March 29, 2007
Water quality in the Clark Fork River below Milltown dam was generally good throughout the month, although turbidity in the Clark Fork below the dam exceeded the trigger value of 12 NTU on two occasions, resulting in daily sampling of metals and arsenic. Turbidity in the Clark Fork above the dam (at Turah) was also elevated during this period. All dissolved arsenic and metal concentrations below the dam were well below warning limits and applicable standards.
Dewatering for the bypass channel continued during February, pumping about 1 cfs of discharge water into the Blackfoot River, just above the dam. Although high in arsenic, the volume of this discharge is small compared to flow in the river, and this discharge is not detectable at the monitoring station below the dam.
Drawdown in the reservoir level varied from a minimum of 10.3 feet to a maximum of 11.9 feet, depending on flow in the river. The average drawdown was about 10.8 feet.
Turbidity below the dam was measured three times per day during most of the month. Monitoring occurred weekly for suspended sediment, dissolved and total recoverable arsenic, cadmium, copper, iron, lead and zinc during the first half of the month, and daily over the second half of the month, triggered by turbidity levels. Upstream sites on the Blackfoot River and on the Clark Fork at Turah were monitored on the same schedule during this period.