British Columbia Mine Reclamation Symposia

Water quality and mine process effluent 2010

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Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 187 WATER QUALITY AND MINE PROCESS EFFLUENT F. Hodgson Pollution Control Branch Ministry of the Environment March 18, 1977 Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 189 WATER QUALITY AND MINE PROCESS EFFLUENT Paper Presented to the Mine Reclamation Symposium, 1977 Vernon, B.C., March 18, 1977 The speakers before me have covered the problems associated with reclamation and have outlined many of the techniques that have been used and are being used to solve them.  One of the principle reasons for spending millions of reclamation dollars is to protect the lakes, rivers and streams that are so often located practically on the doorstep of the mine. There are many regulatory requirements that have to be satisfied and yet each is the result of public pressure exerted upon our legislators and their response to this pressure.  These all have the effect of increasing the cost of bringing a property into production but many of them are necessary if we are to preserve our environment. Now while the large mining complex as opposed to the small mine is usually on a more solid financial foundation and is better able to cope with such costs as reclamation and pollution control, it also brings with it a much larger potential for damage to the environment. Previous speakers have dealt with the acreage involved in reclamation of waste dumps and tailing ponds.  I have been asked to speak on water quality and mine process effluent. From the point of view of protecting the receiving environment, mine process water must include tailing water, tailing pond seepage, mine drainage and runoff from the mine-mill area. Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 190 In British Columbia, we are fortunate that, notwithstanding the fact that our terrain is rugged, most of the mines have installed tailings impoundments with a recycle of supernatent back to the process. However, this does not completely eliminate concern.  These plants are pumping up to 20 million gallons of water per day into the tailing pond.  This water may be carrying up to 40,000 tons of solids or 30 tons per minute.  The water surface behind the dam is a hundred acres or more. A break in the tailing line or a breach of the dam can be serious not only from a siltation point of view but also from the combined toxic effect of dissolved metal ions on the biota in downstream water. I have reviewed the sampling results of some 30 odd mines listed in our computer files and with few exceptions most of these mines are meeting Pollution Control Branch Level A objectives or better (that is on an average value) in the tailing discharge when the principle dissolved metals are considered.  There are some results that exceed P. C.B. requirements; however, there has not been sufficient data accumulated to determine, during this analysis, whether or not they are erratic values or are numbers that represent non-compliance with permit conditions. Test results from one property, where we have been able to accumulate enough data to do a reasonable analysis, is summarized in Table 1. While the illustration may not be an ideal textbook case, it does indicate the wide variation that occurs when the maximum, minimum, 50 percentile and 90 percentile are compared (90 percentile means that 90 percent of the test results are equal to or less than the number listed) The determination of, say, the 90% percentile or the 95 percentile can be a useful tool especially at those properties when permit limits are being crowded. Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 191     Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 192 One of the toughest problems that faces the environmentally conscious operator is to be blessed with a massive sulphide ore body.  This presents problems in both the short term and the long term.  Almost invariably drainage from the mine becomes acid carrying a load of dissolved metals and in a very few years the tailing pond becomes acidic also.  Table 2 indicated the degree to which metal ions can build up in massive sulphide tailings supernatant.  It should be noted that the values shown here are not high when compared to similar tailings ponds in other parts of Canada or the world. So far, we have looked only at the short term. Acid drainage from sulphide tailings can continue for literally hundreds of years unless the acid consuming capacity exceeds the acid producing capacity of the whole tailing mass.  If this balance is not present when the tailings are deposited, there are few options left.  Reclamation of the surface to prevent the entry of water and oxygen is one alternative.  Another is to treat the seepage until acid generation is completed. One problem that faces the environmental regulatory agency is the small operator.  The small mine has in the past, kept many people employed and out of the soap line.  At the same time, he has created his share of pollution as we understand it today.  In some cases, the destroyed areas have healed; however, with the increased encroachment of remote areas by our ever-growing population, and the mobility of our people, even temporary destruction of the environment can not be approved.  On the one hand, the agency has no desire to exclude the small mine from going into production.  On the other hand, we must insist that the environment is not damaged. Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation     Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 194 Table 3 shows the type of monitoring that we are getting from a typical 50 tpd operation. This may be a good plant from the production standpoint; however continued operation at the levels indicated will soon have a deleterious effect upon aquatic life. The Pollution Control Branch with the help of its computer system is attempting to follow trends in the quality of the tailing pond water systems which might develop into problems in the future. By way of illustration, dissolved molybdenum in the tailing pond supernatent at a large copper molybdenum mine (Table 4) has progressively risen in the last few years.  It is interesting to note how this increase has also been reflected in the monitoring well downstream of the tailing dam and in the creek downstream of the well. Monitoring of the second creek upstream of the tailing dam serves as a control point.  The level of the molybdenum in this creek has not risen. Should a trend such as is illustrated here continue, whether we are tracing moly, copper, lead or some other ion, from a mill discharging 30 to 40 thousand tons of tailings per day for 20 to 25 years, the problem becomes enormous. One of the concerns at this plant is that the levels of dissolved molybdenum will continue to rise in the downstream creek, even if a large portion of the seepage water is returned back to the impoundment, since it is practically impossible to collect and return all of it. Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 195    Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 196     Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 197 Table 5 shows the increase in the levels of dissolved sulphate in the same monitoring well discussed in the previous table.  As shown on the graph, the levels of dissolved sulphate has increased in the last few years.  The numbers shown here are not cause for alarm but if the trend continues, another very serious problem may arise. One possible explanation for part of the increase could be due to the fact that sodium hydrosulphite is used as a milling reagent. However, we are finding that the sulphate levels are rising in a number of other mines where the same reagent is not used. A few years ago, many of us were of the opinion that at a well-run mill, reagents with few exception, reported with the concentrates and thereby became someone else's problem.  In addition, those that were discharged into the pond rapidly degraded.  Within the last few years, we have found that some of these reagents, or their daughters, are quite persistent and are detectable in seepage water for at least two years after their use has been discontinued. There is no sound data at this time to indicate that they pose any threat; however, more research is required in monitoring for reagents to determine their effect on the receiving environment. I would now like to turn to the problems associated with what is commonly referred to as suspended solids.  Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 198 OPEN PIT COPPER-MOLYBDENUM MINE-MILL  VARIATIONS IN THE AVERAGE LEVELS OF DISSOLVED SULPHATE (IN mg/1) MONITORING WELL DOWNSTREAM OF THE TAILINGS DAM  TABLE 5 Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 199 We are at a stage in our mining history when there is an increasing demand for coal, A number of large properties are scheduled to go into production and these are concentrated along a limited number of watersheds.  The best example of this is the Elk River and its tributaries where there are three operating companies and possibly three more properties scheduled for production in the near future. Generally, the rocks associated with coal production are much more friable than those in hardrock mines so that we are not only dealing with the tailing impoundment but rather the whole disturbed area. Natural comminution will continue under our British Columbia seasonal changes at a much higher rate than is normally encountered at a base metal property.  Saturation by heavy rainfall and subsequent slope instability resulting in mud slides has occurred on a number of occasions recently and almost invariably some of the fine material has entered a water course which should be capable of supporting a fish population. Accumulated dust and fine debris from the mine operation, mine roads, plant site, tailing area and plant spills appear in runoff and freshet every year. Previous speakers have dealt with reclamation methods.  It must be emphasized that reclamation is an extremely important aspect for the protection of downstream waters at all mining operations and particularly around soft rock mines. In the following paragraphs, I will attempt to deal with some of the effects of water pollution caused by abnormal quantities of sediment entering a water course.  There is a wide variation in the findings reported, but the end result will be the same whether the contaminated discharge originates at the end of a pipe or is runoff from a waste dump or a mine road. Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 200 To simplify the preparation of this section, I have extensively used a paper prepared by O. E. Langer who was with the Federal Fisheries and Marine Services before joining the staff of the Environmental Protection Service Pacific Region.  Dr. Langer1S paper is entitled "Effects of Sedimentation on Salmonid Stream Life." In the introduction, Dr. Langer states "Sediments have always been present in British Columbia streams and since the last Ice Age have played an important role in the development of streams and stream life.  Large amounts of sediments are presently carried by natural processes into many of our streams.  This process is, of course, very active in watersheds that are geologically young, whereas, the more stabilized watersheds have streams that are extremely sediment free during all or at least a portion of the year." While material of any size and shape may be transported or pushed into a water course, stream sediment is generally con- sidered to be material less than 4 mm in diameter.  It is made up of clay - minus 2 microns, silt - 4 to 62 microns, sand - 0.1 mm to 1 mm and fine pebbles - 2 mm to 4 mm. The first level of the aquatic food chain are the green plants, often referred to as periphyton, and the macrophytes which are attached to the stream bottom.  They require sunlight for growth and any increase in turbidity in the stream will reduce the total amount of photosynthetic activity.  If the turbidity Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 201 persists, the entire plant community may be significantly reduced.  One study group indicated that aquatic plants cannot be expected to survive if exposed to less than five percent of the light incident on the water surface over periods exceeding seven consecutive days.  Whether this means at all times or at critical stages during specific growth cycles, I am not certain but in any event five percent represents approximately half the light that will reach the bottom through six feet of clear water.  The larger sediments, which may appear as suspended solids or moving bedload in the stream, and particularly the more angular sediments originating at a mining operation, will create streambed scouring. When the stream's hydraulic energy cannot maintain the sediment load, deposition will result and smothering of benthic life will occur.  Secondly, a mobile substrate travelling along the stream bottom does not provide sites upon which plants can fix themselves and therefore prevents growth. Second level or benthic and planktonic invertebrates which graze on the algae or feed by filtering organic detritis are also affected by the presence of silt in the stream.  They lose their natural food, i.e. algae, their hiding sites are removed or blanketed and their feeding organs are clogged or abraded to the point where they starve. Fish are also affected by sediments in the stream.  Burying of organic material by sediments settling on the stream bottom deprives fish such as minnows and suckers of their food source.  When the turbidity becomes excessive, it appears that fish are unable to Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 202 sight their prey and therefore are unable to eat.  In the case of young fry that normally travel at night and hide by day, destruction of hiding areas among the gravel and boulders forces them into open water where they are susceptible to predation. Filling of the larger pools ruins the resident and rearing areas of larger salmoids. The biologists tell us that the adult salmonids deposit their eggs in clean gravel riffle areas.  Percolating water is required for oxygen and the removal of metabolic waste.  Any reduction in the permeability or blockage of the interstitial spaces due to siltation has a pronounced effect on survival.  For instance, (and I quote from Dr. Langer's paper here) five percent composition of silt and sand in the gravel had a minimal effect, whereas a 10% composition of these fines in gravel reduced survival of eggs up to 50 percent.  Since many normal streams can have approximately 15 percent sands and silts in their spawning gravels, any increase in these fines can have disastrous effects on egg survivals, (end of quote). Gravel beds form efficient filters.  The flow velocity within the gravel bed is lower than that of the river, and when this is combined with the small fall distances involved, even the very fine particles can be entrapped.  Fine silt or clay, at 5 microns in diameter and with a fall velocity of 0.00223 cm/sec at 2O0C, theoretically will not settle in the mainstream but will be deposited in the gravel bed.  Add to this any abnormal stream bedload migrating over the gravels and clogging rapidly takes place. Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 203 Many people have carried out research on siltation of spawning beds.  In 1970 Langer planted chum salmon eggs in a section of the Coquitlam River upstream and downstream of a known sediment release and in a clean tributary nearby.  Regular measurements of suspended sediments and subgravel oxygen levels were made.  As can be seen in Table 6 a small increase in suspended solids reduced the subgravel oxygen content and the survival rate. The effects of a high concentration of suspended solids (20,000 rng/1) is reported to have caused serious fish mortality even through the exposure was only for a short term.  For example, a Rocky Mountain white fish kill occurred in the Shuswap River when the sluice gate was opened below a B. C. Hydro dam.  Suspended solids levels in the river reached 30,000 mg/1. In another paper, it was reported that gill damage and mortality occurred in rainbow trout after a ten-day exposure to concentrations of suspended solids ranging from 270-810 mg/1.  At the Pollution Control Branch, we have noted from 96 hours bioassay results, carried out in response to permit monitoring requirements, that there is an adverse affect on test fish when high concentrations of suspended solids are present in the test solution; however, no hard numbers have been established to date. Table 7 shows the progression of increase due to suspended solids in a water course running near a coal mine complex.  This plant dis- charges its tailing into an impoundment from which there is no over- flow.  The suspended solids appearing in the water are originating from around the mining areas and the plant site.  Average flow in the river near the property is approximately 100 CFS at this time of year. Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 204       Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation      Proceedings of the 1st Annual British Columbia Mine Reclamation Symposium in Vernon, BC, 1977. The Technical and Research Committee on Reclamation 206 Various approaches are used by regulatory agencies in setting guidelines and standards for the protection of receiving waters. The British Columbia Pollution Control Branch limits the concentration of suspended solids in a discharge to 50 mg/1 while Environment Canada requires 25 mg/1.  The State of Oregon allows releases to match background levels up to 30 Jackson Turbidity Units but the release cannot elevate background levels by more than 10%.  The U.S. Environmental Protection agency recommends that settleable and suspended solids should not reduce the depth of the compensation point for photosynthetic activity by more than 10% percent from the seasonable established norm for aquatic life.  As more is learned from ongoing research, these criteria or objectives, without doubt, will be modified. It is the policy of the Pollution Control Branch that mine tailings will be impounded.  Deviation from this policy is allowed only after detailed study has been carried out speci- fically outlining the possible effect on the receiving environment.  However, the impoundment of mine tailings and control of seepage is not sufficient by itself.  The problems associated with erosion and runoff control must be addressed. Erosion will take place where there is an exposed surface of unconsolidated material and the debris released will find its way into the nearest water course. This paper has attempted to illustrate some of the findings and concerns of the Pollution Control Branch as they relate to the discharge of waterborne contaminants from the mining industry in British Columbia. The Branch sees reclamation as a very important part of pollution control but all reclamation must not be deferred until the final stages of an operation.  It should begin on disturbed areas around the Construction camp and continue on every unused piece of disturbed surface until the whole area is stabilized. 

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