American Geosciences Institute’s Critical Issues program


The Arizona Geological Survey’s winter e-magazine features an article about the American Geosciences Institute’s Critical Issues program (www.americangeosciences.org/critical-issues).

The aim of this AGI program is to pioneer a new approach to sharing societally-relevant science with state and local decision makers. “Here in Arizona, we are sharing this with state and local decision-makers to help them wrap their heads around the complex issues involving groundwater, geologic hazards, and sustainable natural resource management.”

The program aims to support connections and communication between the geoscience community and decision makers. Although the program caters to decision makers at all levels, it particularly focuses on state and local decision makers because these stakeholders are commonly underserved by geoscience policy efforts.

The program convenes meetings, such as the AGI Critical Issues Forum, but its main interface is a web-based platform of resources that bring the expertise of the geoscience community to decision makers by offering a curated selection of information products from sources that include state geological surveys, federal and state agencies, and AGI’s member societies.

The Critical Issues program offers the following freely accessible information services:

Research database: Over 4,000 publications primarily from state geological surveys and the U.S. Geological Survey.

Webinars: Free webinars on a variety of topics that bring geoscientists and decision makers together to discuss potential solutions to challenges at the interface of geoscience and society.

Maps & Visualizations: 144 interactive maps and visualizations covering all 50 states and the District of Columbia.

Case studies: A new product that is coming online in Spring 2017. Specific applications of geoscience to societal problems.

Fact Sheets: A new product that is coming online in Spring 2017. Provide more in-depth information on the big issues.

Frequently Asked Questions: 105 questions on topics including: climate, energy, hazards, mineral resources, and water.

Read more at:


This AZGS e-Magazine also includes an article about groundwater use in the United States.


Implications of projected climate change for groundwater recharge in the western United States – paper review

A group of 17 researchers, led by Thomas Meixner of the University of Arizona, attempted to assess the possible response of groundwater recharge to global warming in eight basins in the western U.S. In this context, “recharge” means the replenishment of water in aquifers from some surface source.

Meixner recharge fig 1

The paper: Meixner et al, 2016, Implications of projected climate change for groundwater recharge in the western United States, Journal of Hydrology, Volume 534, March 2016, Pages 124–138.

You can download the full PDF.

The authors assume future climate conditions will be as projected in the most recent National Climate Data Assessment (2014) which itself is very speculative and lacks any supporting physical evidence (see links to my articles below).

The authors acknowledge that their study comes with a great deal of uncertainty. That did not stop Tony Davis from asserting in the Arizona Daily Star that “groundwater recharge in the San Pedro will decline faster than in any of seven other Western groundwater basins…” Tony apparently did not read the part about the Central Valley of California nor the part about the San Pedro in the paper itself.

Here is an excerpt from the paper’s abstract:

“Eight representative aquifers located across the region were evaluated. For each aquifer published recharge budget components were converted into four standard recharge mechanisms: diffuse, focused, irrigation, and mountain-systems recharge. Future changes in individual recharge mechanisms and total recharge were then estimated for each aquifer. Model-based studies of projected climate-change effects on recharge were available and utilized for half of the aquifers. For the remainder, forecasted changes in temperature and precipitation were logically propagated through each recharge mechanism producing qualitative estimates of direction of changes in recharge only (not magnitude).”

“Several key patterns emerge from the analysis. First, the available estimates indicate average declines of 10–20% in total recharge across the southern aquifers, but with a wide range of uncertainty that includes no change. Second, the northern set of aquifers will likely incur little change to slight increases in total recharge. Third, mountain system recharge is expected to decline across much of the region due to decreased snowpack, with that impact lessening with higher elevation and latitude.”

“Factors contributing the greatest uncertainty in the estimates include: (1) limited studies quantitatively coupling climate projections to recharge estimation methods using detailed, process-based numerical models; (2) a generally poor understanding of hydrologic flow paths and processes in mountain systems; (3) difficulty predicting the response of focused recharge to potential changes in the frequency and intensity of extreme precipitation events; and (4) unconstrained feedbacks between climate, irrigation practices, and recharge in highly developed aquifer systems.”

In other words, this paper is long on speculation and short on physical data.

Meixner mapHere is what they predict for each of the eight basins due to global warming:

High Plains Aquifer (aka Ogallala aquifer):

The paper projects moderate increases in recharge in the north and shifting to moderate decreases in the south or an overall net decrease in recharge depending on which data set is used.

San Pedro River:

The authors relied on two other studies which project a 30% and a 27% decrease in recharge over the next 100 years. However, the authors also note that depending which climate model was used, “Future recharge varied from a 100% decline in recharge to a 30% increase in recharge across the GCMs used.” That large range of uncertainty detracts from the value of the study.

Death Valley:

The paper predicts less recharge due to decreased snowpack in the surrounding mountains. That project is hedged: “Sources of uncertainty include potential increases in summer precipitation and winter precipitation intensity, which could lead to increased focused recharge. This source of recharge is currently so small that even large relative changes would result in negligible changes to total recharge.”

Wasatch Front Aquifers:

The paper predicts a general decrease in recharge (unless there is more snowpack).

Central Valley Aquifer:

Here, recharge is dominated by irrigation. Modeling projects decreases on anywhere between 5% and 60%.

Columbia Plateau:

There might be a modest increase in recharge if it rains more.

Spokane Valley-Rathdrum Prairie aquifer:

The authors don’t know because of the great uncertainty of the data.

Williston Basin aquifer system:

Some “considerations suggest that diffuse recharge to the Williston Basin may decline. However, model-based projections in multiple studies of future recharge to the northern HPA [high plains aquifer], located directly south of the Williston Basin, indicate that diffuse recharge will increase. Given these inconsistent outlooks, uncertainty in future diffuse recharge is high.” In other words, the authors don’t know about that one either.

The goal of this study was to provide information that would help planners form water policy for the future. Considering the high level of uncertainty, do you think this study will help?

Study funding: This study receive support from the U. S. Geological Survey and the National Science Foundation through a concurrent award (EAR-1328505). Additional support to several authors was provided by the USGS National Research Program and the USGS Office of Groundwater.”

Your tax dollars at work.


See also:

National Climate Assessment lacks facts, an analysis

National Climate Assessment = science fiction and politics

San Pedro River Geology – Implications for water law

How Tucson Water spends Conservation Fund money and a suggestion for a better way

If you are a Tucson Water customer, you may have noticed an item on the back page of your water bill listed as: “CONSRV FEE $.07/CCF.” This means you are contributing seven cents per cubic foot of water used to a conservation fund. That may not sound like much, but according to an article by Tim Steller, that added up to $2.95 million last year. By the way, this “contribution” to the conservation fund will rise to eight cents per CCF on July 15.

So, how is that money being used? The answer to that question is the objective of a Freedom of Information (FOIA) request filed last January by Mark Lewis, one of five members of the City’s Conservation and Education Subcommittee of the Citizens Water Advisory Committee.

Tucson Water has to date refused to provide the information requested by Mr. Lewis. According to Mr. Lewis, the information requested is “to gather the documentation and information necessary to ensure the funds collected from Tucson Water customers under the Conservation Fee program has been properly accounted for, audited, and expensed.” Mr. Lewis has expressed concern, in his role as an appointed advocate for the Rate Payers of Tucson Water, that the millions of dollars which have been spent through this fund have not been properly tracked or audited and that more recent uses of this fund are not consistent with the purpose of the fund: conserving water.

One conservation program promoted by Tucson Water is the replacement of old toilets with new low-flow models. Tucson Water will give you a $75 rebate toward the cost. According to Steller’s article, “water-wasting toilets remain in around 150,000 Tucson homes, and the program to replace them saved almost 11 million gallons in the first eight months of this fiscal year alone.” Mr. Lewis supports this program, but points out that the small rebate may be insufficient, especially for older homes which may have complicated plumbing issues that would make replacement more expensive.

Another conservation program is rainwater harvesting. Tucson Water will provide a rebate of up to $2000 for installing a system. Steller points out that “those rebates have mostly benefitted wealthier residents and so far have resulted in no measurable reduction in water use.” Mr. Lewis notes that the $900,000 in rain water rebates to date saved no water, but had the same money been spent on wasteful toilets it would have saved 173 million gallons of water to date.

You can read about the program in a brochure provided by Tucson Water: http://www.tucsonaz.gov/files/water/docs/Rainwater_Harvesting_Rebate_brochure.pdf

In that brochure, Tucson Water claims that “45% of the water we use goes to outdoor irrigation.” That number surprises me; I wonder if it is true. The brochure also notes that in order to qualify for the rebate, you have to take a free class. And here is where it gets interesting.

The qualifying class is run by Watershed Management Group, a consulting firm that, for a fee, will design a rainwater harvesting system for you. Three board members of Watershed Management Group, Catlow Shipek, Mark Murphy, and Amy McCoy, comprise three of the five members of the City’s Conservation and Education Subcommittee of the Citizens Water Advisory Committee. The classes are also given by a company that sells rain gutters according to Mr. Lewis. This situation has the appearance of crony capitalism and conflict of interest.

There is another scheme afoot. Tucson City Councilwoman Regina Romero has proposed that $300,000 be used to provide interest free loans to low-income residents so they can plant trees and have them watered by rainwater harvesting systems. Romero is concerned about the “unequal distribution of tree canopy in Tucson…” and its effect on the Urban Heat Island Effect (cities are warmer than surrounding countryside because all the asphalt and concrete absorb heat which makes nighttime cooling much slower). I see two potential problems with this scheme. First, we would have to cover a large part of the city with trees to have any significant effect. Second, all those trees will transpire water, losing moisture to the atmosphere rather than conserving water for reuse.

Given the information above, do you think your forced subsidy is being well-spent?

I have a suggestion on how the money could be spent to actually conserve water.

One of the eco-fads promoted by Tucson Water is rainwater harvesting at residences. So far, that program has resulted in no measurable reduction in water use. But perhaps, if that idea was used on a larger scale, it could help recharge our aquifers. Why don’t we collect storm-water runoff from city streets and in ephemeral flows in the Santa Cruz River and pump that water back into the aquifers via dry wells?

That idea is discussed by Chuck Graf, Senior Hydrologist, Arizona Department of

Environmental Quality in a short article in the Spring Issue of Arizona Water Resource Newsletter (link to article).

This idea is not new. Phoenix began recharging storm-water in the 1930s and now has more than 50,000 wells in operation. Many other communities also use this recharge method. Why not in Tucson and Pima County?

The practice of dry well recharge in Phoenix went largely unregulated until 1987 when legislature directed the Arizona Department of Environmental Quality (ADEQ) to license dry well installers and establish a registration program for existing and newly constructed dry wells. The law expressly limited the use of dry wells to the disposal of storm water. This limitation was intended to prevent disposal of hazardous chemicals into dry wells, which in the past had caused severe groundwater contamination plumes (some of which are still under remediation).

Graf explains the dry well method as follows:

“The dry well borehole is drilled in alluvial sediments, through any intervening fine-grained and cemented zones, into a permeable layer of clay-free sand, gravel, and cobbles. The permeable layer serves as the injection zone for the storm water. ADEQ requires at least 10 feet of separation between the bottom of the injection zone and the water table. Because groundwater commonly occurs at great depth in Arizona’s alluvial basins, installers often have considerable leeway to find an exceptionally permeable zone above the water table that maximizes dry well performance while maintaining a much greater separation distance than the 10-foot minimum.”

Graf goes on to write:

“Potential adverse groundwater quality impact is the biggest concern about dry wells. Although the definitive water quality study probably remains to be done, a number of studies, including a 10-year study in Los Angeles conducted by the Bureau of Reclamation and others, found little evidence for groundwater contamination. A 1985 study in Phoenix found that dry wells had a beneficial effect on groundwater quality with respect to major chemical constituents”

This idea should be considered. Perhaps then, our involuntary contribution to the “Conservation Fund” would actually conserve some water.


The Redwall Limestone of the Grand Canyon


Redwall 2

The 350-million year old Redwall Limestone is one of the most prominent features of the Grand Canyon. Its features:

• Diverse and long history over the last 350 million years.
• Magnificent cliffs and red walls.
• Composed of ~99.5% pure limestone, ~95% of which is biologically formed in the presence of organisms.
• Forms very chemically resistant cliffs, yet it is a very soft rock (slightly harder than a
finger nail).
• Has 1,000’s of miles of interconnected caverns spread out over the Colorado Plateau.
• Has many caverns, some with ancient and modern speleothems.
• Is the source of carbonate for the growth of abundant travertine deposits.
• Provides precious minerals, trace metals and uranium in breccia pipes
• Is a major source of high quality groundwater to numerous and voluminous springs in
the canyon and region, consumed by most visitors to the canyon.
• “Living in the Past” implies the past of the Redwall Limestone is living with us today.

Brian Gootee of the Arizona Geological Survey has designed a 27-slide history of the Redwall Limestone intended for guides and educators. It can be downloaded here:

It has great graphics and an interesting story.

See also:

Origin of the Grand Canyon
Origin of the Lower Colorado River – a geological detective story



Rosemont’s Conservation Lands Program

In addition to mine development, Rosemont Copper has a land conservation program which currently includes five sites in southern Arizona, see map below. Rosemont says the program will “permanently conserve 4,500 acres of open space, and allocate more than 550 million gallons per year of private surface water rights to the public.”


The following short descriptions are taken from Rosemont’s brochure on the program.  For that brochure and more details on each  property go to: http://rosemontcopper.com/conservation.html .

1. Fullerton Ranch:

Adjacent to existing county conservation land, acquisition of this property maintains open land for hiking, bird watching, hunting, camping, mountain biking and off-roading. While over-grazed today, sustainable grazing to support local ranching can be supported on the property. The property provides a valuable habitat for the Desert Box Tortoise and other species. Without conservation, the property would be subject to fragmentation and development.

2. Helvetia Ranch North:

The Helvetia Ranch North property connects BLM Santa Rita Experimental Range land to the Coronado National Forest. Its conservation ensures an intact cultural and natural landscape, completes wildlife corridor connections, and maintains public access to the Santa Rita Mountains. The Ranch also provides habitat for vulnerable and endangered species like the Pima Pineapple Cactus, the Mexican Long-Tongued Bat, and the Lesser Long-Nosed Bat.

3. Sonoita Creek Ranch:

Located at the headwaters of the Patagonia-Sonoita Creek Preserve, the Sonoita Creek Ranch property plays an essential role in the recharging of the Town of Patagonia’s aquifer. Prior to its purchase by Rosemont, Sonoita Creek was poised for residential development. Now Sonoita Creek Ranch and its 588 acre-feet per year surface water right, fed by a perennial spring, will be conserved.

4. Pantano Dam:

Rosemont, working with the state and local agencies, hopes to be successful negotiating projects that will use existing private water rights for the enhancement of an important stream habitat in the Pantano Wash, Davidson Canyon, Lower and Upper Cienega Creek and Empire Gulch. These enhancement projects, both downstream and upstream, would create a habitat for endangered species with a priority water right that Rosemont has secured.

5. Davidson Canyon Ranches:

Each of these is a historic homestead, chosen by the homesteader because of a flowing spring. Conservation of these sites ensures the lands will be kept open rather than developed, preserving public views, numerous archeological sites, and the reach of the seasonal Davidson Canyon Wash that a downstream of which has been designated as an Outstanding Arizona Water.

See also:

The value of mining in Arizona

Distinguishing Fact from Fiction about Rosemont

Future of Rosemont Mine Very Certain

Rosemont answers Cyanide Beach

Pima County versus Rosemont

Rosemont’s dry-stacked tailings will be greener than those near Green Valley

Jaguars versus the Rosemont mine

Tucson’s Water Action Plan, Fuzzy Sustainable Development

The City of Tucson and Pima County are collaborating on a region water plan. It’s about time. But you should read the reports: government concepts of priorities might not be the same as those held by property owners and businesses.

Over the past several years, local governments have been devising a plan to maintain and ensure water supply for the future. A “Phase 1” report deals with an inventory of water resources and an assessment of infrastructure. A “Phase 2” report “establishes a framework for sustainable water resources planning including 19 goals and 56 recommendations within four interconnected elements: Water Supply, Demand Management, Comprehensive Integrated Planning, and Respect for Environment.”

The new Action Plan describes a range of activities with time lines to implement the goals and

recommendations in the Phase 2 Report. The City wants your comments.

From my reading of the plan, the City is placing great emphasis on making the Santa Cruz River pretty. That will include riparian restoration projects, a new bureaucracy to propose such projects, and bond elections to buy up land. The report uses fuzzy phrases such as “smart growth” and “sustainable development.” Concerning sustainability, the report admits, ” Our work during Phase I documented how elusive the concept is in practice.”

The Action Plan cites four principles for managing water:

Principle 1: Water is an essential part of life for humans and the environment. Delivery of water and wastewater must maximize both quantity and quality.

Principle 2: The environment must be considered a user, not simply a provider, of water resources.

Principle 3: Policies affecting water and wastewater must be open to wide public discussion in a completely transparent process.

Principle 4: Water is an economically-valued resource and must be managed with due consideration to its economic value.

Your comments are needed to help the City go from concepts to practice.

For some additional background, please read my posts: Water Supply and Demand in Tucson, and How Much Water is There.

The Water-Energy Nexus

Electricity is needed to get water to you, and water is needed to produce electricity. This relationship is explored in the latest issue of “Arroyo” published by the Water Resources Research Center of the University of Arizona.

This 12-page publication has some interesting and little known facts. For instance, do you know the single largest user of electricity in Arizona? It’s the Central Arizona Project which brings water to Tucson.

“Groundwater accounts for 40 percent of Arizona’s water supply. Extraction of groundwater for potable use, on average, consumes 30 percent more electricity than diversions from surface water sources, primarily because of the pumping requirements.”

In Tucson, treating wastewater consumes 1 kilowatt-hour of electricity per 1,000 gallons, while in Benson the cost is 7.3 kWh/kgal and in Patagonia it’s 13.5 kWh/kgal.

Which method of home cooling is more efficient, air conditioners or swamp coolers? “Air conditioners use between 2 to 4 times the electricity of a swamp cooler, but they do not require water. Evaporative coolers use less energy, but require continuous additions of water. The study found that if the electricity is generated by coal, the air conditioner is still a water saver, consuming only 425 gallons per month, while the swamp cooler uses more than 4,600 gallons per month. On the other hand, air conditioners are significantly more expensive to run, and their lower water footprint might not offset their greater energy consumption.” In other words, it depends.

This publication is worth the read. Download it from: http://ag.arizona.edu/azwater/files/Arroyo_2010.pdf

How much water is there?

The answer depends in part on how much you are willing to pay. There continues to be some valid concern about our water supply. These concerns generally cite our current drought conditions and population growth. Tony Davis of the Arizona Daily Star has written a series of articles on the subject, articles that generally sound an alarm. For instance, see Tucson’s source of water runs low and Contrasting views on what to do about dwindling water .

To put such articles in perspective, however, consider this:

The Tucson area currently uses about 350,000 acre-feet of water per year. An acre-foot is 325,851 gallons, enough to supply three-to six family residences for a year (the number of residences depends on who’s doing the estimation). For that 350,000 acre-feet of current usage, we withdraw about 256,000 acre-feet from our groundwater supply. The Central Arizona Project (CAP) provides about 65,000 acre-feet and the rest is from use of effluent and incidental recharge. Natural recharge to the aquifers is about 60,000 acre-feet per year, much less than the amount we withdraw.

Estimates from the University of Arizona imply that our groundwater supply, at projected rates of usage, represents about a 200-year supply. Our CAP allocation is 314,000 acre-feet per year. That would seem to cover our needs, but the CAP supply is subject to natural variation of droughts, and the whims of politics. For more details, please read my blog from last June: Water Supply and Demand in Tucson. For a perspective on droughts, see my article: Drought in the West.

Our CAP supply is drawn from the Colorado River. Currently our Colorado River reservoirs stand at 55% capacity, the same as last year at this time. We are not gaining on the amount stored because water released for electrical generation and river health about equals inflow to the system. See: Bureau of Reclamation weekly water report. See also: Bureau of Reclamation forecasted use for 2010. In contrast, the Salt River system, supplying Phoenix, stands at 97% capacity. The BR report says that our “water year” precipitation is 82% of normal in the Colorado River basin and 122% of normal in the Gila River system. Snowpack is put at 83% and 244% respectively.

The point of this article is that our water policy must be based on facts rather than on perceptions. Conservation measures must also be based on facts rather than on “feel-good” ideas of the day.

The groundwater supply mentioned above counts just the aquifers down to about 1200 feet, but depth to bedrock in the Tucson and Avra Valleys is as much as 15,000 feet deep in places, so the valleys contain more water. That deeper water, however, would be more expensive to pump and process.

A related, but important concern is not just the ultimate water resource, but also the distribution system, how to get the water to the customer. Current peak summer water demand in Tucson is greater than maximum well pumping capacity of 143 million gallons per day. How much water is there? That depends on how much you are willing to pay.

Biosphere 2 Ready for New Research

Biosphere 2, that grand experiment with a checkered history, is being readied for new research conducted by the University of Arizona. Tuesday evening, Dr. Travis Huxman discussed plans for the facility with a group of about 30 people at the Cushing Street Bar.

Huxman, who has a doctorate in biological sciences, and is an associate professor of ecology and evolutionary biology at the U of A, is the new director of the Biosphere 2 research program.

For those who may be unfamiliar with Biosphere 2, here is some background. The concept was to construct a self-contained biosphere to investigate what would be needed to colonize other planets, such as Mars. The main structure, built near the town of Oracle, AZ, is a 3.15 acre greenhouse which was to be a self-sustaining ecosystem containing several plant biomes and an “ocean” to grow fish. The facility was built with $150 million in private funds in the late 1980s.

In September of 1991, a group of “biospherians” (four men and four women) entered the greenhouse for a planned two-year stay. It was intended that they depend only on what was inside the enclosure. As noted in a Wikipedia article: “All seven ecosystems of Earth exist within the confines of Biosphere II. They are a rainforest, a desert, a savanah, a marsh, a farmland (in an area called the Intensive Agriculture Biome), and a ‘human habitat’.” [I guess the ocean makes seven.] “Thus, it contains soil, air, water, animals, and plants. About 4,000 plants and animals were introduced to Biosphere II, and the ocean contained 900,000 gallons of water. It was hoped that these provisions would give the ecosystems enough material to be self-sustaining.”

As with many experiments, things didn’t go as planned. One of the main problems was that organic-rich soil consumed too much oxygen. The original oxygen content of 20.9% dropped to 14.5% after 18 months. That’s the equivalent of an altitude of 13,400 feet, and the biospherians suffered from high-altitude effects. Because they were in a greenhouse, the daily fluctuation of carbon dioxide was about 600ppm (current atmospheric concentration is about 390 ppm). During the day, with strong sunlight, plants revved up photosynthesis and used up carbon dioxide, but respired it back at night. There was also a seasonal variation in carbon dioxide, and wintertime levels reached about 4,000 ppm.

This first phase ended in September, 1993 as planned. After a 6-month transition, another group of seven people entered the greenhouse, but injuries and social problems caused abandonment of the project in 1994.

Columbia University took over in 1995 and operated the facility until 2003. Columbia “broke the seal” and formed a flow-through system to test effects of carbon dioxide among other things.

Through all of this, the facility was open for tours and derived much of its operating revenue from visitors. By 2006 the property was zoned for urban development and in 2007 sold to a developer who had planned houses and a resort hotel. However, the University of Arizona took over management responsibilities in June, 2007. And that brings us back to Huxman.

Huxman said that U of A research will “focus on environmental challenges of the day.” And by that he meant they would study initially, at least, the relationship between carbon, water, and energy, essentially photosynthesis, and how it can be applied to current issues.

Huxman mentioned solar power and the smart grid system since apparently Biosphere 2 gets some of its electricity from solar collectors. He said that with a smart grid system, the power company can turn off an individual’s solar system, which might generate power to the common grid in order to protect workers doing repairs on the lines. Biosphere 2 will not be a participant in the smart grid system so as to prevent such power outages. This will allow researchers to better control variables and also test software that manages smart grids.

Huxman says that under U of A management, Biosphere 2 will be better committed to a relationship between science and society, and that even now visitors can watch graduate students conducting experiments.

One of the planned projects is to build a model of a watershed to study the dynamics of how water gets to plants and how soil structures evolve. He wants to know how water gets into the aquifers. (A geologist could tell him that most aquifer recharge occurs at the mountain front.) After the “naive” model is working, they will introduce plants to see how that changes the soil structure. Once they learn from the model, they plan to try it outside in the real world.

They will also study ways to stabilize mine tailings.

Who is paying for all this? According to Huxman, major funding is coming from the facility owners and foundations. Much of the operating budget will come from visitor admissions; a minor part comes from the University and from corporations.

Will they be successful? Only time will tell. You can visit Biosphere 2. You can get information from www.B2science.org , email to info@B2science.org or call 520-838-6200. Currently admission price is $20 for adults. Lower prices are available for seniors and children.

And, by the way, the Cushing Street Bar has Guinness on tap.

Water Supply and Demand in Tucson

With a growing population and predictions of drought, will there be enough water in Tucson in the future? In this essay I review the supply and demand. The numbers are taken mainly from the Arizona Department of Water Resources (ADWR) website and from “Water in the Tucson Area: Seeking Sustainability” a 1999 report published by the Water Resources Research Center at the University of Arizona (WRRC). This review is confined to the Tucson Active Management Area (TAMA), an area of 3,866 square miles, which includes the Tucson Basin and the Avra/Altar Valleys – the areas from which we pump our water. CAP is the Central Arizona Project which imports water from the Colorado River. Most of the numbers refer to acre-feet (AF) of water. One acre-foot is 325,851 gallons.

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 center parts of Basin and Range valleys such as the Tucson Basin, are filled with porous sediments. The volume of these sediments is typically, 30 miles long, 5 miles wide, 1 mile thick — 150 cubic miles. The upper part of the aquifer consists of young water from the glacial epochs which is fresh, while deeper parts of the basin contain progressively older and saltier waters. The majority of water in the deeper parts of the Tucson basin contains high amounts of dissolved salt, gypsum, boron and lithium; difficult and expensive to treat into drinking water and expensive to pump.

 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.

Pursuant to the 1980 Groundwater Management Code, Arizona was divided into five Active Management Areas to receive water from the Colorado River. The Tucson Active Management Area is allocated about 314,000 AF per year. Tucson area entities are to receive 215,000 AF of which the City of Tucson is allocated 138,920 AF per year. The statutory goal is to reduce dependence on groundwater and to make water usage “sustainable” by 2025. Tucson is currently using only a small portion of the allotment and political pressure is mounting to use it, or lose it. The recharge project in Avra Valley will eventually use all of our allotment. There are some problems associated with depending entirely on the anticipated CAP supply. The original allotments were meted out during years of abnormally high flow in the Colorado River so that these allotments amount to 150% to 200% of normal flow. There is also the danger that if the Biodiversity Treaty were ever ratified, then endangered species in the Colorado River delta and the Gulf of California would have precedence for much more water than they are currently receiving. The Treaty would supercede state laws.

The Avra Valley recharge project, called the Clearwater Renewable Resource Facility (CRRF), is a political compromise. It would be more efficient to use CAP water directly, but in 1992, when Tucson Water tried that, the improperly treated water gave many customers discolored, evil-smelling water as it dissolved the encrustation built up in the water delivery pipes and in home plumbing. Due to the damage, Tucson Water was sued and stopped delivery in 1994.


It seems that we have an adequate groundwater supply for about 200 years and our CAP allocation, if it materializes, will, alone, cover most of our projected needs. However, it isn’t quite that simple because having the water in the ground is quite different from getting enough of it into the distribution system at a reasonable cost and without causing dangerous subsidence. Current peak summer water demand in Tucson is greater than maximum well pumping capacity of 143 million gallons per day. The shortage is currently made up from small storage facilities filled by wells during non-peak periods and from summer monsoon rains. This seasonal shortfall is why Tucson Water promotes its “Beat the Peak” program. The question is: how shall we continue to meet this demand and at what price.

In more recent years Tucson Water seems to have gotten its act together. Their “Water Plan: 2000-2050http://www.tucsonaz.gov/water/docs/waterplan.pdf) seems to be on the right track to provide water for the long run. However, if we are to continue to “Beat the Peak” we must have more water available on a daily basis. Imagine what will happen to property values if the city cannot deliver sufficient water. Depending solely on recharge will not solve the delivery-rate problem. We need more wells (outside the Central Well Field) and perhaps some reservoirs or underground storage. And, there should be a plan to use properly treated CAP water directly in emergencies.

A recent WRRC report estimates that water resources in TAMA could support a population of 2.3 million people if proper conservation measures are used. However, those conservation measures must be sensible for there are already some unintended consequences. For instance, current city code requires new housing to have low-flow toilets. Harvesting gray water is also encouraged. But, according to the people at the sewer treatment plants, neighborhoods using these conservation methods do not send enough water through the system to properly flush the solids to the sewer plant.

And, we will eventually need to recycle the sewer effluent that currently goes down the Santa Cruz. Despite the “yuck factor” this is a growing resource and if treated properly can be merged with other sources of drinking water.


Arizona Department of Water Resources: http://www.azwater.gov/azdwr/

Water Resources Research Center : http://ag.arizona.edu/azwater/