UNDERGROUND DRAINAGE

Timaru Herald, Volume XIIC, Issue 13677, 20 August 1908, Page 2

UNDERGROUND DRAINAGE

THE SEPTIC .TANKS. EXPLANATIONS BY MRMARCHANT. A " Herald" representatve called upon Mr ]•'. \V. Marchanl, the diainage engineer. t<» request- him to elucidate certain point* thai, appeared to be more or less obscure' to'the speakers at the meeting ol' ratepayers and householders at the Smith school on Tuesday night. The first rehired to the question or the; addition of a septic tank at the northern out rail, this lank not being mentioned in the original r-.cheme, placed before the' Borough Council early in 1904, and circulated in print in May of 'that year. Councillor Hawkey produced a copy of i his printed document at the meeting, iv prove that the. original scheme did not comprise such a. tank, whilst it, did comprise one at. the southern outfall. Mr Mai-chant said that a northern septic tank was not provided for, except a, small one for the limited area of Waimataitai Valley, to be located near the stone bridge on the main road, became the flat grade, of the pipe to the sea. outfall would" require the sewage to be wholly liquid. It was not considered necessary to provide a septic tank for the. drainage from the northern side of the present Borough. " But,'" continued Mr Mai-chant, " the material conditions: have been altered since, the original scheme was prepared. The eastern extension mole had not. been completed, and the; drift from the furiW end of the Benvenue Cliff wasalwavs northwards. Since that mole has existed, an eddy current is now frequently seen setting into the Bay south-wards. While the septic tank was being constructed we kept a Watch on.the ciirrents, and about three-fourths of the* time they set. northwards, the rest of the time towards the sands. This is an effect of the construction-of the eastern mole. Then there was'.'so• much sentimental objection to the. discharge of sewage into the Bay, ■yithout passing it through a septic tank, -,o much insistence by the Harbour Board iliat the drainage should bs, carried ..be? yowl the Dashing Bocks, that assail compromise, and to remove objections, the septic tank at the outfall was added. This was done before the scheme was submitted to the ratepayers or to Parliament. Seeing the effect of the eastern mole in modifying the run of the .currents, the. 'inclusion of the tank in the scheme was ■perhaps a desirable thing. . Now there would be no sign of pollution 20ft. away firm the outfall.

' With regard to the southern outfall," said Mr Marehant, "a septic tank was put in there by wuy of perfecting of the scheme. It was iiofc\thbught. to be -absolutely necessary then, and further observations of the flow of sewage and the fate, of sewage in the- sea had' still more convinced me'of that.' Take the case" of Lyttelton harbour. The shipping population there is a big thing, and all their sewage and the sewage of the" town, tonether probably'equal to that which will be delivered at the south end, is poured mUi the harbour between the moles, and there is no offence, nothing offensive to b? seen. Fishes and marine insects destroy it immediately. There is no wave action therei.no circulation of the water,-no active currents, yet- marine life obliterates all offensive matter in no time. As to pollution of the southern beach, we will guarantee that the liquefying tank would prevent that. I have seen the outfalls at Wellington, Napier, New Plymouth; Christchureli and elsewhere, and am convinced that a, peptic tank is not really necessary in such a position as the- southern outfall.- But I- am not going 4o press rhe modification. I believed it would be an improvement; but the opposition toi it shows that it- is a. mistake' to"jtry; to improve an original proposal. "People expect perfection from the first, and they do not approve of proposals to amend details. They forget that perfection has never been.reached anywhere, either .first -or last. The scheme as a scheme has notbeen altered. If we had proposed to shift the outfall, or to add a pumping plant, that would have been an alteration. If they wanted a septic tank, I am quite willing to, put it in. I was just trying to save thp ratepayers a • little money by. the modification and also to make provision: for a later future.

"A septic lank," explainer! Mr Marchant, "is only part of a. purification'nys-. tsiTi; and when you hear' people talking of clear, water, water clean enough 'to drink, you must understand that besides passing* through a septic tank to be broken down, the sewage must pass* through filter beds. And then a man_.wou'id be. a fool to drink it. For inland towns a septic tank is absolutely necessary, and in Boms circumstances—it depends where they can deliver the- effluent —a Alter bed maV be absolutely nececsary too. But where, you can deliver effluent into the open sea, a-liquefying tank is all that is necessary. The chairman •of the meet-: ing' was wrong in saying that I had .said the effluent frcm a- septic tank was fit to drink. I have never known anyone whoi had drunk the effluent, though I have heard of it being done." • ".Mr Black said he saw a man drink it." ..■■-''•

"Then it must have been after filtration."

Asked to explain what a liquefying tank is, and how it acts, Mr Marchant referred to plans prepared in connection with this proposal, showing a tank something like that at Benverrae Clifl l , but smaller -and with different internal •'arrangements, and a different position of'the discharge. The septic tank will always be full; the liquefying taiik might be full at high-water, or run down to l.ffc 9in at.low. wiiter. The solids .that putrcfivclive-gaifes :SvilL:;;have been gene,rated within theni, and;|the discharge' being from the; bottom /clv-the tank into a, : chamber with .a baffle' '-wall;/around : the .discharge; .pipe higher .'than', the ports,;>iu the bottom' pf-thes- tank,., no.Jioating^solid. can ge-t arway^' ; 'TheVeoiidis^float; iiiitili solved .and .then,' having .becoineSmiscible wi th the'; licjuid sewage.. they escapii: . jri liquid Vfqrjni south eiicl : people, feared, would- be throti-n upon arid' pollute the bench ..would be re-' .tained. in; .the tankuntil it became liqiiid, and when discharged 'info, the, eea would disappear, '-...-■ i

Another matter which was mentioned at the South School'.Weetihg,rand discussed privately after the meetirigccsed, wan the fact that in the (jriginal; scheme the fall from George street : to- the southern outfall was given as.- 1 in 700,.whereas in making the proposal : ;to, modify the intercepting sewer; this was. given as 1 in 1200. Asked 'how- -this difference -arose, Mr Marchant said the original-scheme was altered, on the advice of Mr .'.Quthheft, by..]qtj> ering the Gecrge street - s£wei\ '-'As-' o'riginaJly planned this.. eewer: ; was .carried only 4ft beneath: the railway level, and Mr Cuthb'ert, looking to future building possibilities- recommended that it be carried through at a lower level,".and adopting thi6 recommendatipn of .cpurse reduced the grade, of the jntereeptipg sewer. In reply' to the que*tioni ; "Can the concrete sewer -proposal and the septic .tank be combined?" ■■ Mr Marchant said No. It-woidd'load .the scheme wiih extiA expense,'-for „which he would be held responsible.'- If the' Council objected to the omission of the septic tank, he would revert t'q'the original-proposal, which would be sufficient foj- many years to come. ' '■■ '■■' "'"'"_-'-y'

Earlier in the day the town:clerk was asked if he had any. how or when the northern septic tank caiiie to be included in' the, work. .Mr Virtue: sajcli the idea, had lieen adopted before he became town before the' scheme was explained to the ratepayers previously to >the ' taking of the loan poll, and was (as reference to newspaper cuttings showed) frequently re-

ferred to. in the discussion .on thet Bill in the House of Representatives.', Ihe lirst official mention of the 'tank by the engineer was- a letter to the Mayor dated April 4 1905, in which this passage occurs : -It was originally proposed to construct one septic .tank, 'at the. southern outfall. Afterwards, in order to meet, objee ions raised von and vonr Council agreed to construct one also at the northern ..uf'l Mention being made of the small septic tank at the Caroline Bay cottage, the Town Clerk rang up the caretaker,- and) inquired whether the lank ever caused a nuisance, Mr Gibson replied that in hot. weather there was a. smell noticeable) near the vent pipe, but one could not notice it far. It never reached the lea rooms. The vent pipe perhaps wart not high enough, though it had been lengthened once. The tank itself gave no trouble. , , ,';" On this siatenwnl being referred to Mi Marchanr., he said that the- sit m:rm was not a good one for ventilation, i he,-cot-tage being under a cliff. H •1 , -- i ..'F' i l !& were higher there would probihly never be any smell noticeable. Tile gases would be quickly oxydised on i>e:;:g: disseminated in the' air." The L'is« genetated in a septic tank, he add'i.d, art combustible, and therefore, iwith a proper proportion of air, explosive. Several tanks had been blown up by iricaut icu's people .taking lights abonf. t'..cm w..;houti first .getting: thems, 'clearof' -g:}H.'■-■'■■■ '• hegas had even_ been utilised. At Exeter a workshop was lighted with it--burned with Bunsen burners and mnn'Vs, of i course.' >y -■'■ -■ ■'-/■

Asked what he thought -A the South School, meetingy {he Mayor, said he had quite an open mirid on the snb.-ei":':. of the proposed modification. , it w-s a matter for engineers rather than the lot.noil; so far as engineering Went, and i.n that r>;de he had Mr Marchant) and Mr (itlibert in favour of it,-and also the Chief Health Officer.. On the. other,hand, thev had a scheme; which-"-had beat -apprdyed j by the ratepayers, every step taken fy the Council had reference to thai, scheme, and as a. part of it the"rale'ji-, c-rs were told that there would be a seoiic tank. It- would' bebetter,: t-heiij''•'is s ive ser.titnent ,of the people ran that way, to siick to .the original plan and have the tank/' Mr Craigie said he had some property at the south end, and- felt, some sympathy with the south end people in their ob- 1 jection to the proposed omission of the tank. However, it was for the Council to say what should be done. He tyas pleased to see that there was a lively interest taken in the matter, no matter in what form the interest was shown. /'■;.