54 KEPORT — 1870. 



times of heavy rainfall. It occasionally happens that an inch of rain falls 

 in twenty-four hours, and in certain seasons and under certain conditions half 

 that quantity makes its way to the sewers in the same period. Two in- 

 stances recorded in the schedule will serve to show the extent to which a 

 sewerage system may be tried by such influx. In the Nottingham district, 

 where it appears from the return there is a surface of 1870 acres tributary 

 to the sewers, and where the annual rainfall is 25 inches, there fell on the 

 18th of September last (since the Committee has been sitting) 2-14 inches of 

 rain. If at this time half the quantity reached the sewers, about 45 millions 

 of gallons of surface-water would have had to be discharged by the sewers or 

 storm overflows ; and this would be more than eleven times the ordinary flow of 

 the sewage, and thirteen times the water-supply. At Dundee, where the surface 

 contributing to the sewered area appears to be 2120 acres, and the average 

 annual rainfall the same as at Nottingham, viz. 25 inches, there fell in the 

 same month (on the 12th of September, 1869) 1-70 inch of rain. If half 

 of this quantity reached the sewers they had to discharge iqiwards of 

 40 millions of gallons from this source alone, equal to more than thirteen 

 times the water-supply of the town. It is more than probable, however, 

 that, although the returns show the contribiiting surfaces to be as much as 

 stated, the actual quantity is less ; but the figures serve to illustrate the dif- 

 ficulty to be contended with by the sudden admission into the sewers of such 

 large bodies of water, and which only serve a good purpose when the sewers 

 require flushing. 



Subsoil Waters. — ^The removal of subsoil water from beneath and about 

 dwellings having been shown by Dr. Buchanan in the 9th Eeport of the 

 Medical Ofiicer of the Privy Council to be of the highest sanitary importance, 

 it has been deemed desirable to trace as far as possible the means by which 

 local authorities have effected this object. The returns, which are very im- 

 perfect upon this point, show, as far as they go, that about 100 out of the 

 200 towns drain the subsoil by the sewers, which carry away the liquid 

 refuse of their districts. The importance of this branch of the inquiry wiU 

 appear when it is remembered that, having become mixed with the sewage, 

 the subsoil water must be treated in the same way as the sewage itself. 

 This consideration becomes greater in those cases where the discharged 

 quantity has to be lifted by mechanical power at a never-ceasing cost. 

 One or two instances given in the schedule will illustrate this. Torquay, 

 a seaboard town with (according to the returns) about 20,000 inhabitants 

 and a water-supply of 30 gallons per head, amounting on the whole to 

 610,000 gallons per diem, discharges 1,600,000 gallons of sewage a day, 

 the addition of subsoil water being apparently in the proportion of 1*62 to 1, 

 and the sewage discharged being equal to 80 gallons per head of the con- 

 tributing population. In this instance, therefore, if the Local Board of Tor- 

 quay should determine to raise and utilize their sewage instead of dis- 

 charging it into the sea, they will have to pay .£1 12s. 5d. for the raising of 

 subsoil water for every £1 expended in raising the sewage. The river-side 

 town of Leamington affords another example. This town has, according to 

 the returns, a population the same as Torquay (20,000), and a water-supply 

 of 400,000 gallons a day. The quantity of sewage discharged into the river j 

 is 1,000,000 gallons, the difference between the water supplied and th( 

 sewage discharged being 600,000 gallons, or 150 per cent. In the casfe oi 

 Hertford, where the water-supply is returned at 61| gallons per head daily, 

 amounting to 184,500 gallons per diem, the discharge from the sewers if 

 returned at 1,750,000 gallons. This quantity is conducted, after lim« 



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