There is no adequate mitigation plan to address the proposed Rosemont copper mine’s massive and permanent impact on groundwater supplies that provide domestic water to more than 900 privately-owned wells on the east and west side of the Santa Rita Mountains, according to written objections to the Coronado National Forest’s Final Environmental Impact Statement.
“The USFS continues to avoid the bottom line issue of what are the likely impacts of groundwater pumping by the Rosemont Copper Project on individual home owners, existing businesses, and communities,” the objections state.
The FEIS, the objections state, failed to provide a “quantitative or even a qualitative analysis of a reduction in groundwater availability nor any socioeconomic analysis of the effect of groundwater mining on existing well owners.”
The objections were prepared by a citizen’s coalition opposed to the mine and were filed with the U.S. Forest Service Regional Forester, who must respond in writing by the end of April. If the objections are not adequately addressed with substantive changes to mining plans, the issues could be used in potential litigation against the Forest Service that could block construction of mine.
Augusta’s subsidiary Rosemont Copper Company states it will pump up to 6,000-acre-feet of ground water a year from two well fields on the west side of the mountains in Sahuarita and pump the water through a 15-mile pipeline to the mine site high on the eastern slope of the Santa Rita Mountains. The ground water pumping will impact about 550 wells in the Sahuarita area, according to the FEIS.
Groundwater levels in the Sahuarita area “would decrease up to an additional 90 feet from the pumping, declining at a rate of 1.5 to 3.5 feet per year above and beyond existing groundwater declines,” according to the FEIS.
The area within three to four miles from the Rosemont production wells located near E. Sahuarita Rd. and Old Nogales Highway would be impacted during the first 20 years of pumping. The area impacted would expand another one to two miles over the next 140 years after ground water pumping for the mine ceases approximately 21 years after mining begins.
“An estimated 500 to 550 registered wells are located within this area of drawdown,” the FEIS states. “Specific impacts to individual wells, if any, cannot be identified.”
The objections call for the Forest Service to conduct a detailed inventory of the wells that could be affected by Rosemont’s groundwater pumping and an assessment of the “likely impact of the predicted 90-foot drawdown of the regional aquifer over the next 100 to 140 years.”
“The USFS must analyze the reasonably foreseeable effects of groundwater pumping on existing water users in the local community in the upper Santa Cruz Basin and provide this information in a revised (Draft Environmental Impact Statement) that is released for public review and comment,” the objections state.
Rosemont is seeking state and federal approvals to blast a mile-wide, half-mile deep open pit mine into the northeastern flank of the Santa Rita Mountains that would create a hydraulic sink, drawing ground water from the surrounding area into the pit.
During mining, Rosemont will continually pump approximately 13,000 to 18,500 acre feet of water from the pit, thereby immediately reducing groundwater levels in the immediate area. An acre foot is equal to 326,000 gallons.
Since Rosemont does not intend to back fill the pit after mining ceases, a lake will form at the bottom of the massive hole. As the water evaporates, more ground water will be pulled into the pit. The ground water depleting cycle will continue forever. The FEIS projects evaporation from the mine pit lake after mine closure would be between 170 and 370 acre-feet per year.
Groundwater depletion caused by mining operations will eventually impact about 350 private wells currently in place east of the mountain located in an area known as the Sonoita Plain. “Groundwater modeling shows that this drawdown would be greater than 100 feet in the immediate vicinity of the mine pit,” the FEIS states.
The FEIS states the open pit would cause up to an additional 10 feet in drawdown for homes in the Singing Valley and Hilton Ranch Road residential areas near the mine within 20 years of mine closure. Homes in the Corona del Tucson community and residences along Cienega Creek, Gardner Canyon and the Davidson Canyon/Cienega Creek confluence would see more than five feet of groundwater drawdown caused by the mine, the FEIS states.
“An estimated 360 to 370 registered wells are located within this area of drawdown; specific impacts to these wells, if any, are not known,” the FEIS states.
The objections also criticize the Forest Service for classifying a proposed well protection plan Rosemont is offering to the Sahuarita Heights neighborhood as “mitigation” to ground water depletion caused by the mine operations.
According to the FEIS, “Rosemont Copper would mitigate the potential effects of mine related pumping on residential water supply wells in the Sahuarita Heights neighborhood by entering into an agreement with the United Sahuarita Well Owners.
“This well protection plan addresses pump inspection, pump maintenance, pump replacement, well inspection, well maintenance, and well replacement to ensure that residential water wells in the Sahuarita area that are enrolled in the program remain productive throughout the life of minerals production operations.”
The coalition’s objections state the FEIS fails to provide any supporting evidence that Rosemont’s well protection plan should be considered as a “mitigation measure”. Rosemont’s well protection plan, the objections states, “does nothing to actually minimize, rectify, reduce, or eliminate depletion of the regional aquifer in the Sahuarita area.”
The objections also state Rosemont’s plan fails to provide new water sources to provide clear mitigation for declining water tables caused by the mine operations, does nothing to protect well owners who refuse to sign Rosemont’s well protection plan for legitimate reasons, and there is no detailed analysis of how many wells are even in the area.
The “FEIS is silent regarding whether the Rosemont Copper Company will be required to deepen existing wells to mitigate declining water tables in the Sahuarita area or be obligated under the well protection plan to recharge the regional aquifer in the Sahuarita area, reduce pumping at the mine supply well field, or provide for an alternative water supply for residential well owners if groundwater pumping for the mine dries up their existing residential wells.”