Oct 052011
 

By Teri Walker —

Editor’s note: This is the second article of a three-part series dedicated to state water resources. The first article, discussing statewide water resource management, was published Sept. 28.

In the arid Southwest, proposed development of almost any scale comes with a couple of standard ques-tions: Is there enough water to support the growth? And, should available water be used to support the pro-posed new growth?

With deepening drought conditions forecast for the region, questions about water supply and management float ever higher in the consciousness of local, state and federal planners, and natural resource managers.

In northeastern Arizona, the potential to begin revving up in the next few years “world-class, competitive” potash mining operations, which could double to quadruple the nation’s potash production, has man-on-the-street interviews consistently eliciting the cautiously optimistic mantra, “The jobs would be great for the area, but do we have enough water?”

In the next article in this series, a review of the individuals and organizations that are closely watching the potential mining developments and what they have to say about potential water impacts will be presented, along with an overview of how much and what kind of water is used in typical potash mining operations.

This article takes a look at the state of water in northeastern Arizona: how much there is, where it is and who’s using it.

The Arizona Department of Water Resources (ADWR) divides Arizona into seven planning areas contain-ing a total of 51 groundwater basins. Holbrook, Winslow, Snowflake, Taylor and surrounding areas are part of the Eastern Plateau Planning Area, which encompasses areas as far north as Kayenta and Page, west to Flagstaff, east to Window Rock, and south to Show Low and Springerville.

Parts of three counties are included in the planning area, which covers 89 percent of Navajo County, 90 percent of Apache County and 41 percent of Coconino County. Three Indian reservations are located in the planning area, including all or parts of the Hopi, Navajo and Zuni reservations.

As of the 2000 Census, there were nearly 250,000 people living in the planning area.

Where Is The Water?

The Eastern Plateau Planning Area is unique in that it is composed of only one groundwater basin, the Lit-tle Colorado River Plateau Basin.

According to ADWR, there are about 508 million acre-feet of water in storage in the Little Colorado River Plateau aquifers, making it the largest groundwater basin in the state. (An acre-foot of water is a sheet of water one acre in area, and one foot in depth.)

The basin is fed by several aquifers, the three largest of which are the D-, N- and C-aquifers. The largest, and according to ADWR, most productive of the aquifers is the C-aquifer, named for the Coconino Sandstone, which is the aquifer’s primary water-bearing element. The C-aquifer spans 21,655 square miles and extends from the Mogollon Rim to an area west of the Little Colorado River and northeast into New Mexico.

The C-aquifer is used as a water supply south of the Little Colorado River and along the southern edge of the basin by Flagstaff, Heber, Overgaard, Show Low, Snowflake, Taylor and Concho.

North of the river, the C-aquifer is too deep to be considered economically useful or is unsuitable because of high concentrations of dissolved solids, or minerals and other substances, found in the water. ADWR says in general, the water quality of the C-aquifer degrades with increasing distances from where water is recharged, or put back into the ground, and at increasing depths.

The N-aquifer is north of the Little Colorado River and extends 6,250 square miles. Named for the Navajo Sandstone, which along with Windgate Sandstone, are the major water-bearing units of the aquifer, the N-aquifer is used for mining operations at the Black Mesa Coal Mine. The N-aquifer water quality is considered generally good, and is water supply for the Navajo and Hopi reservations. In some areas, however, there are sites of uranium and heavy metal contamination caused by past uranium mining and milling operations. Near Tuba City, groundwater remediation efforts are underway.

The D-aquifer is the smallest of the three regional aquifers, covering about 3,125 square miles under the Navajo and Hopi reservations. The D-aquifer is named for the Dakota Sandstone that comprises part of the aquifer’s water bearing elements. Water quality in this aquifer is considered marginal to unsuitable for domes-tic use because of the high concentrations of dissolved solids present. Still, the water is used in the north-central region of the planning area for home use.

Where regional aquifers are too deep or have unsuitable water quality, local aquifers are important for do-mestic use. Local aquifers include those that occur along washes and stream channels, like the Little Colorado River and its tributaries, and also geologic formations, such as sedimentary and volcanic rocks and some sand-stone. In the southeastern part of Navajo County, basaltic and sedimentary rocks form the Lakeside-Pinetop aquifer, which is a critical water supply for that area.

The Little Colorado River and a series of 70 major springs are important surface water elements in the re-gion.

Precipitation also feeds into the region’s water supply, although rain and snowfall range substantially across the varied geographic landscape. July and August are the months of highest precipitation, with the area receiving more than 43 percent of its annual precipitation during those months. The average planning area pre-cipitation, based on records from 1930 to 2002, is 13 inches per year.

How The Water Is Used

In the Eastern Plateau Planning Area, surface water, groundwater and effluent are key water supplies for municipal, industrial and agricultural demands.

Statewide, municipal needs make up 23 percent of the water demand. Agriculture leads the demand on water supplies, taking 71 percent of the water used each year. Industrial operations demand six percent of the state’s annual water budget.

In the Eastern Plateau Planning Area, industrial demand is the largest user with 49 percent of the take, or 83,100 acre feet used annually. About two-thirds of the industrial demand is met with groundwater.

Municipalities take about 26 percent of the water budget annually, at nearly 45,000 acre-feet. Contrary to the rest of the state, agricultural demand is only 25 percent of the planning area’s annual usage, at approxi-mately 42,400 acre feet. The agricultural sector uses a fairly even amount of groundwater, surface and effluent, while municipal demand is met primarily with groundwater.

As one might expect, municipality water usage varies widely in the planning area. The Flagstaff area de-mands the largest amount, totaling 11,600 acre-feet in 2006. The Hopi Reservation used the least amount of water the same year, at 700 acre-feet. Winslow/Holbrook used a combined 2,785 acre-feet in 2006, with Snow-flake/Taylor requiring 2,700.

Regional power plants are major industrial users in the planning area. From 2001 to 2005, according to ADWR, the electrical generating station in Springerville used an average of 9,900 acre-feet annually, and the Arizona Public Service Co. Cholla Power Plant near Joseph City used an average of 15,700 acre feet annually. The Coronado Generating Station northeast of St. Johns used 10,500 acre-feet annually, and Navajo Generat-ing Station at Page used 27,200 acre-feet yearly.

Other industrial water demands in the planning area include mining, paper production, dairies and feedlots, and golf course irrigation. About 23 miles southwest of Holbrook, the Catalyst Paper Co. pumped about 14,000 acre-feet of groundwater from the aquifer in 2005, and generated approximately 11,900 acre-feet of effluent. That means, for this operation, about 85 percent of the groundwater used to run the industrial paper making operation is being recovered and reused for irrigation.

Up next: How may proposed mining operations affect the region’s water supply?