BASELINE WATER QUALITY OF 243 DRINKING WATER TUBEWELLS INSTALLED AT INTERMEDIATE DEEP AQUIFER (IDA) IN MATLAB, SOUTHEASTERN BANGLADESH

This study focuses on overall evaluation of groundwater quality of the intermediate deep tubewells (IDTW) installed at relatively intermediate deep aquifer (IDA) around a depth range of 120 m in Matlab, Bangladesh. Based on monitoring in depth-specific piezometer nests, this aquifer was identified to tap water which could be arsenic (As) safe and low in manganese (Mn) concentration. Groundwater samples were collected from 243 IDA in April-May 2012. Arsenic, iron, manganese and other drinking water quality parameters such as fluoride, boron along with the major cations were analyzed by high-precision ICP-OES, and major anions by ion chromatography. Bangladesh drinking water standard for As (50 µg/L) was exceeded only in 3 wells and more than 91% (n=222) were found within the WHO guideline value of 10 µg/L. For Mn, 89% (n=216) wells show the concentration within or below the previous WHO guideline value of 0.4 mg/L with a mean value of 0.18 mg/L. Most water samples are dominated by chloride and bicarbonate with a very low concentration of sulphate, nitrate and phosphate. The average concentration of chloride was found 250 mg/L. Water samples have a wide range of Fe concentration with a mean value of 4.2 mg/L. Most of the wells had fluoride concentrations below the WHO drinking water guideline of 1.5 mg/L, with a mean value of 0.38 mg/L. For Boron, mean concentration was observed 0.22 mg/L. Other trace elements such as Cd, Co, Cr, Co, Mo, Ni, Pb, Zr in most wells were below the detection limit. Groundwater samples were dominated by Na-Cl-HCO₃ to Na-Ca-Mg-Cl-HCO₃ type. From the perspectives of water safety plan, assessment of the groundwater quality of the drinking water wells is needed for a comprehensive risk management.