Water System Design Manual, December 2009
Document source : www.doh.wa.gov
Page 120
December 2009
Water System Design Manual
For existing water systems, water suppliers may install "individual service" booster pumps to
meet minimum pressure requirements. However, water systems may only use individual booster
pumps on an "interim basis" and they must manage and control any individual booster pumps
(WAC 246-290-230(8)).
"Interim basis" means until they make the improvements needed to resolve pressure deficiencies.
Water suppliers should describe the time they need to upgrade a water system in a water system
plan (WAC 246-290-100(9)), small water system management program, or project report.
Because water systems must update their water system plans every six years, DOH expects the
interim period to be no longer than six years.
If the pressure in the distribution line meets the minimum requirements, a purveyor may allow
installation of more or less permanent individual booster pumps to serve customers who want
additional pressure. For example, developers may install booster pumps to serve structures built
at significant elevations above the service meters. The purveyor should approve the design,
installation, and operation of such individual booster pumps. Moreover, the purveyor must
ensure the booster pumps do not adversely affect pressure in the rest of the distribution system
(WAC 246-290-230 and 420), and address all cross-connection control concerns (WAC 246-
290-490).
10.1 Determining Pumping System Discharge Capacity Requirements
Engineers must design a BPS to meet peak hourly demand (PHD) (WAC 246-290-230). See
Chapter 5 for ways to estimate PHD.
In most cases, the BPS must also meet fire flow plus maximum day demand ( (WAC 246-290-
230(5)). The local fire protection authority or county fire marshal usually determines minimum
fire flow requirements (WAC 246-290-221(5)). If these officials don't adopt local standards,
water systems must meet the following minimum fire flow standards where required under
WAC 246-293-640):
·
Residential:
500 gpm for 30 minutes
·
Commercial and multifamily:
750 gpm for 60 minutes
·
Industrial:
1,000 gpm for 60 minutes
10.1.1 Open System Design Guidelines
For open systems, equalizing storage is available to help meet PHD requirements. Given this
available storage, the engineer must only design an open system BPS to meet the MDD for the
system or a specific pressure zone (WAC 246-290-230). If the BPS constitutes a critical part of
the water system, the engineer should consider additional capacity or redundancy for purposes of
expansion or reliability. At a minimum, DOH expects the design to ensure the water system can
meet the MDD with all pumps in service and the average day demand (ADD) with the largest
pump out of service.
Summary :
Page 120 December 2009 Water System Design Manual For existing water systems, water suppliers may install "individual service" booster pumps to meet minimum pressure requirements. If these officials don't adopt local standards, water systems must meet the following minimum fire flow standards where required under WAC 246-293-640): · Residential: 500 gpm for 30 minutes · Commercial and multifamily: 750 gpm for 60 minutes · Industrial: 1,000 gpm for 60 minutes 10.1.1 Open System Design Guidelines For open systems, equalizing storage is available to help meet PHD requirements.
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