A dry bore well during drilling can be water bearing after some time. You may check whether this has happened to your dry bore well. You may find some useful information in this regard at https://www.indiawaterportal.org/questions/failed-borewell-hyderabad-andhra-pradesh-need-advice-chances-recharge
Any groundwater occurring in water-bearing fractures beyond 1000 feet will not be able to provide sustainable supply as nature takes very long time to fill back the empty fractures once again. It is therefore not advisable to go deeper in the same bore well.
Although electrical resistivity surveys are best suited to select favourable sites for drilling bore wells in open areas, there are limitations in their use in urban areas. For example, to test groundwater availability at a site at a depth of 100 metres, apparent resistivity has to be measured by fixing four electrodes along a straight line for a distance of 150 metres on either side of the site. Because of space constraints, it often becomes necessary for the geophysicist to guess conditions at such depths without actually taking the readings.
One normal approach followed by geologists is to select a new well site sufficiently far away from the existing wells so that there will be no well interference. Although this approach is good if groundwater occurs everywhere uniformly, it is better to select the well site by ensuring that it lies in a linear zone with successful bore wells on either side along the zone.
Because of serious limitations in the use of scientific methods in urban areas, water diviners claim their method to be superior. There are again geologists, who employ both divining and electrical resistivity surveys to locate well sites. It must be however known that no one can be 100% successful.
Contributor: R Jagadiswara Rao (https://www.indiawaterportal.org/users/rjagadiswara)
Most of us are not aware that groundwater is available in two discontinuous layers. The top layer, which can be thought of as the shallow aquifer extends up to hard rock and the other, the deep aquifer is what is available within the rocky layer. It is the shallow aquifer which can be sustained through artificial recharge during monsoon.
We at the rain centre in Chennai have started creating awareness among urban residents about the importance of “Conjunctive use of aquifers”. According to this newly discovered concept, we suggest to the residents to create a shallow groundwater source (if they do not have one) extending up to rocky strata and start exploiting it immediately after monsoon and switch over to the deep aquifer subsequently.
What is happening now in almost every big city in India is that the shallow aquifer, which gets replenished every year after the monsoon, is completely ignored. People having gone in for a deeper source are totally dependent on that, which over the years has depleted with very little chance of getting replenished through rainwater harvesting.
I would like to offer the following suggestions:
- To find out the depth at which hard rock is encountered within the premises.
- Create a shallow tube well (if there is’nt one at present) up to that depth.
- Arrange for aquifer recharge by means of recharge wells.
- Exploit this shallow aquifer immediately after monsoon till it goes dry and switch over to the deep bore well.
- Try and find out from the bore well digger whether he has provided plain or slotted casing pipe up to the rocky strata. If he has provided only plain pipe get it replaced by a slotted pipe so that recharge will benefit the deep aquifer also.
Contributor : Sekhar Raghavan (http://www.raincentre.net)
