High-resolution measurements of the three-dimensional (3-D) variability in pore water electrical conductivity (EC) were obtained at a clay-rich aquitard research site (the King site, 120 m ¿ 70 m area) in southern Saskatchewan, Canada, using direct-push probing technology (n = 35 boreholes). These measurements revealed complex lateral heterogeneity in the subsurface salt distributions which raised questions on the validity of the commonly used approach of transposing chemical data from distributed piezometers onto 1-D depth profiles for interpretation and solute transport modeling. Two-dimensional numerical modeling simulations demonstrated that distributed, nonuniform salt inputs have existed at the top of the unoxidized till aquitard for the past 3--5 kyr. The source of the nonuniform salt inputs is unclear but may be due to either variations in microtopography (<0.5 m) or variable penetration depth of surface fractures. A suite of generic solutions was developed to estimate the critical depth required to obtain chemical homogeneity in aquitards with nonuniform solute inputs and diffusion as the dominant transport mechanism. These solutions are presented for a range of sinusoidal input functions with varying amplitudes, magnitudes, and wavelengths. The solutions indicate EC distributions at the King site should be laterally uniform below a depth of around 20 m BG, which is consistent with observed EC values at the site. This study shows that aquitards with nonuniform salt inputs at their upper boundary are chemically heterogeneous above some critical depth and thus require careful attention when modeling solute transport processes within them.