dealt briefly serialwise in this paper for the General k..owledge of the users to take full procautions in construction.

Precautions

[i] For every type of underground strata conditions different types of drilling rigs have been manufactured as ultimately the tubewell has to be designed keeping in view the type of sands to be tapped and entrance velocities to be kept below 0.1 foot per second. This can be achieved by using proper type of equipment, 'proper size of bore and to accommodate proper design of the assembly and proper thickness of gravel pack of correct grading of river bed gravel.

[ii] The drilling agency and the clients

must know if the artificial gravel packed tubeweil or natural gravel packed tubewell or cavity, strainer or open bore type is to be designed and got constructed. This knowledge is very essential. Any deviation from the proper type will result in sick tubewell which will ultimately fail in due course.

[iii] Though best quality of material with proper thickness and compositions are available in the market but selection of drilling agency is always by price instead of quality and merits. There is tendency to use substandard material to economise. In most of the cases, this is not in the knowledge of clients but in several cases use of substandard materials is allowed deliberately for various reasons and personal benefits.

[iv] In some cases before placing the assembly, bore collapses and some how or the other, assembly is driven up to position instead of its free placing. Even at the time of shrouding gravel which is a continuous process there is a gap causing bridging. The clients do not come to know about these construction defects which are not visible on completion of the tubewell unless the construc

tion work is being supervised continuously every minute, Precautions can save such situation.

[v] According to the standard practices, the development of the tubewell is to be done by over-pumping to the extent of 25 to 30% which is very essential, Clients hardly know about standards and the construction job is supervised by Civil Engineers who are not aware about this specialised profession of tube well construction. They easily fall prey to unscrupulous drilling agencies and accept under developed tubewells, which is the main reason for sick tubewells and finally becoming and pumper and definite failure due to filling and water way areas. In short if the drilling agency and departments are honest and they educate the clients well in advance about different construction methods and designs of the tubewells, the above enumerated causes can be eliminated. It is always better to conduct survey, exploration or tria bores by spending some additional amounts to ensure properly to construct final tubewell. Though there are several books and standards but clients neither care to study nor the drilling agency care to informs them purposely. However, even if the tubewell is constructed properly, then the responsibility of the clients to safeguard the tubewell & have periodically checks on discharge, depression and quality of the water becomes extremely important. However, (1) if the soils are aggressive, instead of conventional M. S. pipes, fibre glass, U. P. V. C., stainless steel, G. I. and brass and other types of pipes, screens etc. can be used. Moreover, all the material should be brand new, and fresh. If the sed material is introduced either in full or partially this will also lead to various defects in due course, such as, pitting, ho'e corrosion & incrustation. (2) Clients normally consider underground water just like gold or coal mines and start pumping either to its maximum capacity or more than the capacity of the tubewell to

take maximum advantage of Underground water for their projects and production purposes. This tendency of the clients leads to total failure of the tubewell in their short life span, which can be avoided by pumping only recommended yield. (3) Normally after construction of the tubewell, supply of pump and its erection is undertaken separately by the clients. It the job is not handled by experts, the wrong thickness of column pipes or other careless. ness in installation results in dropping of the pump in the tubewells. Some times, the impact of dropping is so great that week points in the tubewells such as reducer and delicate screens are damaged. The cause can be avoided by extra-ordinary care. (4) In most of the cases the completed tubewell is kept without proper guarding and in most of the cases we have come across unloading of truck loads of stones boulders and heavy iron articles on the tubewell which results in breaking of the well cap and then dropping of such heavy external material in the tubewells, in most the cases even miscreants and children remove the well cap and start throwing brick bats, left over gravel in the tubewell. All the problems are extremely diffi. cult as such material cannot be removed either with airlift system or with mechanical methods and tube. wells become total failure.

Having explained the main causes, proper cares to be taken. We still find about 80% of the sick tubewells which were drilled by various agencies on account of above reasons and balance 20% tubewells become sick due to normal wear and tear which is unavoidable but can be reduced by periodical checking.

incrustation can be rectified to some extent by acid treatment or surging to renovate the tubewells to its original capecity. Dropped pumps can be removed by taking impressions or Photographs under water and then preparing special fishing tools for definite catch. The tubewells filled up with soft material can be cleaned by bailing and airlifting. Harder

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material can be partially removed by unscrewing top housing pipe up to water level and then using special tongs and tools to lift heavy material without damaging the tubewell structure, Case History

During 35 years of drilling career author has come across hundreds of cases of wrong designs, wrong uses of drilling equipment defective development and several tubewell have been corrected by re-development of sealing the damaged portion of the tubewell if it happens to be at the bottom and in some cases by providing sleaves if the screene are damaged at the top or middle. Most of the tubewells have been renovated by acid treatments as the organisation controlled by the author has got special crew to tackle such problems after thorough inspections. Out of hundreds such cases I give below the case history of one tubewell which was got constructed by Hotel Corporation of India at Centaur hotel. Palam Gurgaon Road, New Delhi, where all the others had failed to rectity end renovate the tubewell which was constructed only 2 years prior to its failure. The author with great difficulty took impression as this was the case of external filling with bricks, boulders, gravel, ironrodes, leather chappels and empty tins which was due to the combined causes of unloading trucks in the tubewells which was not properly caped and then mischief of village urchins as the tubewell was left unguarded by Hotel, Corporation. As stated above 10 mtrs, of upper pipes were unscrewed by making sloping pit around the housing pipe to handle unscrewing job menually. After removing the main blockages in upper portions of the housing pipe the stuck up boulders and other iron rodes were

pulled up by special tongs, then the softer material was balled out and finally after assembling the tubewell upper housing pipe again and filling the sloping pit the tubewell was developed to its original capacity. In this way the Hotel Corporation of india spent hardly Rs. 10,000 to rectify their tubewell costing Rs. 70,000 By the same organisation we were asked to driil one more tubewell

as the previously constructed similarly designed tubewells were yielding not more than 7 000 g. p h. The author had full knowledge about water potential and the specific yield of that area and anticipated double the discharge out of similarly designed tubewell provided the drilling bore size was proper. Slot size and consequently the gravel size was to match the sand grain of the area. The strata and assembly location chart of the tube wells drilled by the other agency showed the correct design but frankly speaking the work was not exacuted as shown in the chart though work was executed by well reputed drilling agency having 50 years of standing, but they econo. mised in bore dia.

As the top most architects were involved and the author was sure about water potentials having already drilled several tubewells in that area near to Centaur Hotel, the author's organisation took up the challenging job of constructing new tubewell within the same depth and some length of screen and same diameter of bore shown by the provious agency, the job was executed under

direct supervision by the author and as anticipated we got 15,000 g. p. h. discharge slightly more than double of the previously constructed tubewells. The Hotel Corporation of India had to spend practically tha same amount to get double the discharge. This particular case of Centaur Hotel is not disclosed just for authors organisation's advertisement, but as a case study to prove that all the above mentioned points and methods of rehabilitation if taken up sincerely can be in the interest of the nation and total loss saved by Engineering skill.

The normal tendency of advising clients to forget about sick and failed: tubewells & to go in for new tubewells is very common but we believe in using expertise in national interest. There are several other cases where Government departments and other top most agencies drilled tubewells which failed during 2 to 3 years of their operation and we coulp renovale those tubewells which are still working after even 7 to 8 years of their renovation, Now paper is opened for discussions.