NATURALLY OCCURRING GROUNDWATER ARSENIC AND SALINITY AFFECTED SOUTH-WESTERN BANGLADESH: AN ASSESSMENT OF MANAGED AQUIFER RECHARGE (MAR) AND SUB-SURFACE ARSENIC REMOVAL (SAR) AS MITIGATION TECHNIQUES

Naturally occurring groundwater arsenic (As) contamination is one of the major problems in Bornal-Iliasabad union of Kalia upzila, Narail district, Bangladesh. Arsenic concentration was observed as high as 500 µg/L in the field tests. Laboratory analysis of groundwater samples showed As concentrations ranged from 20.33 to 158.90 µg/L. In relatively deeper aquifer (> 45m depth) in addition to As, presence of substantial amount of salinity is another major component deteriorating the quality of groundwater as drinking water. Electrical conductivity (EC) ranged from 1.01 to 7.9 mS/cm indicating the enormity of salinity. Amount of total dissolved solids (TDS) indicated more than 95.78% of the hand tubewells are producing brackish water. The groundwater is mainly Na–Cl to Na–HCO₃ type and is SO₄ limited. Only one sample was Ca–Mg–HCO₃ type water. This research demonstrates the effectiveness of two novel technologies (i) managed aquifer recharge (MAR) and (ii) sub-surface arsenic removal (SAR) for in-situ salinity and As treatment of contaminated groundwater. A two years long experiment revealed that MAR system was very effective in reducing groundwater salinity and As. The groundwater EC reduced 72–81% from the initial value of 3.4 mS/cm to less than 1 mS/cm. Arsenic from an initial concentration of 100 µg/L dropped below 50 µg/L and satisfying the acceptable limit guideline for Bangladesh. During the same research period the SAR system was also found effective in reducing As concentration below 50 µg/L form an initial concentration of 100 µg/L. The system was capable of yielding 1500 liters of As safe water when injected volume of oxygen saturated water was 2000 liters indicating 70–80% recovery per cycle injection. Both systems can provide 1,000 liters of As-safe drinking water at $2.00.