Development of Conceptual Plan for Direct Recovery of Central Arizona Project Water Stored at Tonopah Desert Recharge Project

During the past 15 years, Central Arizona Project (CAP) has developed five recharge facilities for long-term storage of Colorado River water in aquifers in the CAP service area (Maricopa, Pinal, and Pima Counties. More than 1.3 million acre-feet of water have been stored. Conceptual plans are presently being developed to recover stored water during periods when supplies of Colorado River water available to CAP are not sufficient to meet scheduled water orders from CAP customers.

The largest of the CAP recharge facilities is the Tonopah Desert Recharge Project (TDRP), located adjacent to the CAP aqueduct in the lower Hassayampa basin, in Maricopa County approximately 40 miles west of Phoenix. The facility includes 206 acres of infiltration basins and has an operational recharge capacity of 150,000 acre-feet per year. More than 330,000 acre-feet of CAP water were stored at the TDRP facility from start of operations in January 2006 through 2008. To recover the stored water, large-capacity recovery wells will be constructed at and adjacent to the TDRP site.

Conceptual design for the recovery wellfield is being developed for capacities up to 100,000 acre-feet per year. The recovery efficiency for a 20-year recovery period is being evaluated using:  1) analytical modeling methods to project the hydraulic interference effects resulting from variable number and spacing of wells, and 2) an associated cost analysis based on capital and operating costs of the recovery wellfield. In addition, numerical groundwater flow modeling is being conducted to evaluate effects of recharge and subsequent recovery operations on the magnitude and extent of groundwater level changes in the regional aquifer, which will be used to confirm or refine the design recovery capacity for the facility. Based on these analyses, a conceptual recovery plan for the TDRP site will be selected that optimizes recovery efficiency for the design capacity.