An Environmental ‘Burden’ Lifted

Case Studies
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Just as erosion must be controlled on steep slopes during road and bridge construction, the companies that produce your concrete face similar challenges. Read on to learn the erosion control solutions enacted at Lafarge’s limestone quarry.



Situation

Lafarge’s Woodstock, Ontario, quarry supplies limestone for Lafarge’s cement production. In 2001, officials realized erosion control measures weren’t working on the eastern face of an accumulation of mined “overburden.” Unless an effective control method could be found, runoff from the stockpile could eventually affect water quality in nearby streams.


Problem


The stockpile’s eastern face has a 2.5H:1V slope gradient, is about 300 ft high and totals about 10 acres. Corrective action became necessary when rain and snowmelt began creating sizeable rills and sediment movement. Early attempts to stem erosion were unsuccessful.

“The combination of rain, snow, freezing and thawing would wash out the topsoil we’d graded in,” said Michael Bart, LaFarge’s environmental engineer. “It was discouraging and costly.”


Solution


In October 2003, LaFarge accepted a test proposal from Mulch-It, a distribution company, and Profile Products. After grading a 30-ft-wide strip, Future Green, an erosion control contractor, hydraulically applied a mixture of Flexterra FGM (Flexible Growth Medium), seed and fertilizer at the rate of 3,500 lb per acre.

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% effectiveness in controlling soil loss, Flexterra requires no cure time, providing immediate, intimate protection against erosion upon application.

The application was quickly tested. Heavy rains fell the day after the installation was completed. However, in the spring of 2004, Bart said the strip stood out like a “beacon of green.” In the fall of 2005, LaFarge decided to have Mulch-It and Future Green rehabilitate the entire eastern slope of the stockpile.

Pleased with Flexterra's performance over the two years, LaFarge noted there had been some minor rilling in the test area. To ensure a permanent solution, Profile’s Terra-Tubes were installed as a slope interruption device in conjunction with the Flexterra .

Terra-Tubes utilize an engineered composite of thermally processed wood fibers, man-made fibers and performance-enhancing polymers encased in heavy-duty, knitted tubes. They’ve been proven through independent testing to be a highly effective storm water treatment device designed to effectively trap, filter and treat sediment-laden runoff.

The Result

The 2005-2006 winter brought numerous rain, snow and freeze/thaw events. Temperatures were as low as zero degrees Fahrenheit in November. Circumstances didn’t improve in the spring of 2006, which ushered in cold, wet conditions. Despite this, Bart said, it was apparent they had achieved stable cover by the 2006 summer.

The combination of Flexterra's and Terra-Tubes has been successfully demonstrated on numerous projects across North America. A good indication of this best management practice establishment is the fact that Lafarge, Mulch-it Inc. and Future Green are consulting on further applications of Flexterra's and Terra-Tubes in progressive restoration of other stockpiles at the Woodstock quarry.

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