WATER AND DRAINAGE.

Marlborough Express, Volume XLIV, Issue 256, 5 November 1910, Page 3

WATER AND DRAINAGE.

MB DOBSON'S REPORT. At the meeting of the Borough ; Council last night, Mr Dudley .Dobson's report on a water and drainage scheme for the Borough; was >ceivedCouncillor Wiffen moved', and Councillor Dodson.seconded, that a special meeting of the Council be held) on Monday, November 14th, to consider the. proposals contained in it. The motion was carried* The report is as follows:— 1. 1 have the honor to forward! you ■fclio following report upon the proposal to; supply the town of Blenheim. with a high pressure supply of water. ■«On examining the town and its surroundings, two schemes at onee1 suggest themselves. 2. Ist: To make use of the artesian .•supply at present being used, which is most excellent in quality, coming ;io the surface as it does filtered through gravel beds, and which evidently exists in abundance, and to ob--fcain the requisite pressure by raising -the water by machinery to an elevated, tank, viz., a pumping scheme. 3,. 2nd: To obtain water from some -.source up the Wairau Valley and "ifering it into a main to the reticulation, thus supplying the water under' -pressure, viz., a gravitation scheme. Each scheme is equally feasible and presents its advantages and disadvantages, which it will be well to consider. . SOURCE OF SUPPLY. 4. Artesian: This water cannot be «.<©xoelled for purity; it is not affected ■liby floods or drought, and is on the rspot in abundant quantity, and only -requires raising to give the necessary '.pressure for public use. GRAVITATION SUPPLY. 5. This water would have to be obi fcained from one of the streams flowring into the Wairau, and taken at such an elevation above the level of "the town as would give the requisite after allowing for the lossof head due to the friction in the main. The Waihopai would be an excellent x-sourco for this purpose, as sufficient for all purposes can be easily -obtained, and the water is of excellent quality. But the head works Would ' be expensive; the water 'would be too, *-discolored to put into the mains dur:ing flood. Therefore,' a clear waterfcasin would > have to be provided of -sufficient capacity to hold enough "dear water to supply the town during the longest period of flood dis■coloration. This would be a work entrailing very considerable expense, "which, ;added to the cost of a main of < •. sufficient capacity to provide' thepresent needs of the town, and a provable increase in the population, ■would cost a large sum. ESTIMATED CONSUMPTION OF WATER. * 6.'- It has been proved by experience -thai from 20 to 25 gallons per head per day. is ample for, domestic con--jßumption, and that 50 is sufficient for .all' requirements'. The consumption ■varies enormously, being from, 14" gallons- in some European cities to over 100 gallons in some American. Where -these large quantities are consumed it; is evident that either the mains and ; -■services are in a bad state and leak- \ ing badly, or else that great waste has j been allowed. . i ' • { From returns lately published of ' the consumption of'water in 11 Euro- ' pean and 11 American cities, I find -the average as follows: —European 30 .gallons, American 50 gallons. Where , ri/he supply is by gravitation and the ; abundant j there, is no neces- j .-sity to restrict the consumption, but; where the supply is limited, or where \ the water has to be pumped; it is very : -.undesirable to allow waste. I think ; .it will be found that ,50 gallons per jhead per day will' be a very adequate i supply for Blenheim, especially when . it is considered how' many house-j holders have already an artesian sup- , ply-sufficient for many purposes*- I; 'have therefore estimated for a conr\ :sumption of 5Q gallons, which will. provide for domestic consumption, j sstreet watering, flushing of drains, . gardens, ©tc. PUMPING SCHEME. 7. Blenheim has already a pumping plant capable cf, throwing 1000 gallons per minute at a sufficient pres- ; -sure to" cop© with any fire the town is \ likely to fall a. prey to, so that it would-be unnecessary to provide _ en•gine power for this purpose. All that would be required is a. plant capable <of supplying the ordinary consumption. I would therefore recommend' that a pumping plant be installed m • rsome central position, say,_ near the .gasworks. Tto? works required would ■comprise water reservoir; to pump 'Out of, tank on a tower to hold, say, -40,000 gallons, and a plant capable of pumping for the ordinary domestic supply, say, at present to supply 3000 people at 50 gallonsjer head per day —150,000 gallons. The plant should hsve a sufficient capacity to pump this in eight hours. The reservoir ■ .should be a sufficient size to hold, :say, 100,000 gallons.' This, with the water in the tank, and the quantity which would be supplied by flow from the wells, would be sufficient to cope with any fire which is likely to occur. The present pumping plant should be re-erected at the pumping station, ;and in case of a fire the plant could \be> started in a few minutes as at present. If the ordinary plant was -working it would be delivering 312 ..gallons per minute, in addition to the water which would be supplied from the tower tank. This would be available until the fire-pump got to work, and would probably be quite sufficient • to put out any small fire. A small ' ;savmg might be mado by having the ■ reservoir at the pumping station only •sufficient for the domestic supply, and '. Eumping from the river in case of ' re; but I do not think this is desir- i able, as every time the fire-pumps were used the mains would be more : •or less filled with river water, which, in my opinion, would not be desirable, for whatever may be done in : the way of drainage the storm water - from a large area will always be discharged into the river. SITE FOR PUMPING STATION, &c. 8. It would be desirable to have this near the river, as the fuel would have to be imported. If sufficient land could be obtained near the- gasworks :it 'would be a very suitable • position. The works could be placed under one control, pnd arrangements could be made to have the fire brigade located on-the pa me sit-e Half an acre of land would be sufficient for all purposes. - 9. A suction gas plant would be a very suitable orfe to instal for this work. Tli-ese plants are very economical and exceedingly well adapted to work against steady loads. A large number are working in the neighborhood of Christchurcli, giving very ■good results. COST OF RUNNING. In small installations of this nature

the fuel is a small item, the principal charge being the wages and depreciation. A 24-h.p. plant would do the proposed work, ,and would consume, if properly managed, IJd of coke per h.p. per hour, which, at 30s per ton, would airjount to ,2s 8d for eight hours. To this has to be added oil and wages, . allowing 12s for wages . and Is for oil,' the actual running cost/ would be 15s Bd, say 16s, equal' 1.28 per 1000 ■ gallons. This will be the net cost of pumping for eight hours, but in addition to this there will bo a certain amount of stand-by cost and occasional assistance, which will make £300 a fair estimate for the yearly cost. To this has to be added interest on tho capital, cost of the pumping station, sinking-fund, and depreciation. These are shown in- the attached estimate. With the present power engine re-erected in the new works it would not be necessary to .duplicate the plant, as is usually done, to avoid stopping in case of a break-down, as the fire engine would be used in case of accidents. RETICULATION. 10. Until a site for the pumping station has been fixed the plan of the reticulation cannot be determined. The. lithographed' plan of Blenheim shows 25 miles of streets, but I understand that about five more are now included in the late subdivisions. I should think that between 25 to 26. miles would be quite' sufficient to provide for, and I have therefore estimated for 254 miles of mains, comprising fire plugs at every four chains ; and valves to shut off the reticulation into small blocks. The estimate does ; not provide for street stand pipes i : such as are at present in use in the j i town, as their cost is so great com- ] .pared with that of the Moore and Bateman pattern of fire plugs that ] ..their use would unnecessarily load the | I scheme. It is customary to lay seri vice pipes from the mains to the [street line at the public cost, and I , have allowed for * 600 service pipes in i : the (estimate, also a certain number of ■ [meters will be required to meter the i | Water for business, gardening, and i J other purposes; £300 has been set i down.^ for them. ! 11.\I estimate the total cost of the scheme, at £28,371, as will be seen, in detail in the accompanying estimate ;of cost.; This will require a water rate of\ 1.53 in-the £ on the unimproved value, but as half rate only is usually charged on premises not supplied with water a higher rate will have to be charged to make up for these premises which only pay half GRAVITATION .MAIN. 12. I have not sufficient data to give a close estimate of this work, but from the approximate levels I have taken I estimate the cost of amain, capable of delivering 450 gals, per minute at £2000 per mile, the distance being about,..- 11! miles with, head works holding two weeks supply for 3000 people at 50 gals, per day. The ■cost would be for 11! miles of mains at £2000 per mile £23,000. Head works with clear water basin to hold 14 days' supply per 3000 people, at least £5000—£28,000. Interest and sinking fund at 4J plus 1 per cent., 5! per cent —£1540. To this would have to be added the cost of a caretaker's wages at the head works at £2 8s per week—£l24 16s, making a total of £1664 16s per annum for the gravitation main, and head works also. But this only .provides for 450 gals, per minute, which, although sufficient for all domestic and general purposes, will not be nearly sufficient in times of fire. A water supply could not be considered sufficient unless, in a town of the size of Blenheim, at least 1000 gals, per minute could ;be delivered at a presure of not less than GOlbs to the square inch, therefore, some other arrangement would be required to cope with fire, such as making use of the existing engine. As the cost of the town reticulation will be the same whatever scheme is adopted the gravitation main merely does what machinery would do, i.e., puts' power into the mains. It is therefore, merely a question, which wiil give the best results at the lowest .expense. Turning to the estimate in the pumping station, it will be seen that,

taking all the items No. 1 to 8, but allowing £500 for buildings instead of £2000, the total capital cost of the pumping installation is £4650 instead of £23,350, less than the cost of the gravitation main and head works, and the annual cost of the running of the pumping part of that scheme is l-3rd that of the annual cost of the gravitation scheme. I have-the honor to be Your obedient servant. (Signed.) * ' ESTIMATED COST OF WATERW.ORKS. 1 £ s. d. 1. Land, say ..300 0 0 2. Wells ... ... 150 0 0 3. Reservoir, 100,000 gals. ... 700 0 0 4. Water-tower, ,40,000 1600 0 0 5. Suction gas plant, to pump 320 gals, per minute ... ... 1000 0 0 6. Re-erecting present fire engine 100 0 0 7. Meter 300 0 0 8. Buildings, also including fire brigade station ... ... ... ■..,.■ 2000 0 0 9. Reticulation: lOin. main, $-mile ... 900 0 0 Bin. main, 3 miles - ... 3600 0 0 6in. main, 6. miles ... 6240 0 0 4in. main, 6 miles ... 3160 0 0 3in. main, 10.miles ... 4400 0 0 10. Service and "meters... 1200 ,0 0 11. Contingencies: Engineering, raising loan, clerical work, etc ... 1500 0 0 First year's' interest on £27,150 at 4£ per , cent. ..: ... 1221' ,0 0 Total 28,371 0 0 Interest r4£ per cent., ■ ■ sinking fund 1 per ' . , cent-A—s£ per cent, 5£ * per cent, on £28,371— £1560 per annum ... 1560 0 0 Working costs: Wages, fuel, etc. ... 300 0 0 - Depreciation in plant and repairs ... 100 0 0 400 0 0 1960 0 0 This would" require a raffe of 1.53 d in the £ on the unimproved value of £303,654. His Worship The Mayor, Blenheim. I beg to hand you the following report upon a scheme for the drainage of Blenheim: DRAINAGE. 1. 1 have carefully examined the town of Blenheim,and considered the methods by which it could be drained. I find, provision has already been, made for storm water, for which there is abundant outlet in the river running through the town, it is therefore only necessary to deal with the sewage proper—i.e., fowcal matter, household and manufacturers' drainage. The town being situated on approximately level ground, not greatly above high water level, it is evident that the sewage cannot be1 removed by gravitation alone, unless it could be' discharged into the rivers in close proximity to the town.

2. This course appears to me out of the question. There is no strong current running in the Omaka in ordinary times, and the sewage flowing into comparatively still water would rapidly become an intolerable nuisance. <

Two propositions present themselves:—

1. To pump the sewage at once through an iron pipe to the ocean, say somewhere near the Wairau Bar, a distance of about six miles. 2. To-collect the sewage into tanks and treat it by one of the several methods now in vogue—letting the filtrate run into the Omaka.

3. As the town is nearly level, and not many feet above level, it is evident that the sewage being led into some conyeniently situated sump or tank—that to obtain the necessary fall in the sewers the bottom of the tank will be at such a low level that the sewage would have to be lifted in any case before it could be dealt with.

4. If pumped away to the ocean it must be given sufficient velocity to overcome the friction of the pipe. 4. If treated by any system of bacteriolysis, the tanks in which it was treated would have to be at such a level that the filtrate could run off into some adjoining outlet and to onable this to be done it is clear Wat the sewage would have to be lifted at least above the present level of the surface. That being the case a pumping station would have to be provided in any case.

The question then to be considered is. whether an equally efficient scheme could be provided at less cost by say a septic tank, or similar treatment, than by a main to the sea.

5. There are a great many localities where it is impossible to discharge the sewage direct into the open sea, and that it has to be treated before it is desirable to discharge it either on the land or into slow flowing rivers, land locked harbors, etc. In such localities it becomes imperative to purify it in some ' manner, and several variations of septic treatment are now practiced, but it appears to me that if it is possible at a reasonable cost to discharge the sewer into the open ocean, that is the- most desirable method; it is finally done with and can give no more trouble. Sydney, Wellington, and Dunedin are ail sending their sewage into the sea. 6. Since success has been achieved

to a greater or less extent by the septic tank treatment, the system has had many exponents whose, efforts have been far from successful—tanks have been put in many places which were neither more nor less than elaborate cesspits, .the locality of which was readily ascertained by the smell, and. where .most undesirable to have iti the neighborhood.- It is true the solids were brokon up by the action of the bacteria, and that by this means the quantity of sludge has been lessened to an ■enormous extent, but it requires not only efficient design, but skilled management to conduct the operation in such a way that the; installation does not become a nuisance. ;

} 7. Several sanitary engineering firms in Europe, which have made this batericlitic treatment a special study have patented automatic appliances which are said to .ensure complete and certain workings of these installations, and I believe are : prepared ,to design/and erect works of this nature. If it could be shown that a substantial .saving could be made in this way - t and any firm of repute would guarantee to erect an installation capable of treating, „ say, 75,000 gals, of sewage per day, discharging the filtrate at a given standard of purity, create no nuisance in the treatment, and work the installation to the satisfaction of the Council for, say, three months before the works are paid for, it might be well to consider the question. QUANTITY OF SEWAGE TO BE DEALT WITH. The quantities differ so greatly in different towns that it is difficult to estimate closely the probable amount, but if provision is made for double the present population, and allowing 25 gallons per head per day, I consider the estimate will be on the safe side, and sewers designed on this scale should be quite sufficient for i*ll provable increase in the town for very - many years. Where there is no water in the town other than that supplied by a water supply system, it is evident that, provided all storm water is kept out of the sewers, the amount of sewage to be pumped cannot exceed that quantity—in fact, that it must be less as all water used for street watering, gardens, etc., which i will not be allowed to run into the sewers, will have to 'be deducted from the amount supplied by the mains. But in a town like Blenheim, where there are a, considerable number of private sources of supply, a large' quantity of, water may be used and poured into the sewer by : persons who are not connected with the public water supply. It will, therefore, in the case of Blenheim, be necessary to make a liberal allowance, and I think that 25 gallons per i head per day will be. a very fair estimate. SEWERS. The drainage of the town should be carried in stoneware pipes of suit- > able size to some position preferable near the eastern boundary of the town, the sewer pipe beine; laid at such gradient as will ensure velocity -sufficient'to carry the sewage without allowing dfeposit, the pipes discharging into a sump, from which it can be pumped to the outfall. In consequence of the Omaka and Opawa dividing the town into three parts, ' the sewage will have to be carried by sewer pipes in each of these two northern parts to sumps, from which it can be pumped over the bridges into the sewers in the southern part. That part of the town lying between the Omaka and Opawa will some day carry a very considerable population, and that must be borne in mind when designing the sump for that part; but that part lying in the bend of the Opawa is of very small area, and the sump will only require to be of small size. The exact position of these two subsidiary sumps is not a matter ofvery much importance, as the ground is so level, but the nearer they can be placed, to the engine-house from whence the power is derived the better. The amount of land required will be very small in either case, and the most desirable site, both for these and the main sump, can best be determined by a careful study of the local conditions, cost of the required land, and the proximity of houses, the owners of which might be likely to raise objections and make claims for compensation. Until the position of the sumps are fixed and plans prepared showing the levels of all the streets, the planning of the sewers cannot be undertaken, as the size of the sewer pipe in each street1 will to a certain extent be governed by the fall' obtainable. But although it is not possible to definitely plan the sewers at present, it is not difficult to approximate the mileage of the various sizes that will be required. 1 I estimate that the following will practically be quite sufficient to meet all requirements: — ]2in diameter pipe ... 6 miles. 9in diameter pipe ... 9 miles. 6in diameter pipe ••• 10 miles, 25

The sewer pipes should be glazed stone ware pipes, laid with cemented joints and with manholes at all junctions, and at a distance of not more than 330 feet'apart. It is very probable that the deeper sewers Avill have to be laid in concrete if the depth to which they have to be laid takes them into,soft wet ground, and I have allowed a sum of money in my estimates for this purpos». PUMPING PLANT. I would recommend a suction gas plant, the engine to be 25 h.p., .driving a generator which would work three pumps, one at the main sump, the two others at the two subsidiary stations. These pumps would all be motor driven, the two subsidiary ones being actuated automatically by floats in the sewage .wells, as is done in some parts of Sydney. If these works were' installed at the same as the water works it would be a saving to have the power in the same installation, on© staff would manage the whole, and the cost of a second set of buildings would be saved; and there would also be a saving on the plant.,. If worked separately, the machinery should be at the main sump; here the largest pump would be required to lift the whole of the sewage and force it through the outfall pipe to the sea. The two other pumps would not have much to do, but I have allowed fully for every contingency in jp.y estimate of 25 h.p. By making; the sump of sufficient capacity to hold 16 hours' sewage the pumps would oniy need to be run eight hours per day. OUTFALL MAIN. This should be Sin diameter C.I. main. It would be underground till near the outlet of the lagoon, where for a distance of a few chains it would be on tressel work; the seaward end should be placed at about half-tide level. I estimate the total cost of the

work when competed at £36,141, and the yearly cost at £2580 10s; but this is for the. whole scheme when completed, and the ruining costs are for dealing with sewtge from a population of 3000. It will doubtless be quite unnecessary to complete the whole of these woi'js for some years. Many of the. streets, are so little occupied1 that it wculd be money wasted to lay the stwer on them at present. / # j The exact miles of sewage that should be laid at present is chiefly a matter of policy for your Council to decide. It should, ->f course, embrace all the closely-built part of the j town. Generally speaking, I should think that about ten miles would cover all that require Uying at present, and the working expenses would be proportionately reduced. 1 have the honor to be, Your obedient servant, (Signed) . Oct. 22, 1910. ESTIMATED COST OF DRAINAGE WORKS. £ 1. Land, say ... ... ... 400 0 0 2. Main sump and two subsidiary do. 1500 0 0 3. Pumping plant ... 1700 0 0 4. Sewers — 12in dia. 6 miles ... 4800 0 0 9in dia. 9 miles ... 6350 0 0 6in dia. 10 miles ... 6400 0 0 Manholes w 4080 0 0 5. One mile electric connection ... ... ... 300 0 0 6. Outfall pipe, 6 miles.. 6000 0 0 7. Buildings ... ...;.. 500 0 0 8. Contingencies to allow for probable bad ground when laying . the sewer, 5 per cent, on £17,580 ... 879 0 0 Engineering, raising loan, ' clerical wo.rk, etc. ... 1646 Q 0 First year's interest, 4£ ' per cent, on £34.585 1556.: 0 0 ■ £36,141 0 0 Interest at '4& per cent., sinking fund 1 per cent.—sJ per cent.; , • s£. per cent, on £36,W1 1987 0 0 Working costs— . : Wages, fuel, oil, re- J pairs .. ... . 423 10 0 Depreciation in plant / and machinery ... I^o 0 0 £2550 10 0 . This , would require a rarte of 2d in the £ on the tinimproved value of £303,654. ;