Effects of placer mining on hydrologic systems in Alaska; status of knowledge

The report briefly summarizes the current state of knowledge regarding placer mining in Alaska. A review of literature indicates that nearly all of the significant information on the effects of placer mining on the hydrologic system in Alaska is referenced in available reports. The addition of sediment, as well as other indirect changes this generates, appears to be the primary impact of placer mining on Alaskan streams. Other potential water-quality effects that should be considered are: increases in organic loading in the stream system; increases in minor element content; potential for acid drainage; and impacts on fish and other aquatic biota. Existing information is adequate to define parameters that may be affected by placer mining but inadequate to quantify changes resulting from an individual mining operation or to allow the prediction of the magnitude or duration of the impact. Additional studies that would improve the knowledge of the effects of placer mining include: short-term assessments, using available photographic information and existing hydrologic records, to document historical changes and active placer mining features; short-term studies using emperical sediment-transport formulas to estimate the effects of placer mine activities; and river quality assessments of selected basins affected by placer mining. (USGS)