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Water Management

Prescott AMA

 

Prescott AMA Issues

There are many important issues facing the Prescott AMA, most of which involve the increasing demand for groundwater due to continued growth in the area and the Department’s statutory responsibility to reach safe-yield by 2025. Some of these issues include:

 

Augmentation and Recharge

As defined by the 1980 Groundwater Code, augmentation means "to supplement the water supply of an active management area and may include the importation of water into the active management area, storage of water or artificial groundwater recharge." The Prescott AMA Second Management Plan illustrated the fact that even with maximum reuse of effluent, demands would outstrip supplies through the year 2025. Therefore, the need for other augmentation measures to supplement existing groundwater supplies is paramount.

Treated effluent can be used directly or recharged into the aquifer. However, due to the small size of the AMA, the geology that exists within the AMA, and the location of wastewater treatment plants relative to the areas where recharge projects would be the most successful, the potential number of locations for viable recharge projects within the AMA is limited. The future location of regional artificial recharge facility will therefore require very careful analysis.

 

Big Chino

A USGS studyoffsite released in December 2005 underlined the importance of the Big Chino aquifer as a source of the flow of the Verde River.

Big Chino, Paulden
The study:

  • Estimates that 80-86% of the upper Verde River's flow comes from the Big Chino aquifer
  • 14% comes from the Little Chino aquifer
  • Less than 6% comes from an aquifer in the Drake area just north of the Big Chino

Groundwater importation from the Big Chino subbasin of the Verde River Groundwater Basin, northwest of the AMA, which is allowable under state statute, represents the largest source of alternative water supply currently available for municipal water users within the Prescott AMA. Issues related to the potential use of Big Chino groundwater involve the concern that downstream Verde Valley water users would be negatively impacted. The Endangered Species Act could also impact any transfers.

 

Transportation of Groundwater from the Big Chino:

  • Must be done by a city or town to an initial adjacent AMA (Prescott AMA only)
  • There are two types of water that can be transported: water associated with historically irrigated acres (HIA) and water authorized under 45-555(E). Only the City of Prescott is allowed to transport water associated with settlement of the Yavapai-Prescott Indian water rights claims authorized by 45-555(E).
  • For HIA, an annual transportation allotment is calculated based on number of HIA acres * 3 AF per acre; in any year the amount cannot exceed 2x the allotment and cannot exceed 10x in any period of ten consecutive years.
  • For 45-555(E), the statutory limit is 14,000 AF. A final ADWR determination regarding the volume has not yet been issued.  A preliminary opinion stated 8,717 AF.

 

Surface Water

Del Rio Springs

The City of Prescott purchased the Chino Valley Irrigation District’s (CVID) rights to surface water impounded at Watson Lake and Willow Creek reservoirs. Under this agreement, the City of Prescott acquired ownership of the dams, the reservoirs, and through a sever and transfer action facilitated by the Department, acquired the storage rights on approximately 11,000 acre-feet annually of surface water flows. The City chooses to maintain the lakes for recreational uses and releases approximately 1,500 acre-feet per year for recharge at their recharge facility. Most of the CVID surface right holders also extinguished their groundwater rights and conveyed them to the City of Prescott in exchange for municipal and industrial water.


Water Quality

In general, water quality throughout the AMA is excellent. Radon levels that exceed standards have been detected in granitic formations around Prescott. The proposed federal maximum contaminant level (MCL) for radon may force domestic wells situated in hardrock areas to start receiving water from large providers.

 

Exempt Wells

Distribution of Wells Prescott AMA

 

More exempt wells are drilled in Yavapai County than in any of the other Arizona counties. Currently over 30% of all the new wells drilled in Arizona are in Yavapai County. Within Yavapai County, the concentration of these wells is within the Prescott AMA. As of August 2005, there were just over 11,200 registered wells in the Prescott AMA. While some of these wells are drilled in dry lot subdivisions, requiring hydrologic analysis, many are drilled on lots created through lot splits, for which no hydrologic analysis is conducted. Issues related to new exempt wells include well driller compliance, identification of concentrated areas where wells are required to be deepened or replaced, septic and property line setback compliance, and second exempt wells on the same parcel.

 

The graphic to the right shows the distribution of wells (in blue) throughout the AMA.

 

Septic Systems

Groundwater aquifers may potentially be impacted by nitrate and bacterial contamination due to septic tanks, forcing domestic well owners to start receiving water from water providers. Although most portions of the AMA are not subject to this threat, areas where the depth to water is shallow could be at some risk, particularly where municipal growth rates are high. A large portion of the exempt wells and dry-lot subdivisions in the Prescott AMA use septic systems for wastewater disposal, rather than utilizing a central wastewater collection and treatment system.

 

Declining Water Levels

Water levels continue to decline in many areas of the AMA due to the combined effects of long-term drought and the increase in pumping from new wells. An increasing number of homeowners are deepening or replacing domestic exempt wells.

 

Changing Water Demand by Sectors

Future water management in the Prescott AMA will need to consider the changing sector proportions of the overall AMA demand for groundwater. Changes in demand are occurring in each sector of use and are impacting the supply. The demand for water by the agricultural sector is expected to continue to decline over the next ten years at an accelerated rate but cities and towns in the AMA are experiencing rapid growth.