Aquifer storage change, 2018–2021, in the Big Chino Subbasin, Yavapai County, Arizona

This report updates groundwater-storage and groundwater-level trends presented in U.S. Geological Survey (USGS) Scientific Investigations Report 2019–5060, in the Big Chino Subbasin, Yavapai County, Arizona. This earlier geophysical investigation of groundwater-storage change in the Big Chino Subbasin was conducted by the U.S. Geological Survey, in cooperation with the City of Prescott, the Town of Prescott Valley, and the Salt River Project from 2010 to 2017 to understand groundwater-level and groundwater-storage changes. Conclusions were based on precipitation, streamflow, groundwater level, and repeat microgravity data; the latter is a direct measurement of groundwater-storage change. This report focuses on the southern part of the Big Chino Subbasin for water years 2018–2021. These more recent data show relatively small changes in groundwater storage, consistent with the earlier monitoring presented in U.S. Geological Survey Scientific Investigations Report 2019–5060. In the Big Chino Water Ranch area, water levels have increased gradually owing to discontinued pumping for irrigation during summer months, and an in-channel recharge event in summer 2021. In the Paulden, Arizona, area, gradual water level declines have continued a downward trend that started in the 1990s. Seasonal variation is present in the Paulden area, with higher water levels in the winter months when pumping for irrigation and agricultural use is reduced. Two wells showed groundwater-level increases consistent with in-channel recharge in 2018 and 2021, whereas groundwater levels in a well screened in the deeper, confined to semi-confined carbonate aquifer showed no such discrete recharge events. In the area west of Big Chino Wash and east of the Juniper Mountains and Santa Maria Mountains, groundwater levels continued long-term declines, but storage changes were minimal.