Groundwater of Pahvant Valley, Millard County, Utah (SS-173)

By: Greg Gavin, Paul Inkenbrandt, Trevor Schlossnagle, and Rebecca Molinar

This comprehensive hydrogeologic assessment of Pahvant Valley's aquifer systems, conducted during 2022-2023, evaluated groundwater storage changes, recharge-discharge relationships, and anthropogenic impacts. The investigation integrated multiple analytical methods including potentiometric surface mapping, InSAR subsidence analysis, environmental tracer studies, and estimates of evapotranspiration using remotely sensed data. Results indicate significant groundwater level declines averaging 26 feet throughout the basin since 1986; the maximum observed drawdowns were 160 feet observed in the McCornick District. The transition from flood to pivot irrigation in the 1990s increased agricultural water consumption, evidenced by a 23,400 acre-foot increase in evapotranspiration between 2000-2021. Cumulative groundwater storage depletion exceeded 1 million acre-feet between 1960-2022, with storage declines observed in 42 of 62 years. InSAR analysis revealed up to 5 inches of subsidence from 2014 to 2022, indicating permanent aquifer compaction. Clear Lake Spring, a critical discharge point that supports a State Wildlife Management Area, ceased flowing in 2022, exhibiting a strong inverse correlation (r = -0.72) with pumping rates when applying a two-year lag. The investigation establishes that current extraction rates exceed sustainable limits, with annual groundwater pumping averaging 143,362 acre-feet (±7,881 acre-feet) in 2022.

Other Information:
Published: 2024
Pages 57
Appendices: 4
Location: Utah
Media Type: Paper Publication