An Integrated approach to Optimize Managed Aquifer Recharge as Long Term measure for controlling high Fluoride concentration in ground water

By * L D Mahapatra Geophysicist and *N K Shukla   Sr. Hydro geologist.

ABSTRACT
High fluoride occurrence in ground water was first noticed in and around Singh pur village of Khurda district in Orissa in 1987. During the subsequent years different areas in Nayagarh , Nuapada, Anugul disgtricts and sporadically in other districts of Orissa state such instances came to the notice. Efforts to tackle the problem were mostly ad hoc and tending to be curative rather than preventive. Studies by different organizations indicated a geogenic reason for such occurrence. Mostly in the granitic areas such phenomenon was recorded. Variation in the fluoride concentration in the ground water – low ( 0.4 mg/l) in post monsoon and high ( 1.67 to 5.07 mg/l) in pre monsoon lends strength to the notion that dwindling recharge over the decades has given rise to the problem and that by managing the recharge to the hard rock aquifer the fluoride concentration in ground water can be restored to the normal level. An integrated approach involving remote sensing, hydrogeology, geophysics and drilling was made to locate judiciously the appropriate sites for recharging the aquifer. Efforts have been made to identify the recharge areas suitable for accepting recharge rather than the random recharge practice commonly followed.

The investigation activities included source inventory covering all the ponds and open wells; water level measurement in the selected key wells; resistivity profiling in a grid pattern; deep resistivity sounding at selected sites  and drilling (60m) at selected locations to confirm the vertical depth profile of the sub-surface. The bed rock topography /thickness of the weathered zone were ascertained from the field data. The area with thicker weathered zone corresponds to the geologically disturbed zones and is suitable for recharge. Dry fractures at shallow depths of drilling, progressively reducing water availability in the ground water structures indicate lowering of ground water recharge in the area. The fluoride concentration in the ground water ranged from 0.36mg/l to 5.6 mg/l. Very low fluoride concentration (0.05 to 1.00mg/l) was observed in areas with thick soil cover. The average annual rainfall being about 1100mm/year the total runoff was worked out to be of the order of 67500M3. The pre-monsoon water level in the open wells ranged from 3.75M to 4.95M below ground level, while in the hand pump fitted bore wells 3.45 to 7.02m below ground level.

*Rural Water Supply & Sanitation Organization, Rural Development Department,
Government  of Orissa. Bhubaneswar – 751001,  India.
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