Engineering Impacts

Unstable Nature of Karst Makes For Risky Venture

An industrial-scale wind factory of the size proposed for Monroe County on agricultural and conservation ground is not only irresponsible but is dangerous. The wind turbines the developer intends to deploy will be among the largest and heaviest in North America. Much of the land proposed for the project is in the karst-sinkhole plain which is made up of fractured and soluble bedrock covered with loose soil with an average depth of 32 feet (Panno and Lumen, 2018). Because karst landscapes can be unstable and unpredictable in nature there are no clear-cut approaches for measuring or mitigating risk for building this industrial development.

In karst landscapes there are short-term (collapse) and long-term (settlement) risks. The average soil depth within the area of this project is 32 feet which increases the risks dramatically of a wind turbine foundation failure. The instability of karst geology can lead to a wind turbine tilting and even toppling. The limestone bedrock within the project area has voids, fractures, and conduits all of which support the weight of the soil and rock that they now bear. When the soil and bedrock are disturbed by heavy equipment during the construction process and is then exposed to the weight and motion of the installed turbines the soil can have unnatural settlement or even collapse. The vibration from turbines in this development could cause adverse effects on areas miles away from them causing accelerated settling and even the opening of new sinkholes.

There are geophysical methods that could be used to assess the condition of the underlying bedrock (including resistivity, seismic refraction, microgravity, magnetic, and ground penetrating radar), but they wouldn’t be reliable in this area due to the depth restrictions of these tests. Another way to assess the condition of the underlying bedrock would be to test each site by boring holes deep into the ground, but this would not only destroy any ecosystem that lies below but could also increase the risks of Class III ground water contamination. Groundwater in karst regions is very susceptible to contamination because of the fractured and porous nature of the bedrock which commonly provides a direct connection between surface water and groundwater. Groundwater makes it into to the water table in these regions often instantaneously and doesn’t get the benefit of the slow filtration through fine-grained materials that allows the breakdown of potential contaminants. The use of exploratory drilling in this region carries too many risks and the potential to contaminate the water table that supplies many water wells and the safety of those who drink it. Essentially building this project in this area would have unknown consequences which could not be reversed once the damage is done.

Financial Risk Also Is Higher


Risks of turbine construction on karstified areas also include financial ones. Sinkhole collapse can occur even during the construction phase. In Ida County, Iowa, in August 2016, a crane used to erect wind turbines fell into a sinkhole in a field. Although the crane was destroyed, the crane operator, who was not injured in the mishap, was able to jump from the cab before it fell into the hole (Forbes, A., 2016, Ida County Courier).

Even if karst terrain does not cause a catastrophic turbine or installation equipment collapse, the foundation is subject to greater risk of settlement. “Karst can lead to a wind turbine tilting and even toppling. Also, subtle differential settlement of even 3 centimeters (1 3/16 inches) across a 15-meter-wide wind turbine foundation can cause the turbine to be out of tolerance and lead to expensive and time-consuming remedial action” (Bangsund and Johnson, 2013). Bangsund, with Barr Engineering of Minneapolis, and Johnson, with the Oklahoma Geological Survey, note that thick soil cover can mitigate the risk of subsidence. Areas with soil depths thinner than 25 meters (82 feet) above karst formations carry high risk of subsidence. Soil depths in our karst sinkhole plain range from 0 to 20 meters, or 0 to 65 feet, with an average depth of 10 meters or 32 feet. The risk of turbine failure is high.

References:

Bangsund, William J. and Johnson, Kenneth S., 2013. Evaluating Karst Risk At Proposed Windtower Projects. Conference paper, 13th Sinkhole Conference, NCKRI Symposium 2.

Illinois State Geological Survey: Karst Landscapes of Illinois: Dissolving Bedrock and Collapsing Soil. AND Widespread Groundwater Contamination Found in Southwestern Illinois.

Panno, S.V.; Krapac, I.G.; Weibel, C.P.; and Bade, J.D. 1996. Ground-water contamination in karst terrain of Southwestern Illinois. Illinois State Geological Survey, Environmental Geology Vol. 151. 43 p.

Panno, Samuel V., and Luman, Donald E., 2018, Characterization of Cover-Collapse Sinkhole Morphology On a Groundwater Basin-Wide Scale Using Lidar Elevation Date: A New Conceptual Model for Sinkhole Evolution. Geomorphology 318, pp. 1-17.

Photo of rail transportation of turbine parts courtesy Monroe County Independent.

The Burdens May Be Placed on All Residents


Another issue to face is the noise, vibration, and alteration of the landscape in the scenic area in which we live. The system of roads in our area are unsuitable for trucking in the equipment for the towers themselves and the heavy equipment that it would take to construct this industrial factory. Whatever route(s) that would be chosen to access this 15,000-acre industrial wind factory -- spanning 15 miles in length and as much as 5 miles in width -- would have to be heavily modified to allow for the weight and length of the components needed to construct towers that stand over 600 feet tall. Anyone who drives through our area knows full well the roads are narrow, twist and turn, change elevation quickly, and generally are lined with trees and sinkholes. All these characteristics are not conducive to the access needed to construct commercial wind factories. The image at left shows turbine parts on rail flat cars transported through Monroe County in summer of 2018. A comprehensive transportation and traffic plan will need to be put in place to ensure that the costs and responsibility for both the construction and repair of damage to our roads and landscape do not become the burden of residents.

In conclusion the area proposed by the developer for this industrial project is possibly the least suitable stretch of land in the entire state -- possibly the country -- to place a wind factory. There will be many challenges to building and maintaining the integrity of turbines placed in this area. The underlying structure of our local topography, safety of groundwater sources, protections for the many delicate ecosystems, and conditions of our roads and landscapes may all be at risk with this project. Many burdens that arise from this industrial development could be placed on the residents if proper safeguards are not put in place.

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