2012-12-20_REPORT - M1977004

• Permit No: M1977004
• IBM Index Class Name: REPORT
• Doc Date: 12/20/2012
• Doc Name: ANNUAL FEE/REPORT
• From: OPERATOR
• To: DRMS
• Email Name: RCO
• Media Type: D
• Archive: No

Homestake 2012 Geotechnical Observations
Pitch Reclamation Project Indian Creek and Tie Camp Creek Waste Rock Dumps
through 2012. Due to problems in Piezometer IC10300 over several years with
sediment buildup in the casing, in 2011 it was abandoned and replaced by Piezometer
ICI 0300R located approximately 30 feet to the west of IC10300. The piezometer was
terminated at a depth of 210 feet and completed with a 20 feet screen, with a concrete
wellhead and an 8 -inch steel well protective casing and concrete apron. A transducer
was also placed in the Piezometer IC10300R in late 2011 to assist in monitoring water
levels.
In 2012, the water level in Piezometer IC10300R rose by only 0.2 feet reflecting the
reduced snow back in the area and compared to a rise of 11.1 feet in Piezometer
IC10300 in 2011.
2. Tie Camp Waste Rock Dump
a) "10400 - 10100" Level
Site Description: The Tie Camp Rock Dump was re- graded in 1994 following procedures
approved in the February 1994 Technical Revision. During 1995, minor, localized areas
of slope instability were noted, corrected, and reported in the 1995 Annual Geotechnical
Report.
2012 Observations: Piezometer TC10375 monitors the Tie Camp Creek Rock Dump. In
2012, water levels averaged 168.1 feet bgs, with a maximum observed seasonal
fluctuation of 2.4 feet between May and June. The maximum fluctuation was down from
the 2008 rise of 12.3 feet and 6.1 feet in 2009. This is deemed a normal and acceptable
seasonal variation. Field observations indicate that the repairs performed in 1995 were
successful and no new areas of surficial instability were observed from 1996 through
2012. In 2012, grading was performed on the second and third benches from the top of
the rock dump to control rill erosion that had become apparent over the past couple of
years due to the bench filling with silt. This repair work will be described, with photos, in
the Annual Reclamation Report that will be submitted in April 2013. In 2013, we will
continue to monitor the surface conditions of the rock dump after the spring snow melt.
3. Piezometers — 2012 General Comments
The 2012 water level measurements showed a maximum differential following snow melt
at or below that of the past five years due to a reduced snow pack. Following the dry
conditions of 2001 through 2003, the seasonal variations had increased in recent years
as heavier snow packs had occurred. The replacement of two piezometers in the Indian
Creek rock dump in 2011 has alleviated issues in monitoring the phreatic surface in the
Indian Creek rock dump. Homestake will continue to monitor and evaluate the cause
and effect of any seasonal spikes in the piezometric water levels, and also observe any
changes in surface features of the rock dumps. There continues to be no indication of
concern related to instability or foundation phreatic surfaces in either the Indian Creek or
Tie Camp Creek rock dumps.
Homestake Pitch Reclamation Project
2012 Annual Geotechnical Report
M- 1977 -004HR
Page 4
December 19, 2012
2012AnnualGeotechnicalReportText _Fi nal.doc