REQUESTOR: Mr. Scott Holland on behalf of the Sterling County Underground Water Conservation District (UWCD).

Mr. Holland requested a Groundwater Availability Model (GAM) run using the GAM for the Edwards-Trinity (Plateau) and Cenozoic Pecos Alluvium aquifers. Mr. Holland requested that we provide water budgets for Sterling County from a baseline simulation for use in the District’s Management Plan, due in December 2005. METHODS: To determine the water budgets for Sterling County, we used the GAM for the Edwards-Trinity (Plateau) and Cenozoic Pecos Alluvium aquifer systems. We ran the model for the transient calibration and verification period (1980 through 2000) using estimated historic recharge and pumpage from the original GAM model. We extracted annual water budgets from the GAM for an area that corresponds to Sterling County. We then took the average value for each of the water budget components for the 20-year simulation and reported the results. PARAMETERS AND ASSUMPTIONS: • See Anaya and Jones (2004) for assumptions and limitations of the GAM. • The root mean squared error (a measure of the difference between simulated an