A full waveform non-linear P and S wave seismic refraction tomography survey was performed to investigate potential karst and geologic subsidence features located within a proposed engineered stormwater control structure located in the western US. Work was conducted in the vicinity of solution features and subsurface voids identified during site regrading and preliminary cell construction. Original geomorphology and terrain of the area consisted of moderately to steep topography with interpreted northwest to southeast rending fractures. During site construction, highly variable bedrock topography and solution features were discovered and addressed through backfill and compaction. Preliminary survey results indicate areas of both subsidence and air-filled open fracture along coincident inferred joint traces.