Prof. Greene's Report

As many persons may bave forgotten ustwhat is contained in Prof.Greene's report, on sewerage, presnted to the city council March 17, 18'JO, we deem it wise to reprint extracts from it in order that all niay know what tlie plan recomraended involves. The report at the outset emphasized the gteat necessity of a sewerage system. The main features of the plan proposed are as follows: An efficiënt system of Bewers should conyey all the sewage away froininhabted districts before decomposition lias taken place in it. The s#wers stiould be so ventilated that any gases contained in them .should have no ;cseafl to the interior of buildings. The lirst oondition is provided for in the water carriage sybtem, by giving the sewers such an inclination that the sewage may flow with suflicient veiocity io remove the solid matters deposited in it. A mean veiocity of three feet per second is generally sufficient to prevent deposita. By lar the greater portion of Ann Arbor, if not all, needs no underdrainage. Her porous subsoil is able to take up readily and allows to soak away all rainfall that is moderate in amouni. I have therefore planned a system for house drainage exclusively. The moderate cost of the "separate" system makes it possible to carry out a system of sewers, when the expenses of the "combined" system would make it impossible. The amount of tüe sewage derived from the drainage of houses, etc, may be apjiroximately taken as equal to the water supply at present, from Ann Arbor. That amount may be put at from 500,000 to 750,000 gallons daily. The calculations have been based upon uiteen persons per hundred feet of sewer, or five persons to a house on each lot of sixty-six feet. The quantity of sfiwerage calculated isseventy-flvegallons per cap ita, average daily flow, and a nfaximum discharge at times at the rate of 150 nall ons. The contemplated ,outfall is twentytwo niches in diameter, to flow half full. Can one anticípate that the amount of sewage discharged by such a pipe will be noticeable in the Huron river below the city? It will bear but a moderate ratio to the water which runs through one wheel at Swift's mili. The sewer at the outfall is proportioned for the discharge of the sewage of the whole city and for a, population of 10,000 or 20,000. A system of sewers branches and tapcrs like the trunk and limbs of a tree. The main or trunk sewer may empty at, lirst, the first railroad bridge below the city; second, at the highway bridge at the east end of Wall-st; or, third, opposite the slaughter houses near the foot of Thirteenth-st, where the University f ewer now discharges. It passes by thesideofthe Michigan Central railway, crosses underthe railway at Fifthave, to Summit-st, and thence west to Allen's creek up which it runs, partly through streets and partly through private property, as shown, to Madison-st. lts proposed sizesandlengths are as folIowb: irom the outfall at the railroad bridge to Main-st, at the corner of Summil, twenty-two inches, length (Ï.L'UO feet; from Summit-st to Catherine-st, eiglitetn inches, length 2,300 fee.; from Cdthtiiine to l'uot of William-st, lifteen inche?, 2,200 feet; from William to Milist, twelve inches, 3,500 feet; from Hill to Grove-st, ten inclies, 700 feet. At the upper end of lateral tewers, where the grade is moderate, automatic llush tanks will be provided. Manholes are to be placed at all intersections, change of direction and grade, and no more than 300 feet apart. All of the pipes except those of the main sewer, above mentioned, will be eight and six inches in diameter. The cost of the sewers, exclusive of the lower portion of the main sewer,including everything complete, may be put at from $1.00 to$1.20 per lineal toet, or $(i,000 per mile. The city engineer of Kalamazoo reports the total extent of the "separate" sewerage system was, in 1887, twelve miles built at a total cogt of $69,250.13, an average of $109 per foot,' and the total annual maintenance of which, with semi-weekly inspection, was but $204 97. The trunk sewer at the lower end, as far as Main-st, is estimated at $2.00 per foot. The piecefrom tiierailroad bridge to the east end of Wall-at will, then, cost $3,600; from Wall-st to foct of Thir teenth-st, $2,000; from Thirteenth-st to the foot of Main-st, $0,500. The sewer from the foot of Main-st to the foot of Madison-st is estimated, for 6,000 feet, at $1.50, or $9,000. The cost oi the trunk sewer, on a liberal estímate, from Madison-st to the foot of Thirteenth st, where the University tewer now discharges will be $15,000, and here it may termínate until the sewers are used to such an extent that the outfall becomes objectionable there, when it can be extended to the railroad bridge That portion of the city from the old ceraetery and Forest Hill cemetery northward, but thinly built up at present, will be readily sewered down Thirteenth-st, and the fifth ward will be sewered through Wall-st eastward, as shown on the plan.bringing everything together at the same place. Prof. Greene enumerated the various methods which provided for the payment of the cost of building the lateral sewerage, giving the objections to many of the systems, and linally hit upon the followinir from the Kalamazoo ordinance onthis question as the bestmethod. "In the constitution of lateral sewers all property adjoining or abutting upon that portion of the street oralley througU or along which the lateral sewer may extend, shall be assessed at the rate of 33 cents per foot front, and at the rate ot 33J cents for each foot of connecting sewer that nap.y be necessary (or that may be desired by the property owner) to connect said lateral sewer with said property, and the city shall assume and defray all other expenses incident to laying of such lateral and connecting sewers."