The Seneca fly-ash landfill is owned and maintained by Metropolitan Council Environmental Services and permitted by the Minnesota Pollution Control Agency (MPCA). The landfill is currently in the third decade of its 30-year post-closure period. Its cap, designed by Barr, has been in place since 1996.
The Met Council and solar developer Cypress Creek Renewables proposed installing more than 3,000 solar panels atop the capped landfill. The installation posed challenges because solar panel foundations for photovoltaic arrays typically extend 6 to 10 feet below the ground surface; at this site, however, a synthetic membrane sealing in the stored ash and sludge lies just 2 feet underground. To avoid puncturing the membrane, the panels (as well as electrical conduits and site perimeter fencing) had to be installed on ballasts—concrete platforms that support weight without penetrating the soil.
Barr performed an engineering analysis of the project’s feasibility and assisted with stormwater permitting through the MPCA. Additionally, we reviewed the panel layout and ballast specifications to evaluate how the installation might affect the site’s surface hydrology. We then prepared a memorandum that documented the negligible effect the panels would have on site hydrology, demonstrated the feasibility of installing the solar array, and explained why the solar farm would not compromise the landfill cover’s integrity or the owner’s ability to comply with the state landfill permit.