was used with the local model to estimate the concentration of an environmental tracer, sulfur hexafluoride, in 10 USGS transect wells near the Merced River that were sampled for this constituent. Measured and estimated concentrations in the mid-depth and deepest wells, which would be most sensitive to errors in hydraulic conductivity estimates, were consistent. The combined results of particle tracking and sulfur hexafluoride analysis suggest that most water sampled from the transect wells was recharged less that 25 years ago.

Introduction 1 Drilling and piezometer construction 3 Subsurface data 3 Drill penetration rate logs 3 Core sample descriptions 7 Borehole geophysical logs 7 Lithologic logs 11 Summary 11 References cited 11 FIGURES 1. Map showing location of study area 2 2. Map showing location of piezometers drilled on Edwards Air Force Base, 1991-92 4 3. Drill penetration rate logs, construction diagrams, and lithologic logs for piezometers at the Buckhorn, Branch Park, and South Shore sites on Edwards Air Force Base, 1991-92 14 4. Borehole geophysical logs, drill penetration rate logs, construction diagrams, and lithologic logs for piezometers drilled

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