2016-01-20_REPORT - M1977004HR - Laserfiche WebLink

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Homestake 2015 Geotechnical Observations Pitch Reclamation Project Indian Creek and Tie Camp Creek Rock Dumps piezometer reflects the difference in snow pack from year to year, but has always fallen back by the end of summer to its normal range in the fall. If the area receives heavy summer rain the phreatic surface takes longer to fall back. "10725 -10525" Level Site Description: Identical to that of past reports for 1996 through 2014. The minor overlap between this level and other bench designations reflects the original bench configuration. The total dump thickness in IC10525 is approximately 229 feet at this location. 2015 Observations: Piezometers 1C10600 and IC10525 bound this area and similar to piezometer IC10600, the 2015 water level in Piezometer IC10525 rose by 9.0 feet. This is the same rise in the phreatic surface measured in 2014, compared with a 6.7 feet rise in 2013, and a 2.1 feet rise in 2012. The small rise in the water level in 2012 and 2013 reflected a significantly reduced snow pack after several years of heavier snow pack. Between June and December the water level in IC10525 dropped 8.2 feet to elevation 10295.2 feet amsl. Similar to other piezometers located at the Indian Waste Rock Dump, it appears that heavier rainfall during the summer months prevented this piezometer from dropping completely to its January level. c) "10600 - 10400" Level Site Description: Identical to that of past reports for 1996 through 2014. 2015 Observations: Piezometer IC10440 was located in this area of the rock dump. However, it became non-functional in 1996. As such, Piezometer IC10525 is also considered representative of this area of the rock dump and was described in the previous section. d) "10400 - 10370" Level Site Description: Identical to that of past reports for 1997 through 2014. In 1997 Homestake reconstructed the face of the permanent low-grade stockpile located on the Indian Rock Dump. The purpose of the slope reconstruction was to reduce the potential for infiltration and promote more rapid runoff from the slope. This reconstruction appears to have effectively reduced seepage in this area. 2015 Observations: In 2011 replacement Piezometer IC10370R was completed approximately 67 feet to the west of the former location of IC10370. The piezometer was terminated at 208 feet below ground surface (BGS) and completed with an 8 -inch steel protective casing and set in concrete. Upon completion, a transducer was installed in Piezometer IC10370R to assist in monitoring water levels. In 2012, the water level elevation in Piezometer IC10370R rose by 7.1 feet in the spring and fell back to an acceptable range by late summer. In 2013, the water level rose by 10.9 feet during the spring snow melt and lost approximately five feet of that gain by the end of the year. The increase in water level in 2013 compared with 2012 was attributable to heavier snow pack and higher summer precipitation in 2013. The same trends were observed in 2014 when the water level in 1C10370R increased in elevation by 11.4 feet between January and June. In 2015, a rise in the phreatic surface of 6.09 feet occurred between March and May, then dropped back similar to other piezometers in the Indian Rock Dump. In 2015, the water level did not drop back to the normal range until December. Homestake Pitch Reclamation Project 2015 Annual Geotechnical Report M -1977-004H R Page 3 January 9, 20165 2015 AnnualGeotechnicalReportText_Final.doc