Low-Cost Aquifer Storage and Recovery: Implications for Improving Drinking Water Access for Rural Communities in Coastal Bangladesh

Abstract

Fresh water resources are scarce in rural communities in the southern deltaic plains of Bangladesh where both shallow and deep groundwater is frequently brackish, and fresh water ponds have been increasingly salinized by inundation during storm surges and brackishwater aquaculture. Low-cost aquifer storage and recovery (ASR) schemes were constructed at 13 villages in three coastal districts by developing storage in shallow confined fine to medium sand aquifers overlain by variable thicknesses of silt and clay. A typical ASR scheme consisted of a double-chambered graded sand filtration tank with a volume of 19.5 m 3 that feeds filtered pond water to four to six large diameter (d ¼ 30.5 or 56 cm) infiltration wells through PVC pipes fitted with stop valves and flow meters. The infiltration wells were completed at 18-31 m below ground and filled with well-sorted gravel capped with a thin layer of fine sand that acts as a second stage filter. Infiltration rates at 13 sites averaged 3 m 3 =day (range: 3-6 m 3 =day) over one year of operation. At 11 sites where water was abstracted, the recovery rate ranged from 5 to 40%. The source pond source water frequently had turbidity values of ≥ 100 NTU. After sand filtration, the turbidity is typically 5 NTU. Despite this, clogging management involving frequent (monthly to weekly) manual washing to remove fine materials deposited in the sand filtration tank and the infiltration wells is found to be necessary and effective, with post-manual-washing operational infiltration rates restored to annual average values. E. coli counts in recovered water are greatly reduced compared to raw pond water, although E. coli is still detected in about half of the samples. Arsenic in recovered water was detected to be at level of >100 μg=L repeatedly at three sites, suggesting that As risks must be carefully managed and require further investigation.

Influence of surface geology and micro-scale land use on the shallow subsurface salinity in deltaic coastal areas: a case from southwest Bangladesh

“…During the monsoon, rainwater harvesting provides an additional water resource in the region. Furthermore, Managed Aquifer Recharge (MAR) has also been utilised, where rainwater is stored artificially in the shallow aquifer for the use during the dry season (Sultana et al 2015).…”

Microbiological water quality of Managed Aquifer Recharge systems in the salinity-prone southwest coastal Bangladesh

“…During MAR system piloting, several designs were considered; the design found both costeffective and efficient for water storage was selected for scaling up 14, 21 . Ponds were the freshwater sources, pumped into an overhead concrete reservoir comprised two chambers, the first one for filtration and the second for storage.…”

“…The pumped water percolated through a slow sand filter, passed into infiltration wells by gravitational force; there was no chemical treatment of the infiltration water. Four infiltration wells were placed in a square to create a fresh water bubble at the top of the brackish aquifer 21 . The abstraction well was placed in the middle of the infiltration wells and was connected to a hand pump from which people collected drinking/cooking water.…”

“…Tubewells located near latrines, lakes or ponds can be fecally contaminated by unsealed handpumps or leaks at the base 20 . MAR systems use a shallow well with handpump for water abstraction, creating a risk of fecal contamination through surface runoff from unprotected wells 21 . The MAR systems utilized slow sand filters to reduce the risk of fecal pathogen transmission that are common in surface water.…”

“…The MAR systems utilized slow sand filters to reduce the risk of fecal pathogen transmission that are common in surface water. During piloting, MAR systems successfully reduced E. coli in the abstracted water though half of the samples still had low E.coli counts which might be introduced from the pond water or the surface runoffs 15, 21,22 . In the present study, our aim was to evaluate the new MAR systems' microbiological safety throughout the year.…”