Pursuant to Chapter 534 of the Nevada Revised Statues, when the Nevada State Engineer determines that a groundwater basin is being depleted: “…the State Engineer in his or her administrative capacity may make such rules, regulations and orders as are deemed essential for the welfare of the area involved.” Nev. Rev. Stat. § 534.120.
On May 16, 2017, the State Engineer exercised his authority by ordering Cortez Joint Venture (Cortez JV) take groundwater extracted from the Crescent Valley Hydrographic Basin and inject it into the neighboring Grass Valley Hydrographic Basin and Pine Valley Hydrographic Basin.
Mining in the Cortez Mountains, located in central Nevada, began with the discovery of silver ore in 1862. In 1959, American Exploration & Mining Co. a wholly owned U.S. subsidiary of Placer Development Ltd., started extensive exploration activities. In 1964, American Exploration & Mining Co. formed the Cortez JV. The Cortez JV initiated open-pit mining for gold in the 1970s and currently operates the Cortez Hills Gold Mine and Pipeline Mine. Cortez JV holds permits to appropriate groundwater from the Crescent Valley Hydrographic Basin for mining, milling, and dewatering purposes related to its Pipeline and Cortez Hills mines. The total volume of water appropriated under the permits is approximately 65,211 acre-feet annually (afa). Of this amount, 4,998 afa is permitted for consumptive mining use and 60,213 afa is permitted for non-consumptive dewatering use.
Because the perennial yield of the Crescent Valley Hydrographic Basin is estimated to be only 16,000 afa, the groundwater extraction permits require Cortez JV to return any groundwater used for dewatering to the Crescent Valley Hydrographic Basin via injection or infiltration basins. However, groundwater-monitoring data shows that the Crescent Valley Hydrographic Basin is approaching a point where there will be technical limitations on the amount of water that can be infiltrated. Additionally, groundwater flow models indicate that Cortez JV’s dewatering operations are increasing the rate of natural flow from the neighboring Grass Valley and Pine Valley Hydrographic Basins.
The State Engineer estimates that from 1996 until the end of 2015, there was an increase in the flow from the Grass Valley Hydrographic Basin into the Crescent Valley Hydrographic Basin of approximately 11,200 acre-feet due to mine dewatering operations. Similarly, there was an increase in the flow from the Pine Valley Hydrographic Basin into the Crescent Valley Hydrographic Basin of approximately 3,500 acre-feet.
In an attempt to remedy this increased flow of groundwater from the Grass Valley and Pine Valley Hydrographic Basins, the State Engineer has ordered Cortez JV to discharge up to 40,800 acre-feet of groundwater into the Grass Valley Hydrographic Basin and up to 25,800 acre-feet of groundwater into the Pine Valley Hydrographic Basin. Cortez JV is also required to submit to the State Engineer quarterly reports containing water discharge measurements.
The Nevada State Engineer’s orders provide a valuable solution to the very complex problem of increased cross-basin groundwater flows caused by groundwater extraction. It is likely that we will see more orders similar to the Cortex JV orders as cross-basin groundwater flow models continue to be refined. Only time will tell whether these cross-basin groundwater transfers are effective in stabilizing the water balance between the basins. For more information about the State Engineer’s orders in this matter, see generally: http://water.nv.gov; and specifically, see the Orders of May 2017 at: http://water.nv.gov/documents/1283-1284.pdf
(Wesley A. Miliband, Eric R. Skanchy)
