2012 NGWA Ground Water Summit: Innovate and Integrate

Installation of Infiltration Gallery at Greens Creek Mine

Tuesday, May 8, 2012: 9:00 a.m.
Terrace Room A-C (Hyatt Regency Orange County)
Thomas Hanna, RPG, Johnson Screens;
Eric Sundberg, PG, Greens Creek Mine;

The Greens Creek Mine is located on Admiralty Island, near Juneau Alaska.  It is one of the nation's largest silver producers, with a projected 10-year mine life. Bedrock in the vicinity of the mine consists of relatively impermeable agillites and the only reliable water source for the mine and milling operations are the alluvium along the narrow stream bed of Greens Creek.  The original source water for the mine consisted of three wells competed within the bed of Greens Creek alluvium. However, the wells were too shallow and became ineffective in providing an adequate water supply due to freezing in the winter and sediment production at times when the creek was experiencing high run off.  In 2008 the wells were replaced with an infiltration gallery completed in the stream bed that would not be affected by the bedload movement and freezing that would damage the intakes and reducing capacity in the winter months.  A Johnson Screens, Muni-pak screen was selected as the intake to address problems that might occur with excessive stream bed erosion that occurs during large storm events and provide filtration during periods of high flow and turbidity.  The main challenge during the construction phase was to maintain the 700 gpm flow to the mine and mill operations while decommissioning the old well system and installing the new infiltration gallery.  Estimates of the production from a bed mounted infiltration gallery were used (Sterrett, 2007) to determine that a screen length approximately 20 feet would be required to provide the 700 gpm.  Greens Creek was diverted and the infiltration gallery connected to the existing stilling well.  The new system has been operational for about 2 years without problems at a peak capacity of 700 gpm with minimal drawdown in the stilling well.