Sanitary sewer manholes shall be constructed in the following manner:
(a) All sanitary sewer manholes shall be constructed of reinforced precast concrete sections in accordance with ASTM Standard C-478.
(b) All sanitary sewer manhole wall joints shall be rubber O-Ring type conforming to ASTM Standard C-443. All joints shall also be sealed externally with either:
(1) A trowelable mastic such as Fabertite or equal.
(2) Kent seal or equal.
(c) (1) All sewer pipe connections to sanitary sewer manholes shall be sealed with hydraulic gaskets as manufactured by Dura-Tach, Inc., or Press Seal Gasket Co., or equal.
(2) All sanitary sewer manhole lift holes shall be sealed watertight with a non-shrink grout or an expanding portland cement mixture, such as Octoplug, or equal.
(d) Adjustment of the sanitary sewer manhole casting to the final grade shall be accomplished with precast concrete adjusting rings. The adjusting rings should be sized so that the adjustment to final grade will require a maximum of three adjusting rings. The joint between the sanitary sewer manhole frame and chimney, cone or adjusting rings shall be one-half (1/2) inch thick and made using non-shrink grout. The top of the cone section of a precast sanitary sewer manhole shall have a vertical flat surface of three inches internally to facilitate the installation of chimney seal.
(e) An internal rubber chimney seal shall be installed on all sanitary manholes. A rubber seal extension, to cover any additional heights of chimney not covered by the seal itself, shall be used as noted on the typical detail. The internal rubber seal and seal extension shall be as manufactured by Cretex Specialty Products, or equal. The standard drawing showing these seals and extensions and the minimum sanitary sewer manhole cone dimension criteria needed for their use follow the text of this section. The sleeves shall be extruded from a high grade rubber compound conforming to the applicable requirements of ASTM C-923. The bands used for compressing the sleeve and extension against the manhole shall be fabricated from sixteen (16) gauge stainless steel conforming to ASTM A-240 type 304. Any screws, bolts or nuts used on this band shall be stainless steel conforming to ASTM F-593 and 594, type 304.
(f) Where sewer lines pass through or enter sanitary sewer manholes, the invert channels shall be smooth and semicircular in cross-section and shall be formed directly in the concrete of the sanitary sewer manhole base. Changes of direction of flow within the manholes shall be made with a smooth curve with as long a radius as possible. The depth of the flow channel shall be 0.8 times the diameter of the outlet pipe. The floor of the sanitary sewer manhole outside the channels shall be smooth and sloped toward the channel not less than one inch per foot.
(g) Each sanitary sewer manhole shall be vacuum tested from the top of the sanitary sewer manhole cone to the manhole base. All pipes entering the sanitary sewer manhole shall be plugged, taking care to securely brace the plug from being drawn into the sanitary sewer manhole. The test head shall be placed and the seal inflated in accordance with the manufacturer's recommendations. A vacuum of ten inches of mercury shall be drawn and the vacuum pump shut off. With the valves closed, the time shall be measured for the vacuum to drop to nine inches. The sanitary sewer manhole shall pass if the time is greater than sixty seconds for forty-eight inch diameter, seventy-five seconds for sixty inch diameter, and ninety seconds for seventy-two inch diameter, manholes. If the sanitary sewer manhole fails the initial test, necessary repairs shall be made. Retesting shall proceed until a satisfactory test is obtained. All testing costs shall be the responsibility of the permittee.
(Ord. 09-119. Passed 11-17-09.)
