Current Groundwater Use
For residential use, the 2010 Census found 10,669 residents in the Big Chino/Williamson Valleys. At average per capita water use rates, we estimate about 1,800 afy of groundwater is used.
Thus the total current groundwater use is in the range of 4,800 afy to 7,500 afy, reflecting the uncertainty in agricultural usage.
Planned Uses for Big Chino Water
The 8,067 afy of exemption water will be divided 54/46 between Prescott and Prescott Valley. Prescott has committed 900 afy to the phased expansion of the Deep Well Ranch. Prescott Valley has committed 2,000 afy of their 3,711 afy share of Big Chino exemption water to development on a section of State Trust Lands near the city. Prescott Valley has not committed any exemption water, or the effluent collected from using that water, either to safe yield or to mitigation; presumably PV’s share will be entirely used to support growth and development.
Prescott Council Resolution 3688 states that their share of the HIA water will be dedicated to either safe yield in the AMA or to mitigate the effects of pumping on the Verde River and would not be used for development or growth. Prescott Valley has made no official commitments to use their share of HIA water for safe yield.
Future Population Growth
Longview Pumped Storage Project
Longview Energy Exchange, LLC has applied for a preliminary permit to the Federal Energy Regulatory Commission (FERC) to operate a pumped storage energy facility in the Big Chino Valley, about 6 miles south of Seligman. The project will construct a water storage reservoir high on the slopes of Picacho Butte connected by subsurface pipes to another reservoir on the valley floor.
Pumped storage is similar to a battery in that it only stores electric energy; the process is roughly 80% efficient. The project intends to profit by using the price spread between off-peak and peak power rates. Possible sources of off-peak power would be regional coal-fired power plants and wind-generated power. California is a potential market for peak power sales.
The consumptive water use is estimated to be 1,200 acre-feet/year, mainly by evaporation from the reservoir surface.
Longview Energy has not released any reports on the environmental effects of the planned project, despite several requests.
Summary of Big Chino Demand
Future groundwater demand from population growth and development in the valley could exceed 20,000 afy.
Groundwater use for agriculture is not constrained by state water laws, so it is easily possible for a new alfalfa farm to use thousands of acre-feet every year; this is an unknown factor.
The Longview Pumped Storage facility will use substantial but unknown amounts of groundwater.
By 2050 the potential groundwater demand could exceed 40,000 afy – more than three times the base flow of the Verde.
There is little exact information about current groundwater use in the Big Chino; but some estimates are possible. For irrigation water use, 2016 aerial surveys indicate 1400-1900 acres of irrigated lands in the Big Chino (including Williamson Valley), the USGS estimates that 3,000 – 3,200 acre-feet/year (afy) of groundwater is used for irrigation. However, the state law on HIA water indicates that up to 5,700 afy is used - an obvious discrepancy. Historical estimates of Big Chino agricultural groundwater pumping report approximately 20,000 afy.
Although population projections are frequently inaccurate, estimates are possible. First, note that the Yavapai County General Plan classifies Paulden and the Big Chino as a designated growth area. As of 2016, the Paulden area was one of the fastest growing areas in Yavapai County, showing a 1.3% annual growth rate. The Central Yavapai Highlands Water Resource Management Study projects Big Chino growth at 2.25% per year to over 32,000 by 2030, which would then use about 5,000 afy of groundwater. At build-out in the Big Chino, at the current 2-acre minimum zoning, 75,000 homes for 165,000 residents could be built, requiring 26,000 afy of groundwater.
The reservoirs will be initially filled by pumping 17,000 acre-ft of groundwater from the Big Chino sub-basin. In operation, the project will use inexpensive off-peak electricity to pump water into the high reservoir, typically at night. During peak electricity rates periods, typically summer days, water is released from the upper reservoir into the lower reservoir to generate power for sale.
Approximately 3,717 afy of potential HIA water remains unclaimed in the Big Chino Valley. At this time the total legally exportable water from the Big Chino is 18,813 afy, including the Big Chino Water Ranch and HIA water.