Publication Summary

A study of cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb), and zinc (Zn) concentrations in the Spokane River was conducted. Samples were collected on eight occasions between July 1992 and September 1993. Three locations were sampled between river miles 63.5 and 96.0. Dissolved, total, and total recoverable metals were analyzed. Water quality criteria for dissolved Zn were not met at all three sampling locations during high and low flow seasons. Criteria for dissolved Pb were exceeded at all sampling sites during the high flow season. Criteria for Cd were exceeded in the upper river during the high flow season.

A study of cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb), and zinc (Zn) concentrations in the Spokane River was conducted. Samples were collected on eight occasions between July 1992 and September 1993. Three locations were sampled between river miles 63.5 and 96.0. Dissolved, total, and total recoverable metals were analyzed. Water quality criteria for dissolved Zn were not met at all three sampling locations during high and low flow seasons. Criteria for dissolved Pb were exceeded at all sampling sites during the high flow season. Criteria for Cd were exceeded in the upper river during the high flow season.

Nonpoint sources of Cd, Pb, and Zn from historical mining practices in Idaho are considered to be the major reason for violation of Washington's water quality criteria and are considered likely to sustain excessive background loading for many years. Concentrations of trace metals relative to criteria in the Spokane River generally decreased proceeding downstream from the state line. The fractions of dissolved/total metals were similar throughout the study area and generally increased in the order of Pb < Cd < Zn < Cu. Most metals concentrations increased with river flow.

A seasonal strategy was proposed for total maximum daily loads (TMDLs), load allocations (LAs) from nonpoint sources, and waste load allocations (WLAs) for point sources regulated under the National Pollutant Discharge Eliminations System (NPDES). WLAs were proposed for metals with background concentrations potentially greater than the water quality criteria (Zn throughout the river all year; Pb throughout the river during the high flow season and in the upper river during the low flow season; and Cd in the upper river all year).

A phased TMDL approach is recommended which stipulates that USEPA and Idaho develop a schedule for managing and monitoring loads from Idaho to meet water quality standards for Cd, Pb, and Zn at the Washington border. The phased WLAs for point sources in Washington will ensure that Cd, Pb, and Zn concentrations are not elevated above existing concentrations that are sustained by loading from Idaho, ground water inflows, and minor nonpoint sources in Washington. Phased WLAs will be adjusted if monitoring data show progress in reducing concentrations sustained by excessive loads from Idaho.

For metals with background concentrations less than the water quality standards (Cu and Hg throughout the river all year, Cd in the lower river all year, and Pb in the lower river during the low flow season), critical conditions of river flows, hardness, background concentrations, and fractions of dissolved/total metals were proposed for calculating water quality-based effluent limits.

Link to EIM data for User Study ID GPEL0004