Description of Study Area

The occurrence and transport of trace metals in the Spokane River basin are controlled primarily by the metal source and input rate, the tendency of metals to adhere to sediment, and the transport of water and sediment through the basin. Primary sources of trace metals to the South Fork Coeur d’Alene, Coeur d’Alene, and Spokane Rivers include headwater streams, tributary inflows, ground-water inflow, overland runoff from flood plains, and erosion of streambank and streambed materials. Once trace metals are mobilized in an aquatic system, they can be redistributed in streams and rivers, especially during high streamflow when transport is at a maximum.

Figure 3 is a schematic diagram showing relative locations and hydrologic relationships among the 10 sites. Stations 1 and 2, referred to as Canyon Creek and Ninemile Creek, are on tributaries to the South Fork Coeur d’Alene River. Station 3, referred to as Elizabeth Park, is on the South Fork Coeur d’Alene River at Elizabeth Park, Idaho. These three sites are upstream of the area designated by the USEPA as Operable Unit 2 (OU2). Station 4, referred to as Amy Gulch, is on Pine Creek, a tributary to the South Fork Coeur d’Alene River whose mouth is in OU2; however, the monitoring station is upstream of the OU2 boundary. Station 5, referred to as Pinehurst, near Pinehurst, Idaho, is on the South Fork Coeur d’Alene River downstream of the mouth of Pine Creek and in OU2. Station 6, referred to as Enaville, at Enaville, Idaho, is on the North Fork Coeur d’Alene River, which drains a part of the basin where minimal mining activity has taken place. Station 7, referred to as Harrison, near Harrison, Idaho, is on the Coeur d’Alene River downstream of the confluence of the North Fork and South Fork Coeur d’Alene Rivers. Because it represents the accumulated flow from the entire Coeur d’Alene River basin the Harrison site is important for monitoring metals carried into Coeur d’Alene Lake. Stations 8, 9, and 10 (referred to as Outlet, Post Falls, and Long Lake, respectively) are downstream of Coeur d’Alene Lake, on the mainstem Spokane River (figs. 1, 2).

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