Evaluation of sand-based stormwater filtration system for groundwater recharge wells

Abstract

Groundwater recharge wells have proven effective in augmenting and improving the quality of groundwater, but clogging remains a serious constraint in the absence of properly designed recharge filters. A laboratory study was undertaken in a PVC column of 22.5 cm diameter and 120 cm length to evaluate the efficiency of coarse sand (CS) of three particle sizes ranging between 0.35 and 1.0 mm as the top layer of a recharge filter for seven influent sediment concentrations of 250–3,000 mg/l. The performance was evaluated in terms of spatial movement of sediments, removal efficiency, recharge rates and clogging time. The results indicated that more than 60% suspended solids were entrapped in the upper 10 cm layer of CS, the removal efficiency improved with increasing thickness of the CS layer and the recharge rates declined sharply for influent concentrations of more than 1,000 mg/l. The study suggests use of larger particle size CS and reducing sediment load of inflow water. Field adaptation of these findings involves use of CS beds of 0.7–1.0 mm particle size and minimum 75 cm thickness as the top layer in recharge filters and providing a sediment tank or biological filters near the recharge structures to reduce sediment load of run-off water before entering the filter bed.