White Pine Mine
1999, with subsequent monitoring
N 46° 45'
W 89° 33'
Located in White Pine, MI, about 18 miles from Ontonagon, MI, 22 miles from Wakefield, MI, 38 miles from Ironwood, MI, 224 miles north of Green Bay, WI and about 172 miles east of Duluth, MN.
|The White Pine Mine is located on the upper peninsula of Michigan.
The Mine is situated about 2.4 kilometers (km) (1.5 miles) south of the shore of Lake Superior, at a Latitude of 47° North. The climate is cold and wet in the winter and hot and wet in the summer. The growing season is short (June to October). There are seasonal winds, which are from the southwest in the winter and from the northeast in the summer. Precipitation is approximately 96.5 centimeters (cm) (38 inches (in)), distributed monthly as shown in this chart.
The White Pine Mine is owned and operated by the Copper Range Company, a subsidiary of Inmet Mining Corporation. It is located in Ontanogan County, Michigan along the shores of Lake Superior in a region known as the Upper Peninsula of Michigan. The project was in operation for over 70 years and is currently in the process of site wide closure. The project consists of an underground copper mine, processing facilities, and approximately 2,630 ha (6,500 ac) of tailings. The tailings are impounded in three separate facilities: the South Dam; North Pond 1; and North Pond 2. The South Dam was not filled to capacity, and was closed and stabilized by dozing the surrounding remaining embankment clays onto the tailings surface, and revegetating using standard agricultural means. The North Pond 1 and 2 tailings facilities, which total approximately 2,023 ha (5,000 ac), are being stabilized from wind and water erosion by direct revegetation of the tailings themselves. Previous attempts to establish vegetation on the tailings were initially successful, but after two to three years a dieback of vegetation occurred, and ultimately failure. The sand blasting effect of the blown tailings, burial by the moving dunes of tailings, the physical nature of the tailings, and possibly chemical or nutrient imbalances, were all suspected of causing the failure. The tailings have remained relatively barren for over 20 years.
|Monthly precipitation in White Pine, MI
In 1997, a program was undertaken to logically and scientifically identify the reasons for the past failures, and determine if direct revegetation was a feasible means of stabilizing the tailings. The importation of sufficient clay material to cover the tailings facilities would cost over $72,000,000. Therefore, a self-sustaining and permanent means of directly revegetating the tailings was highly desirable. The following paper discusses the methods used since 1997 to control wind blown tailings sufficiently to establish vegetation, which has been the ultimate means of controlling erosion from the site.
Reclamation Goals: The 1997 goals for reclamation of the tailings included the following:
- Minimize Wind Erosion and Wind Born Dust
- Establish a Low/No Maintenance, Stable, Self-Sustaining Plant Community Which Will Promote “Natural” Succession
- Minimize Water Erosion and Sediment Transport
- Reduce Deep Percolation of Precipitation by Increasing Evapotranspiration
The intent of the revegetation plan is to control amounts of organic matter, nutrient inputs and species composition during reclamation in order to encourage microorganism establishment. The successful establishment of soil microorganisms necessary for decomposition will allow natural nutrient cycling to begin. Ultimately, the cycling will lead to improved ecosystem stability, ground cover, and erosion control. Initially, in a barren tailings, establishing this cycle requires adding a supply of organic matter and nutrients approximating a natural system that will lead to a stand of vegetation which functions as a self-sustaining ecosystem. An alternative approach might be to intermittently apply inputs of nitrogen. However, high and continual inputs of nitrogen inhibit soil microorganism development and often lead to stagnant vegetation and soil microbial communities, unable to cycle nitrogen and other nutrients.
Technical Approach: The technical approach taken for the project was to logically and scientifically determine the limiting factors to plant establishment and find the most cost effective method of addressing these factors. The following tasks were undertaken to accomplish this:
- Review existing information
- Evaluate site conditions
- Survey the existing vegetation in the area
- Conduct an agricultural and geochemical soils survey of the tailings
- Conduct a survey for sources of organic matter
- Conduct a greenhouse study
- Test erosion control methods in a field trial
- Develop and implement full scale revegetation
Each of these tasks is discussed in detail below.
Review of Existing Information: An initial site investigation and records search identified that prior revegetation research had been done during the mid to late 1960s. This work had involved the installation of several test plots including a number of species and planting methodologies. No soil agricultural- or geochemistry testing had been done associated with the trials, other than metallurgical work related to ore quality control.
|Barren landscape and blowing dust prior to revegatation
Initially, the results of these trials were encouraging. However, after approximately five years, the vegetation was identified as being chlorotic (yellowing or spotting) or had died. The final conclusions were that the abrasive nature of the wind blown tailings, the sterile and low water and nutrient holding capacity of the tailings, and possibly phytotoxicity related to soil chemistry, were too severe to allow direct revegetation of the tailings. No further study had been conducted.
The 1997 evaluation of site conditions indicated that the tailings facilities were large enough to generate their own microclimate. Although the area is relatively moist, with an average annual precipitation of almost 96.29 cm (38 in) and cool temperatures during most of the year, the tailings are more accurately characterized as a desert ecosystem. The tailings allow precipitation to quickly infiltrate and the surface dries within hours of a rainfall. The surface few inches of tailings, when dry, blow and develop dunes that move across the site. The tailings are a light to medium gray in color, which leads to solar heating. When the moisture levels drop due to drying, and evaporative cooling stops, the soil temperatures can climb to over 37.70C (100° F) in the summer months.
The tailings facilities were constructed by building the embankments around the detainment area, and then depositing tailings. No vegetation removal occurred prior to deposition. The topography of the area includes low ridges and shallow valleys, which traverse the impoundments from east to west. Therefore, where ridge tops occurred, there are areas within the tailings with exposed natural soils, standing dead trees and shallow tailings. Where valleys occurred, there are only barren areas of tailings up to 24.38 meters (m) (80 ft) deep.
The areas of natural soils are islands of well-established native and introduced species. Within the areas of standing dead trees, some re-colonization has occurred. Where enough organic matter had fallen and decomposed, and sufficient protection from wind erosion was provided by the standing and fallen timber, some soil development and sparse vegetation had taken hold. These areas were relatively few, but provided evidence that under the right conditions, vegetation could survive.
The existing vegetation in the area was surveyed to determine if there were species adapted to the local site conditions, which would survive on the tailings. A second purpose of the survey was to determine if any natural means of re-colonization were occurring which could be emulated for reclamation. Numerous species common to the Tsuga-Pinus-northern hardwoods ecotone, typical of the region, inhabit the undisturbed and disturbed clay soil areas around the tailings facilities. The timber immediately around the mine site has been harvested and a secondary forest of Populus tremuloides (Aspen) currently dominates most of this area. Reclamation seed mixtures used over the years have been very successful when sown on the native clay soils and growth from these mixtures is also present around the site.
Historic aerial photographs of the tailings indicated that the North Pond 1 tailings facility had been covered with vegetation to varying degrees over the past 20 years while the other two facilities had remained barren of vegetation. At different times, North Pond 1 had been totally barren, almost entirely covered, and at the time of the study, was approximately one third covered. The survey indicated that the vegetation was composed of just one species; Agrostis alba (Redtop). Apparently, this species had been introduced during the trials conducted in the 60s, or in past reclamation work around the facility, and had been able to spread across the site when conditions were favorable and died back when they were not. Further investigation into the operations of the facility pointed out that the water level and source had fluctuated over the years. When only precipitation water entered the facility the water level was low. However, during some periods mine dewatering was routed into North Pond 1 and the water level would increase dramatically. The mine water was saline and when flows were slowed or diverted elsewhere, a barren beach would develop. Repeated periods of this scenario have enabled the Agrostis alba present on-site to differentiate into a variety well adapted to the site conditions.
The only other species found growing on the tailings was Equisetum arvense (Field horsetail). This species was typically found on the lower slopes of the embankments and near permanently saturated areas.
A systematic survey of the tailings material was conducted by grid sampling each facility. Approximately 50samples were collected and analyzed for agricultural and geochemical parameters. Based on the results, the tailings could be segregated into four different categories: Embankment sands; Saline tailings (only found in North Pond 1 barren areas); Typical tailings (all other tails within the impoundments); and, Slimes (located under the standing pools of water on each facility). The analysis confirmed the suspected results that the tailings were a relatively sterile, silty sand with little to no organic matter. A very neutral 7.0 to 7.5 pH was consistent with all samples. Calcium was relatively high and no acid generating capability was detected.
Unexpected results were that the barren areas within North Pond 1 were significantly more saline than any of the other areas, the surface few inches of tailings were consistently sand while a clay and silt fraction existed below, and almost all of the copper was plant available. The higher salinity may partially answer the question of why approximately one third of North Pond 1 was barren, while another third was supporting Agrostis alba. It was expected that sandier tailings would be found close to the points of deposition, while progressively finer sized tails would be found as you moved toward the standing pools on each facility. The results indicated this to be true for the tailings down more than a half meter below the surface. However, the surface several centimeters of tailings were consistently sand while finer particle sizes were found below. Wind action had most likely scoured the top several centimeters of clay and silt sized particles away as dust and deposited them elsewhere while the sands remained as dunes.
Elevated copper levels are to be expected in copper mine tailings. At the White Pine Mine the total copper levels vary from zero to about 1,300 parts per million (ppm). The ammonium bicarbonate diethylenetriaminepentaacetic acid (AB-DTPA) method was used to extract plant available copper from the tailings. The results indicated that virtually all of the copper was loosely held and could be available for uptake by plants.
Although some heavy metals (Cu and Zn) are essential for plant growth, it is now well documented that when present at elevated levels in soils they are generally phytotoxic and can ultimately cause the death of plants (Antonovics, Bradshaw & Turner 1971, Smith & Bradshaw 1979). Generally the metals in soluble forms or adsorbed onto clays are most available for plants (Neuman, et. al 1987). In the presence of high levels of organic matter, humic materials and fulvic acids the plant availability of copper is reduced through the formation of strong complexes with organic matter and humates resulting in slow dissociation rates (McBride 1978, EPA 1992, and Davies et. al. 1978). Numerical thresholds for heavy metals in soils above which phytotoxicity is considered to be possible have been suggested. The copper levels promulgated by the United Kingdom are 140-280 mg/kg EDTA extractable (UK DOE 1980). J.J.M. Bowen (1979) suggested that soil concentrations above 250 mk/kg of total copper may result in phytotoxicity. Neuman, et. al 1987 suggested that AB-DTPA extractable copper levels in mine soils from selected western coal mines between 50-210 mg/kg were phytotoxic to plants.
Elevated plant available copper levels cause shortening and excessive branching of the roots. Plants cope with high levels of copper in one of two ways: They can either exclude the copper at the root; or, they can take it up and partition it off in the leaves, stem, roots, or a combination of areas. These mechanisms work well for short periods when levels are low. When the levels are high and/or the plants are exposed for long periods of time, the protection mechanisms can be overwhelmed and the plants will be stunted, chlorotic, or eventually even die after a few years. In actual practice high copper levels can stress the plants to a point where they can no longer tolerate the environmental conditions. It is believed that this was the case with the earlier test plots done in the 60s. When the plants could no longer tolerate the heat, cold, dry periods and physical abrasion from the wind blown tailings, due to impacted rooting systems, they eventually died back.
In almost any direct revegetation project, the organic matter (OM) component of the amendment mixture is generally the highest cost item. Therefore, a search for potential materials was conducted early in the process. In addition to cost, many other factors related to the material are important in making a decision on which material will, ultimately be the best value. The following is a list of factors used to make the decision on the OM for the White Pine Mine.
Initially, biosolids, waste from breweries, yard waste, sawdust, wood chips and paper mill sludge were considered. After careful comparison of all factors listed above, wood chips and wood pulp sludge, which are both waste products of the paper mill industry, were selected. Wood chips are sold in the winter as a fuel, but are disposed in landfills during the summer months. Paper mill sludge was previously being transported to a landfill for disposal. Wood chips provide larger particles, which will break down over time to provide a constant source of OM and carbon. Paper mill sludge has a small particle size and provides an almost immediate source of carbon. The combination of these two materials provided an adequate supply of OM, located within a few miles of the site, which had the desired chemical properties and acceptable regulatory restrictions.
- Regulatory Restriction
- Particle Size Distribution
- Labile and Recalcitrant Carbon Content
- Carbon:Nitrogen Ratio
- Moisture Content
- Handling Requirements/Restrictions
Following the acquisition and review of existing data, the vegetation and soil surveys, and the selection of an OM source, a greenhouse study was designed and conducted to test the initial levels of amendments and plant species response. The greenhouse study was a factorial design with the following variables.
- Organic Matter (dry weight) 0, 1, 3 & 5% (50% Woodchips - 50% Paper Mill Sludge)
- Standard Fertilizer:
- Nitrogen = 44.82 kg/ha (40 lbs/ac)
- Phosphorus (P2O5) = 67.25 kg/ha (60 lbs/ac)
- Potassium (K20) = 44.82 kg/ha (40 lbs/ac)
- Additional Nitrogen for Carbon - Nitrogen Balance = 2.5 kg/tonnes (5 lbs/Ton) Woodchips Applied.
- 14 Species Tested
The 14 plant species to be used were selected based on the following criteria:
- Species observed growing on or near tailings (forbs and grasses only)
- High potential to stabilize tailings
- Known capacity to stabilize sand dunes
- Commercial availability/quantity
- Adapted to tailings chemistry
- Adapted to climate
The following list of species were selected for use in the greenhouse study:
|Species Recommended for Inclusion in Greenhouse Trials
The initial results from the trial were not encouraging. Many of the plants were stunted and chlorotic and production was far below that believed necessary to stabilize the site. The data suggested that the more OM added, the worse the plants grew. Based on the symptoms displayed by the plants, a list of potential nutrient and micronutrients, which could be deficient was developed. Foliar applications of liquid forms of these nutrients were applied and the results indicated that a deficiency was present. Manganese (Mn), Boron (B), Nitrogen (N) and Phosphorus (P) were all found to be deficient. These nutrients are all easily bound to OM. Therefore, although possibly present in adequate quantities in the tailings, when the OM was added they may have been bound to a point where a deficiency occurred. Since the availability of N to plants is directly related to the Carbon (C):Nitrogen ratio, it was determined that our C:N ratio balance also needed further adjustment. When copper was added as a foliar nutrient, all of the plants died. Therefore, it was determined that copper was probably still present at just below phytotoxic levels.
Analyses of the AB-DTPA extractable metals levels in tailings before and after the greenhouse study indicated that only minor reductions in metals levels had occurred. This result was believed to be due to the limited (12 week) time for soil reactions to occur during the study. More positive results reported in the literature were from studies conducted over periods in excess of 180 days. Therefore, we believe metals reduction is occurring, but will take more time than could be simulated in the greenhouse.
|Greenhouse experimentation was used to evaluate the effectiveness of several treatments
A second round of greenhouse trials was run with fertilizer and amendment levels re-adjusted based on the findings of the first study. The results of this study were more promising and provided the expected results of a positive correlation of better plant growth with higher OM levels.
As can be seen from the following table, the mean mycorrhizal infection rate increased as OM was increased. It is believed that mycorrizal innoculum is being provided by the OM, and that conditions for growth of the microorganisms are being improved in the soil. The OM provides a food source and holds more moisture in the soil for consumption by microorganisms. It also allows better aeration of the soil and moderates temperature extremes. Although testing was not conducted to identify and categorize all microorganisms in the tailings, carbon decomposition rates have been monitored. A significantly higher decomposition rate occurs with the addition of OM. This may indicate that the generally improved conditions for mycorrhizal fungi also benefits other soil microorganisms such as bacteria and actinomycetes.
|Effects of Organic Amendment Level on Mycorrhizal Infection Rates
* Values with the same letter are not significantly different at the 0.05 confidence level.
Based on the results of the greenhouse study, a factorial design field trial was developed and installed with the following variables.
- Organic Matter (dry weight) 0, 2, & 3% (50% Woodchips - 50% Paper Mill Sludge)
- Standard Fertilizer:
- Nitrogen = 44.82 kg/ha (40 lbs/ac)
- Phosphorus (P2O5) = 168 kg/ha (150 lbs/ac)
- Potassium (K20) = 44.82 kg/ha (40 lbs/ac)
- Boron = 1.12 kg/ha (1 lbs/ac)
- Manganese = 3.36 kg/ha (3 lbs/ac)
- Additional Nitrogen for Carbon-Nitrogen Balance = 5 kg/tonnes (10 lbs/Ton of Woodchips Applied.)
Those elements shown in bold were changed based on results from the greenhouse study. The OM levels in the greenhouse were 0%, 3%, and 5%. The results indicated that adequate growth could be attained somewhere between 0% and 3%. Over 2,023 ha (5,000 ac) a reduction of 1% OM equates to a savings of approximately $2,000,000, therefore it was decided to test 2% in the field trial. Phosphorus and Nitrogen were increased, and Boron and Manganese were added based on the identified deficiencies. Tilling of the applied organic material into the soil was also specified to bring about a better mixture of grain sizes for plant establishment and trafficability.
The seed mixture for the field trials was based on the results from the greenhouse and on commercial availability of the necessary quantities at economic prices. Species which were not available as seed, such as Ammophila breviligulata (American beachgrass), were eliminated from the trial due to the large scale of the site and expense of hand planting sprigs over an area this large. The final seed mixture used for the field trial is shown below.
Standard Seed Mixture*, 1998 Revegetation, Field Trial, Copper Range Company,
White Pine Mine, White Pine, Michigan
* Seed was obtained from: Granite Seed Company
2 PLS - Pure Live Seed. Pounds PLS/ac may vary depending upon actual seeds per pound for each seed lot.
3 VNS - Variety Not Specified = Common
In addition to the variables shown above, ten different erosion control methods were tested in the field trial. Each method is briefly described below:
- Wind Fence: placed 1.22 m (4 ft) high wind fence 9.14 m (30 ft) upwind of each block of plots, and within plots
- Land Imprinting: used imprinter with 30.48 cm (12 in) wide X 45.72 cm (18 in) long X 10.16 cm (4 in) deep prints over entire plot
- Contour Furrowing: cut 1.22 m (4 ft) wide X 0.61m (2 ft) high furrows across plot at 2.44 m (8ft) intervals
- Dozer Basins: embankment slopes only, cut 3.35m (11 ft) wide X 1.22 m (4 ft) long X 0.61 m (2 ft) deep basins at 3.05 m (10 ft) intervals
- Slag incorporation: 56 and 112 tonnes/ha (25 and 50 tonnes/ac) slag tilled into tailings 15.24 cm (6in) deep
- Windrowing with Slag: slag placed in 0.91 m (3ft) wide X 0.61 m (2 ft) high windrows
- Hardwood Bark Piles: 3.05 m (10 ft) long X 0.61m (2 ft) wide X 0.30 m (1 ft) high (1 cu yd) piles placed at rate of 62/ha (25/ac)
- Soil Binder: M-Binder™ applied at rate of 112kg/ha (100 lbs/ac)
- Surface Mulch: straw placed at 4.48 and 8.96tonnes/ha (2 and 4 tonnes/ac)
- No erosion control method: control
The trial was intended to test not only the effectiveness of each variable and method, but also the practicality and cost of actual implementation. Therefore, large scale test plots of one half acre or more were used so that full sized equipment could be used. It was discovered very early that accessing the tailings with typical heavy equipment would not be practical. Front-end loaders, over the highway dump trucks, standard tracked dozers, and rubber tired farm equipment could not safely access all areas of the tailings. Ultimately, Caterpillar™ “Challenger” tractors, which are equipped with wide rubber tracks, and tandem axle trailers with tracks over the wheels, were required to access the site. All-terrain vehicles (ATVs) were used for personnel and light duty work. A snow cat, which was used to transport seed and other light materials, could access all areas right up to the waters edge, while most of the other equipment had to avoid these areas. In some cases, equipment could travel over an area once, but could not travel over the same area twice without sinking.
|Caterpillar Challenger tractors were used for test plot construction due to their low ground pressure tracks which prevented sinking into the tailings
More Field Trial Results Photos >>
Even utilizing the low ground pressure equipment described above, equipment was stuck quite often. For safety reasons, it was imperative that cable be used to pull stuck equipment out. Chains and especially nylon ropes, have been known to cause fatal accidents when they break and snap back, throwing metal hooks at the operators. Slow, constant pulling pressure, with a cable was the most effective method of freeing equipment from the tailings when stuck. Any method of breaking the suction between the equipment and the tailings, helped immensely.
On-going agronomic monitoring of the test plots has indicated that approximately 2% OM incorporation, accompanied with the fertilizer application described above, produces adequate growth to control erosion. The 3% plots produced more vegetative growth, but did not contain the diversity that the 2% plots exhibited. Therefore, 2% OM was selected as the soil amendment specification for the full-scale work.
Plant species selection is an on-going process due to the differing availability of each species each year. The goal is to have a wide enough variety of commercially available species identified that work well at the site to be able to adjust the seed mixture as the seed market changes.
One interesting note was that the Agrostis alba variety used in the trials did not perform very well. Apparently, the Agrostis alba on-site has become ecotypically differentiated sufficiently to survive, while commercial varieties, developed in other locations, cannot. If this has indeed occurred in the span of approximately 20 years, further investigation could be warranted since it is generally believed that this process takes many more years than this.
Wind fence was found to be effective on a short-term basis in causing entrained sand to drop out of the wind stream .Placing the wind fence approximately 2.89 m (7.5 ft) up wind for every 0.30 m (1 ft) of vertical height worked well for preventing the plots from being buried by tailings. However, the cost of the fence, and effort required to install it, limits its applicability to the most critical areas. In the future, it will only be used to protect new reclamation areas from burial by tailings up wind which have not yet been stabilized, and possibly on the embankments where wind erosion is the most severe.
The trial involving pock-marking the surface with a roller similar to a sheepfoot, referred to as surface imprinting, was not conclusive. As tested here with a relatively small 1.83 m (6 ft wide) imprinter, it was not considered to be practical over the entire site. Although there was evidence that it provided adequate protection to aid establishment, the tailings were mobile enough to quickly fill in the prints. Therefore, imprinting was not selected for final use, but may be considered in the future, if a larger device is identified.
Contour, or tillage, furrowing was not found to be an effective means of stabilizing the tailings. The furrowing provided both a cut area which ponded water and prevented establishment, and a peak or crest which was not stable enough for plants to take hold. Since small areas without plant establishment can “blow out” and grow into larger areas, which are sources of dust generation, this method was not considered for further trial.
Dozer basins were tested on the slopes of the tailings facility embankments. Although relatively effective in slowing and dispersing water flow over large slopes, they did not appear to be very effective when used on loose, sandy textured soils. The logistics of building the dozer basins and maintaining them while revegetation takes place was complicated and would be easier in more competent soils. Dozer basins did not provide significantly better stabilization than other means, and therefore, were not selected for further study or use.
Slag from the smelting process had been stored at the site and was available for use in reclamation. The slag is a dark, glassy material of approximately 2.54 cm (1 in) diameter. Since it was available on-site, and the erodability of the tailings could be reduced by adding a coarse fraction component, slag was included in the trial. However, for any of the slag methods, including incorporation, or placement in windrows, it was found to be very difficult to transport and apply. It is a very heavy material and trucks or loaders with full loads could not access the tailings without becoming stuck. Smaller loads were used to construct the trials, but methods adequate for the large scale project have not been identified. Therefore, slag was not considered for further trial at this time.
Hardwood bark was available as a waste product from the paper industry in the area. Piles of the bark were tested as a means of directing wind above the surface similarly to the slag piles discussed above. The bark was easier to transport out onto the tailings because it was less dense. However, the piles were not found to be any more effective at preventing wind erosion than other means and were more difficult to construct. Hardwood bark has and is still being considered for multiple purposes in the reclamation of the site, such as a replacement for the wood chips in the amendment mixture. However, hardwood bark was not considered for further use as an erosion control method.
Soil binders, tackifiers and soil cements have been used for dust control on tailings for some time. The drawbacks associated with them are related to their longevity and need for repeated applications. They bind the surface soil and are effective until washed out or broken up by traffic. The stronger and longer lasting formulas tend to inhibit vegetation establishment, especially in an already harsh environment. Therefore, in this trial, soil binder was tested as a potential replacement for crimping the straw mulch on plots, which were imprinted or had furrowing installed. This eliminated the need to run a crimper over and possibly destroy the rather fragile erosion control features. In this regard it worked quite well. However, as described above, the imprinting and furrowing were not selected as methods to use in further work. Should a larger scale imprinter be used in the future, soil binder is likely to be used as well.
Straw mulch was applied at a rate of 4.48 tonnes/ha (2 tons/ac) and crimped in as a standard application on all of the plots that were accessible by heavy equipment. A second level of straw mulch, 8.96tonnes/ha (4 tons/ac), was tested as another erosion control method. The higher rate of straw mulch performed the best of all erosion control treatments. However, straw mulch at 4.48 tonnes/ha (2tons/ac) worked second best and controlled wind and water erosion sufficiently for vegetation to become established. Therefore, straw mulch at a rate of 4.48 tonnes/ha (2tons/ac), crimped in, was selected for use in the full-scale revegetation work. In order to prevent dust events from occurring, it is only necessary to direct the wind a few inches above the tailings surface. As shown below, the straw mulch,crimped perpendicular to the direction of the wind, is capable of accomplishing this.
It is possible that a more robust means of controlling erosion may be required for the tailings embankments. The higher rate of straw application, or the addition of a soil binder may be applicable. However, on the practically flat areas of the tailings, the 4.48 tonnes/ha (2 tons/ac) rate has worked adequately, and is the lowest cost alternative identified to date.
Full scale implementation of the revegetation specifications was initiated in the summer of 1999. Approximately 202 ha (500 ac) of North Pond 2 received the “full treatment” specification of the incorporation of 2% OM, consisting of 50% woodchips and 50% paper mill sludge. Another 486 ha (1,200 ac) received a “green manuring treatment” of seed and fertilizer, of which 202 ha (500 ac) also received crimped straw. The green manuring treatment was used to stabilize the tailings until sufficient paper mill sludge could be obtained for the full treatment. When the full treatment is applied to these areas, the application of OM can be reduced by the amount of OM already applied. In 2000, another 81 ha (200 ac) was fully treated on North Pond 2, and 190 ha (470 ac) on North Pond 1 and 53 ha (130ac) on South Dam were aerially seeded and fertilized.
The test plots and the newly installed full scale implementation areas were monitored in the fall of 1999 and the summer of 2000. Although it is early to obtain useful results from the full scale implementation areas, useful data was collected from the test plots. The data has allowed the fertilization rates and seed mixtures to be modified for improved economics and success. Most of the treatments on the tailings embankments have not shown adequate plant establishment to control erosion. Supplemental applications of fertilizer and possibly, more intensive erosion control treatments may be required in these areas. However, further monitoring will be conducted prior to any changes.
|Reclamation species established following full scale implementation
Accessing the tailings has been extremely variable each year and is closely tied to the severity of the winter and spring precipitation. Therefore, initiation of work each year will be based on the preceding seasons weather patterns. Ultimately, it will take many years to determine if the vegetation is totally self sustaining. However, the site has not experienced severe dusting since implementation of the revegetation program. This is partially due to more favorable weather patterns, and to raising the water level in the facilities to keep more of the tailings wet longer into the summer months. However, it is primarily due to the stabilization of the tailings by revegetation. The fully treated areas appear to be self sustaining and the green manured areas appear to be controlling erosion for, in some areas, going on two years now. Although monitoring will continue in order to allow advance warning of any difficulties and to allow maintenance plans to be developed, the tailings are now stabilized to a point where severe dusting is not believed to be the major issue it once was.
Antonovics, J., A.D. Bradshaw and R.G. Turner. 1971. Heavy metal tolerance in plants. Advances in Ecological Research Vol. 7, pgs. 1-85.
Bowen, H.J.M. 1979. Environmental Chemistry of the Elements. Academic Press, New York.
McBride, M.B. 1978. Copper in Soils and Plants, p.25-45. eds. Loneragan, J.F., Robson, A.D. and Graham, R.D. Academic Press, New York,
Neuman, D. R., James L. Schrack, and Larry P. Gough. 1987. Copper and Molybdenum, In Reclaiming Mine Soils and Overburden In the Western United States. Dean Williams and Gerald E. Schuman (eds.), Chapter 10, p 215-232. Soil Conservation Society of America, 7515 N.E. Ankeny Road, Ankeny, Iowa.
Smith, R. A. H. and A.D. Bradshaw. 1979. The use of metal tolerant plant populations for reclamation of metalliferous waste. J. Applied Ecology, Vol. 16, pgs. 595-612.
United Kingdom – Department of the Environment (UK-DOE). 1980. Interdepartmental Committee on the Revelopment of Contaminated Land, Consultation Paper, DOE, 2 Marcham Street, London SW1 3EB.