Erosion and sediment control at the white pine mine

摘要

The White Pine Mine is a closed underground copper mine with over 2,226 hectares (ha) (5,500 ac) of erosive tailings located in three separate surface impoundments. The site is located between the shore of Lake Superior and the town of White Pine, Michigan. This paper discusses methods used to control wind erosion at the site. During operations, continual slurry deposition protected the tailings from wind erosion. Upon mine closure, the tailings surface dried and severe dusting events occurred during dry, windy periods. During winter the tailings are wet or snow-covered and the prevailing southwesterly winds take dust toward Lake Superior. However, during summer months, the tailings can dry between storms. During this season, the prevailing northeasterly winds can blow a wall of dust over the town of White Pine. To select the best closure alternative, an evaluation was conducted and direct revegetation of the tailings was selected as the primary means of erosion control. Past research indicated revegetation of the tailings would be difficult due to: Lack of water and nutrient holding capacity; Abrasion from saltating sand and si The physical nature of the silt/sand sized tailings; and, Chemical imbalances. A site evaluation was conducted to identify: Existing vegetation tolerant of site conditions; The physical and chemical make-up of the tailings; and, Existing sources of organic amendments in proximity to the mine. During the site evaluation, copper was identified at potentially phytotoxiclevels in the tailings. Local paper mill sludge, previously slated for land-filling, and wood-chips, were identified as inexpensive amendments which would effectively treat the phytotoxicity concerns. A greenhouse study was developed in which four organic amendment rates, two inorganic fertilizer rates, and fourteen plant species were tested. Boron, phosphorus, manganese, and nitrogen deficiencies were identified during the greenhouse study. The results of the greenhouse study were used to develop large-scale field trials that compared ten physical methods of wind erosion protection. Crimped straw mulch, combined with revegetation, was identified as an effective means to control wind erosion. The results of the field trial were used to develop specifications for the entire site. Approximately 202 ha (500 ac) were fully treated using the paper mill sludge and another 486 ha (1,200 ac) were temporarily stabilized using a green manuring approach in 1999. Additional acreage was treated in 2000. No dusting events have occurred since 1999 and the site is well on the way toward permanent stabilization.