Construction from the SunZia transmission line project has created “extensive erosion” and environmental damage because the company has failed to install  control measures, according to a letter from five Southern Arizona environmental groups and joined by Archaeology Southwest. 

In the letter published Tuesday, the organizations argued Pattern Energy has not implemented erosion control measures as part of the company’s development plan for the SunZia Southwest Transmission Project, which includes two power lines that will carry about 3,500 megawatts of electricity across around 520 miles of federal, state and private land between New Mexico’s SunZia Wind project and Central Arizona.

The company has billed the project as an effort to “combine the largest clean energy infrastructure in United States history” by connecting wind farms in central New Mexico to customers in Arizona and California by 2026. 

Announced by the Bureau of Land Management in 2009, the SunZia project has been sharply criticized for the route it takes as it crawls across Arizona. Officials with Archaeology Southwest, along with San Carlos Apache Tribe and the Tohono O’odham Nation, are concerned the construction will create havoc with ancient burial sites. Meanwhile, environmental groups worry the project will damage the landscape and the San Pedro River as the company installs hundreds of miles of new roads, as well as pads for the towers throughout the valley. 

The letter was sent to officials with Pattern Energy, the Bureau of Land Management in Arizona and Mexico, the Arizona State Land Department, as well as the Pima and Cochise county supervisors. 

“SunZia construction and monitoring crews have failed and are failing to prevent major erosion and stream siltation,” wrote representatives from the Center of Biological Diversity, the Tucson Audubon Society, Lower San Pedro Watershed Alliance, the Cascabel Conservation Association, and the Sierra Club’s Grand Canyon chapter. 

They said the installation of towers across the valley is complete except where helicopters will continue to fly towers to remote locations for installation. 

“With ‘substantial completion’ of all work by ‘heavy equipment such as concrete or water trucks, pole delivery, cranes etc.,’ it is past time for the installation of the water bars, cross ditches, and biodegradable silt fences, and for the removal of the downslope road berms not already destroyed by runoff,” the organizations wrote. 

The SunZia project is among dozens of infrastructure projects pushed forward by the Biden administration on an agenda to fast-track clean energy projects under the Inflation Reduction Act, which includes a revised permitting process backed by $1 billion in funding. SunZia—along with the South32 Hermosa mine near Patagonia—is one of four projects in Arizona covered under FAST-41, an Interior Department program designed to speed up permitting.

Earlier this year, the San Carlos Apache Tribe and the Tohono O’odham Nation—aided by Archaeology Southwest and the Center for Biological Diversity—sued and demanded a halt to construction while their lawsuit moves forward. However, U.S. District Judge Jennifer G. Zipps rejected this argument in May allowing Pattern Energy to continue building while the tribes head to the 9th Circuit Court of Appeals. 

The 9th Circuit has not made a decision in the case. 

“Because the erosion control measures required by the SunZia 2023 Plan of Development have not been implemented, rills, ruts, fissures, and gullies are forming and soil and hydrological systems are being damaged,” they wrote, and urged Pattern Energy to “take immediate steps to install the required water bars, additional silt fences, and related measures to counter the steam and watershed degradation that are actively unfolding.”

“Although SunZia has built a few detention basins and installed some silt fences, these efforts have been inadequate to prevent hundreds of rills and ruts on access roads” as well as fissures at tower pads and sites where cables are moored. 

The groups included pictures showing built-up pads, created to moor the towers that will carry high-voltage lines, with deep lines from the summer’s monsoon. 

“The denudation and degradation of land surfaces and loss of soil productivity directly impact habitat and water quality,” they added, writing that by allowing erosion, the construction increases habitat fragmentation and makes it easier for invasive plants to thrive. The silt and clays also decreases water quality in the San Pedro River harming species, including birds, fish, and amphibians.