PRESCOTT, AZ (February 28, 2017) – In action today, the Prescott City Council approved a contract with Golder Associates, Inc., Tucson, Arizona, to create a refined groundwater flow model for the Big Chino Sub-basin. The technical work is a tri-party initiative of the City of Prescott, Town of Prescott, and Salt River Project (SRP), with its extensive surface water rights the largest raw water provider to the Phoenix metro area, for the purpose of assessing the hydrogeologic connection with the Upper Verde River, and potential effects associated with future pumping of approximately 8,000 acre-feet annually of Big Chino Sub-basin groundwater. Prescott and Prescott Valley have invested in a plan to import the Big Chino water into the Prescott Active Management Area (PrAMA), for future municipal water supply, and to contribute to achievement of safe-yield within the PrAMA. Safe-yield is a sustainable balance between natural replenishment and withdrawals from a groundwater aquifer.
The municipalities entered into two agreements with SRP in 2010 and 2012, the first of their kind pertaining to the Verde River basin, demonstrating the commitment of the parties to developing a better scientific understanding of groundwater availability and flow processes, oriented to preserving the long-term health of the River. The agreements set forth a cooperative approach to enhancing groundwater and surface water hydrologic monitoring, creating a new groundwater flow model, and conducting other investigations that may be identified as knowledge of the natural system is expanded.
"Prescott believes that the groundwater flow model, along with continuous monitoring of hydrologic conditions, will form the basis of a feasible plan to import water from its Big Chino property, while avoiding impacts to the Upper Verde River," said Leslie Graser, the City's Water Resource Manager.
Previous groundwater modeling encompassing the Big Chino Sub-basin included the US Geological Survey Northern Arizona Regional Groundwater Flow Model (NAGARFM) released in 2011. Due to its scale and area of coverage, approximately 1/3 of the state of Arizona, that model does not lend itself to the detailed analysis and decision-making necessary at a much more focused, individual project level such as water production and transport from the Big Chino Sub-basin.
“Experience has repeatedly shown that in the southwest, where both a water supply and developable land exist, growth will occur. This is likewise the case with the Big Chino Sub-basin,” he said. “It is not a question of if Big Chino groundwater will be pumped, but rather when and who will pump that water.”
The modeling work by Golder Associates, Inc., is aligned to provide a better understanding of the Big Chino Sub-basin and its hydrologic connections, how those may be affected by the pumping of groundwater, and a scientific basis for addressing mitigation of the groundwater withdrawal, should that be necessary. Additional hydrologic data collected over the past decade in advance of development of the water resource, continuing into the future and augmented by information from newly installed groundwater and surface water monitoring stations, will provide new insights into the hydrology of the Big Chino Sub-basin.
Greg Kornrumph, Manager of Water Rights for SRP, cautions that groundwater models should be supported by a wide variety of meaningful hydrologic information.
“The purpose of a computerized groundwater model is to predict how groundwater moves through the underground system; as such, it relies upon many assumptions. The ongoing monitoring program is intended to equip the modelers with more extensive actual information, in order to reduce the number of unknowns."
The cost of the groundwater flow model contract with Golder Associates, Inc., is approximately $1.1 million. Their work is scheduled to begin in March 2017, and be completed in 2020. Funding responsibilities for the monitoring and modeling programs are defined by Comprehensive Agreement No. 1, approved by the parties in 2012.