Underground Injection Control Solutions for Illinois Coal Mine Wastewater


Underground coal mining has resurged in the Illinois Basin over the last decade with several companies chasing the Herrin #6 seam, a plentiful high-sulfur bituminous coal in the basin. With many of the miners migrating to the Illinois Basin from Appalachia, so has the preferred method of longwall mining. This type of mining is conducted under hydraulic roof supports that advance as the coal seam is cut. As the supports advance, the roof collapses behind the cutting head, causing fractures to propagate upward through water-bearing sandstone formations and can result in very large volumes of water infiltration into the underground workings. The native groundwater contains naturally-occurring elevated chlorides that exceed effluent limitations and are not permitted to discharge to surface water.

Class I non-hazardous underground injection control (UIC) wells provide a safe means of permanently disposing of these waters from the surface environment by sequestering them in deep formations thousands of feet from the lowermost underground sources of drinking water (USDW). The typical injection interval in the Illinois Basin ranges from 3,000 feet (about 40 miles southeast of St. Louis) to more than 12,000 feet below the surface (in south central Illinois). That’s 2.5 miles.

SCS Engineer’s client in the Illinois Basin is a coal mine operator with a water-quality issue that quickly became a water-quantity disaster. The client had excessive amounts of mineralized groundwater inundating their underground workings and there was no place to put it. They weren’t permitted to discharge it to streams, their evaporation ponds were near capacity, and what’s worse…more groundwater was on the way with the anticipated opening of their newest longwall operation. Upon identifying a deep injection well as the best means of permanent wastewater disposal, SCS needed to make quick work of developing a safe plan and implementing the solution.

Although there were already five existing Class I wells in Illinois, they were all located in the northern part of the state and had been completed several decades ago. As a result, little was documented about the geology deeper than 5,000 feet, with less than six penetrations extending to the Precambrian basement rocks in the southern part of the state. In order to characterize the deep hydrogeology of the basin, the SCS team studied regional rock cores and interviewed reservoir engineers specialized in Illinois Basin geology. As we oversaw drilling and completion of the coal mine’s 2.5-mile deep injection well, additional site-specific data became available from log interpretations and our analyses of drill cuttings, rock cores, and water samples.

Because the Illinois EPA, which has primacy over UIC permits in the state, had not permitted a Class I well in decades, SCS Engineers worked closely with the agency to develop an agreeable application format. Illinois EPA staff recognized SCS Engineers as UIC experts, even recommending a review of the SCS Engineers plan to another company who had a troubled pending permit application. Coincidentally, our coal mine client also referred the same company to us, complementing good work with the best reward –confidence in SCS.

Our newest client, also a coal mine with a water-quantity problem and two incomplete injection wells, simply requested SCS Engineers to repair their pending permit application. Within 30 days we produced an accurate replacement application that worked to address the stringent environmental regulatory requirements; within 60 days an emergency permit was issued. Following the permit issuance, SCS was awarded additional work to oversee the completion activities for the two existing injection wells. We were further awarded designing the surface equipment layout, procuring the equipment and overseeing its installation.

SCS’s UIC team began with one coal mine in southern Illinois in 2012, and we are now actively working with four facilities within the state (three coal mines with groundwater infiltrate and one coal combustion residuals landfill with excessive leachate) to permit and construct Class I non-hazardous injection wells. Given SCS’s core capability in solid waste management, deep injection wells are a viable means for safe, supplemental leachate disposal. Although deep injection wells can require some steep up-front capital to initiate, they carry much lower annual operating and maintenance costs than other permanent high-volume wastewater disposal options. SCS has the experience and the environmental savvy to design – permit – and build solutions maintaining the highest regard for human and environmental safety.

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