In 2020, Con Edison Development retained Barr to review the risk of subsidence due to abandoned underground coal mines at the Centerville Wind Project site in Appanoose County, Iowa. Barr completed a high-level desktop evaluation of abandoned underground mine risk to proposed wind turbine locations associated with two potential site layout options.
Barr reviewed existing publicly available information regarding abandoned underground coal mines near the proposed wind project site. Review evaluated the proposed wind turbine locations associated with potential project layouts with respect to coal resources and known abandoned underground coal mine locations. Barr’s engineering and mining experts also assessed the type of mining that was utilized, the length of time that had elapsed since active mining operations, and the potential for abandoned underground coal mines with unknown locations. Our team used this information to provide a risk assessment and recommendations for the layout and development of the wind project. Barr concluded that there was low risk of subsidence due to abandoned underground coal mines at the proposed wind turbine locations based on public data; however, due to the regional risk of unknown abandoned underground coal mines, an enhanced geotechnical investigation was recommended during the design phase of the project.
For the design phase geotechnical investigation, Con Edison Development retained Barr to conduct a geotechnical investigation at each proposed and alternate wind turbine location that extended below the approximate depth of the coal seam to evaluate the presence of abandoned underground coal mines. Barr’s geotechnical investigation included geotechnical borings at the proposed and alternate wind turbine locations, piezometer installation to monitor groundwater levels, laboratory testing, field electrical resistivity testing, laboratory thermal resistivity testing, and road subgrade testing. Barr compiled the data collected during the design phase geotechnical investigation and prepared a geotechnical engineering report. The report summarized findings of the geotechnical investigation and provided geotechnical recommendations for wind turbine foundation design.