3d. Water system analysis for well no. 6 I ------,3(2,„
10 CITY OF
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1 CHANHASSEN
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. .. 690 COULTER DRIVE • P.O. BOX 147 • CHANHASSEN, MINNESOTA 55317
I ,.: (612) 937-1900 • FAX (612) 937-5739 4, _.
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MEMORANDUM
ITO: Don Ashworth, City Manager j2-4'-'1
FROM: Gary Warren, City Engineer ? - '��
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DATE: December 5 , 1990
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ISUBJ: Accept Water System Analysis Study and Authorize
Preparation of Plans and Specifications for Construction
of Well No. 6 and Related Watermains and Appurtenances
IFile No. PW113B and Project Noaz 91-1
I The attached Water System Ana�sis Report was prepared as
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directed by the City Council in order to provide current detail
and documentation as to the City' s current water demand as it
I relates to the City' s production capacity. With the rapid
development the City has encountered over the last four years it
was necessary to review the current system demands since the 1985
predecessor to this current study is somewhat outdated. The
I report goes into sufficient detail to make a recommendation for
the immediate and projected future needs of the City' s water
system. I believe this study to be a good "snapshot" of the
I system needs since it incorporates the most recent population
projections generated during preparation of the current
Comprehensive Plan.
II Two specific recommendations of the study are worthy of
discussion in this staff report. Specifically, the study
identifies the need for the City to add an additional 1,000
I gallons per minute drift well into the system in 1991. As you
know, in anticipation of this recommendation the City recently
bonded for this improvement.
IFigure 3 in the report shows the various growth projections for
the City based on the best information available from the
Comprehensive Plan. Prudent design standards call for the City
Ito have sufficient water production capacity such that the
maximum hourly demand can be produced with the largest well out
of service. The current peak hourly demand in the City based on
I a detailed review of our historic data is approximately 3 ,000
gallons per minute. The current "firm" capacity of the City with
the largest well out of service is 2 ,600 gallons per minute or a
1 deficiency of 400 gallons per minute. By constructing a 1,000
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Don Ashworth
December 5 , 1990
Page 2
gallon per minute well at this time, we will eliminate this I
deficiency and have enough reserve to last until approximately
1995 when the next well would probably be needed.
The other report recommendation of note is the acknowledgement
that the Lake Minnewashta Parkway area is on a long dead-end
service. In other words, there is no redundancy in the City' s
watermains in this area such that if a trunk main breaks on
Orchard Lane, for example, the entire Minnewashta Parkway area
would be out of water service immediately until repaired. There 11 are two ways to address this deficiency. One, the most costly,
would be to extend the City' s trunk watermain from its current
terminus on Highway 5 at Audubon Road west to connect to the
existing main near Lone Cedar at the south edge of Lake
Minnewashta. This would be very costly (approximately $1
million) and would be a very inefficient way of constructing the
main at this time since there would be few users on the system at
this time until development caught up in this area. A less
costly, more efficient way of addressing this deficiency is to
construct a 200 ,000 gallon elevated storage tank in this system
which would provide up to 12 hours of reserve to supply the users
in the area until such time as the water repairs can be made.
Additional benefits in constructing the elevated storage tank in
this area is that it should reduce some of the isolated low
pressure problems and provide additional fire suppression
benefits. The tank would be located on the highest ground
possible to minimize construction costs and to address the
pressure deficiencies. The Forest Ridge Circle area is the
highest parcel of ground in this area.
There are other important recommendations contained within the
report which can be read at your leisure. The report has been
prepared in close concert with the capital improvement program
which was portrayed in the draft of the Comprehensive Plan. '
Based on the above discussion, it is therefore recommended that
the City Council accept the attached Water System Analysis Study
as prepared by Bruce A. Liesch & Associates and authorize the
preparation of plans and specifications for Well No. 6 , and the
watermains and appurtenances modifications necessary to connect
it into the system. '
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Attachment: Water System Analysis Study 1
c: Jim Bullert, B. A. Liesch
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