12/09/02 Hansz to Kukulski/Water SystemCAN,-
of KalispellPublic
Works
Department
Post Office Boy 1997, Kalispell_ Montana 9903-1997 -Telephone
(400)-158-:7720, F'ar (406),759-7831
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December 9, 2002
To: Chris A. Kukulski, City Manager
From: James C. Hansz, PE, Director of Public Works/City Engineer
Subject: Mountain View Plaza Water System
Mountain View Plaza has recently claimed that their development requirements for water
do not require the installation of a looped system as required by the PUD agreement. Further
they have contended that their original design report confirms this and was subsequently
amended under pressure by the City. Frank Castles has reviewed the original report and the
edited report subsequently submitted after the PUD was finalized. His conclusions are somewhat
different from those of MVP.
Briefly stated, the requirements on MVP were, and are dictated by the requirements of
their client, Home Depot. These requirements center on fire flow capability, and Home Depot
(HD) has required a minimum of 50 PSI and 2,250 GPM available to protect their structure. This
is noted in both the original and final edited design report. The final report further notes that the
HD requirements must be satisfied after allowing for a 10% reduction in available pressures. As
a result, the MVP engineer calculated pressures at 59.5 PSI rather than 50 PSI. The original
design report proposed a 10" extension from the existing 12" connection at the college, and an 8"
line on the west side of US 93 with a crossing to connect the 10" at the SW corners of the parcel.
Their analysis showed this combination to meet fire flows but failed to account for the HD
required 10% pressure reduction. No analysis was done to determine the effectiveness of an un-
looped supply using only one of the installed pipes. The final design report amended the
calculations to show the 10% reduction and also revised pipe sizes to reflect 12' mains on each
side of US 93. With these revisions the required flows are available to meet HD's requirements.
In order to determine the accuracy of the MVP statement that a looped system was not
required to meet their requirements, regardless of the clear requirements of the PUD, the City
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performed a hydraulic analysis of the originally proposed system. This analysis shows that when
one of the supply legs is closed the required flow cannot be supplied. Frank Castles' memo
summarizing the analysis is attached. Closing the smaller 8" pipe results in a system pressure at
HD of 6.3 PSI, far below the requirement. The analysis was performed with the 8" line added
back and the resulting pressure is 26 PSI, still below the requirement. In short, the originally
proposed system failed to meet the developer's requirement to serve Home Depot. The revised
design meets the requirement and complies with the requirements of the PUD. The engineer's
calculations confirm this and the City's independent analysis reconfirms this, though there is a
difference in result of approximately 12%, with the engineer's assessment of system capabilities
being higher.
The difference of results is somewhat attributable to different software used for analysis.
To ascertain which system better reflects as -built conditions, the City performed pressure/flow
tests on Friday, December 60'. From these data the City model was found to be within 4% of
actual flows. Therefore, the City analysis software is believed to more accurately reflect as -
installed conditions. However, regardless of the specific differences from the different analysis
tools, it should be recalled that both analysis efforts confirm the need for 12" mains. And, the
PUD agreement requires stand-alone loops to serve the development.