PUBLIC SERVICE COMPANY OF COLORADO
COMANCHE STATION POWER PLANT WATER RIGHTS INVESTIGATION

Public Service Company of Colorado (PSCO) annually requires approximately 7,900 acre-feet of water from the Arkansas River to satisfy the industrial water demands for power generation at the Comanche Station Power Plant near Pueblo. In order to provide efficient and flexible use of its available water supplies, PSCO engaged W. W. Wheeler and Associates, Inc. to perform an engineering analysis to support a plan of exchange to reuse and successively use portions of its raw water supply that derive from fully consumable sources.

The streamflow regime and "exchange potential" within the reach of the river between the mouth of the St. Charles and Pueblo Reservoir was evaluated using a computer model of the Arkansas River developed by Wheeler. The computer model was developed with historic daily streamflow data and diversion records for the ditch structures in this reach. Daily river gains and losses were estimated using measured daily flow values at U.S. Geological Survey stream gages within the river exchange reach. This analysis considered the location of irrigated lands contributing irrigation return flows, as well as the locations of measured and ungaged discharges of municipal wastewater. The exchange model used the calculated river gains and losses, the historic streamflows and the historic diversions by ditches to compute the daily flows immediately downstream of each diversion structure throughout the river exchange reach. The calculated minimum flow at all locations defined the amount of water that could be diverted by exchange at the Comanche Station Power Plant or at Pueblo Reservoir.

As part of the engineering analysis, water quality data for the effluent discharged from the Comanche Station Power Plant was reviewed. A detailed accounting form was developed by Wheeler which enables PSCO to keep track of the different types of water being diverted and/or stored for the Comanche Plant and to ensure that only fully consumable water is used in the exchange.