This report is the second volume of a study on placer mining settling pond design. The first volume, 'Design Principles', reviewed methods and criteria for settling pond design and identified field research needs. This volume outlines the methodology of a demonstration project that generated settling pond design data.

Under existing regulations, the discharge or effluent from placer miners¿ settling ponds must meet certain standards for the amount of clay and silt in suspension (suspended solids) and/or the amount of material settling out (settleable solids). Previous research indicates that manufactured flocculants could help miners meet these standards. Flocculants enable particles within water to contact each other and agglomerate to form larger particles which will settle out more rapidly. However these manufactured flocculants are expensive and may deposit foreign (deleterious) materials in the discharge waters. Based upon prior government research, it appears that volcanic ash might act as a natural flocculant. Seven samples of volcanic ash were collected from various sites in the Yukon which were close to active placer mining areas. The samples were dried, sieved and analyzed to determine their characteristics. The ashes were found be quite different in grain size and possible source. Lab testing concentrated on two samples of ash and sediment from the Big Creek Area (west of Carmacks). A series of tests were completed on the sediment samples, with varying amounts of ash being added. Readings were taken initially, and at 1 hour and 24 hour intervals to obtain the levels of material in suspension (suspended solids) and the measure of light penetration through the sample (turbidity). The objective of adding a flocculant (in this case, volcanic ash) was to decrease the amount of material in suspension and increase the amount of material settling out. Preliminary results from this study indicate that the addition of volcanic ash (in amounts of 1 to 16 grams per litre) to sediment samples appears to be successful in decreasing the amounts of material in suspension and increase the amount of material settling out.

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Under the topic of information needs for mine closure and abandonment, the MPERG priorities for funding in 2009 included an investigation of the use of bioremediation as a treatment option for active and abandoned mine drainage. From the 2009 MPERG call for proposals: “The use of various “passive” treatment technologies is being proposed as a possible panacea to provide efficient, cost effective treatment of pit water and metal bearing water discharges. The long term effectiveness of these treatments in a northern environment needs to be investigated.” Passive treatment of some kind has been considered for many years due to its appeal in comparison with mechanical-chemical treatment plants which are now required to operate almost in perpetuity at many closed mine sites. An observation that makes bioremediation so attractive are the many natural analogues observed around mine drainages that naturally attenuate or otherwise reduce metals burden in mine drainage without apparent harm to the host aquatic ecosystem. These include fen-bogs, swamps and other wetland structures which renovate mine drainage; effectively removing and in many cases sequestering contaminants. The original term “wetland treatment” has given way to “passive treatment” and/or “biological treatment” in recent years.

In May 2003, the proposal for this project was submitted to the Mining Environment Research Group (MERG). At that time Nevada Pacific Gold Ltd. (NPG) was in charge of water treatment operations at the Elsa Property, the location for this project. Subsequent to approval of the MERG project, on June 11, 2003, NPG terminated its option to purchase the property, thereby dissolving its previously accepted responsibility to act as the agent of the Yukon Territorial Government (YTG) to maintain the water treatment systems and monitor effluent water quality at various locations of the property. As of June 11, 2003 YTG assumed direct responsibility for care and control of the site. YTG entered into a contribution agreement with the Nacho Nyak Dun Development Corporation (NND DC) to provide care and maintenance services. Access was retained by the NND DC to provide technical management of the project. ACG proceeded with MERG project activities, conducting desktop research and collecting baseline soil and water quality samples in July. On September 2, 2003 YTG was formally made aware that as a result of the July field inspection under MERG, ACG was of the opinion that the flow from the Galkeno Adit was likely reporting directly to fish bearing waters. Various Yukon and Federal Government Departments and agencies including the Department of Fisheries and Oceans, the Department of Environment, Water Resources, and Energy Mines and Resources met on September 5, 2003 to discuss the situation. As a result of the meeting, YTG decided to redirect the Galkeno 300 flow via pipeline into the forested dispersion area that it previously occupied.

Wetlands have been used for decades in the treatment of municipal wastewater (sewage) in many parts of the world. Since the 1980s, wetlands have been used in the treatment of acid mine drainage, usually resulting from coal mining. Recently, natural and constructed wetlands have been researched and utilized for the removal of metals from mine drainage. Most of these wetland treatment systems have been designed and used in temperate climatic areas where permafrost, extreme minimum temperatures, and limited plant productivity is not a great concern. There is interest in northern regions on the possibility of the application of wetlands as a passive treatment system for metal contaminated mine drainage. A research program investigating this possibility was initiated in the summer of 1995 in the vicinity of the United Keno Hill Mine property in central Yukon. A pilot wetland treatment system was constructed in May 1995 near the Galkeno 900 adit to determine whether it could improve the quality of its discharge. Sedges (Carex aquatilis) were obtained from a local natural wetland unaffected by any mine drainage and planted in the plot. After the plants were allowed to establish, untreated mine drainage was introduced to the wetland. Monitoring of the wetland continued for one season. Initial results showed that treatment within the wetland reduced concentrations of zinc, cadmium, manganese and nickel. Sulphate reduction in the sediments and formation of insoluble metal sulphides appeared to be the primary process responsible for their removal. In 1999, further investigations were completed on this pilot project and on some of the natural wetlands which receive untreated mine drainage. Due to insufficient volumes of water flowing through the examined wetlands, they could not be fully evaluated as to their performance in the treatment of waste water. However, sediment analyses showed that metals had been attenuated. The colonization of the transplanted sedges (Carex aquatilis) in the constructed wetland was evaluated. Successful growth and propagation was apparent. These local sedges appear to be a hardy species capable of withstanding transplanting, and appear to thrive with a minimum of effort. Metal uptake in plant tissues was also examined. Low levels were documented throughout the study area with the exception of high zinc concentration in sedges that were collected from the No Cash wetland. As Carex aquatilis, the dominant sedge found in the local wetlands, is generally unpalatable to herbivores, the low and incidental levels of metals found within the tissue of the sedges, poses little environmental concern. Overall, the preliminary results indicate that there is good potential for the use of wetlands to treat metal contaminated mine drainage.

Placer mining involves washing stream gravel to separate and save free gold particles. Usually a placer mine must discharge excess effluent water, which contains some residual suspended fine silt and clay particles, from a settling pond, back into the stream. This study examines the applicability of introducing placer effluent through a diffuser to lessen environmental impact. A diffuser is a mechanism which introduces effluent fluid into the main current of a receiving stream so that mixing and dispersion are facilitated. A diffuser usually consists of a header pipe with one or more discharge ports. Effluent is ejected from the ports at high velocity into the receiving water. Performance of the diffuser depends on the diameter, spacing, and angle of the ports in relation to the water column. Diffusers are used effectively in many industrial applications. Computer programs have been developed which predict the effluent plume from a diffuser, using input data from both the receiving stream and the effluent discharge. We used the CORMIX model, which was developed for the U.S. Environmental Protection Agency. This program can also be used in the design of diffusers. We modelled two series of scenarios using receiving water data for the Fortymile River. In one series, we varied the concentration of suspended solids in the effluent. In the other series, we varied the flow rate of the effluent. In alll cases from both of these series of models, the CORMIX program predicted that the effluent diffused into the receiving water rapidly. A water quality objective of 12.5 mg of suspended sediment per litre of water was achieved in a very short distance downstream of the diffuser. We also used the CORMIX model to predict effluent behaviour in some hypothetical receiving streams. These scenarios showed that the larger the receiving stream, the better the diffusion rate. It also showed that diffusers would not be as effective on small streams where large effluent concentrations are discharged. Dilution is limited by the flow rate of the receiving water. The CORMIX model cannot predict whether sediment from the effluent plume will settle out on the streambed. Our team hydrologist examined the question of potential sedimentation by using the following techniques:: comparing background to introduced sediment levels, calculating the shear/fall velocity ratio for the sediment, comparison to flume testing, and comparison to other field investigations. He predicted that in the example of the Fortymile River using our mine effluent parameters, there would be little or no sediment deposited on the streambed from a diffuser installation. The use of diffuser systems to disperse placer effluent into receiving water appears to be an effective way of mitigating the impact of placer mining on the aquatic environment, providing there is adequate flow in the receiving stream. Effluent is dispersed into the stream flow, reducing the possibility of sedimentation of the stream substrate.

The Fish Habitat Management System for Yukon Placer Mining replaced the Yukon Place Authorization (YPA) in 15 Yukon watersheds on April 11, 2008. Founded on principles of adaptive management and incorporating a risk-based approach to decision-making, the system is intended to balance the objectives of a sustainable Yukon placer mining industry with the conservation and protection of fish and fish habitat supporting fisheries Adaptive management recognizes that the effectiveness of any management system is hampered by a degree of uncertainty and lack of knowledge. It seeks to improve the system by monitoring the effects of management actions, in order to learn from the results. The Adaptive Management Framework for Yukon placer mining is complemented by traditional knowledge and water quality objectives monitoring, aquatic health monitoring and economic health monitoring programs. The results should provide new information and a rational basis for making any adjustments required to achieve the two management objectives. The water quality objectives monitoring program is governed by the Water Quality Objectives Monitoring Protocol. The Protocol describes the locations, timing, frequency and methods employed during sampling, as well as the methods used to analyze sampling data. Precipitation data was collected from a variety of sources to assist in the interpretation of results. The water quality objectives monitoring program relies upon both continuous sampling and grab sampling. Continuous sampling is performed by automated instruments that pump water from the creek or river at a preset volume and at precise times each day. Grab samples are taken by personnel at a selected location, depth and time. Normally the quantity of water taken is sufficient for all the physical and chemical analyses that will be done on the sample. Grab sampling is also performed during sampling "blitzes", when single grab samples are collected from as many sites as possible within a short timeframe in order to get a snapshot of the water quality in a watershed over a 24 hour period. Distributed from [GeoYukon](https://yukon.ca/geoyukon) by the [Government of Yukon](https://yukon.ca/maps) . Discover more digital map data and interactive maps from Yukon's digital map data collection. For more information: [geomatics.help@yukon.ca](mailto:geomatics.help@yukon.ca)

An Integrated Regulatory Regime for Yukon Placer Mining was the final report of the Yukon Placer Implementation Steering Committee, submitted to the Minister of Fisheries in 2005. Under a proposed new management regime, the Yukon's placer mining industry will be managed through an adaptive management framework, with the aim of striking a balance between maintaining a viable placer industry and the protection and conservation of aquatic ecosystem integrity and fish populations. The effectiveness of the regime at achieving this balance will be monitored and assessed with appropriate adjustments to the requirements as required. The report recommended that a number of protocols be prepared and implemented in order to monitor the effectiveness of the new management system and among these is one with the primary objective of assessing and monitoring watershed health. A draft Watershed Health Monitoring protocol was completed July 1, 2006, and is currently being reviewed and considered by first nation, territorial and federal government agencies, industry and conservation organizations, and the general public. The draft protocol aims to provide for a process to help assess how effective the new management regime is for maintaining watershed health and to generate monitoring results that will be used to guide the adaptive management framework assessment and adjustment phases. After consideration of a number of methods, the Reference Condition Approach (RCA) was selected for assessing and monitoring watershed health under the draft protocol. There were a number of reasons for this choice: - It is the most robust of many biomonitoring methods - It is the basis of regional programs in Canada (it is an accepted design under the federal Environmental Effects Monitoring program), and programs in other countries, several USEPA programs in the United States, national programs in Australia and the United Kingdom, and has been adopted under the European Water Directive. - An RCA program has been underway in the Yukon for a number of years that could be immediately applied to the placer mining areas and augmented by future fieldwork. When the draft protocol was in preparation in the spring of 2006, meetings were held among those already conducting some type of stream sampling program associated with the Yukon placer mining industry. This included The University of Western Ontario, the federal Department of Fisheries & Oceans, and Environment Yukon Fisheries section. These three groups agreed to collaborate and carry out RCA sampling in 2006 in a manner consistent with that provided for in the draft Watershed Health Monitoring Protocol in order to "test drive" the methodology and assess its effectiveness at achieving the new management regime's objectives. Follow-up Geographical Information System March, 2007 3 (GIS) data collection and data analysis were also carried out as provided for in the draft protocol. In addition, reference sites were subjected to simulated impacts and then the RCA models were applied to these impacted sites in order to demonstrate the ability of the RCA models to detect a known degree of disturbance in streams.

A program of placer deposit sediment and water sampling was initiated by Indian and Northern Affairs Canada (DIAND) in the summer of 1998 to investigate possible relationships between the grain size distribution of pay gravels and effluent levels at Yukon placer mines. The sedimentology of placer deposits may be characterized in one way by examining the grain size distribution of pay (gold-bearing) gravels. In addition, the amount of clay and silt in gold-bearing gravels has a direct bearing on the treatment necessary for gold liberation during the placer mining process, and the resulting use of water for this process. The program consisted of sampling the pay or sluiced portion of an actively mined placer deposit (bank material), in conjunction with instrument monitoring and sampling the water upstream and at the discharge point of the mine. Knowledge of the grain size distribution of pay gravels will allow interpretation of the fluvial depositional environment, which can be used as a tool for placer deposit exploration. Sampling and analysis of the water will result in the ability to relate the grain size distribution of the active mine site (bank material) to the suspended solids concentration of the water, and the subsequent impact mining of the deposits has on the water quality in the area. This data will be important for the complete review of the Yukon Placer Authorization in 2001.