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Les diagrammes suivants illustrent la mdthode. rrata o }elure, 1 d D 32X 1 a 3 ' ■• 2 3 4 5 6 SCHEMK OF SEWERAGE FOR THB CITY OF HALIFAX, NOVA SCOTIA, PBKPARRn BT THE CITY ENaiNESE, BY ORDER OF THE BOARD OF WORKS, ODER THB AUTHORITY OP THE CITY COl)\CIL. 1876. HALIFAX, N. S., BLACKADAR BROS., STEAM PRIXTKRS. 1870. '''%'' 9 (If) A SCHEME OF SEWERAGE FOR THE CITY OF HALIFAX, N. S. To TIIK BOAKD OF COMMISSlOXKUS OF CiTY WoiJKS : Gentlemen, — In conformity with your instructions received in July UiBtructions. last, ] have gono very carefully into tlio conaideration of the wh')lo of the matters appertaining to the construction of a thorough system of sewerage for tliis citv ; and T sub- rioposed niit lierewith a plan (marked No. 4 a), upon wiiich is shewn a system of sewers — in my opinion — not only suitable for f)ur pn^sent requirements, but wliich will l>e suilicient when the wdiole district under consideration is thickly built upon. The surveys were commenced on the 27th of July, 1875, Burvey*. .at which date an assistant engineer was engaged, at a salary of 3100 per month, whose whole time has since been taken up in surveying, levelling, and plan drawdng in connection with this scheme. The amount of money granted by the City Council U) Expjnsw. prepare the ]:)lan referred to, was SI, 500, and the entire cost has been Sl,28l.G0. The foUow'ing is a list of the plans which it has been i-ans iircpured. found necessary to prepare, and wdiich are submitted with this report. No. lA. An accurate ]>lan of the w^holy city on a scale of 400 ft. to the inch, w^ith the elevations above city datum marked at all intei'sections of streets, at all changes of grade and undulations in the streets and roads. No. 2 A. A plan of the wdiole city, scale (!00 ft. to 1 in., shew- ing all existing water courses and the water-sheds. No. 3a. a plan, scale, (iOO ft. to 1 in., shewing all existing sewers, their ai)proxirnate sizes and depths. No. 4 A. A copy of No. lA. (without the elevations), shew- ing the proposed new system of sewers, together wnth the oM sewers. No. 5 A. A tracing, scale 400 ft. to 1 in., shewing the drainage areas of all the proposed sew-ers and the (piantities of combined rain water and sewage which they are calculated to discharge wdien running half or two-thirds full according to the nature of the district. 2 Also — Sections or profilus of alltho streets and roa(U, plotted on ])roh'lo paper to a scale of lOO ft. horizontal to ;]() It. vertieal. CMettiaiter^ jjj designin^^ a system of sewerage, tlio prineii)al matters consiiieratiou. requisite to be taken into consideration are — Ist. Tli(» area to be drained. The rainfidl. The topography of tlie district. The jiopulation both present and prospective. The water supply. Existincr sewers. Objwt in prt'IMriiiflf rtohrnie 2nd. :h-d. 4th. Uh. 6th 7th. 8th. Ventilation. The diflleulties in the way ot carrying out the projiosed selieme. 9th. The probable cost. It must be borne in min*l that it is not now proposed Ur construct the whole of the sewers laid down upon the plan. The chit^f object in prejiaring this scheme being that in all new constructions a system miglit be adhered to which would be adapted to our prospective Avants. AREA. Area of City. Ar'a to to ciraiuetl. ■ Sewors at pro.st n r. nnii (|uir>.d. Sewers now le'iulrwl. The area of the whole city is 4,."G3 acres. The total area which will idtinuitely be drained by the proposed system of sewers is 2,281) acres. This may be termed the city proper, as it includes the whole of that portion of the poninsida of Halifax which has been laid otf into streets, besides a large sul>uiban district. Nearly half of the sewers shewn on tlio plan are not now, nor will they bt', retjuired for many years to come. For this reason I have thought it advisable to again sub-divide — what I have termed — the city proper, into two divisions, shewn on the plan by the tinted purple line. ^Vithin tlin pur{)le line the .streets are mostly built upon,. and the town may be considered as growing rapidly inside of this limit. New sewers are therefore more retpiired inside of this sub-divisitm than beyond it, and a separate estimate is given of the cost of constructing these, iiearly all of wliich are now required for the health of the town. The construction of the others may be deferred until they are wanted. RAINFALL. For statistics of the rainfall I am indebted to Mr. Fred- erick Allison, M. A., Chief Meteorological agent to the Dominion Government. 8 Tiie nni()iu:t oT rain \\hicli Ml dininj^ tlio past ycavft>t»tic«, ondiuL,' olst Deconibor, 187'), was 4241)3 inches. Tho ilopth (»f snow was (S7'M inches, and tlir total (irocij)itation, or the combined raintnll and incited snow, was b\\H inclios. The avnraijfc lor ihv last l'\ yt\'irs was as follows ; Rain, 4r,-;](;7 ins. Snow, 82'2U ini. To'tal precipitation, 52172 ins. It is not, however, so much with annual or mi.'in amuial results we have to d(\al in (juestions of si-Aerag.-, as -with nuiximum i'alls within a limited ptniod yf time. The heaviest rainfall in a short time — of which 1 have """y'^,"', any int(jrmation — occnn-ed on tlie lUth June, lo/2, when OlSli of an inch fell in half an hour. On tiio 2'Hh iJoc. , 18(>!) -1 O'li in. loll ill 5. n hours ::- !221 ill !i8tli \»K , 1871 oass :t7 " - oa4o l!»th Vl^\)., " -IKX) 4r. " ::= 22o !>r, •• = 0-270 !)tll J.ili., 1H74-1 040 4 1 " ^ 0-2W per liuiir Other heavy raiiifitik Mr. Allison r(>marks, "it is probable that these rains did'^'^'<'">"[ti<»f " not fall ecju.iUy hour l)y hour ; but where they persist, as "these did, for four or tiv(; hours failinf.f Jicavily, the want '■ of proportion is not so great as an inexperienced jx.'rs )n " would imagine ; and if, for instance we allow 'iil to <,ne " hoiu' of^ the fall of l.Sth Noveml)er, 1873, leaving 115 lo " the remaining 45 hours, I think wo will be within tl»e " limits of disproportion ; for remarkably heavy showers, as " that of l'.)th June, 1872, never last hniir." Two xory heavy rainstorms occurred here during the H.nvy runfaii* past year, occasioning much damage to the streets and roads especially in the steep hill districts, and flooding a ievv cellars — see my annual report for 1875. The first took pi act; on the 10th October, when 44()() inches fell in 18 liours. This is the greatest fall recorded in 18 hours sinct; 1859, or for a period of 17 years. The second occui-rtd on the lOth and lith November, when 2418 inches fell in 17^- hours, and for violence at the time of its greatest height this exceeded the former. The gaiiges were observed every three hours, the result being that during the storm of lOth October the greatest fall was O.OOO inch irom 1) a. m. to noon, while in the storm of llth November 1.003 inch fell from G a. ni. to a. m. Gaugings of Freshwater brook were taken in the Public GauKimts ot Gardens during both of these storms, when it was found BrTik'*''"" that the greatest flow occurred about 40 minutes after the heaviest fall on llth November, at which time 3,500 cubic feet of combined sewage an,38 cubic leet per minute per acre. All the new sewers are arraiij^ced to carry ofl* the com- bined s(!wage and rainfall, and in order to reduce their si/e, and consequently the cost a.s much as possible, storm overflows are intioduced wlierovor ]>racticabl(' on all the long lines, by which moans tho storm waters willbodi.'i- charged directly into the harbour nt the nearest jioint. Tho colcuhitions of t'le recmircd dischariTos and si/.es of the sewers were pre[iarLd in tho following manner. Provision being made for a rainfall of 0.138 inch per hour, (a (|uantity which lias Ix-i-n nearly though never (juite reacla'd, as far as 1 can ascertain) tho yield ]ier acre would be l',i7\) cubic feet. Allowing half of this (piantity to flow directly into tho sewers- :llo cubic feet \)er minute per acre. Providing for a ))f)pula^Jon of 50 persons to the acre ivud allowing seven cubic fei't of .«ewage })er day for each person, one-half of which is found from observation to pa.ss off in from six to eight lioursrrO.oO cubic feet per minute per acre, or a total of 12 cubic feet to .the aero per minute in the tnne our greatest vain storms. In order to provide against the liability of the .sewers being gorged during heavy niina, when the surface may be covered with, largi? quantities of melting snow, they are made large enougli to discharge the above (piantity when luiming two-thirds full in comparatively flat districts, and jialf full in the steep hill districts of the town. J lie new sewers of London arc calculated to discharge only one (piaiter of an inch rainfall ni 24« hours, in addition to the sewage;. In Neville's Avork on hydraulics— contaniing]irobabiy the most reliable data relative to the flow of water in ])ipes and sewers in th(! English language, *the following is stated in reference t:» iome experiments made in the London sewers to ascirrtain the proportion between tlic rainfall and the actual discharge of sewers. " In a town "district, such as that drained by the Savoy and " Novtinuuberliind — street sewers, the (juantity running off "into sewer-, v.'ithiii six hours after the fall, varies from 10 " to tography or coniiguration of the town is highly '''''|p?jy*''"'*' favorabli! to the construction of siiwers. The deepest exca- town rivornMo vation will n(»t exceed IG feet, and tlKi average will l)e about Htnu-tioalif })J feet. »"*"" Owiuii' r.o the steoi> gradients of many of tlie streets, 'Ve<'o'v ■sowers ot ('ouij)ai'atively small size v/iU answer; but tins renders it the more imperative to take special priK'autions for ventilation, as the more rapid the descent of a si*\ver the (juicker will tl»e foul s^iwer — gases, generated, ascemi io tlio higher localities. POPULATION AND WATER SUPPLY. In a scheme of drainage such as thi.s now proposed, where *^«w.i«e8i!ii»ii ii 1 1 , T 1 1 • i- 11 ji wlit-n coin the sewers are adapted to discharge heavy rainialls, tlu^ i.ir«i witii consideration of tlie po])ulation and water-.supply, 1;eeonu's '"''" " 'i^"'* a matter of minor importance ; as tlie amount of 1u)uk!',- di-ainage- water, or sewage, as it is armed, is extremely small, when compared witli the storm waters which the sewers will — at times — have to carry otf. In fact where tlic sewers are ])roportioned--as is here the case — as rarely being taxed to more than twothirds oi' their capacity, the element of sewage, could, without much '.anger, be entirely omitted from the calculations. For the pur-poses of this report, however, it has been ropuiation 1 1 1 11' • i. i. • 1 /• 1 X- !• Cn pi-uvi.lfJ for, deemed amply suthcient to jirovule tor a population oi oi) persons to the acre, over the whole area which it is proposed to drain, and to allov^' to each person a water supply of 50 ^^|^roy'5'!7f,^r gallons per day. As a matter of information it may bo interesting to know, '''4^"',**';',"^^ that in the heart of the town, the pojjulation is 8G to the of tii« town. acre ; the portion taken, being the populated |)arr,s of wards ?> and 4, or that lying between the Citadel Hill on the west and the harbour on the east, Sackville slreet on the south and Jacob street on the north, not including the wharves and H. M. Ordnance Yard. The area of this district is G5| afjre.s, and the population is 5/308, according to the report of the Sn htocp sido-hill {^routid, and the |)n)j)ost'd Kuwers aro of sutiicicnt t'a|>aeity to di.s<,'luir<^^! tlu! Htonii waters nnd ficwajjo coiuUini'il, when runniii'' less than two-thirds I'mIL Totiilnert wlitTu Iimotirablo. Lansth of exiitini; Bowerr Chirftrier o cxistiii^ lewers. Nei'!'!7 to atKUuIon 8 )me of tlio existing Hewers. Kl'inedmini) fhml I be at,tiniiouc>L lv\lSTIN(; SKWKliS. Olio of tho (tldcf points borno in mind in pr.»p;ii'i:i'.'; Miis s(',h(Mii<\ win, t') d''sij]fn tlio n(!W works in sucli a niuincr as to ntiiixo as many of the oxistin.,' sow«!r,s as possible, when? thoy weiv. do'jnr:^ I officient, or tiiat tlicy could bo made so. Theio a.'.'" now known to b(» IS-GO nnles of pulilie, sev,';'rs in ns(\b 'sid-'s a ninnbcrofstontt-box-drains ofdonbtlnl ntility wliicli may, or may not,1mve l)jen coniitrnctuJ at the publie expense. Of these ISGG miles, C'7l miles are })nilt of l)rickwork; 10"77 miles aro common stoiv' sowers, and 4•^^(\ n)iles are earthenware pipea. Many of tiuse S3vvers are wretched constructions, and totally unrttted foi- the work they are su])i)osed to do; causing,' cndhvss tronble and expense in elcanin;^, cf>ntinually chokini;,- np, and frequently tioodiu;/ the cellars in the vicinity. In carrying]; out the ))ropo.sed system, it will 1)r necessary to abandon (5.44 miles of the existing' Howers. The rernaiii- in<^^ l'2"4i miles may, J think— to a large extent — be utilized. Proltably .some of the latter, on beinj; opened and examined,, will b(! ibund utisuitable to be retained. A.sa rule, the ordinary' stnno-box-drain, or sewer — as here constructed — should be abolished ; the only ])lacos where they can safely l»e allowed to remain, being, wheri; they exist in a soil not already, or likely to become " excrement Bodden," or .soaked with sewage matter, where tUey are of suifieient capacity and depth ; and where they have a con- stant and sr.tHcient tlow through them to keep clear of deposits. VENTILATION. D.insers of uiiveiiti'atcd sowi-r.s. That all sewers should be ventilated is an axiotii wJiich wid scarcely be controverted. It lias l)ecn stated— and with much truth — that unventi- lated s((wers are far more dangerous than steam-boilers without safety-valves. The following is quoted from Latham's work on Sanitarv hncrinecrinu: : " It is a roniarkablo fact, but ncvcrtlifloss tnio, that from thoso towns in which no jirojx'r provision is made: for tlie ventilation of the sewers, a certain typo of disease (lyplioid fever) is Hcldoni absent. Tlie normal condition of the <^'onerality of liouses lias an important i)'jarin<^ on the necessity for the ventilation of sewers and drains. The superior tempi.'ratiiro of the' air oi" houses, and the drau<.jht caused by chinuu^ys, liave the efleet of causin«^ the various traps that are used to seal the drains to be relieved from pre.ssure. Oonseciuently, as there is less atmosfdieric ])roa- .sure upon the traps within houses than upon external tra])s, and, moreover, as many of the traps usi>d within a house have far less seal than those usually employed out of doors when no ventilations is provided, <.^ases ar«' sure to escape into houses as the point of least resistance.* TIm; evil etfects of the want of ventilation W(>re conclusively shown in the early .sewerage works of Croydon, in which [)lace, no sooner were the works of drainage drawing towards completion, than the town was visited by an epidemic of typhoid fever, which was traced entinily to the absence of ventilation in the system of sewers. The mortality of Croydon at this period rose from 18'/5.S per thousand in iSol to 2857 per tliousand in l.Soo. These early sewei* works wei'e designed on the principle that all matters were to be so rapidly dis- (^harged from the sowers, and the sewers tiushed with s>ich a coi)ious sup))lv of water, that decomposition could not rake place, and therefore it was thouglit that sewer-gas would never be jiresent ; but in j)ractice this theory was not found to be borne out, and it is a remarkable coincidence as to the cause of the fre(iuent outbreak:" of fever in Croydon, which took place at certain intervals until the year 18(>(j, when the sewers were thoroughly ventilateil, that diseases whieli formerly made their haunt in tlie low-lying districts were transferred, after the completion of the drainage works, to the highest or bastportionsof tlie town, thereby establish- ing the fact that the presence of the disease in the high localities was due i.o something carried in the air of the sewers, which, in obedience to a natural law, accumulated in tiie highest part of the district." *♦*♦«*• " With regard to the results that have arisen where ventilation of sewers has been adopted, the case ot Croydon shows clearly that proper ventilation has been attended with very bsneficial results. Since the introduction of systematic ventilation there havebeen no periodical outbreaks of fever, and the general rate of mortality has so declined, that in a district having a ]io]-)nlation oi nearly sixty thou- Kcrwwlty for VunMlMtion. Kffi'.M of t<'in|>«'r:itiir«i of lioiiHcn. EfTivt of nou-veatlUtion of dpwers at Croydon. Early »ewor worku of Ooyiloii. Transfiir of dUMsc from lower to Iiighur distrio fiwult of Rawer ventilation i 8 t pii ot ToutiUtioi: Objections to ventilation by means of ilowo -spouts. Proposed metlioil (if veufilatioii. sand persons the rate of mortality rarely exceeds eighteehi in the thousand, which is a standard of health unparalleled in the history of sanitary science, for a district having so large a population. The case of London affords another striking example as to the inllucnce of sewer ventilation. Hero tlie sewers are ventilated, though no general plan is adopted ior dealing with the noxious effluvium escaping from the ventilators, and yet London stands at the head of all largo towns hy reason of its small death-rate, which has been ascribed by more than one eminent authority to the somewhat rude ventilation ])rovided for the sewers." Numerous have been the plans })roposed at different times for the ventilation of sewers. One, which has found many advocates, is to ntibae for this purpose the "down-spouts '* or rain-water-condrtctors fix)m buildings, by connecting them, untra])ped, with the sewers. This method has many objections, the principal of which are, that the down-spouts arc seldom made -with tight joints, .so that the sewer-gas may escape freely in its upward course and find its way into the house through loose or open windows ; or even supposing it to be earned safely to the eaves-gutter, it will then gain easy acc(;.s.s to the houses through the dormer windows, if, as a rule, all dowji-spouts were made perfectly tight throughoiit their whole length, were connected witli the crown of the sewer, and could be carried up t-) the highest part of the housL\ this expt'dient would not then bo objectionable, presuming that other conditions were also complied with. But the down-spout would then cease to act as a rain-water conductor and would bo solely a sewer ventilator of a very expensive kind, if applied to all or any largo number of buildings. The practical way, however,, usually adoj^ted in this case, is to connect the rain-water- spout with the house drain at some convenient point, which drain invariably enters the sewer at abput a foot or so above the invert, so that when the sewer is running ]iartially full and the ventilator is much, if not most, needed, its^ mouth will be closed^iid so of necessity it must entirely cease to act in that capacity. The method of ventilation proposed in this scheme is by means of the man-holes in the centre of the streets — jilaced at frequent intervals, seldom exceeding 300 feet apart — and at the head or upper end of all branch sewers. At each man-hole where sufli'^ient fall for the sewer can be obtained without going to much extra expense, a step, or droj) in the invert, is made for the purpose of breaking the ascent of the sewer-gas, which otherwise is found to have a tendency to leap over the opening and to pass upwards along the 9 8ewei". This arrangement has also tho additional advantage of enabling tho sewers to be constructed in straight lines from man- hole to man-hole, thereby affording a better opportunity for inspection and to keep tho whole system entirely under control, without the necessity of digging up the streets. It is scarcely within the limits of this report to enter ^^^''ewity for upon the subjects ol house dramago anu tho trappmg and ventiiatinR ventilating of private drains, but this I think it incumbent p""'****^ upon me to say, that — for the future sanitary condition of the town, and to realize the l>enefit8 whicli shouhl result from tho expenditure of such u larger suib of money as i:^ now contemplated — these are matters of the utmost impor- tance ; in fact, without proper attention being paid to these details, it is questionable if it would not be better to have no sewers at all. I would strongly advise all householders Aiivioe tt>^ ^ to act entirely on the defensive! princi[)lo, i.e., to assume that the sewers have no other means of ventilation than into the houses in which they dwell, in this ca.se they are jiretty sure to ado])t measures which will exclude sewer-gas froni their dwellings. SEWl^lS. use of Ijirtliernvart' pipes. The lengths anpecially in contract works. 10 PI.iCBs where it is propipes; these, however, are oidy for the purpose of continuing existing pipe sewers — that can hi utilized — x little further along the streets in which they an^ laid. With the above exceptions all the [)ropos3d sewers will be built of brickwork laid in Portland cement mortar. Most of these will be o'^g shape, — with the smaller end down — but in some places where tlie flow will 1)3 continuous and always comparatively large, it has been thought better to provide circular sewers. The smallest brick sewer will be 18" X 12", egg sliaped, and the largest one of tlie same kind, 42" X 28". The smallest circular brick sewer is 24", and the largest 48" in diameter. ^''utTc^nJ7'^'"' ^^ ^'^ proposed to use rn) small bricks or bricks of the ordi- nary size in the constructi(m of tliose works, but in all cases, to employ large and specially made bricks for the ])urpose. The large bricks will be of the standard English size, with a certain proportion of radiated bricks. The sewers up to Hi) inches in diameter and those 24" X 30 " will be mostly half a brick or 4^" thick. For sewers above these sizes and up to 45" in diameter — in i)rder to save the expense of double work — it is])roposel to use a still larger description of brick, or one (i inches in width or deptii. All larger sewers will be double ring work or 9 inches thick. Tliere may arise excepticmal cases where it will be necessary or advisable to depart from the alun-e ndes. Among the ordinary bricks which come to this market, the largest I have seen, measure 7i|" in length 3J" in width and 2\" in thickness, though such are rarely to be met with. Tliiclitiess of Sewern. iS!/.ps of snnll brirlts. II The usual size is about 7i" long, "!," wlJe and 2" thick, while some are even smaller. My reasons lor not recom-objootionn mending these to be used are: — Ist. That even though the J',J,g|'f ""f^JJ^ cost per thousand is considt'raljly less than that of the pro- posed bricks, they nre a more expensive article. In my judgment it would be economy to pay nearly double the j)rice per thousand for the large?' bricks on account of the very nuich larger cpiantity of work wliich they will lay. 2nd. That although tlie smaller article is no duulit amply sufficient for the smallest description of sev/ers of half a brick in thickness, yet for a sewer of 2' — 0" or 2' — G" in diameter it would scarcely be safe to construct the work less than one brick thick, thereby adding very largely to the cost. It is proposed to use none but the very hardest burned Hart sewers within itself, with the exception of • listrict No. o, the storm waters from which will overHow and pass through portions of districts Nos. (j, 7 and 0, and from tlience into the harbour. These districts may be briefly described as follows : l)iSTl!I(T No. 1. In the south end of the town, lying to the south of South Street and Victoria Road ; drains an area of 180^ acres and discharges into the harbour thi-ongh the public water lot to the North of Laidlaw's wharf. DiSiuiCT No. 2. Includes the whole Avater shed of Freshwater brook, an area of 704^ acres and di.schargos at Freshwater. District No. o. Lies to the south of Spring Garden Road and to the east of Queen Street, havinir an area of 'V,) acres and discharose(l) will give a velocity of 2"8.') feet per second when running one-third full. In places where the flow will Frjvuion iimd« von ordinary occasions be small, the inclination is increabed '"'" "«•'''»«• as much as possible. But as an additional precaution, and m order to provide against accidental deposits, all the inan- BUtS L'wcrs. 14 (IruiriN. holos will 1)(; so constructed tluiLby the insortion of a tem- porary flushing board or gate tl^.sewago iiiay bo dammed u}) until a largo volume is collected, when, by raising the gate the whole quantity so dammed back will be at onco discharged, the etiect being to Hush the sewers. The man- lioles require to 1)0 arranged in this manner particularly at the heads of all l)ranch sewers, i)ut, for the ])iirposos of flushing, water from the nearest hydrant will ha\e to be used. "^wfthpipe''""' ^'^"^ ^^^^ purpose of making connections between pipe drains and the public sewers, it is [jroposetl to use specially made junction-blocks which will be formed to correspond in thickness, and with the internal figure of the brick sewer. Owing to the exj)ense of providing junctions in the sewers- (as has been the practice for the last three yeai-s) for all buildings, lots, and j)urposes ; the uncertainty of placing them in their proper ])ositions, and the fact that large ninn- bers must unavoidably be built in, where in all probability they will never be used, or — at least — not required for very many years ; T would reconnnend — in ordinary cases — pro- viding them only at points where they arc now required and where they arc wanted by the owners of property. As regards breaking into a sewer for the purpose of inserting a junction, it may bo done without much fear of damaging the sewer when junction-blocks of the proper form are em- ployed, and ordinarj^ care is used by the person doing the work. It would be a wise precaution, liowever, to allow no ]iersons to tap the sewers but such as hold a lipenso from the City for that purpose. There is another matter to which 1 would draw attention, and that is, the great difficulty which exists in getting sewer works — which are let out to contract — constructed in a satisfactory manner. For this reason I would recommend that the proposed sewers be built by " days work " in pre- ference to the contract system. In myjudgment this course will not only result in a large saving of mone_^, but in the works being executed in a thorough and superior manner. Objectioii.s to coiitnvfrt eystem. Difficulties in the way of carrying out the work. No serious (liiiicultio.4. Chief causes of trouble t<> be anticipated. There are no serious difficulties in the way of carrying out the projected system o^ sowers, aud certainly none of any kind which would not be common to any scheme that might be proposed. The chief causes of trouble and expense will be : — 1st. The large amount of rock to be encountered in. almost every section of the town. li 2nLl. The gas and water pipes which Ho at {le[)ths vary in«if ^'p* *^|,'' ^'^^^^ from 4 feet to Hh feet. Cases may arise in wliich it wouM be necessary, or advisahk^, to alter tlie proposed gradijints of soino of the sewers on account ot tliese pipes, (»r for other reasons. Shouhl such occur, ])lan No. ')A will be luund of service in determinini,.biihiicd, Corbett's Wharf and ha-i T>een regularly observed. The following are the results for the seven months ending tUst March : Ordinsiry tii!es. T.ieSixby tklc. Kxtreiiie tvJes. Tlip hi«li<.st ti'lcobservt'OfKnirrod Feb.2n(l,]87f3 .''■'-«" abovei'itv diituiii (stning S. witiil. The lowest t iik" (ilmerved occiirreii Feb. anl, 13TO=2'-7" below tiiy ilatuin (strong N. V\' Aviiid. > Difference lietweeu extreme bigliaiid low tide=;lf-l" M«in biifh tiiln -sS'-S" above eity datiun. Mean low tide r C-lO" below city dutum. I'iffcreiire between mean hifth and low tide. . . - -4'-(j" ])uring the great storm of October 4tli, 18G9, which was accompanied by a tidal wave — commonly known as " the Saxbv tide" — the greatest height to whicli tho tide rose was eight feet above city datum, or only one foot an1« Ime on th.. phin are now requin-d. while n"t7et'T.penef' """^ " ''" '^^^^"' ^^«^^^^ -« "^ «^'-^« S wm "^,,«^^,7'">' «"t this scheme so far as it is con- tained withni the limits of tho purple line; the irreat bulk blwii't^'T'""'^'!'"?';'" '' ''■*' ■^'•''^™^ will n,>t-5n all o habihty-be miuire.l for many years to come. ' town Tt^ 1?^'J^'°-' 'l^^V^'ti^'^ "1" rock in mo.st parts of the ir„o.tu,.ty town, its extreme irrerrularity and the unceitaintv t}.at '^'V"'^ Sr ''' f' r'T ^^"' ^' ''' encountered, it t^. Wn ^^'" rS k!''"l^n 'r^^""^ "?' ^^^'"*' ^^^ -xcavations to be ,.11 p 1. ! ' allowance is deemed to be somewhat in ex- "••'"""»•• cess of what may be expected and consequently the estt '^"'"'"«-^'^ mates may be considered as very Hberal ^ 18 Estimate of the Cost of Constructing the Sewers inside of the Purple Line, Allowing lialf of the excavations to b« in rock uiul the average depth to top of brick invert to be nine ieet. 8ize of Sewer. Inches. 9 12 15 I8xl2 21x14 24 >' 1 G 27x18 30 X -20 33X22 36 X ?4 39x26 24 80 83 S< 45 48 48x36 : Average Length. coat per : lineal foot. Feet. 1900 415 40 54100 7000 9000 2400 9200 5000 3000 1000 700 400 1100 700 1300 400 300 2-75 3 (>0 3-50 3-00 3 10 3-20 3-30 3-40 3-50 3 60 50 40 60 50 80 00 50 00 Total ooit. Remarki. $ 6225 lEarthenwi ire pipe. 1245 " «( 140 " ti 16-23()0 !4i^ inch brickwork. 23560 i< 28mO() " 7920 " 31280 u 17500 l( 10800 « 5500 :6 inch 2380 14 i inch 1440 ■' 6050 :0 inch 4060 << 9100 <> 3400 9 inch 2400 " Total length; 98,555 :feet. . . =; $323,100: 80 Man-holes in existing sewers at i!^60 each 4,800 420 ditto in new sewers at $50 21,000 Extra works at outlets and overflows 5,000 Contingencies 10 per ct. (nearly) 35,100 Total probable cost $389,000 Less amount to be collected for ) 32,000 feet frontage of assessble property at $1.25 . 165,000 Total coat to the city $224,000 The above eKtimiite incluiles -besides the eiirtheiivare pipes there mentioned— S millions of 4^ inch tirieUs in the sewers iinrt 800,000 six inch bricks. 800,000 four-and-a half inch l>ricks in the m iii-holcs, fO.OOO cubic yards of rock excavation and 60,000 cubic yards of earth, besirles tide gates, finishing < (« u 33 x 22 1700 3.50 5950 « «