The statistical structure and filter characteristics of tritium fluctuations in fractured basalt

The statistical structure and spectral‐covariance characteristics of tritium fluctuations are examined from injection of low‐level radioactive waste in a fractured basalt aquifer. The tritium fluctuations are the result of a time‐varying injection well concentration. The integral scale of the fluctuations increases with distance from the source and the observation well spectra are characteristic of a dispersive‐type filter. On the basis of these qualitative attenuation characteristics, a theoretical filter is constructed and transport parameters are estimated. The analysis indicates that environmental tracers may provide a useful extension to controlled tests over large length scales (> 100 m). Although current research has concentrated on the importance of intrinsic variability such as porous media heterogeneities, the present study addresses the control exerted by extrinsic variability as exhibited by source strength fluctuations.