A story in the Arizona Daily Star notes that depletion of our groundwater supply is diminishing in some areas due to use of CAP water (water imported via canal from the Colorado River).  Much of the CAP water is being used to recharge the groundwater aquifer.  The maps below show the state of the aquifer levels for the periods 1970-1979 and 2000-2008.  On the maps, red indicates a falling water table, blue indicates a rising water table, and yellow indicates a stable water table.

The data come from the U.S. Geological Survey.  See an overview page here, and an interactive map page here.

The maps show that the recharge project in Avra Valley and retirement of central city wells have made quite a difference.

Note that USGS provides this disclaimer: “All information on this website should be considered provisional and subject to revision. No judgment on the presence or availability of ground water should be made on the sole basis of information on this website. Neither the USGS nor ADWR will be held responsible for any loss or damages due to the use of this information.”  Comforting, isn’t it.

According to the Star story: “the city this year will put into the ground 140,000 acre feet of CAP water and take out 80,000. This has raised the water table 9 feet a year at the city facility in the central Avra Valley facility for the past decade and 140 feet in the three years that a second city recharge facility and well field has existed in the southern Avra valley.”

Back in 2009 I posted an assessment of Water Supply and Demand in the Tucson area based on information from  the Water Resources Research Center at the University of Arizona (WRRC). I summarize from that post here:

The Demand:

In 1999, total usage in the Tucson Active Management Area was 323,000 AF according to WRRC.  Municipal usage was 154,000 AF which included 17,000 AF used by golf courses (35% was effluent from the sewer plants), and 20,000 AF used by “turf” facilities such as parks, schools, cemeteries (33% was effluent).  Agriculture used 132,000 AF (of which 20,000 AF came from imported CAP water).  Mines used 39,207 AF, sand and gravel operations used 5,167 AF and “other” industrial use totaled 4,026 AF.  Sewer treatment plants produced 70,000 AF per year and are projected to produce 115,000 AF by 2025.  Currently 84% of effluent discharge is released into the Santa Cruz river channel where it infiltrates into a shallow aquifer.  (Alert readers might notice that these official figures from 1999 add up to more than 323,000 AF, so some categories must have been counted twice.)

By 2003, total usage increased to about 350,525 AF.  This is projected to rise to 396,000 AF by 2025 assuming increased municipal and industrial demand, and decreased agricultural use.  Natural recharge provides only about 60,000 AF per year.  In 2003, municipal usage totaled 185,199 AF.  Municipal use includes all domestic and small business consumption.  Industries used 47,430 AF; agriculture used 102,959 AF; Indians used 14,196; all others used 3,705 according to WRRC.

This total usage is about 169 gallons per day per capita, with residential use pegged at 110 gallons per day per capita, a figure that has remained constant for many years.  In contrast, the Phoenix area uses 238 gallons per day per capita, but gets 73% of its water from “renewable” resources such as rivers, CAP, and effluent.

The Supply:

In 2003, groundwater supplied 256,233 AF, CAP supplied 64,554 AF, use of effluent supplied 11,360 AF.  The rest was due to incidental and natural recharge.

Tucson gets most of its water by mining groundwater stored in aquifers down to 1200 feet deep in the Tucson and Avra Valley basins.  This is mainly fossil water deposited during the wet Pleistocene glacial periods.  However, there is even more water in deeper aquifers, but as depth increases, water quality decreases, and water becomes briny with salts and toxic metals.

The 1999 WRRC report states that, “In 1940, when Tucson began to increase its groundwater pumping, these aquifers held approximately 70 million AF of groundwater at depths less than 1,200 feet below the surface.” This resource is equivalent to all the water in Lake Mead and Lake Powell combined.  Since 1940, 10% of this groundwater has been withdrawn.  Simple arithmetic implies at that rate, the remaining groundwater supply shallower than 1200 feet could last about 150- to 200 years.  This time will be extended by increasing use of CAP water and effluent.

See my post linked above for more information.