(A) Horizontal separation of gravity sewers from water mains.
(1) Gravity sewer mains shall be separated from water mains by a horizontal distance of at least ten feet unless:
(a) The top of a sewer main is at least 18 inches below the bottom of the water main; and
(b) The sewer is placed in a separate trench or in the same trench on a bench of undisturbed earth at a minimum horizontal separation of three feet from the water main.
(2) When it is impossible to obtain the required horizontal clearance of three feet and a vertical clearance of 18 inches between sewers and water mains, the sewers must be constructed of water main materials meeting both a minimum pressure rating of 150 psi and the requirements of § 3.02 of this chapter. However, a linear separation of at least two feet shall be provided.
(B) Separation of sewer force mains from water mains. Sewer force mains and water mains shall be separated by a horizontal distance of at least ten feet unless:
(1) The force main is constructed of ductile iron material meeting a minimum pressure rating of 150 psi and the requirements of § 3.02 of this chapter; and
(2) The sewer force main is laid at least four linear feet from the water main.
(C) Separation of sewer and water main crossovers.
(1) Vertical separation of sanitary and storm sewers crossing under any water main should be at least 18 inches measured from the top of the sewer to the bottom of the water main. If physical conditions prohibit the separation, the sewer may be placed not closer than six inches below the water main or 18 inches above the water main. The separation distance shall be the maximum feasible in all cases.
(2) Where the water main crosses under a storm or sanitary sewer or over said sewer with less than 18 inches of separation, both the sewer and water pipe shall be situated such that the joints of both pipes are as far as possible from each other. The water main shall have nitrile gaskets. In the case of storm sewer, the pipe shall be reinforced concrete with flexible O-ring gasket joints. In the case of sanitary sewer, the pipe shall be of water main quality material for a minimum of 20 feet in accordance with SUDAS.
(D) Exceptions. Should physical conditions exist such that exceptions to divisions (A), (B) and (C) above are necessary, the design engineer must detail how the sewer and water main are to be engineered to provide protection equal to that required by these sections.
(E) Connection of dissimilar pipe. Suitable couplings shall be used for joining dissimilar materials. The leakage limitations on these joints shall be in accordance with § 2.11 of these standards. Coupling shall be fernco or approved equivalent.
(F) Sewer crossing under a waterway.
(1) The top of all sewers entering or crossing streams shall be at a depth below the natural bottom of the stream bed sufficient to protect the line. One foot of cover over the top of the line is required where the sewer is located in rock or cased and three feet of cover is required in other material. In major streams, more than the three feet of cover may be required.
(2) In paved channels, the top of the sewer line should be placed below the bottom of the channel pavement. Sewer outfalls, headwalls, manholes, gate boxes or other structures shall be so located that they do not interfere with the free discharge of flood flows of the stream. Sewers located along streams shall be located outside of the stream bed.
(3) Sewers entering or crossing streams shall be constructed of ductile iron pipe with mechanical joints or equivalent approved by engineer. Sewer systems shall be designed to minimize the number of stream crossings. The stream crossings shall be designed to cross the stream as nearly perpendicular to the stream flow as possible.
(4) Construction methods that will minimize siltation (silt fence) shall be employed. Material used to backfill the trench shall be stone, course aggregate, washed gravel or other materials, which will not cause siltation. Upon completion of construction, the stream shall be returned as near as possible to its original condition. The stream banks shall be seeded and planted, or other methods employed to prevent erosion. The design engineer shall include in the project specifications the method or methods to be employed in the construction of sewers in or near streams to provide adequate control of siltation.
(G) Aerial crossings.
(1) Support shall be provided at all joints in pipes utilized for aerial crossings. The supports shall be designed to prevent overturning and settlement.
(2) Precautions against freezing, such as insulation and increased slope, shall be provided. Expansion jointing shall be provided between above-ground and below-ground sewers.
(3) For aerial stream crossings, the impact of flood waters and debris shall be considered. The bottom of the pipe should be placed no lower than the elevation of the 50 year flood.