IMPROVEMENTS TO DRAINAGE OUTFALL.

Wairarapa Age, Volume XXXII, Issue 3151, 31 March 1909, Page 5

IMPROVEMENTS TO DRAINAGE OUTFALL.

BOROUGH ENGINEER'S REfORT. The Borough Engineer, (Mr Wm. T. Mansfield}, submitted the following report to the meeting of the Borough Council last evening on the completed improvements to the drainage outfall:— ' The installation as originally laid down provided for the settlement of the crude sewage in a closed septic tank, the resultant tank effluent being passed and subsequently dipsosed of —thereabouts two volumes through two specially constructed gravel filters, thence direct into the river—the remainder being passed over the surface of an area of land situate at a lower level and tnence into the river also.

At some subsequent date for some reason the character of the closed tank was altered by providing three openings 2ft by 2ft on one side of its length and by piercing several openings in the roof. The filters were dismantled and their use discontinued.

As mentioned in my report, I found in 1907 the closed tank to be retaining a large accumulation of sludge, (approximately 75 per cent, of the capacity of the tank) the effluent passing in a very bad state aloi'ii 5 earth carriers over the surfar< >•'( the land ih°nce direct into ti. ;iv r. Uinex the earth carriers were piactd- 4in agricultural: drain oip'-s which hal sludge '"p,. in consequ :i en nf winch iuc . aiuent simply iJ.iwed oyer and along the carriers.

1 He c laracter of that effluent was mo t iuul and at the point of discharge into the river gave off a most offensive odour indicating a bad effluent.

At that date the Council had. decided, subject to a consent of the ratepayers, to abandon the works for a site further down the river and to extend the sewerage of the Borough so as to connect many parts of the settled district not now sewered.

The consent of the ratepayers was not given, and it thereupon became immediately incumbent upon me to make some effort to improve the character of the liquid discharging into the river.

I represented the situation to you and obtained your consent to make an effort in that direction.

The following is a brief statement of the operations subsequently carried out, and which are now being inspected by you:— In order that no portion of the contents of the tank should enter the river untreated I put the contents into a sludge pit (formed by excavating the adjoining ground) from which the liquid escaped by percolation, leaving behind is in the pit a resultant mass of sludge. After thorougly cleansing and examining the tank I had the openings referred to closed up, and thus restored the tank to its original condition.

I have removed the filtering material from the filters, put in concrete bottoms, and 1 now propose to use wnac were tne filters as secondary settling tanks.

The town sewage, largely diluted as it is with infiltration water due to leaky sewers, enters the tank I y means of a submerged inlet 15 inches in diameter.

After traverisng the .tank, it emerges by means of nine 4in submerged outlets into a well by which it formerly passed, after the filters -■. ere abandoned, through a 15in. pipe on to the land.

Under ordinary working conditions that outlet will not now be used.

By means of an opening 4ft 6in wide, the tank effluent is now made to drop from the well on to a concrete apron, from thence it passes in a chin sheet with a fall of three inches into a well 2ft wide by 25ft Long constructed at the end of one of the old filters —from thence it flows over a sill, formed by lowering the end wall of the old rilter, into one of the old filters and which I now describe as tank 2 from thence the effluent passes by submerged oulets into tank 3 (formerly the second of the old filters) through baffle plates extendng the whole width and oepth of the tank, and returns to a point alignable with the starting point. Thence it trickles in the £,orm of a thin sheet over a sill formed by lowering the end wall of tank 3 into a well 2ft by 25ft placed at 3ft below the point of discharge from tank 1. The effluent then passes by means of a carrier (partly pipe and partly earth) to the land for final treatment.

I have had the land formerly used for treatment, prepared for receiving the effluent irom tank 3 by forming channels on the river shingle and sand of which the land principally consists, spaced at suitable intervals, and the effluent is now intended to pass through the land by percolation and to be; caught finally in a carrier excavated 3ft Gin below surface level along one side and the lower end of the land into a chamber and thence through an outfall into the river. It will thus be seen that the depth' of filtering material is approximately 3'feet. In other words, natural bacterial filters are now available with an area of five acres as against an area of 50ft by 60ft, originally provided. My operations have been carried out with the object of obtaining an effluent, viz.: A liquid incapable of purefaction and of a higher standard than that formerly discharged into the river. By the time the effluent has reached the outfall in the manner described it should be an effluent of a high standard of purification ur> likely to cause de-aeration of the river water, and unlikely to create any offence therein. It is at this point intended that samples should (if desired) be taken by the Health Department for the purpose of ascertaining what degree of purification had been effected between the points of entering tank I and the outfall

I have made ample provision for discharge in times of flood. The total liquid capacity of the three tanks is approximately 166,000 gallons. The duty of tanks 2 and 3 will be to promote quiescent settlement and to render the effluent more uniform in character. The area of land available for filtration is approximately 5 acres, which can if necessary, be increased. From trial made I am satisfied that the land is of first-class quality for filtration, and I am exceedingly

sngauine of its capacity to fcreal properly sotted tank effluent in fargq quantities p<sr acre for some? time to come or unti?3ttch time as thffgrowth in population necessitates exJenI sions. However, analysis of the effluent discharged at the outfall' will indicate its capability or otherwise or when the period has arrived. The tanks will require empting of their sludge contents as often as may be found necessary, that depending mainly upon the character and quality of the sludge. The emptying can j be effected by gravitation through scour valves without occasioning nuisance if proper care be observed. At the date of this report tank No, 1 has been working 61 consecutive days or one-sixth of a year and is working satisfactorily—an evidence that the resolution of solid matter is being effected. The total cost of my operations • have involved the Borough in a sum of £270. The purification works as adapted will not involve the Jtiorough in any additional sum for maintenance, it being a matter of a few moments only each.day to' divert the effluent into fresh channels. The land is- ready for cropping. Owing, however, to the season being too far advanced for a root crop I thi>jk i* better perhaps for this; year to prepare for a green oat or some similar crop which would make excellent feed for the Council's horses in the winter, and the surplus (if any) might be disposed of by sale. As 1 have stated in a previous report the farming of the land must be made sub-servient to the production of a good effluent, but I see no reason wny. with careful tillage, the land should not produce cro s, such, for instance, as mangold wurtzel, Hwedes, ryegrass or maize which could be used, for feeding the Council's horses or sold—thus producing a revenue as a set off against the expenses of management. Hitherto the revenue has been practically til. HI.REPORT DISCUSSED IN COUNCIL. EULOGISTIC REFERENCES BY COUNCILLORS. After the report had been read the Mayor said they were indebted to Mr Mansfield for a very excellent and lucid rep;rt. The drainage outfall had betn., visited that morning by a number of the members of the Council,who had obtained a very good idea of the work that had been done. He had every confidence in the improvements effected and' if they proved successful then the vexed question of the outfall of drainage, which had proved such a trouble, would be solved. He was inclined to the opinion that the fluid would find its way into the river in a perfect state of purity, and if this proved to be the case the residents in the locality of the drainage outfall would have no cause to complain. Cr Elliott said he had visited the wnrk that morning, and the inspection made had given him very great pleasure. The situation which had . e.n a must difficult one had, he thought, been successfully overcome. Cr Yarr said that the condition of th outall had in the past been a serious nu-nace to the health of the puulic of Masterton. The problem nad been tackled by Mr Mansfield, and it was apparently a success, and he thouaht that the residents had uvery re o son to be indebted to their Engineer.

Cr Prentice, in the course of his remarks, expressed the wish that the Council would not lose sight of the undrained portions of the Borough. The Mayor, in reply, said the Council fully realised their responsibility in that direction.

Cr Pauling and other Councillors st-oke in eulogistic terms of the improvements. Tha report was uanimously adopted, the question of cropping the land being left to the discretion of the Engineer.