TMDL IMPACTS TO HIGH ALTITUDE HIGHWAY OPERATIONS

Highway construction, maintenance, and runoff can adversely affect the water quality of streams and lakes by introducing excessive sediment, nutrients, metals and aromatic hydrocarbons. In mountainous, high altitude areas, highways are constructed by creating cut and fill slopes, usually adjacent to stream systems. The erosion potential of these altered slopes is extremely high and large amounts of sediment material can be introduced into the receiving stream. Wintertime, high altitude highway maintenance often requires the application of traction sand in enormous quantities to ensure safe public travel. The accumulation of over 25 years of sediment generated from construction and maintenance activities on Interstate 70 west of the Eisenhower Tunnel in the central mountains of Colorado has impacted adjacent Straight Creek's physical and biological integrity. Straight Creek was placed on the State of Colorado's 303 (d) List of Impaired Streams in 1996 due to the degradation of a Class I Cold Water Fishery and the negative impacts on the treatment of domestic drinking water. The resulting Straight Creek sediment based Total Maximum Daily Loading (TMDL) program is one of the first highway related TMDLs in the country. The challenge is to reduce sediment loading of Straight Creek to restore the designated uses of the stream, while enhancing safe driving conditions on Interstate 70, critical to interstate travel and the Colorado tourist industry.