2011-12-20_REPORT - M1977004

• Permit No: M1977004
• IBM Index Class Name: REPORT
• Doc Date: 12/20/2011
• Doc Name: 2011 Geotechnical Report ‎(M1977-004)‎
• From: Homestake Mining Company of California
• To: DRMS
• Email Name: RCO
• Media Type: D
• Archive: No

Homestake 2011 Geotechnical Observations
Pitch Reclamation Project Indian Creek and Tie Camp Creek Waste Rock Dumps
average water level in IC10525 was 224.9 feet bgs, compared to 225.84 bgs in 2010.
Overall, the total dump thickness in IC10525 is approximately 229 feet at this location.
e) "10600 - 10400" Level
Site Description: Identical to that of past reports for 1996 through 2010.
2011 Observations: Piezometer IC10440 was located in this area of the rock dump;
however, it was lost in 1996. Piezometer IC10525 is also representative of this area. The
2011 data for that piezometer was described in the previous section.
f) "10400 - 10370" Level
Site Description: Identical to that of past reports for 1997 through 2010. During 1997,
Homestake reconstructed the face of the permanent low -grade stockpile located on the
Indian Creek Waste Rock Dump. The purpose of the slope reconstruction was to reduce
the potential for infiltration and promote more rapid runoff from the slope. No seepage
was observed in this area in 2011.
2011 Observations: During the winter of 2007, wildlife knocked off the casing of
piezometer IC10370 and kicked debris into the 2 inch pipe. Prior to this time, the
piezometer had never shown seasonal water levels fluctuations greater than one foot,
with the averaged water level of 190.7 feet bgs. The bottom of this piezometer is 192
feet bgs. In 2009, the piezometer was flushed with pressurized water to within three feet
of its historical depth of 192 feet bgs and reducing the depth of the piezometer to
approximately 189 feet bgs. Again in 2011 the piezometer filled with sediment and
corrosion making it very difficult to obtain an accurate water level elevation.
Piezometer IC10360 is also located in this area. Water levels in this piezometer
averaged about 222.9 feet bgs in 2011, with a seasonal fluctuation of 11.1 feet. Despite
a record snow pack in 2011 and heavy snow packs from 2008 through 2010, the water
level rise in IC10360 over the past four years is below the levels recorded from 2002
through 2007. The total depth of this piezometer is 260 feet and the thickness of the
dump is approximately 240 feet.
g) "10300 - 10100" Level
Site Description: The Indian Creek Waste Rock Dump was regraded in 1994 following
procedures approved in the February 1994 Technical Revision. During 1995, several
minor, localized areas of slope instability were noted, corrected, and reported in the 1995
Annual Geotechnical Report.
2011 Observations: Field observations indicate that the repairs performed in 1995 were
successful and no new areas of surficial instability (slips) were observed from 1996
through 2011. Piezometer IC10300 is located in this area. Field records indicate that the
10300 piezometer was originally drilled to a total depth of 210 ft. The final depth of the
installation was not recorded in the field record at that time. Inspection of IC10300 in
2008 indicated that the bottom of the standpipe had become filled with silt to a depth of
about 180 ft. bgs, as indicated by sounding the total depth of the standpipe. A steel
surge block was lowered into the standpipe, and rather than encountering a blockage,
the surge block became partially submerged in the slurry -like material, which covered the
steel surge block when it was returned to the surface. It was concluded that the water
Homestake Pitch Reclamation Project
2011 Annual Geotechnical Report
M- 1977 -004HR
Page 2
December 19, 2011
2011 AnnualGeotechnicalReportText _Final.doc