Sanitary sewers shall be designed and constructed in accordance with the following minimum standards.
(a) Minimum Size. No public sewer shall be less than eight (8) inches in diameter except that six (6) inch diameter pipe may be used for short, dead-end sewers where no possibility of future extension exists.
(b) Depth. In general, sewers shall be sufficiently deep so as to receive sewage from basements and to prevent freezing.
(c) Slope. All sewers shall be so designed and constructed to give mean velocities, when flowing full, of not less than 2.0 feet per second, based on Manning's formula using an "n" value of 0.013. The following are the minimum slopes which shall be provided:
Sewer size
Minimum Slope in Feet per 100 feet
6 inch
0.62
8 inch
0.40
10 inch
0.28
12 inch
0.22
15 inch
0.15
Sewers on 20 percent slope or greater shall be anchored securely with concrete anchors, or equal, spaced as follows:
- Not over 36 feet center to center on grades 20 percent and up to 35 percent.
- Not over 24 feet center to center on grades 35 percent and up to 50 percent.
- Not over 16 feet center to center on grades 50 percent and over.
(d) Alignment. Sewers shall be laid with straight alignment and constant slope between manholes.
(e) Increasing Size. 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 obtaining these results is to place the crown of both sewers at the same elevation.
(f) High Velocity Protection. Where velocities greater than 15 feet per second are expected, special provisions shall be made to protect against internal erosion by high velocity. The pipe shall conform to appropriate ASTM or AWWA specifications which provide protection against internal erosion.
(g) Materials.
(1) Any generally accepted material for sewers will be given consideration, but the material selected should be adapted to local conditions, such as character of industrial wastes, possibility of septicity, soil characteristics, exceptionally heavy external loadings, abrasion and similar problems.
(2) All sewers shall be designed to prevent damage for superimposed loads. Proper allowance for loads on the sewer shall be made based on the width and depth of trench. When standard strength sewer pipe is not sufficient, the additional strength needed may be obtained by using extra strength pipe or by special construction.
(h) Joints and Infiltration.
(1) Sewer joints shall be designed to prevent infiltration and to prevent the entrance of roots. When clay sewer pipe is used, the joints shall be compression joints for vitrified claybell and spigot pipe and made in conformance with the appropriate ASTM Specification. When concrete pipe is used, single rubber ring gasket joints shall conform to the appropriate ASTM specification. When asbestos cement pipe is used, joints using couplings and gaskets shall be made in conformance with the requirements of the manufacturer. Joints for organic material pipe shall be compression gaskets. No joints or material shall be less than those hereinafter described.
(2) An acceptance test shall be specified for all gravity sewer lines. The test may be either a water test or an air test. Where water testing is used (infiltration or exfiltration), the leakage outward or inward shall not exceed 100 gallons per inch of nominal pipe diameter per mile per day for any section of the system including manholes. Where the exfiltration test is employed, the line shall be subjected to a minimum of 4 feet of head or head to top of the manhole, whichever is the lesser above the crown of the pipe at the upstream manhole of the section being tested. The infiltration test shall be allowed only when it can be shown that the hydrostatic head at the pipeline is a minimum of 4 feet above the crown of the pipe for the entire length of the pipe being tested.
(3) Where air testing is used, test methods and acceptability criteria shall be in accordance with the appropriate ASTM specifications. Air testing shall generally be acceptable for all types of pipe materials. If air testing is employed, the manholes shall be tested by exfiltration. Inflatable stoppers shall be used to plug all lines into and out of the manhole being tested. The stoppers shall be positioned in the lines far enough from the manhole to insure testing of those portions of the lines not air tested. The manhole shall then be filled with water to the top. A 12-hour soak shall be allowed. Leakage shall not exceed ½ gallon per hour.
(i) Bedding.
(1) The sewer pipe shall be bedded in compacted granular material placed on a flat trench bottom. The granular bedding shall have a minimum thickness of 6 inches under the barrel of the pipe and shall extend up the sides to a minimum height of one-half the outside diameter of the pipe. The remainder of the side fills and to a minimum depth of 12 inches over the top of the pipe shall be filled with compacted select backfill material, containing no stones.
(2) Bedding material shall be placed in maximum 6 inch layers and compacted of 98% density in accordance with ASSHTO T-99.
(j) Backfill and Tamping. The following procedures shall govern for placing and compacting backfill above the bedding zone (the bedding zone extends to at least 12 inches above the crown of the pipe):
(1) Trenches shall be carefully backfilled with excavated material approved for backfilling, consisting of earth, loam, sandy clay, sand and gravel, soft shale or other approved materials, free from large clods of earth or stones larger than four inches in diameter.
(2) Backfill above the bedding zone shall be placed in maximum two (2) foot layers and thoroughly tamped to 95% density.
(3) Trenches in state highway right-of-ways shall be excavated, backfilled and compacted in accordance with the requirements of the West Virginia Department of Highways and Transportation.
(k) Manholes shall conform to the following requirements:
(1) Manhole location. Manholes shall be installed at the end of each line; at all changes in grade, size or alignment; at all intersections; and at distance not greater than 400 feet. Terminal cleanouts may be acceptable on lines less than eight inches in diameter in lieu of manholes on a case-by-case basis.
(2) Drop Manholes. Drop pipe shall be provided for a sewer entering a manhole at an elevation of 24 inches or more above the manhole invert. Outside drop connections shall be encased in concrete. Where the difference is elevation between the incoming sewer and the manhole invert is less than 24 inches, the invert shall be filleted to prevent solids deposition.
(3) Manhole Diameter. The minimum diameter of manholes shall be 48 inches. Manholes shall be constructed with an eccentric top.
(4) Manhole Materials. Manholes shall be constructed of precast concrete conforming to ASTM designation C-478. Manhole wall and bottom construction shall be such as to ensure water tightness.
(5) Manhole Flow Channel. The flow channel through manholes shall be of such shape and slope to provide smooth transition between inlet and outlet sewers and to reduce turbulence. Benches shall be sloped to the channel to prevent accumulation of solids.
(6) Manhole Connections. Line connections directly to the manhole or to short stups integral with the manhole shall be made with flexible joints. Flexible joints are joints which permit the manhole to settle without destroying the watertight integrity of the line connections.
(l) Building Connections.
(1) Building connections to the sewer mains shall be made by means of full-body eye fittings.
(2) Sewers shall be designed and constructed in a manner that will protect the water system from any possible contamination. Wherever possible, sewers should be laid at least 10 feet, horizontally, from any existing or proposed water main. Should local conditions prevent a lateral separation of 10 feet, a sewer may be laid closer than 10 feet to a water main if the elevation of the crown of the sewer can be maintained at least 18 inches below the invert of the water main. Whenever sewers must cross under water mains, the sewer shall be laid at such an elevation that the top of the sewer is at least 18 inches below the bottom of the water main.
(3) Properly engineered plans and specifications for the sewage collection system shall be submitted to the City of Keyser for review and approval. In addition, documentation shall be submitted showing that State Health Department approval of the plans and specifications and a permit to proceed with construction have been obtained.
(4) During construction, the City of Keyser shall have the right to inspect the work and to ascertain that the system has been tested and meets the minimum requirements set forth in the approved plans and specifications.
(5) If the proposed sewage collection system contains special items such as pumping stations, inverted siphons, aerial sewers, etc., the design shall be in accordance with standard engineering practice, subject to the final approval of the City of Keyser.
(6) The City of Keyser shall be reimbursed by the applicant for all costs incurred for plan review, construction inspection, testing, administrative activities, and related matters.
(Ord. 252. Passed 9-9-99.)