308 



THE WATER-sriTLY OF TOWNS I\ THE TROflCS 



The difficulty 

 solved by 

 cutting off 

 upper strata 

 with cement 



Concltuions 



be shown, /?. coli gave clear indication of the contamination or. if you will, admixture of 

 the true deep water with superficial water. Even supposing the R. coli found were to 

 fall wholly into Clemesha's third group, I think it would have been the height of 

 absurdity to pass wells which at very heavy expense presented the town with water — 

 one half of which at least, let us say, was derived from the very river which flowed past 

 30 yards away from one of them. This, too, apart from the important question of the 

 contained iron and manganese. 



Happily, the laboratory representations prevented this water being supplied to the 

 town, and in my Public Health Report for 1908, I wrote 



" one can only hope that some means will be devised whereby the water may be obtained free from chemical 

 and or^nismal impurities. 



" If this is found impossible then filtration must be employed or, if necessary, the Blue Nile water utilised 

 and passed through bacteriological filters. The threatened invasion of cholera last year renders this water-supply 

 question most urgent and important." 



Fortunately, the question was solved, and satisfactorily solved, along the lines suggested 



by Messrs. Abel and Todd. The upper strata were cut ofif with cement, and as a result the 



colony count fell nearly to zero, H. coli vanished, and the quantity of iron and manganese 



greatly diminished. As this engineering device may not be generally kno%vn to medical men 



it may be well to indicate how it was carried out. I am indebted, for particulars, to 



Mr. J. E. Williams, the engineer in charge of the works who, at all times, was most 



courteous and obliging. The process is simple enough. As noted, with the exception 



of No. 7, which was of smaller bore, the wells down to a certain depth were lined with a 



casing tube of 9| inches diameter. A second tube of 6J inches diameter was passed down 



each well to the depth where it was desired to cut off the upper strata, i'.e. to one or other 



of the deep beds of impermeable cla)'. This inner tube, therefore, descended in the 



open bore-hole below the level of the end of the outer tube. In order to facilitate 



operations, the well was first of all filled with sand which provided the necessary cushion. 



Liquid cement was then poured between the two tubes down to the depth desired, and, 



in cases where it did not settle properly, it was blown down and packed by means of 



compressed air. It set for the most part under water and formed a hollow column 



or ring, the lower portion of which, confined between the inner tube and the wall of 



the bore-hole, in some degree soaked into the porous sandstone with which, as stated, 



it was in contact, and rendered the latter absolutely impermeable. Although transverse 



fissures may occur in such a column, it is scarcely conceivable that any lengthy vertical 



crack can be produced in it. Hence the cutting off is regarded as efficient. Finally, 



the cushion of sand was blown out of the well which, if the clay bed is both extensive 



and impermeable, is thus wholly protected from any local influx of water from upper 



and possibly contaminated strata. 



I will now conclude what, despite manj- omissions, has proved a somewhat lengthy 



paper, by quoting from portions of my final report to the Sudan Government on the 



examination of the well-waters before and during special and continuous trial pumpings of 



twenty-one days duration in the months of March and April, 1909. 



" The wells tested were Nos. 1, 5, 6 and 7, and the first three at the time of the special pumpinsr trials had 

 undergone very extensive alterations since the examinations conducted in 1907-8. For one thing the air-lift 

 pumps and air compressors had l>ecn introduced, while Well No. 5 had been deepened, and, in all, the upper 

 strata had been cut off by the special process. No. 7 was a new well to U8. It had been Iwred since the 

 last examination. As a result of these changes we soon found that we were dealing with quite a different 

 water from that which had led to a condemnation of the original welLs. Nos. 2. 3 and 4 have been discarded 

 and filled up with sand. 



"As, from previous experience, confirmed by the results obtained by Mes.srs. Abel and Todd, we were 

 aware that the old wells had been contaminated by the intlu.t of polluted water from the upper strata, it 

 was of the highest importance to a.sccrtain. 



