A beefed-up plan to compensate for damages to washes from the proposed Rosemont Mine faces an Army Corps of Engineers decision in the next few weeks, a Corps spokesman says.
Mine owner Hudbay Minerals Inc., parent of Rosemont Copper company, has a revised mitigation plan that it says would preserve nearly 1,200 additional acres and restore more habitat than proposed in earlier plans that the Corps rejected as inadequate.
The revised plan would protect four parcels of more than 4,800 acres at a $48 million cost.
The Corps will rule on this mitigation plan as part of Rosemont’s application for a federal Clean Water Act permit needed to build the $1.5 billion open-pit copper mine in the Santa Rita Mountains southeast of Tucson.
Neither the Corps nor the Environmental Protection Agency has publicly commented on the plan.
But an EPA consulting team wrote a scathing report last summer warning that a key element — building a series of new artificial channels at one large mitigation site near Sonoita — won’t work. The Arizona Daily Star obtained that report through the U.S. Freedom of Information Act.
The EPA has veto power over Clean Water Act permits and was critical of Rosemont’s earlier mitigation efforts.
The latest Rosemont plan proposes to re-create and restore several washes and a creek on the Sonoita Creek Ranch, about 12 miles south of the proposed mine site.
The plan comes in response to Corps criticism in 2014 that previous plans wouldn’t do enough restoration or enhancement.
Ranches key to plan
Mitigation — buying and preserving or restoring land — is a Corps legal requirement for a Clean Water Act permit. Rosemont must compensate for what the Corps says will be direct and indirect impacts to about 68 acres where the mining company would dredge and fill in federally regulated washes.
The EPA, in a November 2013 letter to the Corps, said construction “would permanently fill approximately 18 miles of streams across an approximately 5,000-acre project footprint and result in the fragmentation of an intact natural hydrologic landscape unit composed of hundreds of streams stretching many linear miles.”
The Sonoita Creek Ranch, containing 1,580 acres of grassland, mesquite, native vegetation, a spring and two ponds, is the core element of its 354-page mitigation plan, Hudbay says.
The company’s purchase of the ranch is “a unique opportunity to return a major Santa Cruz River tributary to its historic floodplain and secure a valuable conservation parcel on the landscape,” the plan says.
The ranch, between Sonoita and Patagonia, includes 4.8 miles of Sonoita Creek, a tributary to the Santa Cruz River. Unlike the better-known stretch of Sonoita Creek near Patagonia where the Nature Conservancy runs a birdwatching preserve, the stretch through the ranch is dry except after rainstorms.
Much of the ranch has been used for agriculture, which required constructing an artificial channel for significant reaches of Sonoita Creek to reduce flood risks, the mitigation plan says. Until that happened, Sonoita Creek flowed through a system of channels in a broad floodplain, laden with wetlands and traditional riparian trees and shrubs, the mitigation plan says. But the creek was realigned, straightened and deepened to keep flows from flooding roads and fields.
The plan would try to reverse man’s past work by re-establishing at least five channels, totaling 65 acres, adjoining the creek. The restoration would create another 113 acres of floodplain and desert-like riparian habitat. The ranch also lies within a wildlife corridor linking the Patagonia and Santa Rita mountains, the plan says.
The ranch includes a spring whose owner has nearly 600 acre-feet of water rights and contains 6 acres of wetlands associated with the two ponds.
The mitigation plan quotes Arizona Game and Fish as saying the ranch has “rich riparian values” and describing its environs as “a well-known core area for biodiversity in Southeastern Arizona.”
Problems cited
In their report, EPA consultants Mathias Kondolf and James Ashby faulted a Rosemont consultant’s conceptual design for re-creating the Sonoita Creek side channels on numerous grounds.
The Rosemont mitigation plan says that decades of human alteration of Sonoita Creek have created a channel that maximizes the speed of water flows, causing an unstable channel. Rosemont proposes channel improvements that include removal of large debris and bank stabilization.
The re-established Sonoita Creek floodplain would direct high flows into parallel, meandering, constructed channels, reducing the amount and speed of flood flows through the creek and creating a more stable channel that improves habitat.
But EPA’s consultants said:
- Rosemont consultant Water and Earth Technologies, which designed the constructed channels, used computer models that significantly overestimated how much water is available for the creek and channels. Its forecast for flood flows was two to three times higher than what has been measured in the area by the U.S. Geological Survey and estimated in computer models by the Federal Emergency Management Agency.
- The computer model used by the Rosemont consultant unrealistically assumed the Sonoita creekbed would stay at fixed elevations, although Sonoita Creek’s flow varies wildly year to year. Even a slight change in the creekbed’s elevation could make a difference in whether the flows in the constructed channels behave as planned or don’t happen.
- The constructed channels probably can’t hold the flows they get because much of the bottom soils in the Sonoita Creek valley are highly permeable and have high infiltration rates.
- The lower 6,000 feet of Sonoita Creek through the ranch are “extremely active and complex,” supporting valuable riverfront vegetation such as Fremont cottonwoods. If some of this creek is diverted into constructed channels, the creek’s flows will be reduced and that could result in reduced success for cottonwoods.
- The design of the proposed constructed channels will require considerable maintenance and won’t have the same ecological value as the original Sonoita Creek channel.
Kondolf is a University of California-Berkeley environmental planning professor and a consultant in environmental planning, hydrology and the science of rivers. Ashby works for PG Environmental LLC in Golden, Colorado. Water and Earth Technologies is a water resources and environmental engineering firm in Fort Collins, Colorado.
In response to the Star’s request for comment on the EPA consultants’ report and other matters, Hudbay released a statement saying, “We respect the time needed by the agencies for a thorough review and await their decision.”
Removing grazing also key
The mitigation plan also calls for rehabilitating 22.4 acres of existing Sonoita Creek channel and enhancement of 6 acres of ponds. It also would enhance existing riparian habitat by keeping cattle out of the area by building wildlife-friendly fencing.
Removing grazing is also a key element in restoration plans for a second Rosemont mitigation parcel, the 1,763-acre Fullerton Ranch, in the Altar Valley about 28 miles west of the mine site. The ranch has been “intensively overgrazed,” offering opportunities for restoration to improve the watershed’s condition and operations, the Rosemont plan said.
By kicking out cattle and building wildlife-friendly fencing, the mining company can rehabilitate about 312 acres of stream channels and surrounding riparian areas, the plan said. Another 310 acres at a third Rosemont mitigation spot, Helvetia Ranch parcels two miles northwest of the mine, will also be rehabbed in part by removing cattle, the Rosemont plan said.
Of the three mitigation sites, the Fullerton Ranch has been the most heavily grazed and stands to benefit most from cattle removal, the plan says.
It cites more than a half-dozen studies to make the case that cattle removal can quickly improve grass cover and riparian vegetation and reduce erosion.
