Section Env-Dw 405.17 - System Concept(a) For any particular water supply project there is likely more than one approvable water system design concept.This part shall not be interpreted to specify a particular design concept, but to ensure water system adequacy and reliability. Factors which shall govern the design criteria of the 4 most common water system design concept types used for small community water systems and for those NTNC water systems whose reliability is directly important to public health as specified in Env-Dw 405.02(g) are listed in (b) through (e), below. Modification of the design concepts identified in (b) through (e), below by the water system designer shall be allowed where the modification can be justified as a waiver pursuant to Env-Dw 405 .35 .(b) A hydropneumatic or pressure storage only type of water system, also known as a straight pressure system, shall require multiple high capacity wells and pumps.(c) An atmospheric storage and hydropneumatic storage type of water system shall require: (1) One or more wells with low or intermediate yields that discharge into a relatively large capacity atmospheric storage tank; and(2) High capacity booster pumps rated at the peak flow of the water system to re-pump or re-pressurize water from this tank into a smaller hydropneumatic storage tank for direct feed into the water distribution piping system.(d) An atmospheric storage and variable speed booster pumps type of water system shall require: (1) One or more wells with low or intermediate yields that discharge into a large capacity atmospheric storage tank; and(2) High capacity variable speed booster pumps rated at the peak flow of the water system to re-pump or re-pressurize water from this tank for direct feed into the water distribution piping system.(e) A gravity storage type of water system shall require atmospheric storage at a high elevation, wherein: (1) A minimum pressure of 20 pounds per square inch (psi) during peak flow periods shall be required at the highest service connection on the water system, requiring that the highest service connection be at least 6 feet lower, measured vertically, than the bottom of the storage tank; and(2) Additional elevation shall be required to compensate for frictional losses through the water distribution piping system and atmospheric storage tank drawdown.(f) If limited fire protection service is to be provided, the following water system design criteria shall be observed: (1) Where fire hydrants are planned by the water system owner, at least one additional separate water storage tank shall be installed and the fire hydrants shall connect to only the separate water storage tank(s). The re-fill pipe for this water storage tank shall incorporate an air gap. There shall be no connection between the domestic water system and the fire storage tank(s);(2) Where residential sprinklers are planned to be installed within the premises of one or more customers, the service line and domestic plumbing shall be appropriately increased in size. The service line shall be sized to accommodate a design flow rate specified in the state fire code, Saf-C 6000. The sprinkler piping shall be isolated from the domestic plumbing by at least a testable double check valve. The minimum duration of sprinkler flow shall be assumed to be 10 minutes; and(3) Additional provisions for source capacity and storage facilities shall be made in the water system's design to accommodate fire flows.N.H. Admin. Code § Env-Dw 405.17
(See Revision Note at part heading for Env-Dw 405) #10612, eff 6-1-14