Current through Register No. 13, March 27, 2025
(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.
(See Revision Note at part heading for Env-Dw 405)
#10612, eff 6-1-14
