08/08/07 Castles/US 93 Utility Main ExtCity of Kalispell Public Works Department
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Post Office Box 1997, Kalispell, Montana 59903-1997 -Telephone (406) 758-7720. Fax (406) 758-7831
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August 8, 2007
CTA Architects Engineers
P.O. Box 1439
Billings, Montana 59103
Attention: Pat White, P.E.
Sr. Project Manager
RE: Silverbrook Estates
U.S. 93 Utility Main Extension
Kalispell, Montana
Dear Pat,
The City of Kalispell 2007 Wastewater Facility Plan Update (draft) addresses the
sanitary sewer collection system deficiencies below the Silverbrook Estates
development. The areas of concern are (1) the Grandview Lift Station and (2) the
gravity collection system below the Grandview Force Main discharge.
The existing peak flows at the Grandview Lift Station and in the gravity system (just
below the force main) are 251 gallons per minute (gpm). The lift station and the
gravity lines have an existing capacity of 460 gpm. This is derived from the (single)
pump capacity in the duplex lift station and the open channel capacity in the 8" line (8"
vitrified clay, d/D=0.94, n=0.013) below the force main.
Silverbrook Estates will create a peak flow at the Grandview Lift Station of 378 gpm
(610 equivalent residential units X 0.62 gpm peak flow per unit). The City has current
unused commitments at the lift station of 215 gpm. This will create a peak flow of 844
gpm.
The facility plan update defines two projects that will create the necessary capacity to
serve Silverbrook Estates. These projects include: (1) Replace the existing 20 hp
pumps with 30 hp pumps, which will increase the (single) pump capacity to 860 gpm,
and (2) Install a parallel gravity main from Northridge Drive (along Parkway Drive) to
Meridian, which will divert excess flows from the existing 8" gravity main.
When these construction projects are completed, the Kalispell sanitary sewer collection
system will have adequate capacity to serve this development. The City will monitor
the time line of the construction of the residential units within Silverbrook Estates and
construct the upgrades prior to the need for the capacity.
The Kalispell water distribution system has adequate capacity to provide service to
Silverbrook Estates. Please feel free to call if you have any questions. Attached are
copies of the approval letters sent to the Montana Department of Environmental Quality
and the Flathead City -County Health Department.
Sincerely,
Frank Castles, P.E.
Assistant City Engineer
Attachments: a/s
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