FRP Troughs Key to Water Treatment System’s Iron Oxide Eco-Solution

by Dennis Vorse

• First-of-its-kind passive mine drainage system treats 600,000 pounds of Fe per year from Pennsylvania’s former March and Mine.

For over 60 years, iron oxide and ensuing orange sludge deposits polluted water discharging from the abandoned Marchand Mine near Lowber, PA, into Sewickley Creek and the Youghiogheny River. The recently constructed Marchand Mine Treatment System is a patented six-pond/large wetland passive mine drainage system that incorporates specially designed FRP (fiberglass reinforced plastic) troughs that manage the hydrology in treating a 1,200-2,250 gpm of discharge containing 65-90 mg/L of iron (Fe). In addition to providing vital ecological cleaning of the stream/watershed, the first-of-its-kind system has pioneered recovery of iron oxides/sludge into a marketable pigment product.

Polluted History

Early coal mining production from the Marchland Mine produced the unavoidable byproduct of discharge of polluted mine drainage, which began flowing from the mine’s portal shortly after its shutdown in the early 1940s – resulting in almost a million pounds of iron oxide discharge contamination every year since.

Environmental laws of the 1970s made water pollution an unacceptable consequence of coal mining and led to development of chemical and mechanical treatment technologies. While these technologies are effective in eliminating new sources of pollution, they’re expensive and often created solid waste problems. That didn’t serve the long-term needs of solving the Marchland Mine problem.

In 2002, $1.3 million in Growing Greener grant funding was awarded from the Pennsylvania Department of Environmental Protection to the Sewickley Creek Watershed Association (SCWA) to design and construct an effective passive mine water system. SCWA enlisted Hedin Environmental/Iron Oxide Recovery (IOR), of Pittsburgh, PA, to design the system and assist in permitting, monitoring, management and construction by DeBaldo Brothers Inc., of Glenshaw, PA, which began in October 2005.

Because the project would involve significantly high flow rates, IOR contracted MFG Water Treatment Products Co. to specially design and manufacture an inlet/outlet FRP trough system that could optimize the hydrology distribution and passive precipitation of Fe throughout the projects’ six ponds – all while avoiding short circuiting due to high flow rates.

Trough Challenge

Since the IOR systems’ design process incorporates passive technologies that take advantage of naturally occurring chemical and biological processes to cleanse the contaminated mine waters, the MFG-WTP trough system was designed to set in earth embankments while aerating and breaking up the water of the large flow system. Discharge from the production ponds also had to be directed into the constructed wetlands where residual iron would be removed and a final discharge produced that didn’t pollute the receiving stream.

Molded Solution

Twelve 50’ troughs were built using open-mold production. The custom design configured the troughs to be embedded in the earth with optimal FRP strength to handle corrosive elements and high flow rates associated with the project. FRP materials included corrosion resistant resins and glass configured in directional and random chopped glass to maximize performance and strength (see Figure 1).

Due to the high volume of water coming out of the mine and to maximize its potential, the design also had to incorporate a segregated gate to prevent any water from passing and allow it to be cleaned out periodically. A notched weir also was incorporated to control the volume of fluid which passed through – with a weir flow rate @ full 2" head pressure @ 48.6 cubic feet per second.

Once delivered on-site, the trough system assembly was smooth, according to DeBaldo Brothers’ president Pete DeBaldo, “It was a simple process of bolting the troughs together and drilling them into anchor points – four people to set the trough and a two to assemble them – essentially six man-hours per unit.”

Conclusion

With construction completed in November 2006, the passive mine water system at Marchand Mine cleaned the stream, helped recover iron oxides and optimized the production of recoverable, saleable iron oxide. The waters’ excessive iron-turned-to-sludge was made into pigment branded by IOR as EnvironOxide™ for Hoover Color Corp., of Hiwassee, VA.

Since its first year of operation, the system – testing shows – has decreased Fe concentrations, on average, from 74 mg/L to less than 1 mg/L. The ponds remove 85% of the Fe and are 25-50% more efficient than other passive systems treating similar water. The system also has successfully treated flows as high as 2,250 gpm and functioned well in February 2007, when much of the wetland was frozen. Over the next 25 years, the Marchand System will treat 21 billion gallons of water at a cost of ~7 cents per 1,000 gallons.

According to Bob Hedin, Hedin/IOR president, “The system represents the next wave of technical innovation for mine water treatment. The FRP troughs were instrumental in providing superior strength and handling large flow rates which can be incorporated into larger flow systems on future projects.”

About the Author: Dennis Vorse is general manager of MFG Water Treatment Products Co., of Union City, PA. For over 30 years, MFG – a unit of Molded Fiber Glass Companies, of Ashtabula, OH – has supplied the industrial water and wastewater treatment industry with advanced fiber reinforced polymer (FRP) products. Contact: 877-826-2509, [email protected] or www.mfgwtp.com