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The EIS's conclusion that conventional water treatment will remove enough of the heavy metals in raw water supply to meet drinking water standards on a consistent basis,is unsubstantiated. More data on instream metals concentrations needs to be reviewed, together with the performance of existing treatment systems in the area. It is risky to assume that treatment beyond conventional techniques is unnecessary without further evaluation of heavy metals loading, removal efficiencies of conventional treatment systems, and contingency plans for dealinq with emergencies. These evaluations are especially important in view of the local capital expenditures that must be made for treatment facilities before the water can be put to use. The CPR indicates: Heavy metals are present in the Animas River at Durango, as described earlier in the section on present conditions. Some of these heavy metals already present a water treatment problem for _ Durango's domestic water supply. New water treatment facilities for Durango service area, to be built in coordination with the project, should be desiqned to reduce the excessive metal concentrations. Durango's raw water would continue to be supplemented from the Animas River through a connection with the line supplying water into Ridges Basin Reservoir. During those times when the pumping plant is not operating and when Durango's water demand is qreater than that being pumped, the city's raw water supply would come from the reservoir. Therefore, Durango's water treatment problems due to heavy metals will remain the same with or without the project. Given the past history of mining development upstream from Durango, if any future mininq takes place and water pOllution occurred from such mining, the Durango Pumping Plant would be shut down to prevent the contamination from being pumped into the reservoirs. The EIS indicates that the fate of the heavy metals in the Ridges Basin Reservoir is dependent on many factors, most of which indicate that the reservoir sediments would retain most of the metals, substantially reducinq the potential for water quality problems. The Bureau proposes to establish and maintain monitoring programs in both the Ridqes Basin and SouthernOte Reservoirs so that water quality studies analyzinq data on nutrients, salts, suspended solids, trace elements and bacteria could be performed. In addition, the retention of heavy metals would be monitored in Ridges Basin 32