Historical patterns of well drilling and groundwater depth in Arizona considering groundwater regulation and surface water access

Abstract

Arizona has a long history of groundwater use, and there is concern about long term groundwater sustainability across the state. We explore groundwater trends across Arizona and how they vary with respect to: (1) whether groundwater pumping is regulated, and (2) relative access to local or imported surface water. Well observations from the Arizona Department of Water Resources are used to quantify water table depth trends and groundwater drilling patterns. There are more than 85,000 groundwater wells in Arizona, and new wells are routinely being drilled. The number of new shallow wells (<200 ft) has decreased over time in all parts of the state. But midrange (200–500 ft) to deep (>500 ft) wells have increased in the past 10 years in regulated and groundwater dominated areas. Most wells are small with low pumping capacities that fall below the regulatory limit; however, there are still large wells being drilled in unregulated areas. Results show statewide decreasing water storage and groundwater levels. Groundwater declines are less severe in the parts of the state that have groundwater regulation. However, looking closer at this trend, groundwater recovery is strongest in areas receiving imported Colorado River water which also implement managed groundwater recharge with the imported water. Our findings indicate that groundwater recovery is very localized and driven more by managed recharge from surface water as opposed to decreased groundwater pumping.