Cleaning Up A Coal Mine
In rural northwest Pennsylvania, Jim Irey, a civil engineer and vice president of Berner Construction of Gap, Pa., located about 4-1/2 hours away to the southeast, is working on his fifth area coal mine reclamation project in the area in the past two years. Irey is involved in constructing acid mine drainage systems and reclaiming abandoned coal mine sites nearby.
Like much of the state, the area has numerous abandoned coal mines with a great deal of sulfur residue from the mining. The sulfur reacts with air and pyrite to form sulfuric acid that contaminates water flowing through the mines. The acidic water, which cannot support aquatic life, finds its way to Chesapeake Bay to the east, where it adversely alters the bay's ecosystem, as well as those of watersheds en route.
Pennsylvania's coal-mining legacy problems are generally considered to be more widespread than states such as West Virginia and Ohio. The Pennsylvania Bureau of Abandoned Mine Reclamation estimates that the state has about 250,000 acres of abandoned surface mines in 45 of its 67 counties with dangerously high walls, and about 24,000 miles of streams in the state do not meet water quality standards due to drainage from abandoned mines.
In late 2007, the U.S. Office of Surface Mining provided Pennsylvania with the first installment of $1.36 billion that the federal government is giving the state over 18 years to reclaim 184,000 acres of abandoned mines on 5,100 sites. The state calls acid mine drainage its biggest water pollution problem.
A look at one of the contaminated watersheds, Dents Run, located just outside of town, illustrates the severity of the problem. Much of the water flowing through this creek has a conspicuous bright orange tint, revealing the effects from the acid mine drainage. By winter 2008, Berner Construction was reclaiming the fifth abandoned coal mine in these parts by constructing a passive treatment system and relying heavily on the use of a Global Navigation Satellite System (GNSS) from Topcon Positioning Systems for site preparation and construction machine control.
On the way to a current project that his company is working on, Irey stops at a reclaimed mine that was completed from June to October 2006. Inside of a gate, he walks several hundred feet into a valley to where three cuts in the side of surrounding slopes are visible.
Those cuts are abandoned mine openings, and the surrounding hillside had been covered with 8,000 tons of coal tailings before Berner Construction began its work. After his company removed the coal tailings and had them shipped to a recycling facility, a channel network and several basins were constructed starting from the mine openings and extending downhill toward Dents Run.
The channel network and basins comprise the passive treatment system. One channel extends from the opening of one mine located to the left, through which runoff flows that is free of acid mine drainage. This runoff flows into a basin lined with compost and wood chips that imparts bacterial activity to the water.
Another channel, which is lined with high-calcium limestone, starts at two mine openings located on the opposite slope and flows into another basin. The limestone in the channel lowers the acidity of the mine drainage flowing over it.
The water from all three mines collects in the second basin before being dispensed into another channel and eventually finding its way to Dents Run. With the pH lowered and the biological building blocks added to the water in this part of the watershed, Dents Run is on the comeback trail toward supporting aquatic life.
High-tech tools help
This project was the first in which Berner Construction used the GNSS system. A Topcon HiPer Light+ base receiver that was located on high ground received satellite positioning signals. These signals were transmitted to a HiPer Light rover system and used to create a three-dimensional survey model of the site. The dozer operator viewed the 3-D model inside a monitor mounted in the cab and the base station transmitted signals to the rover — then mounted on the front of a dozer used for finish grading — while the site was graded. The GNSS data — information drawn from Topcon's dual-constellation system, which uses both GPS and GLONASS satellites for constant reception — indicated to the operator how near to specification the dozer blade was at any given moment, allowing precise, continuous grading adjustments.
For remote jobs like this, Irey says, GNSS is particularly valuable because of the availability of few surveyors local to the area. "We can be more competitive with the [GNSS]," he says. "It gives us an advantage because we do our own surveying. Our Topcon dealer, Boyd Instruments [of Horsham, Pa.] has been invaluable in helping us set the system up, [coming] to most of our sites to help set up the system, providing the best coverage for the GNSS system."
Off in the distance, an excavator clears trees while two dozers rough-grade a slope between the valley floor and the high wall by leveling out the ridge. Like the rough grading dozers, a fine-grading dozer pushes the dirt uphill, but unlike the other two machines, it is equipped with the rover unit, which captures the dozer blade's precise location from the base station and plots the location on the cab monitor for the operator. Says Irey: "You can put the blade down anywhere and [the 3-D modeling will] tell you if you need soil or not."
Irey accesses the same 3-D model on his handheld Topcon FC-100 field monitor that the fine-grading dozer operator sees on his in-cab monitor. Irey can also see a black line on his field monitor indicating where a high calcium limestone-lined drainage swale will be dug to channel acidic runoff from the slope.
"This is the entire job site — it's about 8,000 feet from end to end," Irey says, pointing to the crescent-shaped model on his field monitor. Then he turns to the charcoal-colored stockpiled limestone that will be placed after grading is complete. "This material is a byproduct that we use," he says. "It's waste material from a quarry that met the specification for high-calcium limestone material. The quarry had 400,000 yards of it, and we got it approved through the state as a beneficial waste material. They sell it to us for a reduced price. For this job, we'll use about 3,000 tons. On the last job, we used 25,000 tons — it just depends on the site conditions and what the designer is trying to do. This job doesn't have a lot of mine seepage."
Although these mine reclamation projects present their own challenges, the grading does not have to be quite as precise as on a paving project, for instance. The GNSS provides Berner Construction's dozer operator with accuracy within several inches of the blade's actual location; the real benefit of GNSS in this situation is productivity. The company essentially does its own surveying and site preparation, keeping its machines moving dirt as much as possible.
Irey is a civil engineer by education who was taught conventional surveying methods by a contractor during his practical college studies. A condition of his teaching was that he teach the art of surveying to someone else, and now Irey has taken note of how the use of GNSS is changing surveying and site preparation methods. "There are fewer and fewer people who can do traditional survey work," he says. "But it will always be required in certain situations. In today's world, you are now looking at computer screen similar to the screen that a kid looks at when he's playing an electronic game."
The conditions of the abandoned mine sites in this part of the state provide an advantage to productivity, Irey explains. In the south central part of the state, for example, miners were more likely to pile dirt from their excavations near the high walls, necessitating downhill grading. For downhill grading, a GNSS provides more of a benefit in terms of grading accuracy. "These jobs are all uphill pushes, so as long as we have pretty consistent grades throughout the site, we're OK. The issue with downhill grading is that it goes much faster, so if you overfill an area you overfill it fast, and it may take you three to four times as long to level it out."
The use of GNSS minimizes the need for Berner Construction to use the conventional method of site preparation involving the use of grade stakes. "We would just put stakes up the hill and run a level on it, which is very hard to do to get control on the hill," Irey notes. "What [the GNSS] does is allow me not to be here. We pride ourselves on the fact that once the site is set up, short of moving the base station around, it's good to go for the entire job."