(a) Location. Manholes for sanitary sewers shall be placed not more than 300 feet apart whenever possible, and in no case shall they be more than 350 feet apart. Manholes shall be placed at every change in grade, direction and pipe size and at the end of each sewer line. When convenient, manholes shall be placed at street intersections.
(b) Drop Manholes. Drop manholes shall be used whenever a sewer enters the manhole at an elevation of twenty-four inches or more above the manhole invert.
(c) Design.
(1) Diameter. The minimum inside diameter of all manholes shall be forty-eight inches.
(2) Wall thickness. The wall thickness of manholes constructed of various materials and at various depths shall be as follows:
Depth Brick Precast Concrete Concrete Block
(ft.) (in.) (in.) (in.)
0 to 10 8 5 6
10 to 16 12 5 12
16 to 25 16 5 18
(3) Precast manholes. Precast concrete manholes shall conform with A.S.T.M. Specification C-478-68 or the latest revision thereof. Brick or block shall be laid to a minimum height of twelve inches above the crown of the pipe. A minimum of one foot of bricks or concrete blocks shall be placed on top of the cone section of all precast manholes for adjustment purposes.
(4) Manhole bottoms. All manholes shall rest on a six-inch, 3,000 psi, concrete slab which shall protrude a minimum of six inches beyond the outside diameter of the manhole. Precast reinforced concrete slabs may be used.
(5) Manhole steps. Steps for block and brick manholes and for precast manholes shall be according to standard engineering practices as specified by the Division of Water.
(6) Manhole frames and covers. Manhole frames and covers shall be according to standard engineering practices as specified by the Division of Water.
(7) Manhole cover grades. Manhole covers shall be set at finish grades. Finish manhole cover grades shall be shown on the plans.