Development of Guidance Document for Heap Leach Extraction Facilities January 1998 The Division of Water Quality (DWQ) began regulating cyanide heap leach operations in the late 1980s when a number of applications for construction permits were received from various mining companies. During the review process for these initial heap leach permit applications, and the subsequent application reviews for facility expansions and permit renewals, DWQ staff developed a scientific and engineering knowledge base for the design and construction of heap leach facilities. This knowledge base was augmented by formal staff technical training, on-going interaction with mining companies and/or their consultants,
and benchmarking of regulations for other western states including Colorado, Idaho, Montana, Nevada, New Mexico, and South Dakota. Although DWQ considered promulgating regulations for the design and construction of heap leach facilities, the agency recognized that specific, detailed regulations could unnecessarily constrain facility designs and restrict consideration of site-specific conditions or application of new technologies. Instead of prescriptive rules, DWQ used its extensive experience and knowledge base to develop guidelines for the design and construction of heap leach facilities including leach pads, solution ponds, solution collection systems, and solution conveyance systems that are adequate for protecting ground water quality while considering the economics of facility construction. The resulting document, Design and Construction Guidance Document for Precious Metals Heap Leach Extraction Facilities (June 1998), is intended to be used by applicants in preparing designs that may be expected to result in DWQ approval if the scope of issues in the guidance are adequately addressed and site-specific geologic, hydrologic, and climatologic conditions are taken into consideration using best available technology.