FLOW SEPARATION IN UNDISTURBED SOIL USING MULTIPLE ANIONIC TRACERS .3. UNSTEADY CORE-SCALE INFILTRATION EXPERIMENTS

Solute transport through structured, undisturbed soil has been studied in transient, unsaturated experiments using columns from grass and wo odland sites on the Lancaster University campus. Three anionic tracers have been used, bromide (Br-) and two fluorinated organic acids (pent raflurobenzoic acid and 2,6-diflurobenzoic acid). The process of displ acement of stored water from undisturbed columns was investigated usin g successive inputs of different tracers under similar antecedent cond itions. The results indicated that initial breakthrough was rapid, wit h a relative concentration of 0.8 being reached between 0.4 and 0.5 po re volumes of discharge. It was found that there was an apparent conti nued discharge of 'old' water, stored in the column before any additio ns of tracer, even after the addition of a total of 4.9 and 5.4 pore v olumes of water for the grass and woodland columns, respectively. The implications of the results of these tracer studies for modelling solu te transport in structured soils are considered.