BLD2022-1343+Letter+10.4.2022_10.34.39_AM+3144339Engineers I Planners I Surveyors
PACE
An Engineering Services Company
MEMORANDUM
DATE: August 11, 2022
TO: Bob Danson, Marty Henninger & Chris Scott, OVWSD
FROM: H. Peter Paulsen, PE, PACE Engineers, Inc.
SUBJECT: Fire Flow Availability — Housing Hope 236th ST SW, Edmonds
Per your request PACE Engineers, Inc. evaluated the fire flow (FF) availability for the above proposed
residential project site using the District's H2O Net hydraulic model.
The subject site is located on the north side of 236th ST SW between existing Edmonds Lutheran Church
to the west and the Park Edmonds Apartments to the east. An existing 10" Ductile Iron (DI) water main
(WM) fronts the property to be developed that is located within the District's High Zone (612 HGL). The
project involves the construction of four multi -family buildings. An 8" DI WM loop will be constructed
around the buildings and connect to the existing 10" WM. Preliminary plans indicate that three (3) fire
hydrants (FH) will be installed off the 8" loop.
For the purpose of this analysis, we determined the FF availability at the 8" main at the approximate
location of the proposed FH that is furthest from the connections with the 10" main and that is located
near the northwest corner of the proposed buildings. The screenshot below shows the existing and
proposed system, including node J164 that represents the approximate location test node/FH.
PROPOSED FHI
FURTHEST FROM
CONNECTIONS
J"
XL-2"0
' 236th ST SW
H 37 40 M•2576
EX. 1 T
CONNECTIONS
TO EX_ SYSTEM
:4"
PROPOSED 8"
ONSITE LOOP '
Z;
•
rry
r`-`v
4 sv/
WIA L3i2
JNN I W2SW I XL-2111/9
236th Street
LFM & CHK VLV
PACE Engineers, Inc.
11255 Kirkland Way, Suite 300
Kirkland, Washington 98033-3417
p: 425.827.2014 1 f:425.827.5043
www.paceengrs.com
August 11, 2022
Olympic View Water & Sewer District
Housing Hope Fire Flow
Page 2 of 3
Engineers I Planners I Surveyors
www.paceengrs.com
The proposed project is located in the High Zone. The High Zone is normally pressurized to an Hydraulic
Grade Line (HGL) of 612' by a booster station that pumps out of the District's 2.5 Million Gallon (MG).
The station includes one booster pump with a design point of 140-gpm @ 90' of head, and three
parallel pumps that have a design point of 430-gpm @ 90' of head. The station maintains a constant
HGL during all normal demand conditions. The booster pump station does not include a fire pump. It is
equipped with a generator that needs to be manually operated and started in the event of a power
failure.
The 612 High Zone and the 540 Low Zone are interconnected. The 2.5 MG tank that supplies the
booster station also feeds water into the Low Zone via s pressure reducing valve (PRV). Also, when
pressures in the High Zone drop sufficiently during very high demands, the Low Zone will 'back -feed'
into the High Zone through check valves at several locations.
The initial hydraulic model was run under a Max Day Demand (MDD) scenario with all normal interties
and supplies in service. This includes the SPU interties supplying water through PRV's into the Low Zone
via the 8th Avenue and Fremont Zones. The water level in the 2.5 MG was set at 5' below the OE. The
initial model analysis was also performed with the pump station off because automatic back-up power is
not available to the booster pumps.
Results were calculated at the proposed 8" main at the approximate location of the indicated fire
hydrant. The analysis was further performed to obtain FF results to meet the following pressure and
velocity requirements:
Maintain minimum 20-psi residual pressure at the test node (flowing node on the new 8"
main)
Maintain a minimum of 20-psi at all nodes in the zone and in the system where water service
is provided to customers
Maintain velocity in the main at maximum 10-feet per second (fps) under FF demand
conditions
The model shows that the proposed 8" loop under the above conditions can approximately provide the
following:
Static: 65±-psi (Booster Pump Station in operation)
FF: 1,900±gpm with 20±-psi residual and min. 22±-psi Zone
Max. Velocities: 6.7±-fps through proposed 8" from south
The modeling results indicate that the existing system and the proposed 8" main supplying the fire
hydrant should be able to provide a FF of approximately 1,900-gpm at roughly 20-psi residual pressure
without exceeding 10-fps flow velocities. Actual conditions may vary from the modeled settings, and
unanticipated events and additional unplanned demands, may affect the FF availability, and can reduce
the actual water that is available at the site under the typical pressure and velocity requirements.
The booster pump station in theory can provide additional FF capacity at the test FH. However, pump
stations for which there is no automatic back-up power should not be considered to be operational
during for FF availability calculations. It should also be noted that the booster pump station does not
PAP22\22091 HOUSING HOPE DE\ENGINEERING\CALCS\OVWSD - Housing Hope Fire Flow Results.doc
PACE
M Engineering Services Company
August 11, 2022
Olympic View Water & Sewer District
Housing Hope Fire Flow
Page 3 of 3
Engineers I Planners I Surveyors
www.paceengrs.com
include a large capacity 'fire' pump designed to provide high flows under FF situations. Therefore, high
fire flows will eventually exceed the booster pump station's capacity to maintain pressures, and when
pressures drop low enough, the Low Zone will start back -feeding into the High Zone.
In reality, as long as power is available to the pump station, the booster pumps still have the capacity to
slightly increase the FF availability in the High Zone, even during back -feeding conditions when the
pump station can't maintain pressures due to capacities /parameters being exceeded. However, the
model also shows that more water being pumped results in less water flowing through the PRV into the
Low Zone, thus reducing the capacity of water that can be backfed into the high zone.
PAP22\22091 HOUSING HOPE DE\ENGINEERING\CALCS\OVWSD - Housing Hope Fire Flow Results.doc
PACE
M Engineering Services Company