2012-03-15_REVISION - M1977300 - Laserfiche WebLink

Home Browse Search

Whetstone, Associates To: John Hamrick, Randy Whicker (Cotter Corporation (N.S.L.)) From: Susan Wyman, P.E., P.G. (Whetstone) Date: March 9, 2012 Subject: Technical Revision 19: Bedrock Groundwater Monitoring Wells Technical Memorandum Whetstone Associates, Inc. 104 W. Ruby Avenue • Gunnison, Colorado 81230 ♦ Phone 970 - 641 -7471 ♦ Fax 970 - 641 -7431 4109C Bedrock monitoring wells are planned for the Schwartzwalder Mine to supplement data from two existing bedrock monitoring wells and eight active shallow alluvial monitoring wells. In a letter dated January 9, 2012, the Colorado Division of Reclamation, Mining and Safety (DRMS) directed Cotter Corporation (N.S.L.) (Cotter) to submit a Technical Revision (TR) to the mine reclamation plan describing an expanded bedrock groundwater monitoring program. Cotter received the letter on January 30, 2012, and met with DRMS on February 14, 2012, to discuss well locations and well completion details. Whetstone Associates attended that meeting and has prepared this technical memorandum to describe the locations, drilling depths, methods, well completion materials, and well development specifications for these monitoring wells. 1. WELL LOCATIONS Well locations will be staked by Cotter personnel or their consultants. Drill pads and pits will be prepared by a qualified excavation contractor. DRMS identified seven new bedrock well locations in the January 9, 2012 letter. The well locations were based on a generalized regional geologic map provided in the Environmental Protection Plan (EPP) submitted as Mine Reclamation Plan Amendment No 2 (AM -02). In the February 14, 2012 technical meeting, Cotter presented more detailed geologic mapping and cross sections. Cotter and DRMS agreed to a phased approach to the downgradient well pairs, whereby the need for the distant bedrock wells (identified here as L8 and L9, near the south boundary of Section 25) would be determined based on data obtained from the closer monitoring wells. Further discussions led to the conclusion that an alluvial well near the South Waste Rock Pile would provide more pertinent data than a bedrock monitoring well at that location. In addition, in a December 14, 2010 Adequacy Review of AM -02, DRMS had previously directed Cotter to replace two existing bedrock monitoring wells upgradient of the mine workings that had become compromised by bentonite intrusion into the filter pack (MW -10 and MW -11). Based on the above correspondence from DRMS, a list of proposed monitoring wells and their target depths are shown in Table 1. Approximate locations are shown in Attachment 1. Because several of the wells are intended to target specific geologic structures (e.g., the Illinois Fault zone), and because access may be difficult, the exact final locations will be determined in the field based on surface geologic mapping, subsurface geologic projections, and contractor access. Where paired wells are proposed, separate wells will be drilled rather than dual completions in a single boring. The paired wells will be drilled on the same drill pad, with the deeper paired well designed to target the structure of interest (e.g., Illinois Fault) and the shallower paired well designed to provide water level and water quality in bedrock above the structure.