British Columbia Mine Reclamation Symposia

Waste rock management and environmental monitoring components Reeves, Gerald S.; Thorner, Jim A. 1990

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Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation LINE CREEK ROCK DRAIN WASTE ROCK MANAGEMENTAND ENVIRONMENTAL MONITORING COMPONENTS by Gerald S. Reeves  Senior Development Planner and Jim A. Thorner  Senior Engineer, Environment CROWS NEST RESOURCES LIMITED LINE CREEK MINE SPARWOOD, B.C. Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation  ABSTRACT Crows Nest Resources Ltd. has been operating the Line Creek Project near Sparwood, British Columbia since 1981. The steep mountainous terrain and limited economic opportunities for waste rock management have dictated an innovative approach to mine planning. Rock drain applications at the Line Creek Project have been vital in maintaining the viability of the project. DV2DH.2 revised 900424(GR/jb) Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation 1.0        INTRODUCTION The Line Creek project is located in the southeast corner of British Columbia between Westar's Balmer operations at Sparwood, British Columbia and the town of Elkford. Production began in 1981 and the mine produces both thermal and metallurgical grade coal. Our coal is sold primarily to Korea and Japan and other customers include Europe and the United States. The Line Creek project is a shovel-truck operation scheduled to produce 1.5 million product tonnes of metallurgical coal and approximately 1.0 million tonnes of thermal coal annually at raw coal ratios of approximately 4.3 bank cubic metres of waste per tonne of raw coal. The current equipment fleet is capable of moving 14 million bank cubic metres of waste annually. Since 1987 the mine has been operating in both an Upper and a Lower South Pit as well as the North Line Creek Pit. Not long after commencing operations, the coal market became depressed, resulting in a drastic change to the original project economics. By continuing with the feasibility study strategy of depending totally on the main Upper South Pit for coal release, the mine was clearly not going to be a viable operation by 1989. By proving up and developing other smaller but lower ratio pits and optimizing waste management. Line Creek will be more competitive in today's markets. As a result of the new pit evaluation studies, significant economic improvements will be achieved in cumulative strip ratios over the next five years. The waste management opportunities associated with the pit locations and rock drains greatly improve waste truck productivities. These efforts create the largest cost improvement and are complimented with other team efforts to reduce costs in other aspects of the operation. At Line Creek, waste mining makes up 40% of total operating costs (Figure 1). Haulage costs associated with waste mining have a serious affect on overall viability. A reduction in waste haulage productivity of 10% per year will increase total operating costs by 4%. Over a five year period, this will accumulate to a 20% increase if compounded.  DV2DH.3 revised 900424(GR/jb) Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation By 1989 with the current market conditions and the feasibility plan, it was clear that the Line Creek project would not be viable because the waste haulage productivities decreased at a rate of 10% per year as the basal sandstone was exposed which extended our uphill waste haulage at an 8% grade. The effect of strip ratio was also a major concern as the mine was developing towards a 5.0:1 bank cubic metre of waste to raw tonne of coal ratio by following the upper pit feasibility study. This occurs because one of the coal seams in the Upper South Pit has been totally depleted leaving a large volume of waste associated with the coal released in the Upper South Pit for the next five year period. An increase in strip ratio from 4.3 to 5.0 would mean a 16% increase in operating costs at Line Creek. The gravity of this situation made it imperative that lower ratio coal outside of the Main Pit be developed at greatly reduced waste haulage costs. This presented a very difficult problem considering the limitations in managing waste rock in steep mountain topography with stream flows in the valleys. Considering the rate at which geological data could be accumulated for smaller tonnage but lower ratio pits, a decision was made to provide a Five Year Mine Plan which would reduce stripping ratio and improve waste rock management while meeting or exceeding the environmental and reclamation standards. Expansion plans were also developed beyond the five year period. Mine plans were developed using proven reserves to the year 2000 to provide waste dump and rock drain abandonment positions and provide reclamation requirements. Figure 2 provides a property location map and the relative size of the mining and dumping areas.  DV2DH.4 revised C00424(GR/jb) Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation 2.0        GENERAL STRATEGY Mining in the Lower South Pit began in 1987 releasing metallurgical grade coal to provide an alternate source of supply and blending capabilities with the main Upper South Pit. The main reason for starting the Lower South Pit was that waste management opportunities from this pit provided cost savings compared to the Upper pit. A whole new strategy for managing waste rock from the main Upper South Pit was realized as a result of conceptual waste rock disposal plans from the Lower South Pit in the Line Creek valley. Strategy and timing go together and in this plan certain critical activities must be implemented, outside of normal pit scheduling, at specified times in order for the plan to succeed. The most critical activity is the earliest start time of a major dump from the Upper South Pit over the Line Creek Rock Drain at 1675 metres elevation during 1990. DV2DH.5 revised 900424(GR/jb)   Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation 3.0 ROCK DRAIN DESIGN 3.1 General In a rock drain design, site specific topographic, hydraulic, and mine planning considerations dictate the approach which should be followed. Studies should begin by defining the applicable environmental and water quality standards in effect. The basic components adopted in the design process for the Line Creek project rock drains are summarized in the following section. Flow capacities of the rockfills were determined using hydraulic equations for turbulent flow in rockfill as stated by Leps (1973), which are based on work done by Wilkins (1956). The basic flow equation is:  Upstream ponding is available above all of the proposed Line Creek waste dumps with rock drains and will provide storage of that portion of the flood hydrograph exceeding the mean daily flow. In addition, the rock drain itself will attenuate the peak flows. Hence, the mean daily flow was selected for use as the design flow in all analyses. 3.2 Determination of Stream Hydrology At least four stream flow conditions should be considered in the design of a rock drain. First, the low flow state should be evaluated under natural conditions and the effect of introduction of the rock drain on steady state low flow determined. Second, the project design flood flow should be determined, based on conventional hydrological analysis. The return period adopted for the design flood flow is frequently taken as 200 years. A third flow condition is also of interest: the mean annual flow. If the mean annual flow can readily be transmitted by the rock drain, the possibility of a gradual build-up of water levels upstream of the dump over the long term should be precluded. The probable maximum flood is the fourth flow condition and was considered in our situation when assessing long term stability. 3.3 Waste Rock Properties The anticipated range of rock gradations and other physical properties should be determined at an early stage in rock drain design. Estimations of material properties can be based on available outcrop and drillhole data, combined with data available from existing dumps at the mine site and at other mines in the region, or as reported in the literature for similar rock types and dumping practices. Once the range of gradations of the blasted rock has been estimated the effect of natural segregation associated with dumping practices should be evaluated. End dumping tends to result in the larger, more durable rock rolling to the bottom of the dump, thereby forming a zone of the largest sizes and most competent rock along the base of the dump. A procedure for estimating the degree of segregation from top to bottom of a dump is presented by Nichols (1986). DV2DH.6 revised 90042<XGR/jb) Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation 3.4 Inlet Capacity The capacity of the drain inlet to transmit water is controlled by the dump slope, valley side slopes, dump height, amount and nature of sediments accumulating upstream of the inlet and potential obstructions such as may be formed by debris from landslides and organic materials. In the long term, the possibility that stream alluvium which would normally be transported downstream during the freshet and storm events will completely fill in the headpond above the waste dump should be examined and the impact on long term performance of the dump evaluated. 3.5 Outlet Flow and Slope Design The most important component of the rock drain is the outlet, which should be capable of transmitting at least the 200 year flood flow without compromising the stability of the final dump slope. Design aspects to be considered are the final geometry of the slope, the height of the seepage line predicted to occur on the slope during the flood event, seepage forces at the outlet which could destabilize the slope, and scour forces at the outlet which could undermine the toe. In addition, environmental effects downstream of the dump should be assessed, accounting for the new stream regime following rock drain construction. A rockfill is usually incorporated into the toe region design of the final slope to ensure against undermining of the dump slope. The apron should be constructed to above the level of discharge predicted for the design (200 year) flood. The slope of the apron and size of the rockfill therein should be determined on the basis of predicted flows, discharge velocities and stream gradients, but is normally not steeper than about 5:1. 3.6 Interim Slopes Overall mine planning considerations will dictate whether dumping will proceed in the upstream or downstream direction. Upstream dumping is preferred because it permits construction of relatively flat slopes on the outlet side of the dump and therefore minimizes the potential for failures in the critical zone. However, mine development will frequently require a downstream method of dumping whereby repose angle interim dump slopes will be exposed to periodic seepage pressure associated with flood events. In the absence of a protective apron, introduction of seepage into the lower part of the dump may cause the toe to be scoured and undermine the slope, thus causing the overlying waste rock material to slump. In repose angle dumps, any seepage emerging on the face will result in some degree of failure, the consequences of which must be evaluated by the designers. This necessitates a prediction of the distance that the failed material can flow and assessment of resultant damages. A decision then has to be made whether to attempt to limit those damages through construction of downstream containment structures. Alternatively, it may be sufficient to simply establish a conservative estimate of the distance that the debris can flow and the associated impacts. A safe dumping procedure can then be devised to incorporate monitoring data for stream flows and dump movements so that dump operations personnel and equipment are removed from the operations at a safe time prior to when flood conditions are forecast which could result in a failure contingency. 3.7 Overflow Channel An overflow channel should be considered in the event of future blockage of the inlet to the rock drain, or in the unlikely event that the voids become plugged with fines over DV2DH.7 revised 900424{GR/jb)    Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation time. The function of an overflow channel is two fold: first, it will serve to channelize flow which is not absorbed into the inlet, where it will then have the opportunity to seep downwards through the waste dump into the rock drain. Second, the channel can be designed to direct flow in a controlled manner such that the integrity of the downstream portion of the dump is not compromised during a flood event. 3.8       Construction Aspects A minimum dump lift height of 20 - 30 metres is generally necessary to ensure that natural segregation of sizes occurs, resulting in the formation of a coarse gradation rock drain. In portions of the dump less than 20 - 30 metres high, or where the quality of rock is inadequate for rock drain construction, a manufactured rock underdrain consisting of hauled in coarse, durable rock may be required. Within the part of the dump where the rock drain is generated, a high percentage of the placed rock should consist of good quality, durable rock. To ensure that the coarsest rock sizes are exposed to the flow, portions of the inlet and outlet slopes should be constructed with end dumping procedures whereby the slopes are formed at the repose angle, thus facilitating natural size segregation. DV2DH.8 revised 900424<GR/jb)   Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation 4.0 LINE CREEK VALLEY ROCK DRAIN AND 1675 ELEVATION DUMP 4.1 Plans By developing a rock drain in Line Creek Valley which will carry Line Creek at a maximum 200 year mean daily flow of 37.5 cubic metres per second, a viable operating plan was achieved. The first stages involve building an access road with a 30 metre wide running surface in the form of a rock drain with material from our Lower South Pit to the terrace on Horseshoe Ridge. This will permit us to relocate our coal haulage and property access out of the rock drain area. (Figure 3) It will then be possible to dispose of waste rock from the Upper South Pit by end dumping a 150 metre high lift over the valley surface at an elevation of 1675 metres. The 1675 elevation rock drain will be keyed into the 1530 elevation roadfill initially. The dumping will then proceed at right angles to the keyed in portion in a downstream direction. The rate of advancement will depend on the results of stability monitoring. This 1675 elevation lift will wrap around the south end of Line Creek ridge. The dump will progress up the West Line Creek valley to be keyed in as a flat surface against the previously placed 37° dump slopes on the east side of the valley. This dumping strategy provides a better opportunity to enhance the mine abandonment plan while optimizing haulage costs. The rock drain is shown in cross section in Figure 4. The rock drain design and the stability of the 1675 dump are discussed below. The total area covered by the rock drain will be 84 ha. 4.2 Line Creek Valley Rock Drain Design The Line Creek valley slopes downstream at an overall gradient of about 3%. As the dump is developed in a downstream direction the maximum segregation, and hence flow capacity, will be achieved by end dumping competent waste rock directly onto the face of the dump. It is expected that a layer of 500 mm size or larger boulders will form in the bottom of the drain two metres thick. The overlying rockfill in Zone 2, to approximately 10 metres above the valley bottom, is assumed to be finer - conservatively estimated to have a minimum nominal diameter of 150 mm. The level of saturation required to convey the 200 year design flow of 37.5 m^/s, calculated using the basic equation for flow through rockfill as presented, Leps (1973), is shown in Figure 4 and averages approximately 7 metres above the valley bottom. Unsegregated rock in Zone 3 above the 200 year saturation level is assumed to have a nominal diameter of 100 mm. The theoretical flow capacity of Zone 3 is approximately 80 m3/s. Sections through the inlet and outlet of the rock drain are shown in Figure 5. At the inlet, a wedge of coarse sandstone with a minimum nominal diameter of 600 mm is planned at a slope of three horizontal to one vertical to protect the upstream face from possible slumping following any potential ponding and subsequent drawdown of the water level within the dump. At the outlet end of the ultimate dump (Figure 5), a 20 metre wide berm is planned at mid height to assist in maintaining the stability of the slope. The portion of the slope DV2DH.9 revised 900424(GR/jb) Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation above the berm will be reclaimed to 2:1, but the lower portion will be left at the repose angle. An apron of select coarse sandstone will be placed at a slope of 5:1 in the outlet as shown in Figure 5. Flattening of the upstream face and the lower portion of the downstream slope to less than the angle of repose is not proposed because finer rockfill than is desired for efficient functioning of the rock drain would be pushed into the active drain cross section across the valley floor. Overtime, sand, gravel and other organic debris from the active channel of Line Creek will tend to accumulate at the inlet to the rock drain. This may reduce the hydraulic conductivity of the rock drain in the immediate area of the active flood plan, but is not expected to diminish the overall performance of the inlet because of the large area of the drain available. Up to 18,000 m2 of area is available on the upstream face of the rock drain, compared to only 1600 m2 of area required to conduct the 1:200 year flow through the rock drain. The excess area will ensure that through-flow is maintained even if part of the drain entrance in the active channel becomes blocked with sediment or organic debris. Up to 30 metres of head is also potentially available to drive the flows into the drain. In the unlikely event that the inlet to the drain becomes plugged, an overflow channel described below will serve to direct water from the side of the dump into the drain. As the rock drain will be in place for perpetuity an assessment of the impact of floods exceeding the one in 200 year event was given consideration. To do this an estimate of the probable maximum flow (PMF) had to be generated. This was derived from the probable maximum precipitation that can be expected from the largest rainstorm that has occurred near the mine. On this basis, a flow of 300 cubic metres per second was derived from a 48 hour precipitation of 480 mm. The level of saturation within the dump would rise sufficiently to cause some downstream face slumping. The extent of the regression, however, would be contained within the 20 metre wide berm. As a PMF would create natural erosion and flooding, limited damage to the rock drain is considered acceptable. Also the overall stability of the rock drain would remain intact during a PMF event. 4.3       Overflow Channel An overflow channel (Figure 6) and rock-lined spillway has been conceptually designed and sized. The capacity of the channel is designed for the 1 in 200 year mean daily flood flow of 37.5 m2/s. This capacity has been provided, although the rock drain can easily pass the 1 in 200 year flow within seven metres of the valley floor. The channel would serve as a contingency overflow when the mine is fully developed and abandoned. In the event of long term plugging of the voids in the rockfill, the overflow will channel flow along the east side of the dump to the spillway. A settling basin will dissipate the energy of the flow before being returned to Line Creek downstream of the rock drain. A plan view of the Rock Drain and West Line Creek dumps is provided in Figure 7.    DV2DH.10 revised 900424(GR/jb) Fig 6Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation  Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation 5.0 ROCK DRAIN MONITORING The monitoring program for the rock drain has been designed to ensure any stability or environmental impacts are recognized immediately. As well as short term concerns, the monitoring program will address issues that have been raised about the long term performance of the rock drain. The program consists of the following: 5.1 Stream Flow Continuous recording dataloggers are installed at the drain inlet and outlet, during the ice free season. Concrete stream gauges have been constructed at these locations and the datalogger probes are installed in monitoring wells and record water depth of flows through the gauges. The recorded depths will be converted to flows using stage-discharge data developed at each gauge location. See Figure 8, Stream Gauge Installation. The primary objectives of the flow monitoring program are to establish the flow rate relationship between the inlet and outlet of the rock drain allowing assessment of flow attenuation provided by the rock drain and any changes on flow through the rock drain overtime. Changes may indicate rock degradation, void plugging and/or water impoundment within the drain. The flow data collected will also be utilized in conjunction with piezometer and sediment data. The stream gauges have been constructed to remain intact and provide a constant stream cross section during high flow events which should allow us to assess the rock drain performance under high flows. Also dye traces, with a florescence dye, will be performed to build a relationship of the water velocity through the drain over time and assess any changes. 5.2 Water Level Within Drain A row of pneumatic piezometers have been installed across the valley bottom in the base of the rock drain. This row of piezometers consists of nine (9) pressure transducers, layout as indicated on Figure 3. The transducer lines run back to a remote station where readings can be obtained. The readings give us water pressure within the rock drain at each transducer. The piezometer data will be used to assess changes in water levels within the drain over time, assess performance of the drain under high flow events and identify any stability concerns at the outlet due to high water levels. 5.3 Inlet Pond, Water Elevation A staff gauge has been installed just upstream of the inlet to the rock drain. The scale on the gauge was zeroed at the original stream bed elevation at this location. The gauge rod itself is a heavy walled steel pipe set approximately three meters into the original stream bed so it will remain resistant to movement from its original position. The staff gauge will be used to assess changes to the inlet pond water elevation over time under various high flow events. Also the gauge will be used to measure the accumulation of material such as sand, gravel and other organic debris expected to be deposited at the inlet from the active channel. This data will be used to assess the long term hydraulic conductivity of the inlet to the rock drain. DV2DH.I1 revised 900424(GR/jb) Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation  Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation 5.4 Bedload Movement, Profile Survey A baseline elevation survey was performed at the upstream and downstream ends of the rock drain in the Line Creek channel. The survey at the upstream end consisted of 15 cross sections which encompass the total stream area where the 1 in 200 year flood pond is expected. The survey at the downstream end consisted of 4 cross sections just downstream of the drain outlet and a centerline survey from the outlet to the culvert road crossing. Annual surveys will be performed after freshet, the main time of bedload movement. Bedload infill data at the drain inlet will be used to again consider the effects of material deposited at the inlet. Data collected on bedload depletion, expected at the outlet, will be used to assess any channel stability concerns downstream of the rock drain and any potential depletion of spawning gravels used by migratory Bull Trout downstream of the culvert road crossing. 5.5 Bedload Movement, Particle Size Sampling Suspended sediment grab samples are taken at the inlet and outlet area and analyzed for particle size. The samples are taken at various stream sections during freshet as flows increase. Also McNeil core samples have been performed at various sites upstream and downstream of the rock drain on Line Creek and on Line Creek downstream of the confluence of South Line creek and a baseline report prepared. Annual core sampling will be performed. The objectives of the suspended sediment sampling will be to record any changes in sediment particle sizes between the drain inlet and outlet and assess if the changes indicate any rock degradation or rock void plugging within the drain. The data collected with the core sampling program will be used to assess any bedload changes downstream of the culvert road crossing on Line Creek and in particular on Line Creek downstream of the South Line Creek confluence and assess any impacts on the spawning gravels used by migratory Bull Trout in this portion of stream. 5.6 Suspended Sediments, Nutrient Monitoring Suspended sediment grab samples are taken at the inlet and outlet of the rock drain. Sampling conforms to our Waste Management Permit and occurs generally weekly during freshet and rock drain construction activities, monthly otherwise. The samples are analyzed for total suspended solids, turbidity, PH, total nitrites, nitrates and ammonia. Also a baseline report on nutrient loading has been prepared. The objectives of this sampling is to assess sediment and nutrient levels and maintain these within our Permit objective levels. Waste Management Permit levels are: − PH, no change − nitrate, less than 40 mg/l − nitrite, less than .02 mg/l − ammonia, less than 5.68 mg/l − turbidity, not more than 5 NTU's, above natural value − TSS, not more than 10 mg/l or not more than 10% above natural value, whichever is greater DV2DH.12 revised <W0424(GR/jb) Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation 5.7 Stream Temperature Monitoring Continuous water temperature recording dataloggers are installed: (a) on Line Creek at the rock drain inlet and outlet (b) downstream of the confluence of Line Creek and South Line Creek (c) on South Line Creek upstream of the Line Creek confluence. A baseline report on water temperatures within Line Creek prior to rock drain construction has been prepared. The data will be used to review any changes overtime the rock drain is having on water temperatures and assess any impacts this change may have on downstream fisheries in Line Creek. 5.8 Rock Drain Construction Quality Control Rock used in the various sections of the rock drain must meet certain specifications for durability and size. To ensure this select rock will be used from specific pit and dump areas when required, ie. construction of low level sections where adequate free dump height can not be obtained, the following measures are taken. Hammer hardness testing of select rock is performed. Operations personnel, involved with excavation and placement of rock, are trained. High dumping of waste rock is utilized whenever possible to ensure the largest and most durable rock forms the base zones of the rock drain. Objectives of our quality control procedures are to ensure the rock drain is constructed as per design specifications. 5.9 Dump Stability Dump stability monitoring will follow methods as per our existing rock waste dumps. These include extensometer, visual inspection and survey continuous over dump construction coupled with periodic engineering consultant review. The objectives of this monitoring are to maximize dump stability by using construction techniques developed on previous dumps and identify any potential waste dump instability as soon as possible and take corrective measures. Should an incident occur which impacts the water quality of Line Creek a contingency plan has been developed to minimize impacts and is outlined under Contingency Plan. The extensive monitoring program we have undertaken wil be performed as a joint effort of the Environment, Engineering and Mine Operations Departments at Line Creek. DV2DH.13 revised 900424(GR/jb) Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation 6.0 CONTINGENCY PLAN 6.1 General In the event of a dump stability concern that could lead to a water quality problem, the following plan will be put in place: a) Dumping will be halted in Line Creek Valley and an alternate site will be used. b) A stability assessment will be carried out to determine the appropriate action plan. E.G.: i. Slower dump advance to allow more consolidation time. ii. Low level lift wrapping in front of dump face to contain toe bulge. iii. A combination of other measures depending on the specific case. c) If required the attached Water Quality Contingency Plan for sediment control will be implemented. 6.2 Water Quality Impacts The objective of maintaining water quality in Line Creek downstream of the Rock Drain is to minimize potential negative impacts on fish populations below the confluence of Line Creek and South Line Creek. The ability to remove suspended sediments from Line Creek that may occur as a result of Rock Drain development can minimize downstream sedimentation potential at critical times during the life cycle of Bull Trout using Line Creek for spawning and rearing. Crows Nest Resources Ltd. proposes to upgrade the existing unused West Line Creek Sediment Ponds to receive sedimented flows from Line Creek for abatement prior to release back into the stream system. The critical period for ensuring minimal sedimentation occurs in the Line Creek mainstream below South Line confluence is from early September to early May. This period covers Bull Trout spawning and egg incubation, and is characterized by the lowest annual stream flows. Using the Sediment Ponds in conjunction with flocculant addition capability during this period should provide adequate opportunity to minimize fishery impacts that could result from excess sedimentation. Sampling to determine when to activate the contingency plan will be undertaken on Line Creek at the confluence with South Line Creek, recognizing that most fishery values are below this point. The precise suspended solids levels in Line Creek during the critical period for Bull Trout (early September to early May) that will negatively impact the fishery after dilution with South Line Creek have yet to be determined. When this threshold value has been determined, a sampling method that yields immediate values will be developed. In light of the intense monitoring of dump development that will be undertaken to control potential failure possibilities, it is anticipated that the risk of sedimentation that could negatively impact the downstream fishery is low. Upgrading of the Sediment Ponds to enable a short response time should the need arise will involve preparation of an inlet channel through the existing haul road and installation of a gated control culvert that can be opened as required. A control berm will be constructed in the active Line Creek channel just downstream of the inlet to the control culvert. The berm will be constructed in such a manner that flows, in excess of 1.3 m^/S, will spill over the berm and continue DV2DH.14 revised 90042 (GR/jb) Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation down Line Creek. This is required to protect the Ponds from being damaged in an extreme flood event. The flow of 1.3 m^/S is the predicted 1 in 10 year maximum mean daily flow for the early September to early May period. The cell dykes within the pond itself will be modified to ensure stability under anticipated flows. It should be repeated that use of this pond as a contingency would occur in response to conditions that could negatively impact the downstream Bull Trout fishery during the critical low flow period specified. 6.2       Fisheries Impact Mitigation Construction to accommodate the haul road relocation associated with development of the rock drain on Line Creek involved realignment of the lower 150 metres of South Line Creek, as well as 380 metres on Line Creek itself. The areas of stream realignments are described as follows: (see Figure 3) a) The section of Line Creek immediately upstream of the road-crossing culverts, was modified to direct Line Creek squarely into the culverts under the new haul road. No enhancement activities will be undertaken on this section of stream, since it is believed that fish will not access through the culvert to the short channel length remaining between the crossing location and the downstream face of the Line Creek rock drain. b) Downstream of the road-crossing culverts. Line Creek was realigned to position the stream setback from the new haul road. The new channel is approximately 330 metres in length, which is essentially the length of the old channel being displaced. Because migratory Bull Trout have been recorded this high up on Line Creek, the new channel will be enhanced to provide spawning opportunity for migrant adults and rearing habitat for juvenile Bull Trout. c) The 500 metre realignment of South Line Creek replaces the lower 150 metres at the mouth of South Line Creek. The resulting gain of 350 metres of channel also reduces the gradient from 3.3% to 2.4%, and provides significant opportunity for habitat enhancement for Bull Trout use. This is in an area of stream that previously provided negligible spawning and rearing capability. These stream realignments, and the subsequent habitat components that are incorporated into them, represent the initial activities related to the mitigation commitment that formed part of the Line Creek rock drain submission. The structures incorporated are proven techniques for stream rehabilitation, and will focus on migratory Bull Trout as the target species. Channel and structure construction was performed "in the dry", and water was introduced through the new channel during the August 15 to September 5,1989 window, which on Line Creek represents the period after cutthroat fry have emerged from the gravels, and prior to any Bull Trout egg deposition. The other "window" for additional work or modifications to existing structures would be in late April and May, just prior to freshet. Although the channel design was based on the hydrology of this specific stream, regular monitoring will be done to evaluate the effectiveness of the enhancement work in terms of both hydraulic stability and fisheries capability. An ongoing monitoring program is an integral part of the overall stream enhancement strategy and will identify modifications or structure upgrading that may be required. The detailed enhancement measures to DV2DH.15 revised 900424(GR/jb) Proceedings of the 14th Annual British Columbia Mine Reclamation Symposium in Cranbrook, BC, 1990. The Technical and Research Committee on Reclamation be incorporated into this stream realignment program will be subject to ongoing review with the Ministry of Environment, Regional Fisheries Biologist. ACKNOWLEDGEMENTS Appreciation is extended to the Management of Crows Nest Resources Limited for permission to prepare and submit this paper. Crows Nest Resources Ltd.'s managerial and technical staff have been extensively involved with developing and monitoring waste dumps and rock drain applications at the Line Creek project. Assistance with hydrological aspects of the rock drain designs was also provided by Mr. M. Thompson of Nanuk Engineering Ltd. REFERENCES Leps, T. M. 1973 Flow-Through Rockfill in Embankment - Dam Engineering (Casagrande Volume), J. Wiley & Sons Nichols, R. S. 1986       Rock Segregation in Waste Dumps. Proceedings of the International Symposium on Flow-Through Rock Drain, Cranbrook, September Wilkins, J. K. 1956         Flow of Water Through Rockfill and its Application to the Design of Dams, Proc. 2nd Aust. - N.Z. Soil Conference Claridge. F. P., Piteau Engineering Planning for Survival, International Symposium on Mine Planning and Equipment Selection 1988 DV2DH.16 revised 900424(GR/jb)  

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