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Chloride Mass Balance (CMB) has been widely applied to estimate groundwater recharge rates. However, the impact of preferential flow on CMB results has not generally been considered. Measured chloride concentrations from two sites were modeled to provide an indication of the probability of preferential flow at a scale smaller than the core. One site was in long-term, dryland winter wheat near Stillwater, OK, while the second was in the Borrego Valley, CA. Results indicate that core sample concentrations at both sites may be replicated with small dispersivity values, which is consistent with little or no preferential transport within the cores. Likewise at Stillwater, replicate cores provided similar values of recharge indicating near uniform flow at the field scale. Contrarily, the Borrego Valley replicate cores gave greatly different values for groundwater recharge, indicating larger scale preferential flow was present.