Challenging Restoration Project of the Columbia Riverbank and Hillside at Teck Cominco Metals Smelter in Trail, British Columbia, Canada

摘要

Teck Cominco Metals Ltd. has operated a lead-zinc smelter in Trail since the late 1800's. A number of attempts to re-vegetate the riverbank have been made; however, these have been met with poor to, at best, moderate success. The hillside below the smelter was divided into four treatment units, and the adjacent riverbank into five treatment sections. Live cuttings used in the soil bioengineering structures were collected locally within the project area near Trail, British Columbia. In the spring and fall of 2006 soil bioengineering structures were installed along the Columbia River. These consisted of brush layers with protective layers and live cutting pockets in rip-rap, as well as brush sills and fascines within a gravel bank. The cuttings that were used consisted of a mixture of Willow, Black Cottonwood, Red-Osier Dogwood, and a small amount of Pacific Willow. Planting was machine-assisted using excavators. During the summer of 2006, survival and growth of the spring-planted structures was assessed as good to excellent. Installation of soil bioengineering structures on two of the hillside units commenced in the fall of 2006, with the exception of two small areas with a slope gradient less than 40% (22~0) that were planted during the spring using an excavator. On slopes gradient greater than 40% (22~0), which is the majority of the hillside, machine-assisted planting was done in the fall using a Schaeff Walking Excavator (Spyder Hoe). On slopes gradient greater than 60% (31~0) the excavator was tethered to a skidder located at the top of the slope. Materials were transported onto the slope using an overhead cable system. The soil bioengineering structures consisted of brush layers using a species mixture of black cottonwood and willow. In combination with the brush layers, a custom soil amendment was utilized to increase soil fertility, retain moisture and regulate pH. Straw wattles were also installed across the slope, designed to act as sediment traps, shortening the slope length to reduce risk of surface erosion leading to rill formation. Survival and growth of the spring and fall-planted areas was generally good, although in areas survival was poor due to soil factors (high salts/contamination). The hillside units were also planted with container type native shrubs and conifer trees. The following spring of 2007 the second and third units were completed and hydro-seeded with native grasses using pulp mill bio solids as mulch. Irrigation system was installed and application of compost tea was carried out in the fall of 2007.