Norwich — It probably would be hard to think of a more difficult spot for a water main break than directly beneath an active railroad track on a busy road just before a bridge.

But that’s the scenario Norwich Public Utilities engineers are facing as they work with the Providence & Worcester Railroad to design a fix for a break directly beneath the freight rail tracks on Eighth Street in Greeneville.

The 75-year-old, 8-inch diameter water main serves homes and businesses on the East Side, including the AHEPA apartment complex, senior public housing on Hamilton Avenue and several urban neighborhood side streets.

The main broke sometime in mid-February, and NPU shut off water to the line, still supplying the East Side with water from a Route 2 main along Hamilton Avenue-Route 165, NPU spokesman Chris Riley said. The water service is strong enough for normal water use by residents and businesses, and a test of the sprinkler system at the AHEPA apartments showed no loss of water pressure.

But tests of water hydrants in several spots for potential firefighting showed “significant” drop in pressure, Norwich fire Chief Tracy Montoya said. The fire department has alerted several volunteer fire departments in the area of the potential need for tanker trucks if a significant structure fire were to occur on the East Side before the water main is repaired.

Norwich Fire Department tanker trucks carry 500 to 750 gallons, and typically rely on city fire hydrants throughout the urban area along the city water system routes.

Tanker trucks at volunteer fire departments typically have greater capacities — 1,000 to 2,000 gallons — because they serve more rural areas with fewer hydrants and water sources. Montoya has contacted the Taftville and East Great Plain volunteer departments in Norwich, as well as the Poquetanuck and Preston City departments in Preston, on the potential for needing their mutual aid should a structure fire occur on the East Side before the water line repair is done.

Riley said NPU has been working with P&W to secure necessary easements to repair the broken line. The work must be done during a 24-hour period on a weekend, when freight trains are not running. The existing pipe also does not meet railroad depth requirements and does not have the required protective casing.

The new pipe will be upgraded to 12 inches, which will allow an upgrade to the remaining pipe over Eighth Street “in the near future,” Riley said.

“We have a contractor preparing a construction plan to meet P&W’s engineering requirements, which is a challenge given the number of underground utilities in this very confined area,” Riley said.

c.bessette@theday.com