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Remarks on Results of Gaugings.-The whole of the gaugings taken from the 12th of June 1870 to the 15th of July 1871 (a period of 399 days) have . been calculated and tabulated, with the following results :
Town Sewage. The sewage received on the farm from the town of Romford during the above period has been
85,999,445 gallons=383,926 tons,
and the number of days on which it has been delivered is 373, giving an average quantity of
230,562 gallons=1029 tons per day.
This quantity does not, however, represent the total discharge from the town of Romford, because, from the middle of November 1870 to the middle of April 1871, the day-sewage only was delivered on to the farm, the nightsewage being allowed to run on to the meadows at Wybridge between the farm and the town; and for sixteen days in February and March the whole of the sewage was so disposed of, and there are no means of estimating the quantity during this period.
Respective flow of Day- and Night-sewage.-Since the 15th of April last, the new tanks being completed, and the sewage, with a few exceptions, being received continuously on the farm, it has been possible to calculate the respective flow of sewage during the working hours of the day and during the remaining period, and the following are the figures:
Day-sewage (average time 10 hours).... 139,153
tons. = 621
The day-sewage is calculated on the basis of gaugings in the sewer during the working hours of the day; the night-sewage is obtained by calculating the difference of quantities in the tanks between the times of stopping the pump one day and starting the next, allowing for the effluent water entering the tanks in the meantime.
By equalizing the time of day- and night-sewage (12 hours each) and computing the quantities on the basis of the above figures, the following is the result:
According to these latter figures the night-sewage would be to the day as 79 to 100, or the day to the night as 137 to 100.
It should be borne in mind that the night-sewage of Romford fluctuates very much, owing to the Brewery frequently sending down a large quantity of water after working hours; this is especially the case on Saturday nights, as a reference to the detailed records will show.
Diluted Sewage pumped.-The diluted sewage pumped includes, as was explained in the last Report, a certain amount of effluent water, which flows into the tanks, and is there mixed with the sewage as it comes from the town. The engine has worked 366 days during the above period; the average time
of working since April 15th was 10 hours per diem. The total quantity pumped has been
Average per diem.... 264,876 = 1,182
Effluent Water discharged.-Owing to floods at the outlets of the pipes, the quantities of effluent water discharged could not always be gauged. On the 343 days during which the observations could be taken,
39,449,178 gallons=176,112 tons
were discharged, being
115,012 gallons=513 tons per day.
Assuming this to be the average quantity for the whole period, the total quantity intercepted from the lower subsoil and discharged through the pipes would be
45,889,788 gallons=204,865 tons,
or 47.3 per cent. of the sewage pumped.
Rainfall.-The rainfall at Breton's during the total period of 399 days has been 22.64 inches, or on 121 acres about 624 million gallons, equal to 277,900 tons, or 2287 tons per acre.
Temperatures.—It will be seen that the temperatures of sewage and effluent water have been very uniform as compared with that of the air, being lower during extreme heat and higher during extreme cold. This was very noticeable during the severe frost of last winter. In one week, when the mean noon-day temperature of the air was 28°.5, that of the sewage received, sewage pumped, and effluent water was 43°. The ranges of variation over the total period have been :
A remarkable feature in the record of temperatures is the extremely slow rate at which the temperature of the effluent water fell, and the length of time which elapsed before it recovered again. The first week that the average temperature at noon fell below the freezing-point was the one ending 31st December, when the average temperature of the air was 28°.5 F., and that of the effluent water was 43°; and after this, although the former rose, the latter fell, so that in the week ending February 4th the average temperature of the air was 36°, and that of the effluent water 41°. The next week the temperature of the air was 44°, the second week 47°, and the third week 47°, yet it was not until the third week that the temperature of the effluent water recovered to 43°.
SECTION III. (a) Observations on the Sewage-Farm at Tunbridge Wells.
Before describing the results of the investigation by the Committee, it is desirable to state that, in the selection of the land to be irrigated at Tunbridge Wells, it has been a sine qua non condition that it should be at such a level that the sewage should reach it by gravitation; and to this end two farms
have been laid out, one to the north and the other to the south of the town, and an outfall sewer made to each.
Underdrainage has not been uniformly adopted on both farms; but where it previously existed, a peculiar arrangement has been made for the reapplication of the drainage-water.
The distribution of the sewage is chiefly effected by what is known as the catchwater system, which is necessarily, under ordinary conditions, accompanied by an overflow, in preference to its application in smaller quantities, sufficient to satisfy the demands of vegetation and to wet the land thoroughly without any overflow; while the absence of storage-reservoirs necessitates the continuous application of the sewage to some parts of the land by night as well as by day.
The population of Tunbridge Wells is 19,410.
The total quantity of sewage discharged is 1,000,000 gallons per 24 hours, of which about 400,000 gallons are supplied to the northern farm, and about 600,000 gallons to the southern one.
The northern sewage is applied to 123 acres of land, which have cost £21,000, and the southern to 167 acres, which have cost £27,000.
To deliver the sewage from the two main outlets of the town to the land, culverts or conduits, with precipitating-tanks for the separation of the larger portions of the solid matter from the liquid, have been constructed in a very substantial manner. The delivering-conduits on the north, extending for a length of two miles with the precipitating-tanks, have cost £258713s.1d., while those on the south (of which the length is three miles) have cost £5809 17s. 8d. The tanks on the north farm have cost £833 3s. 9d., those on the south £1188 5s. 1d.
Thus the total cost of external delivering works amounts to £10,418 19s. 7d., which, added to the cost of the land, will be £58,418 19s. 7d., or £201 8s. 11d. per acre.
The solid matter collected in the tanks is removed from time to time, and used on the farms as additional manure. The tanks are not covered; and there is consequently a strong smell in their proximity, which is not discoverable in any other part of the farms.
The sewage having been delivered on to the land, is conveyed from one part to another by open main carriers and iron pipes, the former following contourlines, and the latter partaking of the nature of inverted siphons in order to cross existing valleys or hollows.
The cost of these internal works per acre has been—
The soil of nearly the whole of the northern farm is of a stiff clayey character, manifestly requiring underdrainage. It had for the most part been drained by the late owners before the Commissioners of Tunbridge Wells purchased it; but owing to the work being done as ordinary farm-drainage 1871.
independently of surface preparation, it was soon found that the sewage descended to the drains so rapidly as to prevent its profitable distribution on the surface. It was stated to the Committee that when this effect was discovered it was determined that the drains should be stopped by digging down to them and plugging them, the result of which then was to keep the soil in a state of saturation, and to allow the unpurified sewage to pass over the surface into the stream. The engineer employed by the Commissioners has since superseded this state of things by adopting the special mode of treatment referred to, which consists of intercepting the existing drains at the depths at which they were originally laid, and bringing the underdrainage water to the surface by outlet drains discharging into lower carriers for redistribution.
At the time of the inspection by the Committee the lowest carriers were receiving effluent liquid of an impure character from the surface, at the same time that the underdrainage water was being discharged into them in the way described.
The land of the southern farm is not generally of so heavy a description as that of the northern, though portions of it contain clay. Other parts are peaty, and are naturally very poor. Wherever the engineer has considered it necessary to drain the subsoil, this has been effected in a manner similar to that adopted on the northern farm.
The striking features in the case of Tunbridge Wells are:
1. Instead of concentrating the sewage at one farm under one management, it has been divided, in accordance with the watersheds, into two parts, involving two separate systems of works and management.
2. The main conduits and carriers are more than ordinarily substantial, and are therefore expensively constructed; and, following contour-lines on the surface, have a tortuous course, and so must interfere with approved cultivation.
3. The character of the underdrainage, being designed for the redelivery of the sewage on to a lower surface by drains gradually getting nearer and nearer to it, must necessarily prevent alike a frequent and deep working of the surface-soil.
4. The sewage being run over the surface of the land on the catchwater system (by night as well as day), with the intention of reapplying the overflow, its distribution is necessarily unequal both in quantity and quality, the first land sewaged receiving more than it requires, while the last must suffer from a deficiency unless there is a positive waste of sewage, as the analyses really show that there is.
These several features illustrate the advantage of combining with the services of the civil engineer and the chemist those of the practical agriculturist when laying out a sewage-farm. If they were not pointed out by the Committee thus carly in the progress of sewage-irrigation, they might be a source of disappointment and surprise to those who contemplate the utilization of the sewage of their own towns by this the most profitable mode of treatment at present known, when properly conducted. While saying this, it is desirable to point out the superior character of the works carried out at Tunbridge Wells, and at the same time to express approval of the enterprising manner in which they have been undertaken by the Local Authority.