The City of Tucson Water Department's Central Avra Valley Storage and Recovery Project (CAVSARP) is located on City-owned land near Sandario Road and Mile Wide Road. Field testing of the project began in 1997. Delivery of drinking water from the project began in May 2001.
The Purpose and History of CAVSARP
The CAVSARP project allows Tucson Water to productively use Colorado River water as a drinking water supply through a process known as recharge and recovery. Groundwater overuse in the latter half of the 20th Century led to severely declining groundwater levels and the beginnings of subsidence (land sinking) in and around Tucson. In addition, Arizona law requires Tucson and other groundwater dependent communities to reduce reliance on this limited resource and switch to renewable supplies. To eliminate overpumping, the City has been switching from groundwater to renewable Colorado River water delivered via the Central Arizona Project (CAP). Water quality issues that occurred when Colorado River water was first delivered to Tucson Water customers in 1992-94 led to the passage of Proposition 200, the Water Consumer Protection Act, which prevented the delivery of CAP water directly to customers. To meet the requirements of the Act, Tucson Water developed the CAVSARP project to recharge, store and recover a blend of Colorado River water and groundwater. This allowed the City to shut down many of its groundwater wells in and around urban Tucson.
Overview of a Storage and Recovery Project
In general, a storage and recovery project stores surface water (in this case, Colorado River water) in the ground and later recovers it for use. Storing water in the ground is similar to putting money in a bank. River water is released into constructed basins to percolate naturally through the earth until it reaches the underground water table and mixes with the groundwater. Many of these projects are designed to store river water underground for use in the future. At CAVSARP, specially designed wells have been constructed to recover the blended water and deliver it to Tucson Water customers.
The CAVSARP project includes eleven basins, totaling over 300 acres, along with pipelines to transport Colorado River water from the CAP canal to the recharge basins. The project allows up to 80,000 acre-feet of river water to be recharged and stored underground each year. The project also includes more than 27 wells and a reservoir/booster station that allows the City to recover the CAP/groundwater blend and deliver it to customers. Recovery is ramping up to 70,000 acre feet per year. (One acre-foot equals 325,851 gallons.)
Groundwater Levels and Water Quality
The project is designed to recover a blend of Colorado River water and native groundwater. Because each year the amount of river water recharged by the City will exceed the amount recovered, water levels elsewhere in Avra Valley should not be negatively affected by this storage and recovery project.
The quality of the water recovered from this project and delivered to Tucson Water customers will change over time. Initially, it was very similar to the native groundwater. As the recharge of Colorado River water continues, the recovered water will become more like river water in terms of mineral content. The City is examining several treatment methods which could be used to modify the recovered water if necessary to meet the water quality and water cost goals determined by Tucson Water customers.
It is important to note that the quality of groundwater varies in different locations. For instance, levels of total dissolved solids (TDS) in groundwater are lower than Colorado River water in some areas and higher in others.
What Does the Future Hold?
Over time, this facility may expand to recharge and/or recover larger volumes of Colorado River water. In addition, Tucson Water is currently developing the Southern Avra Valley Storage and Recovery Project (SAVSARP).
The following links provide additional information about recharge projects and activities: