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.

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.

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.

not_specified

골재자원조사의 결과에 따라 세부내용으로 골재자원(육상, 산림, 하천, 바다 등 천연골재)의 물성을 실험하여 8단계로 규격화된 수치로 표시했음

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.

A series of tools (spreadsheets, a database and a document) to be used in conjunction with the SELDM simulations used in the publication: Stonewall, A.J., and Granato, G.E., 2018, Assessing potential effects of highway and urban runoff on receiving streams in total maximum daily load watersheds in Oregon using the Stochastic Empirical Loading and Dilution Model: U.S. Geological Survey Scientific Investigations Report 2019-5053, 116 p., https://doi.org/10.3133/sir20195053

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.