THE WATEK-SUl'l'LY OF TOWNS IN THE TKOPICS 301 



The advantages of a deep well supply were, that in all probability a clear and pure 

 water would be forthcoming and that such water would be safe from pollution and would 

 not require filtration. Its disadvantages consisted in possible heavy expense and in the 

 chance that the supply might be inadequate or the quality unsuitable. It might be 

 excessively hard or contain iron in undesirable quantities, or be of such a nature as to 

 require special treatment. In short, though one knew where one was with the river 

 supply, one was totally in the dark as regards the deep wells, for nothing was definitely 

 known regarding the geological formation, and there was nothing to guide one in a new 

 country like the Sudan. 



After some discussion, it was decided to have a trial boring sunk, which would both 

 furnish information regarding the strata and enable samples of water to be obtained for 

 chemical and bacteriological examination. At the same time I set on foot some enquiries 

 into the flow of the subsoil water and its relation to the Blue Nile. A site was selected Khartoum 

 above the town and close to the southern bank of the Blue Nile, and operations were eJ'peHme^ms'' 

 commenced with great energy. Indeed, so great was the energy displayed that instead of 

 a single trial bore, the whole of an elaborate scheme of well-sinking was carried through ; 

 nor could it be checked despite protests and representations from those responsible for the 

 public health. Proper samples for analysis could not be obtained for months, and when at 

 last the engineers declared themselves ready to submit such samples, it was found that 

 six wells had been sunk, but as a seventh was afterwards drilled it will be convenient to 

 describe the installation at a period just prior to that when the final tests were made. 



The site has already been stated. It suffices to say that no great distance away lies 

 the village of Buri which is served by shallow wells liable to pollution. 



The water works, as will be seen (Fig. 94, page 288), consisted of seven wells and 

 a pumping plant. Since then, a large, covered reservoir has also been provided. The 

 wells lie along two lines, one at right angles to the river, the other nearly parallel to it. 

 Well No. 5, in the first line, is 30 yards from the river bank. The wells are about 

 60 metres apart, are drilled, and at that time were of the following depths, i.e. Nos. 1, 2, 3, 

 4, 5 and 6 of 75 metres, and No. 7 of 176 metres, these depths being, to all intents and 

 purposes, from ground level. 



Wells Nos. 1 to 6 were alike in being fitted down to a depth of 22-40 metres, with a 

 casing pipe of 9-| inches diameter. Below this point, the bore-hole, 8 inches in diameter, 

 extended, unguarded, to the full depth of 75 metres. 



Well No. 7 was cased with a 6j inches pipe down to 54 metres, while the unguarded 

 bore-hole, of 6| inches diameter, extended below this to the full depth of 176 metres. 



As has been said, there was originally no reliable information regarding the geological 

 structure of the site. Some details had been gathered and sections prepared when Well 

 No. 1 was drilled, but as there was no core-boring and the material was washed out in a 

 finely comminuted state, the information furnished could not be regarded as very reliable. 

 Indeed, subsequent observations proved it to be incorrect in certain particulars. 



So far as could be told the upper strata down to a depth of 23 metres consisted of 

 layers of sand, clay, mud and gravel. Immediately below, cajne rock seamed, so it was Geological 

 said, by beds of clay. This rock, there was reason to believe, was a porous limestone, a 

 "Travertine," but at the time the first tests were made, no information was forthcoming 

 regarding its nature. It was understood, however, that the casing pipes ended in it and 

 not, be it noted, in any impermeable bed of clay. At first, indeed, this rock was said to be 

 sandstone with a layer of clay marl overlying it, and it was assumed that a more or less 

 similar formation existed in the case of each of the first six wells. Anyhow, below this doubtful 



conditions 



