Combined erosion control technologies eliminate runoff from a quarry stockpile slope.

 With some 900 quarries around the world to sustain its industry-leading building materials operation, Lafarge is committed to achieving sustainable development hand-in-hand with environmental compliance. However, attempts to stabilize a large stockpile at its Woodstock, Ontario, quarry were challenging this commitment. The Woodstock Quarry is an open-pit operation that supplies limestone for Lafarge’s cement production. In 2001, officials realized erosion control measures were not working on an accumulation of mined overburden in one of the quarry’s stockpiles. The overburden is a mix of clay, sand, and rock devoid of topsoil, making it susceptible to erosion and extremely difficult to revegetate. Unless an effective control method could be found, runoff from erosion of the stockpile could eventually affect water quality in nearby streams.

Acceptable cover had been established on the stockpile’s western face, which drains into the quarry. However, the eastern face was not able to sustain similar vegetative cover. This face has a slope of approximately 2.5H:1V, is about 300 feet from top to bottom, and totals about 10 acres. It was apparent that corrective action was needed in this area when rain and snowmelt began creating sizeable rills, moving sediment down the unstable mixture of materials and pooling sediment at the foot of the slope.

The first attempts to stem this erosion and create better growing conditions were fairly conventional. Lafarge contracted with a company to have topsoil hauled up the slope, graded in, and then hydroseeded.

"We tried this (conventional method) twice, with little success," said Michael Bart, environmental engineer for the Lafarge Woodstock operation. "The combination of rain, snow, freezing, and thawing would wash out the topsoil we’d graded in and create large gullies. The only evidence of growth was in a few areas where the soil hadn’t eroded away. It was not only discouraging, it was costly. As a result, we were unwilling to make further investments until someone could demonstrate an effective technique on this site."

In the spring of 2003, John Reynolds of Mulch-It, located in Putnam, Ontario, and Dwight Johnson, regional manager for Profile Products, met with officials at the Woodstock operation. Aware that Lafarge needed proof before they’d make further investments in erosion control, Reynolds and Johnson proposed applying Flexterra Flexible Growth Medium (FGM) to a 30-foot-wide test strip down the problematic east-facing slope of the stockpile.

Flexterra’s patented technology combines Thermally Refined wood fibers; crimped, interlocking, man-made fibers; and performance-enhancing additives to provide erosion protection and seed germination on slopes. With greater than 99 percent effectiveness in controlling soil loss, Flexterra outperforms rolled erosion control blanket and bonded fiber matrix products, according to Profile Products. Flexterra requires no cure time, providing immediate protection against erosion upon application. It creates an intimate bond with the soil surface to form a continuous, porous, and erosion-resistant blanket that allows for rapid germination and accelerated plant growth. Flexterra also absorbs and holds 15 times its weight in water, delivering more moisture to the seedbed for faster vegetation establishment.

Lafarge officials accepted the proposal and work on the test site began in October 2003. Future Green, an erosion control contractor located in Schomburg, Ontario, applied the FGM. The area was graded with a bulldozer to smooth out rills. Next, the area was track-packed by a bulldozer with the cleat marks running horizontally across the slope to act as a basic erosion retardant. Finally, a mixture of Flexterra, seed, and fertilizer, which included a slow-release nitrogen, was hydraulically applied at a rate of 3,500 pounds per acre.

"We knew the history of problems with the slope, so we tailored a seed mix containing grasses and legumes that we had observed would grow in that environment," said Ken Wray, president of Future Green. "This combination was designed to help establish a quick cover while providing deep rooting and nitrogen fixation. We knew we were at the extreme edge of the growing season, but our experience with Flexterra was that it works well in situations where dormant seeding is needed."

This combination was quickly tested. Heavy rains fell the day after the installation was completed.

"We observed very little erosion," Bart said. "But we wanted to see how the test area would hold up over a winter of snow, freezing, and thawing."

In the spring of 2004, Bart said the strip stood out like a "beacon of green." Lafarge continued to monitor the area and, in the fall of 2005, decided to have Mulch-It and Future Green rehabilitate the entire eastern slope of the stockpile—an area of about 10 acres.

In late 2005, Terra-Tubes Fiber Filtration Tubes and Flexterra Flexible Growth Medium were applied to the 2.5H:1V slope of a quarry overburden stockpile.

"Compared to their previous method, they were pleased with how the Flexterra had performed," Reynolds said. "However, over nearly two years, there had been some minor rilling in the test area. To ensure a permanent solution, it was agreed that we would incorporate Terra-Tubes as a slope interruption device in conjunction with Flexterra."

The team agreed to use Terra-Tubes Fiber Filtration Tubes (FFT) based on the product’s construction—an engineered composite of thermally processed wood fibers, man-made fibers, and performance-enhancing polymers encased in heavy-duty, knitted tubes. Terra-Tubes had been proven through independent testing to be a highly effective stormwater treatment device designed to effectively trap, filter, and treat sediment-laden runoff.

The entire slope (with the exception of the original test strip) was graded and track-packed vertically. Next, four rows of 6-inch-diameter FFTs were placed along the face of the 2.5H:1V slope. Each row was spaced about 75 feet apart. Finally, the previously evaluated mixture of FGM, seed, and fertilizer was hydraulically applied at a rate of 3,500 pounds per acre. The project, beginning from initial grading to placement of the FFTs, was completed in two weeks.

The winter of 2005-2006 was, according to Bart, "tough to the ’nth’ degree." The winter brought numerous rain, snow, and freeze/thaw events and temperatures were as low as 0 degrees F in November. Circumstances didn’t improve much in the spring of 2006, which ushered in cold and wet conditions.

"Because of the unfavorable weather, we didn’t see much germination and growth until late May," Bart said. "But then it seemed that the vegetation literally exploded out of the ground."

During the spring and summer of 2006, Bart said he made frequent trips to inspect and photograph the project. "It was apparent that we had achieved a good, stable cover," he said. "We were able to find only one minor rill in the entire 10-plus acres. The rill was only about 10 inches wide by 3 inches deep, which we believe was caused by an unforeseen flow pattern. However, by the end of August, the rill was fully grown in and virtually indiscernible."

By fall 2006, stable cover was established on the clay, sand, and rock stockpile.

According to Stephen Zwilling, market development manager for Profile Products, using Flexterra and Terra-Tubes in combination is becoming well-established as a Best Management Practice for controlling erosion and improving water quality in slope management. Lafarge, Mulch-it, and Future Green are consulting on further applications of the products in progressive restoration of other stockpiles at the Woodstock quarry.

Lafarge affirmed its environmental commitment by stabilizing its erosion-prone slope and returning the stockpile to the natural appearance expected by Ontario’s Ministry of Natural Resources. The company has a secure, established slope and, even more importantly, a blueprint for handling similar challenges in the future.

Sarah Willnerd is a writer for Swanson Russell Associates in Lincoln, Neb. She can be contacted at sarahw@sramarketing.com.