TRANSACTIONS OF THE SECTIONS. 213 



fluid existing inside a sewer may pass as vapidly out of it into tlie surrounding' 

 {ground as the subsoil-water may pass from that g-round into the sewer. This eftect 

 will be conceded when the height and pressure of the one exceeds the height and 

 pressure of the other. Though the dilhculty of ascertaining- the quantity of sewage 

 which escapes is great, and the facts will only become apparent when disease 

 becomes localized in the neighbourhood of leaky sewers, there exists no difficulty 

 in determining the extent to which the influx of subsoil- water takes place. The 

 greatest increase from the infiltration of subsoil-water known to the writer is at 

 Tring and Hertford. In the first case, although the sewers are only connected 

 with 30 houses, and the whole influx of sewage does not amount to 1000 galls, per 

 diem, the dry-weather discharge from the main sewer amounts to upwards of 

 1,000,000 galis. per diem. The eftect of this abstraction of water from the subsoil 

 has been to lower all the springs in the neighbourhood, and to lay nearly dry the 

 head of the silk-mill in the town, from whence the Grand Junction Canal Com- 

 pany obtained a supply of water at a summit level. In the case of Hertford, the 

 discharge from the sewers is more than nine times the water-supply. At Black- 

 pool, for instance, with a standing population of 7000, the water-supply is about 

 a quarter of a million gallons daily, and the discharge from the sewers about 

 1,000,000 gallons. There is, therefore, an infiltration of water from some source of 

 three-quarters of a million gallons, and no effort is made to keep the sewage ou 

 the flow when the tides rise above the sewers. In the town of Dover, with a 

 standing population of about 25,000, where the water-supply is upwards of 

 1,000,0110 galls, daily, the ordinary dry-weather discharge from the sewers amounts 

 to nearly i3,600,000. Here, in order to keep the sewage "on the flow," pumping 

 is resoi-ted to for two hours before and two hours after each high tide ; and it is 

 possible that by such means the escape of sewage is in some measure reduced by 

 avoiding the extreme pressure of maximum accumulation. Vnder any circum- 

 stances it will be observed that the expense of pumping is increased by the influx 

 of subterranean water in the proportion of 1 to 85, and, as a natural consequence, 

 that £S')0 is spent when about £'100 would suffice if the sewage alone was dealt 

 Avith. If the returns of mortality in these places could be brought to bear, it 

 woidd doubtless be found that certain epidemics are localized in the low parts of 

 the town, while other diseases prevail in the higher parts, cau?ed by the pent-up 

 gases generated by detention finding their way upwards. This periodical condi- 

 tion of surcharged sewers is not confined to seaboard towns. In cases where the 

 sewage is lifted, the sewer authorities may allow the sewage to accumulate in the 

 sewers in order to avoid the expense of pumping at night, when precisely the 

 same eftect is produced as in seaboard towns under tidal influence. In many of 

 the Lancashire towns, such as Bolton, Livei-pool, Oldham, and "^^'arrington, the 

 aggregate daily excess due to subsoil-waler in these four towns alone reaches, I 

 have reason to believe, something between 20 and 25 millions of gallons, which, if 

 lifted 100 feet, would cost, at 20-?. per million gallons, upwards of £8000 a year. 

 At Cardift" in South AVales, the increase is 1,500,000, without any advantage in 

 the way of flushing and cleansing (which, it has been stated, always accompanies 

 the influx of water), for there the inflowing subsoil-water brings in with it a share 

 of the sand, which deposits itself in the sewers, and is likely to become an in- 

 creasing source of impediment and difficulty. In many instances of both seaboard 

 and inland towns the sewage has been more than doubled : and wherever it 

 becomes necessary, on the groimd of health and economy, to lift the sewage by 

 mechanical power (as we may safely assume will be the case in all towns, without 

 exception, where the sewers have not a free flow), the difficulty and cost of dealing 

 with such an increased quantity will become proportionately greater. These 

 observations are made with a full recognition of the difllculty, almost amounting 

 to an impossibility, of making ordinary sewers completely water-tight, and of the 

 truth that water finding its way into sewers sometimes acts beneficially in flushing 

 them, and that at certain seasons the dilution of sewage applied to irrigation is 

 advantageous. It is to the evil of indiscriminatel}' admitting a largely dispropor- 

 tionate quantitv of water, without any power to regulate the time and extent of 

 dilution, to wliicli attention should be called with a view to dctLimiue future 

 proceedings. 



