WILLCOX — The Arizona Department of Water Resources (ADWR) released a 100-year modeling study of the Willcox Basin in July that revealed a growing problem of depletion of groundwater.

The three-year modeling project showed “the high rates of groundwater pumping in the Willcox Basin” has impacted the system “to a significant extent,” according to the study performed by ADWR staff groundwater modeling supervisor Keith Nelson, hydrologists Dale Mason, Dianne Yunker and John Mawarura, and chief hydrologist Frank Corkhill.

The Willcox Basin covers about 1,911 square miles running north of Willcox into Graham County to the Aravaipa Creek Basin, east to the San Simon Valley Sub-basin and the Chiricahua Mountains, south to the Douglas Basin and the San Bernardino Valley, and west to the Dragoon Mountains and the Upper San Pedro Basin. The region includes Willcox, the towns of Cochise, Sunizona, Pearce and Sunsites, and the community of Kansas Settlement.

ADWR staff developed the modeling plan to gain a “better understanding of the regional groundwater flow system and associated parameters and to project future groundwater flow conditions” in the Willcox Basin. The study indicated a draw down so low and recharge in such decline that the aquifer could be in trouble in less than 100 years.

The amount of groundwater removed from storage between 1940 and 2015 ranged from 4.9 million to 6.2 million acre-feet. An acre-foot equals 325,851 gallons of water, or the amount of water needed to cover an acre of land 1 foot deep. So, over the course of 75 years, 2.02 trillion gallons of water was withdrawn.

In 1940, the estimate of the amount of underground water in the basin was 80-97 million acre-feet. In 2015, they estimated a drop to 73-92 million acre-feet. By 2115, 57-78 million acre-feet would remain in the aquifer.

Over 100 years, an additional 19.8 million acre-feet to 24 million acre-feet of water would be pumped from the aquifer. That is another 6.5 to 8 trillion gallons of water gone.

The modeling also simulated long-term draw down in various portions of the aquifer and found a range from a minimum of 354 feet in the aquifer system north of the Willcox Playa to as much as 917 feet in the Kansas Settlement area over a period of 100 years.

They also note, “Much of the remaining groundwater in storage” would be “at significant depth and may not be practical to remove.”

Both data and modeling indicate that significant declines in regional groundwater levels will continue to occur.

In addition, they reported at least three sub-regional cones of depression in the southern aquifer area, including the general Kansas Settlement area, the Cochise agricultural/power plant area and the Sunsites area. Data indicate that the cone of depression associated with the Kansas Settlement area is generally coalescing into a broader, regional-scale groundwater depression due to pumpage in the Sunizona area.

No help in sight

As the drought continues, there is no help in sight for those whose wells have declined in production or have gone dry.

The state did approve a program whereby industrial-level water users, including agricultural irrigation users, could donate to a fund so neighboring property owners could get help paying to have wells drilled deeper if they lost access to water.

However, as the county Board of Supervisors pointed out in a November work session, there was no way to take advantage of that program as no industry responded to inquiries and no funds were donated.

The estimated cost of drilling deeper was around $20,000. So it would take a large sum of money to offer any real help.

There is nothing the county can do to regulate underground water withdrawal and nothing the state can do as the Willcox Basin is not an Active Management Area or Irrigation Non-Expansion Area.


Groundwater decline

The Willcox groundwater basin has the highest land subsidence rate in Arizona. Due to groundwater pumping far exceeding the natural mountain front recharge, water levels are likely to continue to decline, resulting in continued land subsidence.

There are no external sources of surface water currently available or planned for the Willcox Basin that could supplement groundwater use and slow the declining groundwater levels. It is estimated that current groundwater production exceeds recharge by a factor of three to eight.

Wells going dry

During the summer of 2014, ADWR began to receive concerns about declining water levels in private residential wells and in some cases, reports of wells going dry, in southeast Arizona. As a result of declining groundwater levels, some individuals and representatives of groundwater users have expressed interest in developing water management practices for the area with the hopes of slowing the water level declines.

ADWR believes that in order to develop the best water management solutions for the area, it is important to first conduct an analysis of the water conditions in the area. ADWR field services staff conducted a detailed inventory of water level conditions throughout wells in the Willcox and Douglas Basins and the San Simon Valley Sub-basin.

Prior to conducting the well sweep, ADWR established a web-based reporting portal whereby individuals impacted by wells going dry could report those incidents online. Those wishing to volunteer their well to be part of the investigation were also encouraged to complete the survey.

The results of the survey indicate that many domestic wells have been impacted by declining water levels in the Willcox, Cochise, Sunsites, Pearce and Sunizona areas. Many wells have been deepened or replaced, and there has been almost universal concern expressed about water conditions from survey participants.

Subsidence issues prevalent in Willcox Basin

In one area of the Dragoon Mountains, land has subsided an estimated 4 to 6 feet. Land in an area around Pearce and Sunsites has subsided an estimated 5 feet, concluded ADWR’s GIS Application Developer Karen Fisher and Brian Conway, supervisor of the Geophysics/Surveying Unit, after completion of a specialized map of the Willcox Basin produced for ADWR.

They concluded the Willcox Basin has the highest land subsidence rate in Arizona due to groundwater pumping that exceeds natural mountain front recharge. Groundwater levels will likely continue to decline, resulting in continued land subsidence. There are no external sources of surface water currently available or planned for the Willcox basin that could supplement groundwater use and slow the declining water levels.

The map depicts land subsidence in the Willcox Groundwater Basin, where ADWR recently completed work on a comprehensive groundwater-flow model.

Focusing on the prevalence of land subsidence in the Willcox Basin, the map uses interactive imagery as a complement to textual descriptions of the area’s subsidence issues. It paints a clear picture of the dramatic subsidence issues facing the region.

ADWR regulation of wells

ADWR regulates all groundwater wells in Arizona, but there are no regulations in place for limiting the pumping of underground water in the Willcox Basin.

Sandy Stewart Lee, ADWR public information officer stated, “The Willcox Basin is not located within an Active Management Area (AMA) or Irrigation Non-Expansion Area (INA). Areas outside AMAs and INAs have no ADWR limitation on the amount of groundwater that may be pumped. There are no requirements for measuring or reporting groundwater use outside AMAs and INAs.”

There is a requirement to obtain proper authorization and use a licensed well driller for new wells that are constructed, she continued. “Prior to drilling a new well, or deepening or modifying an existing well, a person must file a Notice of Intent to Drill (NOI) with ADWR. Authority to deepen an existing well or drill a new well is valid for one year.”

Lee went on to say, “An exempt well is one equipped to pump 35 gallons per minute (gpm) or less. A nonexempt well is one equipped to pump over 35 gpm. Within AMAs and INAs, withdrawals from nonexempt wells are generally required to be measured and reported to ADWR. This requirement does not exist for wells outside AMAs and INAs.”

“The NOI requires information such as well location, planned depth of well, and driller information,” added Lee. “ADWR will then issue drilling authorization to the well drilling contractor. After a well is drilled, the well driller must provide to ADWR a drilling report and well log containing information such as actual well depth. There are no requirements for public notice for new wells to be drilled.”

Load comments