2008-12-23_REPORT - M1977004

• Permit No: M1977004
• IBM Index Class Name: REPORT
• Doc Date: 12/23/2008
• Doc Name: 2008 Annual Geotechnical Report
• From: Homestake
• To: DRMS
• Email Name: RCO
• Media Type: D
• Archive: No

Homestake 2008 Geotechnical Observations
Pitch Reclamation Project Indian Creek and Tie Camp Creek Waste Rock Dumps
The water levels recorded in 2008 are from a small interval of water that is perched on the
soil in-filling, and because of the blockage in the standpipe, is not necessarily indicative of
water pressure in the underdrain. The10300 Piezometer is constructed of steel pipe,
perforated with a cutting torch, and has been in operation for over 20 years. It is possible
that degradation of the standpipe has allowed infiltration of soil fines.
The 10300 Piezometer issue outlined above will be further investigated, and hopefully
resolved, during the 2009 field season. An attempt will be made to clear the silt by flushing
the casing with high pressure water. In the event that flushing does not restore the
functionality of the piezometer, we will evaluate the purpose and need of the piezometer
and decide if replacement is critical to long-term monitoring of the Indian Creek Waste Rock
Dump.
Tie Camp Waste Rock Dump
a) "10400 - 10100" Level
Site Description: The Tie Camp Waste Rock Dump was regraded 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.
2008 Observations: Piezometer TC10375 monitors the Tie Camp Creek Waste Rock Dump.
In 2008, water levels averaged 169.9 feet bgs, with a maximum observed seasonal
fluctuation of 12.3 feet in June. Even though the average water level in the piezometer was
consistent with previous years, the maximum fluctuation was the largest increase since the
repair work was completed in 1995. The water level dropped back to its normal range the
following month, a condition similar to that of the piezometers on the Indian Creek dump
and is deemed as an acceptable seasonal variation. The increase in the water level in the
May-June period was likely related to the heavy snow pack in 2008. Field observations
indicate that the repairs performed in 1995 were successful and no new areas of surficial
instability were observed from 1996 through 2008. In 2009, we will continue to monitor
closely the surface conditions of the Tie Camp dump after the spring snow melt.
2. Piezometers - 2008 General Comments
The 2008 water level measurements continue to show above average maximum increases in a
couple of the piezometers in the waste rock dumps and, therefore, the thickness of the
saturated zone at the base of the waste rock dumps. Following the dry conditions of 2001
through 2003, the seasonal variations have increased in recent years as heavier snow packs
have occurred. We believe the increases in the maximum water levels are related to the spring
snow melt and the saturated zone within the dumps remains thin. Homestake will continue to
monitor and evaluate the effects of the seasonal spikes in the piezometric water levels, and
also observe any changes in surface features of the dumps. At present, there continues to be
no indication of any concern related to instability in either of the waste rock dumps.
Homestake Pitch Reclamation Project Page 3
2008 Annual Geotechnical Report December 15, 2008
M-1977-004HR 2008AnnualGeotechnicalReportText_Final.doc