BLM warns Forest Service of Rosemont mine’s potential negative impact to Las Cienegas National Conservation Area

After years of standing quietly on the sideline in the tumultuous debate over the Rosemont copper project, the U.S. Bureau of Land Management has finally weighed in and expressed serious concerns over the proposed mine’s impact on the Las Cienegas National Conservation Area (NCA).

The BLM manages the Las Cienegas NCA that lies in the valley directly east of the proposed Rosemont open-pit copper mine planned for the northeastern slope of the Santa Rita Mountains on the Coronado National Forest southeast of the Tucson. The conservation area includes the northerly flowing Cienega Creek that bisects the 45,000-acre federal preserve.

“Cienega Creek, with its perennial flow and lush riparian corridor, forms the lifeblood of the NCA and supports a diverse plant and animal community,” the BLM states on its website.

The mile-wide, half-mile deep Rosemont open-pit copper mine is likely to have negative impacts on Cienega Creek by lowering the groundwater table and reducing the surface flows on important tributaries, including Empire Gulch and Davidson Canyon, BLM states in its comments to the Coronado National Forest’s preliminary Final Environmental Impact Statement (FEIS) for the Rosemont mine.

“The FEIS documents that impacts to the Las Cienegas National Conservation Area (NCA) are likely to occur which are detrimental to the purposes for which the Las Cienegas NCA has been established,” David Baker, BLM’s Tucson field manager, stated in an Aug. 15 letter to the Coronado National Forest Supervisor Jim Upchurch.

“The Bureau of Land Management would like the opportunity to provide a dissenting opinion to be included in publication of the FEIS concerning the nature, scope, and intensity of these impacts on NCA resources,” Baker stated.

BLM also made it clear the agency was determined to protect its water rights for the Las Cienegas NCA.

“BLM does not relinquish existing BLM surface and groundwater rights,” the agency repeated six times in its comments on the FEIS.

The BLM now joins the U.S. Environmental Protection Agency as federal agencies raising serious concerns about the suitability of the Rosemont mine and its likely impacts on waters of the United States and possible violation of federal laws.

The Forest Service cannot legally issue a Record of Decision approving the proposed mine if the mine creates environmental impacts in violation of federal laws that cannot be fully mitigated.

The BLM took exception with the Forest Service’s characterization of ground water impacts on Cienega Creek and two of its tributaries, Davidson Canyon and Empire Gulch. The Forest Service, BLM notes, takes contradictory positions on the impact of the mine on Davidson Canyon and Empire Gulch.

On the one hand, the FEIS acknowledges the potential impact on Cienega Creek and its tributaries by stating: “Groundwater drawdown greater than 100 feet is expected to occur in the immediate vicinity of the mine pit. Less drawdown would occur to the north along Davidson Canyon, to the east toward Cienega Creek, and to the south toward Empire Gulch. Drawdown estimates vary between models.”

Despite acknowledging there will be ground water draw downs, the FEIS then makes a sweeping conclusion: “No change in riparian habitat along Cienega Creek is expected to occur as a result of the proposed mine.”

BLM states in its comments that “even very small levels of groundwater drawdown, which has been supported by modeling as stated, may have impacts to water depth, stream flow and vegetation.”

“Any drawdown, even less than 100 feet, would be significant to Empire Gulch and Cienega Creek, and BLM’s existing water rights,” BLM stated in its comments.

Davidson Canyon and Cienega Creek are also listed as Outstanding Arizona Waters and protected from any degradation by federal regulations. The EPA stated in a Feb. 2012 letter to the Coronado National Forest that it has serious concerns over the mine’s impact to both streams and that Davidson Canyon and Cienega Creek “must be afforded the highest level of protection” because of their status as Outstanding Arizona Waters.

Tucson wildlife biologist Dennis Caldwell has worked for three years on protecting Chiricahua Leopard Frog habitat in the Las Cienegas NCA. The frog is listed as a threatened species and one of its last significant populations is in Empire Gulch that relies primarily on ground water that emerges through springs.

Empire Gulch drains the Santa Rita Mountains south of the mine site and flows directly into Cienega Creek. Caldwell says even a small drop in the ground water table caused by the Rosemont mine pit is likely to have a direct and negative impact on Empire Gulch that could turn the lush riparian corridor into muddy flats.

“It’s liable to completely dry up the surface water here,” Caldwell says while standing next to Empire Gulch Spring in the Las Cienegas NCA. “We’ve got endangered Leopard Frogs here and this is a major tributary to Cienega Creek where have got three endangered native fish species that need water to survive.”

There used to thousands of the frogs in Empire Gulch and Cienega Creek, providing a rich protein source for predators, including jaguars, Caldwell says. The Chiricahua Leopard Frog population has been decimated by reduced habitat, disease and invasive species such as non-native fish. The Las Cienegas NCA provides one of the last large habitats for the frogs.

A few miles to the east of the Empire Gulch Spring, Caldwell describes how the ground water that comes to the surface in springs along Empire Gulch plays a vital role in providing water to Cienega Creek.

“We know that anything that impacts the water in Empire Gulch is going to have a ripple effect all the way down here in the valley bottom,” Caldwell says while hiking along the banks of Cienega Creek beneath a thick canopy of cottonwoods.

Caldwell says that even a small drop in the water table as a result of ground water being drawn to the Rosemont open pit mine could destroy the riparian area. “Even a slight loss of water can be tragic,” he says.

“It’s not like in other places in the world where water just flows on top of the ground everywhere,” Caldwell says. “In Arizona, ground water is everything.”

Caldwell’s field expedition next moved about 20 miles north to the confluence where Davidson Canyon flows into Cienega Creek. After flowing off the Las Cienegas NCA, the northern stretch of the Cienega Creek is protected by Pima County’s Cienega Creek Preserve.

Caldwell says Davidson Canyon will be directly impacted by the proposed mine site and will suffer a decrease in surface and ground water flows and will be impacted by any pollution draining from the mine site.

“Rosemont’s promoters keep insisting there will be no surface water pollution. I don’t think anybody really believes that or how that could even be possible when you’ve got that big of a disturbance happening in a watershed,” Caldwell says. “There will be accidents and spillage and this is where we are going to see the most impact from any potential accidents.”