A recent 18-month period of “resting” Prescott Valley’s Central Well Field has resulted in rebounding water levels and shows the health of the aquifer over which the Town is located.
The Town’s water supply depends largely on water stored in a vast underground geologic formation called the Prescott Active Management Area Aquifer. The Town is located directly above a portion of the aquifer which runs from Dewey to Williamson Valley and north through Chino Valley. According to Arizona Department of Water Resources (ADWR), the aquifer contains around 950 billion gallons of water and is one of the aquifers from which the State of Arizona limits groundwater pumping (Fourth Management Plan for the Prescott AMA, ADWR, 2014). The Town must manage its water system pumping under State regulations.
Prescott Valley purchased the Central Well Field in January 1999 from the former Shamrock Water Company and decided to add another well. The drilling contractor was skeptical that he’d find water at the site. When that well was found capable of pumping 3,000 gallons-per-minute, it was named “Fat Chance Well.” Over the past 20 years, the Town has pumped about 11.3 billion gallons of water from the Central Well Field’s four wells.
During the Great Recession the Town needed to reduce the number of operating wells to save money. “It was natural to depend heavily on the Central Well Field because it is located close to the center of Town near the storage tanks and contains some of our best producing wells,” said Town Utilities Director Neil Wadsworth. “However, that continuous pumping had a significant impact on the water levels in the area, creating a localized drawdown of about 150 feet in the water table.”
The Town rested the well field beginning in the summer of 2018, to the current time, pumping sparingly from the field in summer 2019 to meet peak demands. During that time the Town pumped primarily from its well field north of Highway 89A. The Town also rested the Central Well Field in the mid-2000s, with a significant recovery. The latest rest period allowed water levels to recover and even increase above the original levels at the time of the Shamrock Water purchase, according to the latest ADWR measurements.
The recovery is encouraging as the Prescott Active Management Area works to reach the mandated Safe Yield by 2025, replacing through natural and treated wastewater recharge the same amount of water pumped each year.
“If the water table was significantly declining here, we wouldn’t see the level of recovery we’ve seen in the Central Well Field. When we let it rest, the entire well field has a chance to fill back in. When we measure the depth to water now, and compare it to 20 years ago, the field shows no decline despite population growth and 20 years of use,” Wadsworth said.
The Town has continued to improve its water pumping and storage capacity with three new wells, refurbishing several older wells, and completing the construction of a two-million-gallon new storage tank.
“We will continue to manage the Central and North fields, pumping from various locations and allowing areas to rest on a more consistent basis so we don’t see a big decline at any single well,” Wadsworth said. Managing the drawdown caused by pumping at each well is important to maintain pumps and equipment.
ADWR has a monitoring well at a location in Prescott Valley’s Central Well Field. “Their data and independent measurements through May 2020 confirm the recent increase in the water level,” Wadsworth said.
“To see no decline in the local water levels after resting this well field speaks to both the resiliency of the aquifer and the wisdom of spreading out pumping to other locations,” said Town Manager Larry Tarkowski.
View a graph of historical water levels here.