9582 - Laserfiche WebLink

Home Browse Search

Volume III - Comments and Responses FEIS - Navajo Reservoir Operations . come from domesticated animals' waste, sewer lagoons/ponds, and other sources of E. coh contamination (i.e., improper disposing of waste from recreational vehicles/campgrounds). Increased turbidity results from soil erosion. NDWUA and BWUA water supplies realize the greatest impacts from storm events due to their limited amount of storage-110,000 gallons and 80,000 to 90,000 gallons, respectively. Each of these facilities has approximately 1 to lih days of user demand storage. The - WHDWA has greater flexibility with a storage facility (pond) that impounds 75 acre-feet of - water (approximately 24,500,000 gallons). This storage allows WHDWA to meet daily user demand for approximately 15 days. It also has the ability to use the larger storage facility to dilute contaminants, reduce associated treatment costs, and shorten the "recovery rate" (to - the point at which water treatment returns to normal). When managers of these treatment plants were asked what cost increases would be realized when releases were reduced to 250 cfs under the Preferred Alternative, they stated that it - would be difficult to determine. Increased treatment costs are a function of storm events - (severity and duration), dilution factors, and recovery time of treatment plants to provide treated water to their user areas. Therefore, without an extensive study over an extended period, increased treatment costs are indeterminate. General Comment 24: The negative impacts of increased flooding due to 5,000 cfs releases combined with tributary inflow or due to increased risk of reservoir spills include inundation of septic systems, damage to diversions, contamination of drinking water, and - release of seepage into the river. Reclamation should install and maintain gages on the - tributaries to reduce this problem. Response: Maximum releases of 5,000 cfs from Navajo Dam do not exceed the safe - channel capacity of the San Juan River as established by the U.S. Army Corps of Engineers • (Corps). Peak releases of 5,000 cfs are usually timed to coincide with natural peak flows of the Animas River-generally during May or June of each year. Downstream from the A i n mas River, the safe channel capacity increases substantially. Historically, major cloudburst or precipitation events in the area occur during late summer or early fall, but - may occur in the spring. During scheduled peak releases, Reclamation has monitored, and will continue to monitor, weather conditions and will continue to coordinate with the National Weather Service and the Corps_ When possible, releases from Navajo Dam - are/will be adjusted when weather conditions and tributary drainage inflows indicate • possible flooding. Flash floods occur in this region and San Juan River tributaries can contribute large volumes of water from those events. - The amount of reservoir space allocated for flood storage is based on historic inflow data - coupled with required free storage space and time of year. This information is used to determine needed storage space for potential water inflow coupled with the time of year