Are there any spacing norms between Bore wells and Open wells?

There are no spacing norms between bore wells and open wells in Kerala. The wells are located scientifically based on the local hydrogeological condition of the area through field groundwater investigation which is a mandate for every well construction. However to protect the source of a public water supply scheme, prior permission is required from Groundwater Authority to construct a new bore well within 30 meters from any exciting drinking water source from where water is pumped for public purpose.

Will my Open well go dry if a new Bore well is drilled nearby?

Bore wells and open wells are totally different groundwater extraction structures tapping separate groundwater storages called aquifers. Bore wells tap fractured aquifers in confined/semi confined condition. Whereas open wells tap unconfined aquifers only. According to the general principles of Groundwater Hydrogeology confined and semi confined aquifers are not interconnected as their terminology denotes, and so extraction of water from the confined/semi confined aquifer through bore wells will not normally interfere with the adjoining open well tapping the unconfined aquifers. But bore well tapping the same aquifer (confined/semi confined) may interfere each other if they the area falls under the same structural continuity of the other well, while mutually pumping. But there are places where open wells interfere with the adjacent bore wells if fractures present at the open wells extend deep in to the fractures yielding bore wells. In such cases there may be chances of open well getting dry. The adjacent open wells may also become dry if bore well casing is not properly seated in to the bedrock and that if the soil thickness is less and that the fractures are on the same line with the bore well.

What is an inner casing and outer casing in a Bore well?

The outer casing pipe referred to a bore well is the protective pipe inserted in to the bore hole to protect the soil profile present above the rock in the vadose zone called overburden. The purpose of the casing pipe is to protect the bore hole from falling or debris in to the bore well and also to prevent leaching of surface contamination. The outer casing is normally seated in to the hard strata by drilling few centimeters in to the bedrock. The inner casing on the other hand is only an optional protective pipe inserted into the well till the lower end of the borehole. An inner casing is not needed in ideal condition but it is preferred under suspicious geological conditions. Inner casing would have lesser diameter than the outer casing and is normally used with perforations at certain depths for the easy flow of groundwater in to the well. Inner casing acts as a shield and gives extra protection to the pumping devices especially while using submersible pumps.

Is there any permission required for bore well drilling?

The Groundwater department is the nodal agency in the State for groundwater exploration and development. It is mandatory for all the government departments to seek the feasibility report from groundwater department before taking up the bore well drilling. The amendment of Kerala Building rules 93 (a) enforced the clearance from groundwater department to issue permits for the construction of bore wells/tube which is mandatory to obtain from the bodies. The clearance stipulated is nothing but the feasibility issued by the department after conducting a field study considering the existing users in the locality and other hydrogeological conditions in the area. The feasibility report would have the recommendation of the location of the spot for drilling, diameter of the well, and also the depth to be drilled. In addition to the above, all notified blocks in the State would have to obtain prior permission for both construction and conversion, which means to modify the depth, diameter, changing the horse power of the pumping device etc.

What is the difference between Bore wells and Tube wells?

As the term denotes, the bore wells and tube wells are two different groundwater abstraction structures to extract groundwater from subsurface aquifers. Bore wells are drilled in hard crystalline rocks whereas tube wells are drilled in soft sedimentary strata especially along the coastal stretch. In bore wells casing pipes are used only up to the bed rock while tube wells have pipes lowered up to the full depth of the bore. The method of construction of bore wells and tube wells are also different. Bore wells are drilled using down the hole drilling (DTH) technique. The DTH hammer is one of the fastest ways to drill hard rock. The fast hammer action breaks hard rock into small flakes and dust and is blown clear by the air exhaust from the DTH hammer. The tube wells are drilled using Rotary Drilling method. The rotary rigs are provided with rotational drill bits in which clockwise rotational force is applied to the drill string to facilitate the process of drilling a borehole. Rotary speed is the number of times the rotary table makes one full revolution in one minute (rpm). In Direct Rotary method, muddy water is pumped into the bore through the hollow of the drill pipes allowing the mud to rise up to the ground surface along the outer surface of the drill rod carrying the drill cuttings with the flow. Water is used in controlled quantity to maintain viscosity of the mud so that it can carry sufficient drill cuttings (mostly sand) during its upward circulation and also prevent the bore from collapsing temporarily. Conversely, in Reverse Rotary method, water is allowed to enter the bore hole along the outer surface of the drill rod and is sucked out to the surface through the central hollow of the drill rod (pipes) carrying the drill cuttings. Reverse rotary method provides a more accurate strata chart.

Is cleaning a bore well/tube well possible?

It is reported that over a long period of constant use the yield of bore well/tube well declines. The clogging of well screens in tube wells and also cementing of clay particles in case of limited number of fractures would be the reason for this situation. In some other cases falling of silt and sand size particles due to the transient flow inside the pipes reduce the yield of the well and making pumping difficult. The remedy is to clean the well with water jetting or pressure injection called flushing. Groundwater department offer such services to the clients on demand for which a fee of Rs.5250/- is charged.

Why two nearby bore wells have different yields?

The yield of the well depends on the Transmissivity (T) and Storativity(S) of the aquifer. This depends on the thickness and nature of the aquifer material present. The bore well taps groundwater from fractured aquifer which may be interconnected. Yield of bore wells depends on the limit of these fractures. It may be possible that the depth of penetration of inclined fractures and its extend may vary in a vertical cross section even within few meters of horizontal distance on the ground. This is the reason for the differential yield in bore wells even within a small distance.

What is the maximum drilling depth permissible in Kerala?

The drilling depth of bore wells is determined through filed investigation by considering the depth and occurrence of fractures of the existing wells in the locality. This is employed to maintain equilibrium of groundwater regime as part of groundwater management. The normal depth of drilling in Kerala is 60-100m below ground level. However the drilling depth varies from place to place. Hence depending upon the heterogeneity and the hydrogeological condition of the terrain the recommendation of depth is confirmed through field verification.

Will a 150mm bore well give more water than a 110 inch bore well?

The occurrence of groundwater in hard rocks areas is very much limited. The top portion of hard rocks in many areas develops extensive fractures and secondary porosity to a considerable depth due to weathering. The highly weathered granular hard rock yields water to bore wells. Presence of deep sheeted intensive fracture system in granite, contact zones between two similar or dissimilar hard rock formations, sets of joints, fissures, veins etc. transmit sufficient quantity of water under confined and semi-confined conditions. The aquifer pressure exerts a driving force for the movement of groundwater within in the fractured aquifer through interconnected fractures. Hence the diameter does not have any significance to the yield of bore wells. The yield of both 110mm bore well and 150mm bore well may be same. But the choice of diameter is based on the depth requirements of bore well for which larger diameter would help easy installation of pumping device of higher capacity in deeper bore wells.

What type of pump do I require to lift water from a low yielding bore well?

The static water level of low yielding bore wells decline rapidly while pumping hence often have less water column for pumping. The rate of recovery in such well would also be poor which leads to dry run of the motor in submersible pumps causing damage to the pumping device. Hence air compressor pump is used to lift water from low yielding wells. The compressed air is introduced into the nozzles at the foot of the delivery pipe, which is fixed in the well from which water is lifted. In the delivery pipe, which is partly open to the well or sump which contains water, a mixture of air and water is formed. This air-water mixture is discharged through the delivery pipe. The flow will continue as long as the compressed air supply is maintained. This type of pump is good enough to lift small amount of water from low yielding bore wells.

How will I know the yield of the well?

The yield of the well is carried out through a pumping test. It is carried out to determine how much groundwater can be taken from a well, and what effects pumping will have on the aquifer and neighbouring well supplies. There are different methods and different approaches to carry out pumping test in different type of wells. Groundwater department is equipped with four pumping test units to carry out pumping test in different types of wells. The yield testing of wells are normally done during the dry periods to get most accurate result.

Can I recharge my open well directly from roof water?

Rainwater harvested from rooftops serving as a “catchment area” particularly in urban areas with moderate to high rainfall and stored in tanks for domestic use. Excess rainwater can be diverted for recharging the groundwater. If groundwater recharging is proposed in a domestic dug well used for drinking. It must be ensured that the impurities from the roof top are removed through filtration before recharging in to a well. First few showers are normally avoided as it may likely to contain dust particles and impurities present in the atmosphere. A roof water recharging system should have a clean roof top connected to a proper filter mechanism with provision to divert the impure water.