Section Env-Wq 704.12 - Manholes: General Construction Requirements(a) All component parts of manhole structures shall have the strength, leak resistance, and space necessary for the intended service.(b) Manhole structures shall have a life expectancy of at least 25 years.(c) Manhole structures shall be designed to withstand HS-20 loading and shall not leak in excess of one gpd per vertical foot of manhole for the life of the structure.(d) Barrels, cone sections, and concrete grade rings shall be constructed of precast reinforced concrete.(e) Base sections shall be of monolithic construction to a point at least 6 inches above the crown of the incoming pipe.(f) Horizontal joints between sections of precast concrete barrels shall be of an overlapping type, sealed for water-tightness using a double row of an elastomeric or mastic-like sealant.(g) Pipe to manhole joints shall be as follows:(1) Elastomeric, rubber sleeve with watertight joints at the manhole opening and pipe surfaces;(2) Cast into the wall or secured with stainless steel clamps;(3) Elastomeric sealing ring cast in the manhole opening with seal formed on the surface of the pipe by compression of the ring; and(4) Non-shrink grouted joints where watertight bonding to the manhole and pipe can be obtained.(h) Manhole cone sections shall be eccentric in shape.(i) All precast sections and bases shall have the date of manufacture and the name or trademark of the manufacturer impressed or indelibly marked on the inside wall.(j) All precast sections and bases shall be coated on the exterior with a bituminous damp-proofing coating.(k) Manholes that are not replacing existing manholes shall have a brick paved shelf and invert constructed to conform to the size of pipe and flow. At changes in direction, the inverts shall be laid out in curves of the longest radius possible tangent to the center line of the sewer pipes. Shelves shall be constructed to the elevation of the highest pipe crown and sloped to drain toward the flowing through channel. Underlayment of invert and shelf shall consist of brick masonry. Inverts and shelves shall be placed after testing of the manhole.(l) Replacement manholes where there is an established line and grade through which the sewer enters and exits the manhole shall have:(1) A brick paved shelf and invert constructed to conform to the size of pipe and flow as required in (k) above;(2) A precast concrete shelf and invert with the shelf constructed to the elevation of the highest pipe crown and sloped to drain toward the flowing through channel; or(3) A fiberglass insert with the shelf constructed to the elevation of the highest pipe crown and sloped to drain toward the flowing through channel.(m) When manhole depth is less than 6 feet, a reinforced concrete slab cover may be used in lieu of a cone section, provided the slab has an eccentric entrance opening and be capable of supporting HS-20 loads.(n) The minimum internal diameter of manholes shall be 48 inches. For sewers larger than 24-inch diameter, manhole diameters shall be increased so as to provide at least 12 inches of shelf on each side of the sewer.(o) In the flow channel, a drop of at least 0.1 feet shall be provided between incoming and outgoing sewers on all manholes.(p) Slope across manholes shall be the average slope of the incoming and outgoing sewers. Design shall include measures to prevent hydraulic jumps across the manholes.(q) Watertight manhole covers shall be used for all manholes located in flood-prone areas as determined by the municipality.(r) Electrical equipment installed or used in manholes shall conform to the National Electric Code (NEC) adopted by reference in the state building code pursuant to RSA 155-A:1, IV, for installation in areas classified by the NEC as Class 1, Division 1.(s) Precast bases shall be placed on a 6-inch layer of compacted bedding material that conforms to the ASTM C33/C33M No. 67 stone standard in effect when the stone is processed by the manufacturer, available as noted in Appendix D. The excavation shall be dewatered while placing bedding material and setting the base or pouring concrete.N.H. Code Admin. R. Env-Wq 704.12
(See Revision Note at chapter heading for Env-Wq 700) #8590, eff 3-25-06
Amended byVolume XXXIV Number 46, Filed November 13, 2014, Proposed by #10693, Effective 10/15/2014, Expires10/15/2024.