To meet the basic need of providing safe and Potable drinking water, the Nature's bountifulness of underground water reservoir is tapped by mankind by constructing a well with advanced technology and Engineering-what is called a Tube, well, with Pumping plant installed thereover and operated with power The tubewell as such is energised and commissioned and put to the use and benefit of mankind.

But like any animated or in-animated object, the tubewell has a life of its own, and after it has outlived its life, it naturally loses its useful purpose and utility value. Many a time, the tubewell although with a shorter life span as compared to its usual normal one, is said and found to have failed. It is in this context of failure of tubewells that we are touching upon in the paras to follow that are the probable causes thereof and as to what we should do Or we can do by way of remedial meas. ures in that direction so that the chances of failure are minimised and the performance of the tubewell could, in terms of its life span/quality be ameliorated upon, effecting economy as well.

Mr. Zahirul Hasan

Probable Reason of Tubewell Failures

Generally the discharge of tubewell may diminish due to the following

reasons.

(1) Depletion of ground water supply. (2) Faulty construction of tubewell. (3) Corrosion/encrustation of pipe slots.

Without going into any details on what is enlisted at (1) & (2) above, we hereinunder confine ourselves to precisely elucidate and detail on what is enumerated at (3).

Corrosion & Encrustation of Slots

Corrosion and encrustation of slots resulting well failure (decrease of yeild of tubewell with respect time] are the most commonly prevalent causes of tubewell failure. Encrustation i. e. scale formation takes place due to deposition of certain salts namely-carbonates, phosphates Silicates or Sulphates of Calcium (Ca); Hydroxides, phosphates and silicles of Magnessium (mg) and/or deposits of slimes or iron bacteria, Sudden pressure

drops associated with water entering well under heavy pumping releases certain CO and causes precipitation of CaCO, 3. Water saturated with Caco, are said to be responsible for scale formation in tubewells. Ferric ions present in soluble form can also be converted to insoluble ferric hydroxides by oxygen. Encrustation thus reduces the area of slots resulting into decrensed yeild of tubewells.

Corrosion may be due to chemical action of the ground water or due to galvanic cell formation when two dissimilar metels come into contact, or when there exists some areas of dissimilar oxidation potential in the same metals. This many reduce the yield of tubewell due to rupture of slots and thereby the pea gravels entering into tubewell pipe, effect reduction in the yeild of the tubewell.

The philosophy of treatment is based on the concept that wells yielding water having scale forming tendency, should be given acid treatment to disscive the scales which are clogging the slot's and the tubewells containing corrosive water should be treated with chemicals like

Where C & D are constants and Caion concentration and alkalinity are expressed in terms of mg/1 as Caco3 equivalent.

Positive value of saturation index indicates that water has tendency to deposit CaCo3 (scale forming property), where as the negative value indicates a tendency to dissolve CaCe, (Corrosive property) and zero value indicates that water is in equilibrium with calcite.

negative Langliers satutation Index to the positive and encourages the formation of a thin protective Layer of CaCo3 which will inhibit further corrosion as long as protective Layer exists.

The quantity of chemicals to be added and frequency of addition of chemical depends on the quality of water, volume of standing water column in the well with pumping not being in operation and the rate of water witdraw! from well,

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Due importance should be given while selecting the pipe material, i... eppropriate slot sympathetic to grain size, open area, quality of M. S. material of the well casing commensurate with the quality of ground water.

Development of tubewells should be done properly prior to their being put to use.

Delay in energising the well should be avoided - minimised, otherwise chances of encrustation/corrosion will be there.

If mineratised water is found in the area, the casing pipes should be made of/treated/coated with anti-corrosive paints e g. bitumen, alluminium, plastics and apoxy esins.

A resonably accurate Idea of the various chemical constituents and hydrogeological conditions likely to be encouraged at various places should be assessed in the area wherever the tubewells are to be

-Residual chloride 0.20 mg/1 Hypochlorite

-5% chlorine dioxide -continous chlorination

Hydrochloric Acid-30% -Hydro-Oxyacentic Acid-10%

-Sulphoanic Acid-10%

Roxel

Hyamine.

constructed, so that matching/appropriate material could be used.

7. Individual zone testing for the water quality/quantity is important to identify the zones to be tapped.

8. It is advisable that during the last phase of drilling a 5% hyprochlorite treatment be given to kill iron bacteria that may be present in the well and accelerate encrustation effect,

BLEACHING POWDER DOSER, GASIOUS CHLORONOME AND IT'S SPARES ETC.

CHLORINATOR FOR BACTER FREE DRINKING WATER

Wheel Type

RUBBER MOULDING COMPANY

39. Strand Road, Room No. 32. Calcutta-700 001. Phone: 25-1958