Proceedings Tailings and Mine Waste 2015 Vancouver, BC, October 26 to 28, 2015 Tailings dams in Nevada – an overview G. Tortelli Golder Associates Inc. L. Opperman Nevada Division of Water Resources ABSTRACT If the State of Nevada were a country, it would rank as the eighth largest gold producer in the world (NMA, 2014). The state is also a significant producer of silver, copper, barite, lithium, and other minerals. Nevada currently has over 30 active tailings dams permitted through the Nevada Division of Water Resources (NDWR). A variety of conditions, including geology, seismicity, and climate present challenges to both the design and regulation of tailings dams in the state. This paper provides an overview of historic and current regulations and design practices by combining the authors’ experience with information from the NDWR’s Safety of Dams Program database to present a general overview of the tailings dams in Nevada. The goal of the paper is to familiarize mine owners, regulators, and tailings dam designers with regulations and general engineering concepts currently used in Nevada. Keywords: regulation, safety, permit, design, stability 1. HISTORY OF MINE TAILINGS IN NEVADA 1849 - 1880s: The '49ers discover gold in Nevada and the famous Comstock Lode silver ore deposit is found in Virginia City. A silver and gold rush soon followed with many individual miners using sluicing and panning techniques to recover minerals. The Nevada Territory was inducted into statehood in 1864, in part so that the state’s gold and silver resources could finance the Union Army in the Civil War. 1890 - 1920s: The first mining renaissance begins. Stamp Mills become common and produce the first tailings. The early stamp mills deposited the tailings on the ground and the water was lost. Tailings dams were created to store the tails and more importantly to reuse the limited water resource. Early tailings dams were unregulated and haphazardly constructed. The working conditions around these dams were dangerous and environmental contamination was prevalent. Evidence of fugitive tailings at 11 historic sites indicates that catastrophic failure of abandoned mill tailings was more common in Nevada than has been reported in the literature. 1920s - 1970s: More silver and gold is discovered in Tonopah and Goldfield. Copper mining begins near Ely. World wars and industrial expansion revive significant demand for base metals. In 1962, the Carlin Trend gold deposit is discovered, sparking a resurgence in precious metals mining. 1980s - Present: The current mining boom is marked by the consolidation of mining companies and development of large, low-grade ore deposits. Initially, oxide ore is processed using heap leach technology. As close-to-surface oxide ore reserves are depleted, mining companies are increasingly digging deeper and processing low-grade sulfide ore using milling techniques. Residual tailings produced during processing are stored in modern engineered and regulated tailings impoundment facilities. The locations of active tailings dams in Nevada are shown on Figure 1. Proceedings Tailings and Mine Waste 2015 Vancouver, BC, October 26 to 28, 2015 Figure 1. Active tailings dams in Nevada 2. TAILINGS DAM REGULATION IN NEVADA – PAST AND PRESENT 2.1 Dam Safety Regulation History The earliest laws pertaining to construction of dams were enacted in 1913 when the State Engineer required notification of any proposed dam construction. These laws were likely to protect downstream water users from being cut off after the erection of a new dam. These notices likely did not pertain to tailings dams since there were no regulations against placing tailings in streams prior to 1935 when greater water laws were adopted. In 1951, Nevada Revised Statues (NRS) Chapter 535, specific to dams, was enacted marking the first time regulatory approval was needed for the construction of a dam. This statute also gave the State Engineer the authority to conduct inspections on dams for public safety. These new regulations also required operators to operate dam safely to protect downstream interests. The first dam permit specifically issued for a tailings dam was permit J-130, issued in 1971 for Cliffs Copper Corporation at the Rio Tinto Mine located north of Elko. The dam was 7 meters tall and impounded 390,000 m3 of “sludge resulting from treating acid mine water”. Eight other tailings dam applications had been submitted by 1980 to support copper, gold, and other mineral mining processes. These early tailings impoundments were designed and permitted with dam safety considerations, not specifically to prevent tailings waters from seeping into the environment. In 2003, Nevada Administrative Code (NAC) Chapter 535 was developed for the regulation of dams, and tailings dams were given special consideration. This was the first time that submittal Proceedings Tailings and Mine Waste 2015 Vancouver, BC, October 26 to 28, 2015 of an application and the approval of plans for a tailings dam was defined for the first time in detail. A hazard classification system was written into the regulations and provided the State Engineer a way to categorize the immediate consequences to persons and property located downstream from the dam in the event of a dam failure. Dams are placed into one of the three following hazard classifications: High Hazard - Failure carries a high probability of causing a loss of human life Significant Hazard – Failure carries a reasonable probability of causing a loss of human life or a high probability of causing extensive economic loss or disruption in a lifeline. Low Hazard - Failure carries a very low probability of causing a loss of human life and a low to reasonable probability of causing little, if any, economic loss or disruption in a lifeline. As used in these regulations “lifeline” included: A road that is the sole means of access to a community A major trunk or transmission line for gas or electricity, the disruption of which could pose significant risks to the public health, safety or welfare of the affected community Transmission lines for gas or electricity that serves hospitals or other comparable facility. In 2014, the definition of a lifeline was expanded to include any lake, reservoir, stream or watercourse that serves as a potable water supply, the possible disruption of which is to be considered when assigning a hazard classification to each dam. 2.2 Current Dam Safety Regulations In 2014, NAC Chapter 535 was updated and expanded to form the regulations that are currently in place today and enforced by the State Engineer through the Safety of Dams Program. Currently, the State Engineer oversees 54 active tailings dam permits through the Safety of Dams Program. However approximately 12 are in various stages of closure or reclamation and some are in various stages of phased construction. A list of tailings dams currently permitted in Nevada is shown below in Table 1. 2.2.1 Hazard Classification Report As part of the permit application, a proposed dam owner is required to prepare a hazard classification report, which ultimately suggests the hazard classification and also further defines the requirements of an Emergency Action Plan for High and Significant hazard dams. The Emergency Action Plan: (1) must follow a format presented by the Federal Emergency Management Agency or approved by the State Engineer; (2) must address appropriate steps to be taken in the event of a potential or actual emergency at the dam; and (3) for those sections requiring numeric analysis, calculations or mapping, must be prepared under the direction of a professional engineer. Proceedings Tailings and Mine Waste 2015 Vancouver, BC, October 26 to 28, 2015 Table 1: Active Tailings Dam Permits in Nevada Name Owner Length Height Storage Storage (m3) Primary (m) (m) (acre-ft)* Minerals Giroux Quadra 3840 59 130,624 161,122,092 Cu N. block Barrick 4938 158 103,194 127,287,735 Au, Ag Mill 5/6 Newmont 5700 91 85,000 104,845,800 Au, Ag Juniper Newmont 6888 54 71,000 87,577,080 Au, Ag Mill 5/6 East Newmont 6103 67 67,500 83,259,900 Au, Ag Phoenix Newmont 7077 53 41,433 51,106,777 Au, Ag Mill 5/6 West Newmont 437 64 35,661 43,987,130 Au, Ag Cortez Area 28 Barrick 4061 66 31,229 38,520,347 Au, Ag Cortez Cell 4 Barrick 3688 82 31,000 38,237,880 Au, Ag RMG West Round Mtn. Gold 4038 27 28,816 35,543,960 Au, Ag RMG cell B Round Mtn. Gold 4100 53 28,450 35,092,506 Au, Ag McCoy/Cove Premier Gold 4633 43 25,000 30,837,000 Au, Ag Jerritt Canyon Jerritt Canyon 4267 45 24,000 29,603,520 Au, Ag Lone Tree Sec. 23 Newmont 2933 55 20,040 24,718,939 Au, Ag A-A Barrick 1727 67 17,054 21,035,768 Au, Ag Getchell Turquoise Ridge 1164 46 10,000 12,334,800 Au, Ag Paradise Peak FMC Gold 1097 40 8300 10,237,884 Au, Ag Mill 4 Dam 2 Newmont 2469 50 8264 10,193,479 Au, Ag Copper Canyon Newmont 2344 23 6900 8,511,012 Cu Mill 4 Dam 1 Barrick 1859 55 4878 6,016,915 Au, Ag Simplot Simplot 770 43 4400 5,427,312 Au, Ag Carlin Gold Newmont 762 82 4030 4,970,924 Au, Ag Cortez No. 6 Barrick 2204 18 3988 4,919,118 Au, Ag Cortez No. 7 Barrick 2211 19 3673 4,530,572 Au, Ag Mill No. 3 Newmont 701 33 3200 3,947,136 Au, Ag No. 2 Jerritt Canyon 2247 33 2766 3,411,806 Au, Ag Tonkin Springs Tonkin Springs 1272 20 2625 3,237,885 Au, Ag Cortez Cells 4 & 5 Barrick 2118 13 2417 2,981,321 Au, Ag Springer tungsten Springer 3094 5 2350 2,898,678 W Midas Phase 4 Klondex 1305 15 2008 2,476,828 Au, Ag Midas Phase 5 Klondex 576 46 2008 2,476,828 Au, Ag Yerington mill Arimetco 30 27 1166 1,438,238 Cu Simplot Raise Simplot 3048 30 1000 1,233,480 Si * Nevada Dam Safety regulations are based on acre-feet of storage.