EVALUATION OF SUB-SURFACE TRANSPORT IN A COMBINED WETLAND/RECHARGE BASIN

A tracer study was done using bromide and rhodamine dye to evaluate sub-surface transport and commensurate water quality transformations during sub-surface transport in a combined wetland/recharge basin. The system studied was a ‘leaky’ wetland that recharges at an average rate of 0.72 feet per day and approximately 72% of the water applied to the wetland infiltrates into the ground. After studying water quality transformations with both horizontal and vertical sub-surface flow, a tracer study was done in September of 2001 to evaluate the travel time during sub-surface transport. The results demonstrated that vertical infiltration rates at specific points varied from 6 ft/d to close to the average rate for the entire basin. The variation in infiltration rates did not have an effect on water quality transformations since an excess of carbon has accumulated in the wetland sediments, however, less sulfate reduction was observed at the higher infiltration rates.