 3 2018 Annual Geotechnical Report M-1977-004HR