An economic and institutional assessment of groundwater recharge in an arid environment: Tucson Basin case study

The City of Tucson, located in a semi-arid region, faces escalating pressure on its groundwater resources associated with rapid urbanization and population growth over tbe past 50 years. Because of concern that the declining water table will threaten the city's development, bringing water from Colorado River via the Central Arizona Project (CAP) was perceived as the sole solution for Tucson's water problem. As soon as CAP water arrived in Tucson in 1992, its quality provoked a quarrel over its use for potable purposes. A significant outcome of that quarrel was the enactment of the 1995 Consumer Protection Act (CPA). The primary objective of the CPA is to preclude the use of CAP water for drinking purposes at least until year 2000, unless it is treated to achieve the same quality as the groundwater previously supplied. The CPA encourages using CAP water for non-potable purposes and for replenishing Tucson aquifer through recharge. This study examines the economic and institutional issues involved in utilizing CAP water for recharge and non-potable purposes in the Tucson Basin. The economic assessment focuses on the impact of CAP water recharge on the water table, the resulting pumping cost savings, and the concomitant benefits of saving groundwater and of using CAP water instead of reclaimed water. The institutional assessment focuses on the effectiveness of using CAP water in stabilizing groundwater withdrawal and replenishing Tucson's aquifer. Four planning scenarios were designed to measure and compare the costs and benefits with and without CAP water recharge. Cost-Benefit Analysis was utilized to measure recharge costs and benefits and to derive a rough estimate of cost savings from preventing land subsidence. The results indicate that the institutional requirements can be met since one scenario relatively stabilizes groundwater and the two other scenarios will recover it. The economic benefits from reducing pumping cost and saving groundwater are not economically significant. Yet, when combing the use of CAP water for recharge and non-potable purposes, scenario 3 would not only augment the water table, but also demonstrate positive net economic benefits from savings groundwater, decreasing pumping costs and using CAP water instead of reclaimed water