What happens when soils become damaged? Environmental soil scientist Rick Stehouwer rebuilds them. In 1999, Stehouwer “revived” 300,000 tons of incinerated soil at the Drake Chemical Superfund Site in Lock Haven (see “Lawn Trimmings Revamp Superfund Site.”). Now he’s focusing on abandoned mine lands, the leading cause of surface water pollution in Pennsylvania.

Rick Stehouwer replaces the battery in an automated surface water sampler, which is just visible inside the culvert pipe. The device collects samples whenever there is enough rainfall to produce runoff. The runoff samples will be analyzed for several water quality parameters, including nutrients.

“Abandoned mine sites have both physical and chemical problems,” Stehouwer explains. “For one thing, the surface isn’t even a real soil. It’s material that was originally deeply buried above the coal seam—mostly big stones. There’s little fine material, like clay, and almost no organic matter, so it can’t hold much water when it rains. Because the material is often dark black, it also absorbs a lot of heat, which makes it even harder to hold water. When the sun shines, the temperature of the first couple of inches on the surface can easily get up over 100 degrees Fahrenheit.”

Chemically, these sites are often very acidic and salty, and most plants can’t tolerate either condition. As a result, abandoned mine lands tend to be either acidic moonscapes or sparsely vegetated. Erosion at these sites deposits sediments in streams and ponds, degrading aquatic habitats and contributing to flooding problems.

If pyrites are exposed, acid mine drainage enters the water, too. When water runs over pyrite in the presence of air, chemical reactions add metals, sulfur, and acidity to the water. This acid mine drainage turns the water orange, kills organisms, contaminates water, and corrodes bridges and other structures.

To reclaim mined lands in Pennsylvania, the Pennsylvania Department of Environmental Protection (DEP)
coordinates a program that uses biosolids—treated municipal wastewater solids, or sludge—to promote revegetation. In the 1970s and 1980s, Penn State hydrologist William Sopper showed that biosolids could enhance plant growth at abandoned mine sites. Since the early 1980s, about 700,000 tons of biosolids have been used to reclaim 5,000 acres of mined lands in various parts of the state.

“Biosolids improve fertility by adding nitrogen, phosphorus, and organic matter, which promotes topsoil development,” Stehouwer says. “There’s also anecdotal evidence that applying biosolids can help mitigate acid mine drainage.

“Biosolids are typically applied at a rate of 60 dry tons per acre for mine reclamation—that’s about six to seven times what you’d put on a farm field,” he says. “When biosolids are applied at these high rates, nutrient management, which is more often associated with animal agriculture, becomes a concern.”

To find out what happens to nutrients following reclamation, Stehouwer travels to Tangascootack Creek, north of Lock Haven. The creek’s south fork—once a good trout stream—is now seven miles of dead water due to acid mine drainage. DEP is working to reclaim the entire watershed, which was once extensively mined.

Since pollutants can leave a site in many ways, Stehouwer is sampling surface runoff, leachate that flows through the soil, and groundwater.

“Before the biosolids were applied, the surface runoff was in pretty good shape,” he says. “But the groundwater, which shows acid mine drainage impact, flows directly into a stream 20 feet away.”

Biosolids from the City of Philadelphia Water Department were spread and chisel-plowed into the soil in May 2001. Lime was added to reduce acidity, then the site was seeded with a mix of plants to stabilize the soil and attract wildlife. Stehouwer will monitor the water for nutrients and acid mine drainage-related pollutants for 18 months following application.

“This will tell us if biosolids do help mitigate acid mine drainage, and whether using them creates a new problem with nutrient management,” Stehouwer says.

Mary Ann Bruns is also analyzing soil and water samples from the Tangascootack site before and after biosolids application. Her goal is to assess the fate of microorganisms in biosolids added to the land. This will provide information on how biosolids
affect soil microbial communities as well as the persistence of potential human pathogens.

Most sewage treatment plants produce what are known as Class B biosolids, which can contain high numbers of residual microorganisms from sewage. These include many harmless bacteria that inhabit human intestinal tracts, but can also include some disease-causing microorganisms, or pathogens. Bruns and food scientist Stephanie Doores checked the biosolids for certain types of pathogens, including salmonellae, Staphylococcus aureus, and Listeria species.

“It’s not possible to test biosolids routinely for every possible pathogen,” Bruns says, “so microbiologists also test for indicator bacteria such as E. coli.”

Although indicator organisms are not pathogens, they are a way of detecting microorganisms that come from biosolids.
The biosolids applied at the site contained none of the tested pathogens. After the biosolids were applied to the mine site, Bruns analyzed the soils for total as well as indicator organisms. The results will show how biosolids affect the native microbial communities in mined soils and whether indicator organisms can survive in these soils. The researchers can use DNA fingerprinting tests to confirm whether the indicator organisms came from the biosolids.

This project has been adaptable to classroom use. “I’ve used it as the basis for a case study in my soil ecology class,” she says. “Students find applied, public-oriented research interesting, because it touches them personally. It gets them more engaged.”