City wells lowering regional water table
Proposed solutions include a water pipeline from Lake Powell

By Lisa Rayner
Tea Party Publisher

A new study by the U.S. Geological Survey, produced in cooperation with the City of Flagstaff, reveals that Flagstaff has been pumping ground water from a number of wells at unsustainable rates. A number of localized draw-downs in the regional aquifer are occurring faster than the areas are being recharged through precipitation.

Until new city wells come on line, the city is dependent upon a good snow year to ensure adequate supplies for city water customers. The last few years have been drier than normal, drying up surface waters like Lake Mary and forcing the city to rely entirely on ground water pumping. It will take at least two years to bring new wells on line. The new study identifies promising locations for new wells, including a location near the Flagstaff Mall

If current drought conditions continue, the city may impose water restrictions this summer says City Utilities Director Ron Doba. “I’m certainly hoping that we get some inflow into Upper Lake Mary next spring, otherwise we’re going to be entirely dependent on ground water, and quite frankly, we don’t have enough ground water developed to meet all of our peak needs in the summer.”

The city recently signed an agreement to sell water to Williams, which is also suffering from similar water shortage problems. The agreement specifies that if Williams’ wells are unable to meet demand during a drought, then up to 400,000 gallons of Flagstaff water will be trucked to Williams each day to meet essential water needs. The sale is contingent upon the City of Flagstaff having extra water during a drought, which now seems unlikely.

According to Doba, one of the city’s favored long-term “solutions” to the water problem is reliance on a proposed water pipeline from Lake Powell. However, local environmental groups strongly oppose this proposal.

The 143-page report, Hydrogeology of the Regional Aquifer near Flagstaff, Arizona, 1994-97, summarizes new research on how the Flagstaff area’s ground water characteristics and movements are related to the region’s underground geologic structures. The study was undertaken in 1995 primarily to determine the best locations for new city wells. Existing wells were becoming inadequate to fully supply Flagstaff’s domestic and industrial water needs. The study area encompasses the greater Flagstaff area from Ashurst Lake to the south to north of Wupatki National Monument and from Parks to the west to Winona to the east.

In the early 1960s, when Flagstaff’s population reached 18,000, the city developed the first of its deeper wells tapping the regional aquifer. From the mid-‘80s to the mid-‘90s, water use within the study area increased about 30 percent. This ground water makes up the majority of the city water supply, with the rest coming from shallow, perched wells in the Inner Basin of San Francisco Mountain and from surface waters of Lake Mary.

Results of the study indicate that while fluctuations of the water table of as much as 400 feet occur due to seasonal and climatic changes in precipitation and fluctuations in the amount of water pumped from city wells, there is also a long-term general trend toward a lowering of several localized water table levels within the Flagstaff area.

The wells showing the greatest draw downs are in the Lake Mary well field. A 1993 hydrology study mentioned in the new USGS report “indicated that large groundwater withdrawals from 1985 through 1991 resulted in a 90-foot water-level decline in the Lake Mary well field.” In the new study, City Water Engineer Ron Doba is quoted as writing in a 1995 written communication to USGS personnel that “By the mid-1990s, development of high-yield wells ... had reached the point where the water table was being drawn down.” In a recent interview, Doba confirmed this trend, saying that it has become necessary to “back-off” the Lake Mary well field and to seek new sources of ground water to meet the growing demand. New wells had been planned for the Lake Mary well field, but the declines caused the city to drop the idea.

According to the new study, some observation wells in the Lake Mary area have shown a drop of as much as “400 feet when production wells were pumped for extended periods. Water levels in some parts of the Lake Mary well field have declined about 100 feet in the last 34 years, and most of the decline occurred in the last 10 years.” The Lake Mary wells and surface waters from Lake Mary comprise two of the City of Flagstaff’s four main water sources.

Furthermore, “In the Woody Mountain well field, water levels in observation wells declined 100 feet or more when many of the production wells were pumped for extended periods. The average decline of water levels in the Woody Mountain well field over the last 42 years is about 35 feet.” In addition, “The Forest Highlands 1 well to the south of the Woody Mountain well field shows about 85 feet of decline in the water level since 1985.”

Doba said, “As we found out in recent years, you can’t drill all your wells in one specific location just because it’s a good producer of water, because you’re going to have an impact on that location. ... We need to do a better job of managing how we’re withdrawing the ground water, and by managing it I mean locating wells in more diverse areas of the city.”

A number of other wells, especially two new wells located in the Continental area and Fox Glenn Park show no discernable trends at this time or appear to be recharging. Discharge of treated effluent from the Rio de Flag wastewater treatment plant is recharging the regional aquifer to the east of the plant. However, because this area’s groundwater is in its own pressure zone, water from these wells is only being used by homes and businesses in the Continental-Fox Glenn area.

In order to better understand what the water table declines mean, a brief description of the region’s geologic structure and ground water is needed. The area’s geology is complex. The region is underlain by a series of rock layers. Volcanic deposits form the surface layer over much of the study area. Below this layer is red Moenkopi Sandstone and below that, light-colored Kaibab Limestone and Coconino Sandstone. The Moenkopi and Kaibab layers are occasionally exposed at the surface. A number of small, localized aquifers are perched in the volcanic deposits and Moenkopi sandstone. These shallow aquifers fluctuate greatly with changes in precipitation levels. They are not suitable for long-term, high-yield wells, except for the Inner Basin, which is already fully tapped by city wells.

The geologic layers in which the deeper regional aquifer exists are the Kaibab Limestone, and a series of lower rock layers that can be seen exposed in the walls of the Grand Canyon. The top of the water table ranges from 250 feet to more than 2,000 feet below the Earth’s surface. The great depth of the aquifer makes drilling wells difficult, expensive and time-consuming.

Much of the aquifer’s water is stored within the rock layers themselves, filling pore spaces between minerals like water in a sponge. The entire region is also crisscrossed by numerous vertical and horizontal fractures and faults in the rock layers, from the surface down as far as geologists can study. Fracture spaces hold water too. Ground water travels the fastest along these fractures. The fractures break up the aquifer into smaller sections. The aquifer is uneven, due to differences in the permeability of rocks and the extent of local fracture zones.

The aquifer is recharged through precipitation, treated waste water pumped into the Rio de Flag, seepage from lakes, and leakage and overflow from the shallow, perched aquifers. Most of the recharging occurs during the colder months. In the summer, high temperatures create an evapotranspiration rate from the ground and vegetation that exceeds precipitation levels. Annual recharge to the aquifer within the study area is estimated to be about 290,000 acre-feet. An acre-foot is the equivalent of water covering one acre to a depth of one foot. An acre-foot of water can meet the needs of a family of four for one year. The total volume of the aquifer may be as much as 4,800,000 acre-feet. Donald J. Bills, the USGS project chief and principle author of the new study, estimates that because of technological and practical limits on the amount of water that can be accessed by wells, “Probably 10 percent of that storage would be available for extraction for ground water pumpage.”

About 5 percent of the annual recharge is currently pumped out by wells every year – roughly 11,000 acre-feet. Ron Doba estimates that 6,000 of those acre-feet are pumped by the city, with the remaining 5,000 acre-feet pumped by a number of private water companies such as those serving Doney Park and Kachina Village.

While this amount of withdrawal may seem small, the bulk of the recharge moves through fractures to discharge as springs along the Little Colorado and Colorado Rivers, Oak Creek and the Verde River. Removal of more than a small percentage of the aquifer may adversely impact those “downstream” riparian ecosystems. Impacts to those stream flows would not show up for hundreds or thousands of years because the ground water travels very slowly. Water in the regional aquifer ranges in age from less than 200 years old in the Lake Mary area to more than 5,000 years old in the Wupatki area.

In addition, the difficulties involved with drilling wells in this geologically complex region create lag times of two or more years between the determination of potentially good drilling spots and the first testing of a new well. Furthermore, not all areas identified as having plentiful ground water in hydrological studies turn out to be good producers. The city has drilled a number of wells in promising spots that turned out to be poor suppliers. Those wells are now used as observation wells only.

Ron Doba is enthusiastic about the possibility of a water pipeline making surface waters from Lake Powell available to Flagstaff. Such a pipeline proposal would be quite expensive. Doba says that the city or state could not afford to pay for the project. He seems to be hoping that the federal government will consider subsidizing the pipeline.

The city of Prescott has also been pumping groundwater from its aquifer unsustainably. Water table levels have dropped an average of 75 feet. Prescott and the Chino Valley are in an Active Water Management Area that does not allow draw downs in the aquifer.

Flagstaff has the option of forming a local Active Management Area to help protect the regional aquifer. The Arizona Department of Water Resources has a water use code that was put in place to control water table overdrafts across the state. Currently there are five AMAs, including one managing Prescott’s aquifer, which has declined as much as 150 feet in some areas. The Code specifies that ground water in an AMA cannot be drawn down faster than it recharges. It also requires proof of assured water supplies for any new growth within the AMA area. New AMAs can be designated by ADWR if necessary to protect the water supply or on the basis of an election held by local residents of an area.

The City of Flagstaff has a water conservation program that charges higher rates for high volume water users, encourages xeriscaping and the use of reclaimed water for landscaping purposes and provides a $50 rebate for the replacement of high water use toilets with low flush toilets. Xeriscaping is landscaping that utilizes low water use and drought-adapted plants, particularly native species. New regulations that broaden the potential uses of reclaimed water go into effect this year.

There are a number of other water conservation measures that the city could adopt, including relaxed regulations on the use of compost toilets and graywater re-use, rebates for low flow shower heads and faucet aerators, and promotion of roof water collection.

The underlying issue behind the current water crisis is the city’s high rate of population growth, estimated at 3 percent a year. If trends continue, Flagstaff will have 100,000 residents by 2020. The high growth rate makes keeping up with the rapid increase in demand for water more difficult. It would seem that a sound growth-management policy to slow down or cap growth temporarily or permanently is the prudent course of action.