For the Salt River Project (SRP) and the Mojave Generating Station Co-Owners (Southern California Edison, SRP, Nevada Power Company, and Department of Water and Power of the City of Los Angeles), SSP&A developed a regional groundwater flow model of the C-Aquifer of Arizona and New Mexico. The groundwater flow model was designed to test the impact of a proposed well field on groundwater levels, baseflows in two habitat-critical streams (Clear Creek and Chevelon Creek) and flow at Blue Springs – a major discharge point for the C-Aquifer and a locale of cultural sensitivity to indigenous inhabitants.
The model was developed using the program MODFLOW 2000 and was based upon regional hydrogeologic, topographic, geologic, and other data from sources including published reports and databases from the U.S. Geological Survey (USGS) and Arizona Department of Water Resources (ADWR). The model was calibrated with the assistance of a non-linear parameter estimation program, PEST. Calibration targets included historical water levels, water level changes, and stream flows. The calibrated model is consistent with observed historical water level trends, baseflows in Chevelon and Clear Creeks, and transmissivity values derived from recent longterm aquifer tests in the vicinity of the proposed well field.
To evaluate the impact of the proposed well field, several scenarios were analyzed for the period 2010-2060. Two baseline scenarios for regional pumping projections were combined with three potential project pumping programs for a total of six (6) future pumping scenarios. The results indicate that under all potential project scenarios there is an adequate water supply for the proposed well field. The project pumping has a relatively small impact on wells outside of the well field, and virtually no impact on the annual discharge rate at Blue Springs. The greatest impact on baseflow in the lower, perennial reaches of both Chevelon and Clear Creeks is due to future regional pumping under either baseline scenario. The increased stream depletion due to project pumping is a small fraction of the total impact; it is also a small fraction of the total flow in these streams. An upper bound sensitivity analysis was completed for the maximum project pumping future scenario, and yielded similar results. Evaluation of water quality data from within the area of probable capture suggests that the water obtained from the potential well field will be of adequate quality for public and industrial use.