FRP troughs help remove iron from mine water discharge

For more than 60 years, iron from iron ore deposits has polluted water that flows out of the abandoned Marchand Mine near Lowber, Pa., into Sewickley Creek and the Youghiogheny River. After it was shut down in the early 1940s, the mine began to discharge iron — almost 1 million lb (more than 450,000 kg) annually. In 2002, the Sewickley Creek Watershed Assn. (SCWA) enlisted Hedin Environmental/Iron Oxide Recovery (IOR, Pittsburgh, Pa.) to design a solution and oversee construction by DeBaldo Brothers Inc. (Glenshaw, Pa.) beginning in October 2005. The result was the Marchand Mine Treatment System, a six-pond/large wetland passive mine drainage system, which incorporates specially designed fiberglass reinforced plastic (FRP) troughs that help treat a 1,200-gal/min to 2,250-gal/min discharge that contains 65 mg/L to 90 mg/L of iron — well over the legal limit of 3 mg/L. MFG Water Treatment Products Co. (MFG-WTP, Union City, Pa.) designed and manufactured the inlet/outlet troughs, which are set in earthen embankments to consistently and predictably meter water flow through the pond system. As they do, the troughs also aerate the iron, thereby creating iron oxide, which settles to the pond bottoms, cleaning the water before it enters the creek.

MFG open-molded 12 50-ft/15.2m troughs to a nominal thickness of 0.25 inch/6.35 mm, using corrosion-resistant isophthalic resin from Ashland Performance Materials, Composite Polymers (Dublin, Ohio), continuous oriented and random chopped E-glass from Owens Corning Composite Solutions LLC (Toledo, Ohio) and a weatherable gel coat with UV inhibitor provided by Valspar Composites (Elkhart, Ind.). The troughs met all ASTM minimum standards: tensile strength of 12,000 psi/82.74 MPa, flexural strength of 19,000 psi/131 MPa, flexural modulus of 900,000 psi/6,205.28 MPa, Barcol hardness of 35, notched Izod impact of 13 ft-lb/inch and maximum water absorption of 0.2 percent.

Construction was completed in November 2006. After a year of operation, tests show that the system has decreased iron concentration, on average, from 74 mg/L to less than 1 mg/L — up to 50 percent more efficiently than other passive mine water treatment systems. The troughs are designed to last 20 to 25 years; over that period the system will treat 21 billion gal of water at a cost of $0.7 per 1,000 gal. Additionally, harvested iron oxide sludge is made into a saleable yellow pigment, branded by IOR as EnvironOxide for Hoover Color Corp. (Hiwassee, Va.).