Geology of the Clean Water Coalition?s Proposed Reach 4 Tunnel and its Effect on Design, Las Vegas, NV

Treated effluent from the Clean Water Coalition (CWC) member agencies is currently discharged at an annual average rate of 6,570 l/s into the Las Vegas Wash, and is increasing annually. As the effluent flow increases, the nutrient loading of the treated effluent will approach the maximum limits allowed under the current regulations. To manage this flow while maintaining water quality in Lake Mead, the CWC is implementing a 44-km-long conveyance system. This paper discusses the geological and geotechnical aspects of the 13.4-km-long tunneled section through the River Mountains and their effect on design. The tunnel alignment traverses a heterogeneous package of volcanic and sedimentary rocks exhibiting widely variable rock conditions.