by Dennis Vorse
For over 60 years, iron oxide and ensuing orange sludge deposits had polluted the 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 GMP discharge containing 65-90 mg/L Fe. In addition to providing vital ecological cleaning of the stream/watershed, the first-of-its-kind system has pioneered the recovery of iron oxides/sludge into a marketable pigment product.
Polluted History/Innovative Wt System
Early coal mining production from the Marchland Mine produced the unavoidable by-product 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 the development of chemical and mechanical treatment technologies. While these technologies have been effective in eliminating new sources of pollution — they are expensive and often created solid waste problems, which 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 Sewickley Creek Watershed Association (SCWA, www.sewickleycreek.com) to design and construct an effective passive mine water system. The SCWA enlisted Hedin Environmental/Iron Oxide Recovery (Pittsburgh, Pa.) to design the system and assist in the project’s permitting, monitoring, management, and construction by DeBaldo Brothers, Inc. (Glenshaw, Pa.), beginning in October 2005.
Because the project would involve significantly high flowrates, IOR contracted MFG Water Treatment Products Company (www.mfgwtp.com) 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 flowrates.
Trough Challenge
Since the IOR systems’ design process incorporates passive technologies, which 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. In addition, the discharge from the production ponds had to be directed into the constructed wetlands where residual iron would be removed and a final discharge produced that does not pollute the receiving stream.
Trough Solution
A total of 12 fifty-foot troughs were built using open-mold production at the MFG Union City manufacturing facility. The custom design configured the troughs to be embedded in the earth with the optimal FRP strength to handle the corrosive elements and high flowrates associated with the project. The FRP materials included corrosion-resistant resins and glass configured in directional and random chopped glass to maximize performance and strength including:
FRP Material Specifications:
▪ Nominal Thickness: ¼".
▪ Gel-Coat Finish: On all surfaces, contain ultraviolet inhibitor.
▪ Glass: Type E, random chopped with chrome or silane finish.
▪ Color: Aqua. color molded-in with ultraviolet inhibitor.
Minimum FRP Laminate Physical Properties:
▪ Tensile Strength, ASTM D 638: 12,000 psi.
▪ Flexural Strength, ASTM D 790: 19,000 psi.
▪ Flexural Modulus, ASTM D 790: 900,000 psi.
▪ Barcol Hardness, ASTM D 2583: 35.
▪ Notch Izod Impact, ASTM D 256: 13 ft-lbs/inch.
▪ Water Absorption, ASTM D 570: 0.2 percent. (maximum)
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 so it wouldn’t allow any water to pass by and could be cleaned out periodically. Also, a notched weir was incorporated to control the volume of fluid that passed through with a weir flowrate @ full two-inch 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 two to assemble — essentially six man hours per unit."
Results
With construction completed in November 2006, the passive mine water
system at Marchand Mine cleaned the stream and helped in the recovery of
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 EnvironOxideTM for Hoover Color Corporation (Hiwassee, Va.).
Since its first year of operation, testing shows the system has decreased Fe
concentrations, on average, from 74 mg/L to less than 1 mg/L Fe. The ponds remove 85 percent of the Fe and are 25-50 percent more efficient than other passive systems treating similar water. The system has also 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 approximately seven cents per 1,000 gallons.
According to Bob Hedin, IOR/Hedin 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 flowrates, which can be incorporated into larger flow systems on future projects."
Dennis Vorse is the general manager of MFG Water Treatment Products. He can be reached at 814 438-3841 or [email protected].
