214010-020-mtn-home-2019-10-31-wfps-report

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Mountain Home Water Facilities Planning Study Update October 2019
Table 3.5 – Booster Pumps and Pressure Zones
Pressure
Zone
Source Water
Primary Delivery
Backup
Delivery
Available Storage
High
All Wells (indirectly via
Pilot Booster)
Pilot Booster Station
Well 14
(emergency intertie
into zone)
Tank 3 (directly); Tank
1A, 1B, 2 (indirectly via Pilot
Booster)
Medium
All Wells (indirectly via
Boosters)
Medium Pressure
Booster; Pilot Pump
3
PRV located near
Tank 2
Tank 3 (indirectly via PRV);
Tanks 1A, 1B, and 2 (indirectly
via Boosters)
Lower (Main)
All Wells (directly)
All Wells plus
Peaking Storage
from Tanks 1A, 1B,
and 2
PRV from High
Zone
Tanks 1A, 1B, 2 (directly);
Tanks 3 (indirectly via PRV)
3.7.1. High Pressure Zone
Water is delivered to the Upper Pressure Zone by the Pilot Booster facility (formerly referred
to as the Edgemeade Booster Station). The upper reservoir (Reservoir 3) provides fire
storage to the pressure zone. The City installed an intertie between the Well 14
transmission pipeline and the upper pressure zone, as an emergency supply provision to
the upper pressure zone. This intertie was used when the Pilot Booster Station upgrades
were completed and requires manual operation of valves.
Keller Associates completed an analysis of fire protection for this zone and found that the
City could provide 3000+ gpm for a period of 4 hours using 71% of the tank capacity (29%
reserved for operational and peaking storage) plus the combined capacity of the two booster
pumps. Well 14 was not assumed to pump into this zone to comply with DEQ’s requirement
for mechanical redundancy. Based on the fire demand requirements from the Idaho
Insurance and Rating Bureau, the highest existing fire demand in this zone is only 2500
gpm. If the two booster pumps are out of service, the upper zone can supply 2 hours of
3,000+ gpm fire flow.
As part of this Facility Plan update, Keller Associates performed an update to the Declining
Balance. We estimate that the Upper Pressure Zone can add approximately 240 EDUs
before the booster pumping capacity needs to be increased. The Declining Balance Update
is further discussed in Section 4.7 of this report.
3.7.2. Medium Pressure Zone
The Medium Pressure Zone is isolated from the system by normally closed isolation valves,
a check valve, a pressure reducing valve, and booster pump stations. The medium pressure
zone is served primarily from a booster station located near Legacy Park. This pump station
is able to deliver approximately 1450 gpm. Since the last planning update, the Pilot Booster
Station was equipped with another pump capable of supplementing this pressure zone with
approximately 500 gpm. There are two backup supply sources to the medium pressure
zone. A check valve located near the booster station will allow flow from the lower zone
(approximately 40 psi), and a pressure reducing valve located near the Reservoir 2 (Pilot
tank) site will supplement peak demands. The upper pressure zone provides fire storage
and backup supply to the medium pressure zone via the pressure reducing valve.
Similar to the Upper Pressure Zone, Keller Associates performed a capacity analysis on the
Medium Pressure Zone. The medium pressure zone was determined to have the ability to
handle an additional 318 EDUs before the zone reaches capacity.
For planning purposes, Keller Associates has assumed that Well 9 will eventually be piped
to the Medium Pressure Zone. Connecting Well 9 to the Medium Pressure Zone requires
that Well 9 operate using a variable frequency drive (VFD). Installing a pressure reducing
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