The state of Tucson’s water supply is always a concern. So how are we doing? Recently, Docents at the Arizona Sonora Desert Museum had an update by Wally Wilson, chief hydrologist at Tucson Water. The reason is that we Docents often have to explain to museum visitors what all those rectangular ponds are doing in Avra Valley just west of the museum. The following material is taken from his talk.

Tucson gets water from four sources: pumped groundwater, water transported from the Colorado River via the Central Arizona Project canal (CAP), water reclaimed from sewers, and water treated from former industrial usage (Tucson Airport Reclamation Project, TARP). Water is measured in Acre-feet (AF). One AF is 325,851 gallons and one acre-foot will serve four residences in Tucson for a year. Mr. Wilson presented the following graph on water usage (as of 2011):

Notice that total water usage has been declining and has reached the level it was in 1994.  That was surprising to me. Perhaps our conservation efforts are paying off. Mr. Wilson noted that average residential use in Tucson is about 90 gallons per day per capita (versus 200 in Scottsdale). Tucson is conserving groundwater by using more and more CAP water. This graph shows that our groundwater use has declined to what it was in 1959 in spite of our increasing population.

In 2011, CAP supplied 64% of our water while groundwater supplied 20%. The remainder was made up of reclaimed water. Total production in 2011 was 120,350 AF. In 2013, Mr. Wilson expects CAP will supply 80% of our needs allowing us to decrease primary groundwater pumping.

Below is a map of the CAP system. It consists of ponds to recharge the aquifer, wells to pump the water, a treatment plant, and a reservoir which stores 60 million gallons.

There are three recharge areas which Tucson Water fondly calls CAVSARP, SAVSARP, and PMRRP. These are the areas featuring recharge ponds filled with CAP water and wells to reclaim the water after it recharges the aquifer.

Why put the water in ponds to sink into the aquifer rather than treating it and pumping it directly to consumers? There are several reasons. When we first began to receive CAP water it was treated and sent to households, but the water wreaked havoc with some of our old plumbing. The current system is plan B and it has several advantages besides being kinder to plumbing.

Water from the ponds sinks into the ground at the rate of about 1.5 feet per day. As it travels 300- to 400 feet to the water table, soil filters out any viruses and bacteria that may be in the water. This filtering method is much less expensive than disinfecting the water in a treatment plant. The water still goes through the Hayden-Udall treatment plant for filtering and chlorination.

Some numbers: CAVSARP recharges 70,000 to 80,000 AF/year and recovers 70,000 AF/year. SAVSARP is permitted to recharge 60,000 AF/year and recovers about 15,000 AF/year. We are still ramping up to use our total CAP allocation. PMRRP is permitted to recharge at the rate of 30,000 AF/year and recovers water at 14,000 AF/year.

Tucson Water claims that it loses about less than 2% of the water due to evaporation from the recharge ponds. The overall CAP system loses about 5% of its water due to evaporation. Most of that occurs in Lake Pleasant which acts as a storage buffer between supply and demand.

Mr. Wilson says Tucson will have plenty of water through 2050 and beyond because we are banking water in the recharge system (and we still have the groundwater). Tucson Water is also pursuing additional sources of renewable water such as water owned by Indian Tribes. For more information see http://cms3.tucsonaz.gov/water .

See also my older posts on our water supply:

Water Supply and Demand in Tucson

How much water is there?

Trends in groundwater levels around Tucson

EPA war on coal threatens Tucson water supply

Southern Arizona gets about 43% of its water by pumping groundwater aquifers.  The geology is well-suit for this because Southern Arizona is in the Basin and Range province which contains very deep, fault-bounded valleys.  In some places, bedrock is as much as 15,000 feet below the surface.   Portions of the Tucson and Avra valleys are over 8,000 feet down to bedrock.  Such valleys are filled with alluvium and water.

Currently, water for drinking exploits aquifers down to a depth of about 1,200 feet.  Generally water below that depth is too salty for drinking.

Following up on two previous studies, Estimated Depth to Bedrock in Arizona and Preliminary evaluation of Cenozoic Basins in Arizona for CO2 sequestration Potential, the Arizona Geological Survey in a new study, examined the salinities of Arizona groundwater.  The study is A Summary of Salinities in Arizona’s Deep Groundwater, Arizona Geological Survey Open-File Report, OFR-12-26.

As part of that study, geologists of the Arizona Geological Survey (AZGS) reviewed geophysical well logs to catalog the concentration of total dissolved solids (TDS, i.e., salinity) of 270 water wells.  This included all water wells that penetrated deeper than about 2,600 feet, which is the minimum depth necessary to sequester carbon dioxide.

Among the results of that study, AZGS found that on the Colorado Plateau and in the Basin and Range province, there are some areas where “Fresh water can extend as deep as 5,000 feet (1,500 m), but below 6,600 feet (2,000 m) only brackish or saline groundwater was encountered..”   Water is considered “fresh” if it contains less than 1,000 ppm (parts per million) TDS.  Water is “brackish” if TDS are 1,000- to 30,000 ppm.  “Saline” water contains greater than 30,000 ppm TDS.  Sea water is about 35,000 ppm TDS.

This means that we may be able to extract drinking water from deeper aquifers in some areas.

See also:

Water Supply and Demand in Tucson

How much water is there?

Trends in groundwater levels around Tucson

Tombstone, Arizona, “the town too tough to die” just might be killed off by the US Forest Service. Tombstone gets most of it water supply from springs in the Miller Canyon Wilderness Area in the Huachuca Mountains about 25 miles west of the town. This water supply dates from 1881 when it was first developed by the Huachuca Water Company. Tombstone bought the pipeline and water rights in 1946.

In the early summer of 2011 the massive Monument wildfire denuded the eastern part of the Huachuca mountains. With vegetation destroyed, subsequent heavy monsoon rains caused flooding, mud slides, and debris flows that buried springs and crushed waterlines, thereby shutting off the main water supply to Tombstone.

Since that time, the City of Tombstone has tried to repair the damage, but has been stymied by a very obstinate Forest Service who will not allow heavy equipment into the wilderness area, even though the water rights pre-date establishment of the Wilderness Act.

According to the Goldwater Institute, who are suing the US Forest Service on behalf of the City of Tombstone, “Tombstone’s pipeline is under 12 feet of mud, rocks and other debris; while in other places, it is hanging in mid-air due to the ground being washed out from under it. In response, federal bureaucrats are refusing to allow Tombstone to unearth its springs and restore its waterlines unless they jump through a lengthy permitting process that will require the city to use horses and hand tools to remove boulders the size of Volkswagens.”

This is a case where bureaucratic regulations make no common sense and put citizens in danger even in spite of the fact that the City of Tombstone and the governor of Arizona declaring a state of emergency. The Goldwater Institute says, “The 10th Amendment protects states and their subdivisions from federal regulations that impede their ability to fulfill essential health and safety functions. Just as the federal government cannot regulate the States, it cannot regulate political subdivisions of the States, like the City of Tombstone. And despite what power it may claim, the Forest Service certainly has no power to regulate Tombstone to death.”

As water law expert Hugh Holub once wrote: “Though the water may originate on National Forest lands, Bureau of Land Management lands, and other federally managed lands, the rights to that water belongs to the farms and ranches and cities.” It seems that the Forest Service is ignoring that right.

The Forest Service has been portrayed as the villain here and perhaps they are. But maybe, they too are trapped by an inflexible process intrinsic to environmental laws such as the Wilderness Act and the Endangered Species Act, a process that makes timely, common sense responses to emergencies very difficult if not impossible.

See also:

Red Tape Rising – Federal Regulations Choke Economy

Repeal the Endangered Species Act

Red Squirrels and Green Dollars

Do we need the US Forest Service?