(a) New sewer systems shall be designed on the basis of an average daily per capita flow of sewage of not less than 100 gallons per day. When sewers are designed on a running full basis, the following per capita sewage contributions exclusive of industrial flow should be used:
(1) Building sewers - 400 gallons per capita per day.
(2) Main sewers - 250 gallons per capita per day.
(b) No building sewer shall be less than six inches in diameter.
(c) No sanitary sewer main shall be less than eight inches in diameter.
(d) In general, sewers shall be sufficiently deep so as to receive sewage from basements and to allow for further extensions. At no time shall a sewer be less than two foot in depth unless encased in concrete.
(e) Slopes of sewers may be greater but not less than the following:
Sewer (inches) Minimum slope in feet per 100 feet 6 0.60 8 0.40 10 0.28 12 0.22 14 0.17 15 0.15 16 0.14 18 0.12 21 0.10 24 0.08 27 0.67 30 0.058 36 0.046 |
Sewers shall be laid with uniform slope between manholes. Sewers on twenty percent (20%) slope or greater shall be anchored securely with concrete anchors or equal, spaced
as follows:
(1) Not over thirty-six feet center to center on grades twenty percent (20%) and up to thirty-five percent (35%).
(2) Not over twenty-four feet center to center on grades thirty-five percent (35%) and up to fifty percent (50%).
(3) Not over sixteen feet center to center on grades fifty percent (50%) and over.
(f) Sewers twenty-four inches or less shall be laid with straight alignment between manholes.
(g) When a smaller sewer joins a larger one, the invert of the larger sewer should be lowered sufficiently to maintain the same energy gradient. An approximate method for securing these results is to place the 0.8 depth point of both sewers at the same elevation.
(h) Where velocities greater than fifteen feet per second are attained, special provision shall be made to protect against displacement by erosion and shock.
(i) Sewer pipe must be either strength clay pipe meeting ASTM specifications
C-700, or asbestos-cement class C-428 or greater sewer pipe. Cast iron sewer pipe shall be used where the Superintendent sees the need for added strength or safety. No pipe joints of less than four foot shall be used. No concrete shall be approved.
(j) Joints for all sewer pipe shall be of the “O” ring type compression joints as defined by ASTM designation C-425. Poured joints and joints of the slip seal type shall not be approved.
(k) Sanitary sewers and sewage force mains should be laid with at least a ten foot horizontal separation from any water main. Sewers (or sewage force main) may be laid closer than ten feet to a water main if it is laid in a separate trench and the elevation of the crown of the sewer (or sewage force main) is at least eighteen inches below the bottom of the water main. If it is impossible to maintain the eighteen inch vertical separation when the sewer is laid closer than ten feet to the water main, the sanitary sewer should be constructed of (or encased in) water main type materials which will withstand a fifty p.s.i. water pressure test.
If a sewage force main is laid closer than ten feet to a water main, in no case should the sewage force main be laid such that the crown of the sewage force main is less than eighteen inches below the water main.
(l) Whenever sewers cross under water mains, the sewer shall be laid at such an elevation that the top of the sewer is at least eighteen inches below the bottom of the water main. When the elevation of the sewer cannot be buried to meet the above requirements, the water main shall be relocated to provide this separation or the sewer constructed of cast iron, or asbestos-cement pressure pipe for a distance of ten foot on either side of the water main.
(m) Inverted siphons should have not less than two barrels, with a minimum pipe size of six inches and shall be provided with necessary appurtenances for convenient flushing and maintenance; the manholes shall have adequate clearances for rodding; and in general, sufficient head shall be provided and pipe sizes selected to secure velocities of at least 2.0 feet per second for average flows. The inlet and outlet details shall be arranged so that the normal flow is diverted to one barrel, and so that either barrel may be cut out of service for cleaning.
(n) Trench Specifications for Water and Sewer Lines. Minimum trench width pipe o.d. + 18 inches; pipe to be bedded in clean, compacted sand with minimum of six inches on sides, top and bottom.
Balance of trench to within six inches of ground level, to be bank-run river gravel well compacted or flooded.
Remaining six inches to be of top soil and seeded if in lawn type area; if in street or alley area to be surfaced with same type material as surrounding area.
(Ord. 12-2-74-A. Passed 1-20-75.)