Theme 2-8-Revitalization of tubewells yielding saline water in Delhi - A case study

Abstract

The National Capital Territory of Delhi is besieged with the problem of acute shortage of good quality drinking water. The problem is further aggravated by the fact that the contribution of groundwater to the drinking water supplies of Delhi is only about 15% due to limited resources. This is more so because of occurrence of brackish to saline water at shallow depths in almost en¬tire Delhi. The top fresh water aquifer is not separated with the underlying brackish/saline aquifer by an aquiclude. This results in the up-coning of the fresh-saline water interface due to heavy pumping being resorted to in several areas. This in turn leads to pumping of saline water and the tubewell being abandoned and precious investment going waste. One such case of up-coning of the fresh-saline water interface and pumping of saline water as well use of remedial measures successfully were taken up and the results are presented in this paper.

Quaternary Alluvium underlain by Alwar Quartzites of the Delhi System occupies the NCT of Delhi. The Fruit and Vegetable Project of National Dairy Development Board located in western part of Delhi depends on groundwater for running it’s plants. However, two tubewells constructed in the campus started yielding saline water soon after being commissioned. The electrical conductivity values were in the range of 9400 micro mhos/cm. at 250 C. The tubewells were only 29.5 and 30.5 meters deep and the saline-fresh water interface was at 39 meters below ground level (mbgl). But due to continuous pumping at discharges of about 45 m3 / hour, the pumped water became highly saline due to up-coning of the interface. A safe discharge was worked out based on an equation to work out the position of the moving fresh-saline water interface in response to withdrawal of fresh water by shallow wells penetrating a short distance above the interface. The depth of one tubewell was also reduced by sealing the bottom three meters with cement slurry. The safe discharge, base on the equation, was calculated to be 18 m3/day. The well was pumped continuously at this discharge for 480 minutes and the electrical conductivity of pumped water at the beginning of pumping was 3182 micro mhos/cm. at 250 C and at the end of 480 minutes it was 3084 micro mhos/cm. at 250 C.

The experiment, based on scientific basis, thus proved to be successful in revitalisation of a tubewell which was otherwise yielding highly saline water. The same technique can be used to revitalise thousands of other tubewells lying defunct all over Delhi.