This report reviews methods and criteria for placer mining settling pond design. The mining and processing of placer gold generates wastewaters containing high concentrations of fine sand, silt and clay. Reduction of sediment discharges is required primarily to minimize impacts of sediment and turbidity on the aquatic environment and fish. Sediment discharge control to avoid sedimentation of water supply intakes of downstream mining operations and to allow recycling of process water in water short areas are secondary factors.

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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.

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.

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.

Two MERG-sponsored mine reclamation projects were surveyed during the summer of 2002. These included the Brewery Creek Mine where local shrubs were planted in large open areas at the mine site in 2000, and Noname Creek near Big Creek west of Carmacks where, in 2001, live willow cuttings were used at an abandoned placer mine to stabilize an eroding gully in permafrost. Because the effectiveness of reclamation projects such as these can only be determined after several year of observation, the two mine sites were revisited in 2002 to record the successes and failures of the experimental work and to make suggestions on where improvements can be made.

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.

This metadata document describes the data file 'Sinking_Pond_volume_stage_relationship.csv' for the relationship between pond volume and pond stage (i.e., the volume rating curve) for Sinking Pond. This relationship was used to transform simulated pond volume into simulated pond stage in the Sinking Pond hydrologic model.