Alice Pickering
Wyoming Area Reporter

Wyoming City Council authorized a feasibility study on July 5 to determine the cost of extending a city water main, across I-35 to the western part of the city.

Approval came after Engineer Mark Erichson made a presentation of an updated model of the cityís water system, the purpose of which was to analyze existing system pressures. The vote was unanimous.

Erichson used data supplied by the city for the years 2000 to 2005 to develop the model.

It reflects the cityís actual water use, including some peaks in use, rather than assuming the same use and pressure everywhere in the city. The actual demands of the five top water users in the city were used in the analysis.

The cityís water tower storage capacity is about 375,000 gallons, which equals the average daily demand. According to Erichson, this is the ìminimum amount recommended for a system not providing fire protection.î

The three city wells can pump 2020 gallons per minute. Erichson explained that a water system model is designed with the largest well out of service, using the two smallest wells. This is called ìfirm capacity.î

Average day to peak day water usage was updated. The tests were run assuming extended peak demands and with the towers nearly full. Pressures within the towers are dependent upon how full they are the wells are running at firm capacity.

The existing water main transmission lines were added based on the overall Wyoming water main map.

Other factors

Pressures within the system are influenced by the diameter and looping of the transmission mains. While acceptable, the fire flow at some locations in the city needs to be higher.

The areas west of the freeway and that between the freeway and Forest Blvd. (CR-30) in the northern part of the city have the lowest water pressure which could negatively impact fire fighting capabilities.

There is only one water main crossing the freeway to serve the west side of the city. Extending water mains would solve some of the low pressure problems. The theory behind looped water mains is to maintain consistent pressure throughout the system.

Erichson identified two places for the water mains to cross the freeway. The first choice is a crossing at 260th Street west to 261st Street. A second connection would be from 273rd Street on the east to Kettle River Blvd. west of the freeway.

He recommended the south connection be completed first because it will have the biggest impact on system water pressure. It would result in an increase in flow from 1500 gpm to 3000 gpm west of the freeway.

The second phase would result in fire flow from 1500 to 3500 gpm west of the freeway and from 1000 to 2500 gpm north of 272nd Street.

Differences in the pressures are due to the water mains not being looped.

One question about the possibility of color-coding hydrants based on available pressure would not work too well, because with changes in the system, the pressure at hydrants would change.

Erichson said potentially there could be a lot of repainting.

Fire Chief Dennis Berry said that the engineers watch the gauges on the trucks and adjust the pumping to the available pressure.

Erichson urged planning for an anticipated additional water tower to allow adequate time for construction. The process takes about 18 months. Further analysis of the amounts needed for emergency and fire-fighting capacity should be determined in consultation with Berry.

In answer to questions about new developments, Erichson said there is enough water to provide for more homes, but fire fighting would be the problem.

A rough estimate of the cost for the water main might be about $250,000 to $300,000, but the feasibility study will provide firm figures. According to City Administrator Craig Mattson, cost of some of the trunk line could be picked up by the water and sewer fund.

Basic findings of the water system model were that likely an eight-inch main will be needed when a water-main is extended under the freeway. So storage is fine for now, but the city will have to create more storage as it grows.

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Forest Lake Times
P.O. Box 218
880 SW 15 St.
Forest Lake, MN 55025
651-464-4601
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