Forensic isotope analysis to refine a hydrologic conceptual model

Area of Science:

• Environmental Science
• Hydrogeology
• Geochemistry

Background:

• Water resources in the arid southwestern US face conflicts between competing interests.
• Owens Valley, California, is a critical water source for the Los Angeles Aqueduct (LAA), relying on river and groundwater diversions.
• Effective groundwater management for the LAA requires understanding aquifer quantity, interconnections, spring impacts, and recharge rates.

Purpose of the Study:

• To evaluate the hydrologic system in Owens Valley using targeted sampling.
• To corroborate existing conceptual and numerical groundwater flow models.
• To apply forensic isotopic approaches for independent verification of model interpretations.

Main Methods:

• Conducted targeted sampling of springs and wells within the Owens Valley aquifer system.
• Measured intrinsic isotopic composition, including boron (delta(11)B), sulfur (delta(34)S), oxygen (delta(18)O), hydrogen (delta D), and tritium ((3)H).
• Utilized basic chemical data alongside isotopic data to characterize aquifers and groundwater flow.

Main Results:

• Stable isotopic data provided rules for characterizing upper and lower aquifer systems.
• Confirmed interpretations of groundwater flow patterns near faults and flow barriers.
• Detected hydraulic connections between the Los Angeles Aqueduct and perennial springs along its unlined reach.

Conclusions:

• Forensic isotopic analysis serves as an independent check on conceptual and numerical groundwater models.
• The study successfully corroborated hydrologic interpretations and identified critical groundwater flow dynamics.
• Findings support improved technical analysis for managing Owens Valley's vital water resources.