Norwich – The upgrade to the Norwich Public Utilities municipal water system soon could reach Mohegan Park with a $2.5 million plan to replace the 45-year-old, 5-million-gallon water tank with a tank half its size but 35 feet taller.

NPU has submitted plans to the city planning office for a special permit – required for any water tank above 50,000 gallons – to replace the aging tank with one that NPU officials say will allow for both better water quality and pressure. The Commission on the City Plan will hold a public hearing on the application at 7 p.m. on June 21.

The existing ground-based steel tank at 19 Park Center Road measures 140 feet in diameter and 52 feet high. The new 2.5-million gallon concrete tank would be built on the same foundation with “minimal earthwork and grading,” project engineering firm Dewberry Engineers of Boston wrote in the application.

NPU officials said although the new tank would be 35 feet taller than the one to be removed, it would not be visible above the tree line or from any neighboring homes.

NPU Assistant General Manager Chris LaRose said the main reason for replacing the tank is improved water quality. Water in a smaller and taller tank would be recirculated through the system quicker with less time to become stagnant. The modernized NPU water storage system now has several large sources, including a new tank near the Deep River reservoir in Lebanon, allowing for more reliability of large volumes of water if needed for fire suppression or to replace systems pulled off line for some reason.

“The existing tank was designed for maximum storage for fire protection and not for circulation,” LaRose said. “So it's much too large.”

The average home water use also has declined in recent years, NPU spokesman Chris Riley said, with smaller toilets and other improved water-efficient appliances.

Riley said the $2.5 million project cost would be funded through the Drinking Water State Revolving Fund, which would provide both a low-interest loan and a grant. The exact financing will be determined once the project is put out to bid, he said. The engineering design is expected to be completed within two weeks and must be submitted to the state Department of Public Health for approval before the project can be put out to bid.

If the project is approved, LaRose said NPU would drain the tank by using most of the 5 million gallons through normal water usage. When the level becomes low, the tank would be taken off line, and the remaining water drained out. The tank would be cleaned of residue and sediments and then demolished.

Construction of the new tank is expected to be done in late fall and next winter. The new tank could come on line next spring, with exact timing based on the weather.

During the construction, other NPU water systems would make up for the loss of the Mohegan Park tank, LaRose said.

“We have facilities for taking any of our infrastructure off line,” he said. “We have sufficient supplies to handle a majority of fires, and we will work closely with (Fire Chief Kenneth Scandariato) for the backup plan in the downtown area.”

c.bessette@theday.com