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From Mine to megawatts...

A mothballed copper mine site-that is also a Superfund site-in a remote part of Vermont has now become the 7-MW Elizabeth Mine solar power farm, the largest solar array in the state and one of the largest solar projects in the region.

By Tony Kryzanowski

The 7-megawatt Elizabeth Mine solar power project, built on a reclaimed copper mine site in Vermont, offers a rare glimpse into both the past and the future. It demonstrates human progress over 200 years from the fossil-fuel era to the renewable energy era, which is still unfolding right now, world-wide.

The $18 million solar project, owned by Boston-based Greenwood Energy, is built on 28 acres of what was the Elizabeth copper mine within the Vermont towns of Strafford and Thetford. It is a reclaimed Environmental Protection Agency (EPA) Superfund site, which has benefited from 14 years and $70 million of federal funding to stabilize and reclaim it. The solar farm takes up the entire reclaimed area.

The reclamation work was done by the U.S. Army Corps of Engineers. Greenwood Energy contracted Conti Solar, a subsidiary of the Conti Group, to build the project. They have extensive experience developing solar projects on Superfund sites.

"I would say that we are right up there and maybe number one in the country as far as building solar projects on both reclaimed landfill and Superfund sites," says Sean Harrington, New England area regional manager for Conti Solar. "In total, we've built over 115 megawatts of landfill solar projects across the country." As of November 2017, they had another 15 megawatts under construction, including the Elizabeth Mine site.

The EPA and the Corps of Engineers had a strong desire to ensure that the Elizabeth Mine solar project resulted in minimal ground disturbance both during the construction phase and over the lifetime of the installation. The key features to address their concerns were ensuring that loaded trucks and equipment driving on site roads and working on the cap did not exceed a weight distribution of more than 8 pounds per square inch (psi) and that there was proper weight distribution with the concrete ballasts anchoring the racking system.

As with many other capped Superfund and reclaimed landfill sites, the only anchoring option for the racking system was to use concrete ballasts that did not penetrate the cap. To accomplish this critical aspect of the Elizabeth Mine project, Conti chose Solar FlexRack as its concrete ballast and racking system designer. Conti had experience working successfully with Solar FlexRack on other Superfund and landfill projects where a ballast anchoring solution was required.

 
The $18 million Elizabeth Mine solar project, owned by Boston-based Greenwood Energy, is built on 28 acres of what was the Elizabeth copper mine within the Vermont towns of Strafford and Thetford. 
  

"Working with Solar FlexRack on this project was great," says Harrington. "They have a great design team and a good quality product. A lot of the process related to the racking has as much to do with design as it does with the logistics. The team at Solar FlexRack was great to work with in getting their product manufactured and delivered on time."

This project consists of 2,222 precast concrete ballasts designed by Solar FlexRack and supplied by Connecticut-based, United Concrete. Solar FlexRack supplied the racking system with part of its galvanized steel support structure cast within each concrete ballast.

"There were tons of challenges in the design of the ballast blocks because we had to keep them below a certain bearing pressure, and we also had this impervious soil restriction to maintain," says Greg Lewis, Solar FlexRack director of sales for the Eastern United States. "There were a few iterations of ballast designs. The level of due diligence by the Army Corps of Engineers was extremely high on this project."

Another important consideration when using concrete ballast foundations is something called differential settlement, and Lewis says the solution provided by Solar FlexRack is another reason its design was selected early in project development.

"We used an individual table design maximizing two ballast blocks," says Lewis. "So we didn't use a continuous [racking] design, and that was important for the developer because if one ballast block settles differently than the adjacent one of the same table, they did not want any stress placed on the structure or the modules."

The Solar FlexRack solution, which Harrington describes as an "extremely intelligent design, which is extremely efficient to install," consists of individual 2X9 configuration racking tables attached to two ballast blocks, so that if one block settles differently from the other, the table stays in a straight line.

 
 As with many other capped Superfund and reclaimed landfill sites, the only anchoring option for the racking system was to use concrete ballasts that did not penetrate the cap. To accomplish this critical aspect of the Elizabeth Mine solar project, Solar FlexRack was selected as the concrete ballast and racking system designer.
  

Needless to say, there has been a drastic change in the visual appearance of the reclaimed and repurposed mine site since reclamation began in 2000. Prior to the site's makeover, local press described it as "a moonscape of waste rock and tailings that leached orange effluent into nearby streams."

The mine, once the largest copper producer in the United States, operated for nearly 150 years, from the early 1800s to 1958, producing about 90 million pounds of copper and offering regular paychecks to thousands of workers. However, like many other spent mine sites from the past two centuries, while the Industrial Revolution produced immeasurable amounts of mineral resources from smelters and processing equipment powered by fossil fuels, those living in the midst of the remnants of the Elizabeth Mine were left to live with the scarred landscape.

In 2001, the EPA went to work with the Army Corps of Engineers to stabilize the old tailing piles and cap the materials under an impermeable geosynthetic membrane that was then covered with soil, thus making it possible for the mine site to be repurposed as a solar installation. Initiated by solar developers Wolfe Energy and Brightfields Development, the project was sold to Greenwood Energy who took the project across the finish line.

Today, the site consists of 1,255 groups of 18 solar panels (310 watts each) generating 7 MW of power under a 30-year power purchase agreement between Greenwood Energy and Vermont power utility Green Mountain Power.

 

The Elizabeth Mine solar project is the largest solar array in Vermont and is contributing to the state’s mandated goal under which power companies were required to generate 55 percent of their sales from renewables by the end of 2017.

 
  

Officially known as the Elizabeth Mine Solar I LLC, the project is the largest solar array in Vermont and is contributing to the state's mandated goal under which power companies were required to generate 55 percent of their sales from renewables by the end of 2017. The goal is to achieve 90 percent by 2050.

The project took just over four months to complete—construction started in May 2017 and was completed in August. It began generating power in October. At peak construction, it provided about 200 jobs, and over its lifetime, Greenwood Energy will pay $20,000 annually in tax revenue to the state and between $10,000 and $30,000 in local property taxes. The array will provide enough power for 1,200 homes and will offset 6,000 tons of carbon dioxide every year, or the equivalent of the emissions from about 14,000 barrels of oil.

In addition to Solar FlexRack providing the racking system, Hyundai provided the solar panels. The Vermont-based environmental, engineering, and design consulting firm, Weston & Sampson, was hired as the required third-party engineering firm to monitor construction for compliance. Harrington says this level of monitoring is common on these types of projects. Northwoods Excavating set down the ballasts and erected the racking system, while Peck Electric installed the solar panels. Both are based in Vermont.

The location of the solar array is described as being rather remote, requiring satellite phones for communication and presenting logistical challenges for transporting and coordinating the delivery of components to the site.

"I think the biggest challenge of this site versus other sites that we've built was the access," says Harrington. "This job was built in rural Vermont, and this had some challenges in terms of the capacity of some of the access roads and the ability to get from the highway to the site with large trucks."

He estimates that over the project construction period, there were more than 1,000 trucks driving to and from the site. Conti Solar was keenly aware of possible damage to the roads, so a survey of all access road conditions before project start was taken, it was monitored throughout the construction period, and then compared to the state of the roads after project completion. Conti Solar also stayed in close communication with local municipal authorities.

"Any damage would have been our responsibility to repair, and we had no issues," says Harrington. "There was no damage caused by the trucks coming through town or any of the highway roads."

The project also required improvements to the local power transmission line. The interconnection included an upgrade of approximately four miles of utility lines, 10 miles of dedicated fiber optic communications line, and an upgrade to the regional substation. Green Mountain Power also upgraded three-phase lines up through the town of Strafford as part of its reliability improvement program.

The changes, in total, benefited the community with an improved electrical system that upgraded the reliability of the entire system. Greenwood Energy paid to upgrade six miles of the 10-mile transmission line, representing about $2.7 million of the overall project cost.

 


January/February 2018