Land Reclamation on the Garden Site
When Allegheny County agreed to the lease over 430 acres near Settlers Cabin Park to the Pittsburgh Botanic Garden, the site seemed nearly perfect: great location, wooded slopes, wide plateaus, beautiful vistas, streams for irrigation – quintessential Pittsburgh.
Everyone knew the property sat above abandoned coal mines, like a lot of land in Pittsburgh. What wasn’t obvious was that three of the four streams on the site were seriously polluted with Acid Mine Discharge (pH 2.8) from the mines. Acid Mine Drainage occurs when iron pyrite in the mines is exposed to oxygen and water, producing salts and heavy metals including iron, manganese, nickel and cobalt.
When Hurricane Ivan dumped 6 inches of rain on Pittsburgh in September 2004, the mines overflowed, and caused flooding and landslides. It was then determined that the streams could not be used for irrigation. This was dire news. Depending on municipal water for the Garden would be grossly expensive in the future, and simply “cleaning” the Acid Mine Discharge on the site was cost prohibitive.
An innovative plan was developed working with Allegheny County, the PA Department of Environmental Protection (DEP), and the U.S. Office of Surface Mining and Reclamation (OSMRE) to remove the mines. The Garden re-negotiated its lease with Allegheny County to allow a reclamation process known as day-lighting. Removing the mines stabilizes the land, protecting future buildings from mine subsidence. It cleans the water for irrigation and reduces pollution entering the streams. The project also included building an intelligent rainwater system that will provide for future irrigation needs.
- Daylighting is occurring under two of the three major ridges at the center of the site. The Pittsburgh Coal Seam is present in all three. Each ridge was deep mined in the 1920s; in the 1940s the southern two ridges were strip mined. The southern ridges suffer from a host of problems including high walls, mine subsidence and acid mine drainage. Daylighting eliminates the acid mine drainage that brews in the open spaces of abandoned coal mines. The process involves removing the soil on top of the old mines, scooping out the remaining coal (approximately 26% of original coal seam) and then replacing the soil. The sale of the coal covers the cost of its removal. Cherep Excavating is the contractor tackling the reclamation work. When the soil is replaced it will be contoured to allow soil improvement for gardens. Unfortunately, planting the gardens designed for the area must wait until the reclamation is complete.
- The Garden has an intelligent rainwater system for future irrigation needs including three irrigation ponds, supplemented by a 400,000-gallon underground cistern. The ponds are now filled with water. Minnows and crappies were introduced into one and a second pond feeds the tree nursery via a solar-powered pump. The system will provide over two million gallons of rainwater a year. The Garden’s President Greg Nace points out, “Even with a dry summer, our water system will ensure the Garden is properly irrigated without the significant expense of bringing in municipal water.” Building of the $510,000 underground cistern was possible through a PENNVEST grant. PENNVEST funds water projects throughout the Commonwealth. Engineered Concrete Systems of Cleveland was responsible for the cistern project.