Borehole Tracer Study: Ogallala Formation - northern High Plains
Objective:
Use empirical data and numerical simulations to test a long-standing
hypothesis regarding focused recharge to the High Plains aquifer; that leakage
and rapid movement of water and chemicals may occur down a poorly sealed
annular space of irrigation wells.
Approach:
Infiltration rates will be measured using a potassium bromide (KBr) tracer
applied at land surface at existing unsaturated zone study sites in the
northern High Plains.
Cores of unsaturated zone sediment will be collected before and after
tracer application to determine movement of bromide in one year.
Numerical simulations will be used to extrapolate experimentally determined
infiltration rates to periods representing typical irrigation-well life
expectancies.
Timing:
Initial coring to measure background concentrations of bromide and application
of KBr tracer occurred in November, 2003.
Laboratory analyses and numerical simulations began winter, 2003.
Final coring is planned for early Fall, 2004
Targeted Results and Benefits
Measure infiltration rates in the near surface under natural precipitation
and applied irrigation water (including ponded conditions) conditions at
hypothetical irrigation well sites.
Identify the potential and assess validity of hypothesis that poorly sealed
annuli of irrigation wells offer focused and rapid pathways for water and
chemical to reach the water table.
Complement the unsaturated zone studies already completed in the southern,
central, and northern High Plains.
Extend our understanding of water and chemical fluxes from land-surface
to the underlying aquifer.
