Publication Summary

In March 1989, Ecology included the Little Spokane River on Washington's 304(L) mini-list as water quality impaired due to toxics because of mercury and cyanide contamination. This assessment was based in part on Ambient Monitoring Section (AMS) mercury data for WY87 and WY88 which showed occasional mercury levels in excess of EPA's chronic criteria of 0.012 mg/L.

Memo to Ken Merrill. In March 1989, Ecology included the Little Spokane River on Washington's 304(L) mini-list as water quality impaired due to toxics because of mercury and cyanide contamination. This assessment was based in part on Ambient Monitoring Section (AMS) mercury data for WY87 and WY88 which showed occasional mercury levels in excess of EPA's chronic criteria of 0.012 mg/L. The objectives of the study were to determine whether or not a mercury problem actually exists in the Little Spokane River; and if mercury contamination is found, to identify which general area within the basin is the source of the contamination. In addition, the usual suite of conventional constituents were sampled in order to further characterize general water quality in the basin.

Five stations in the Little Spokane basin were monitored monthly for one year using low-level methods for metals analyses. Although no water quality standards violations were detected for mercury, copper and lead probably violated standards in February and March near the mouth of the Little Spokane River. Upper stations were more likely than lower stations to violate water quality standards for conventional constituents, particularly fecal coliform bacteria.