Norwich - Maintenance workers at the Norwich Municipal Ice Rink sent an anonymous complaint to the state Department of Labor April 8 predicting a second cooling system failure, saying they had not been trained to handle ammonia and that a new ammonia alarm had not been installed.

The April 8 letter was sent to city officials this week after the cooling system did fail a second time Monday, forcing the rink to close. The rink was closed for a month after the system failed Feb. 13 with an ammonia leak that forced evacuation of the building and cost $74,000 to repair.

"With the refrigeration plant not operating at 100 percent efficiency, we are afraid to work around the system," the letter to the DOL's Division of Occupational Safety and Health said, "and would like a new ammonia alarm installed as our supervisors stated."

Nancy Steffens, communications director for the labor department, said Wednesday the Conn-OSHA division received the letter and is investigating the complaint.

The employees also complained that the rink's boiler footings have rotted and they fear if the boiler collapses, it could rupture the natural gas line below. And with warmer weather, the rink's dehumidifier does not work properly, allowing mold to build up inside the building, they said.

Rink Authority Chairman Francois "Pete" Desaulniers said he was aware of the complaint and said state inspectors toured the plant last week to investigate the claims. Desaulniers said an ammonia-handling training session has been scheduled, and a new ammonia alarm had been ordered before the complaint.

Desaulniers also said National Refrigeration Inc. will be at the rink today to assess the new damage. Desaulniers said the firm also will dispose of the 200 gallons of contaminated liquid leaked from the system.

The employees' complaint surfaced as the city received four bid responses Wednesday for designs to replace the rink's aging cooling system. The bids did not include the actual new equipment cost.

Bid prices ranged from $48,500 from Frank Zaino & Associates of North Stonington to $96,000 from CJL Engineering of Johnstown, Pa. A proposal was submitted by Michigan-based Thermo Source, which had previously presented the city with a plan to install a geothermal system beneath the rink property. Thermo Source would charge $49,500 to design the geothermal system.

CJL Engineering proposed a new ammonia-based system, saying new ammonia technology is much improved since the current system was built at the rink nearly 20 years ago.

MacLaughlin Management & Design of Exeter, N.H., offered to present the city with a number of equipment options for a fee of $64,850. Zaino also did not specify a cooling technology.

City Purchasing Agent William Block suggested the agency enlist a third-party engineering expert to help review the bids and the firms' credentials.

The project schedule calls for the authority to select bid finalists by May 16 and select the winning firm by May 23. The firm would present final design specifications by June 18.

c.bessette@theday.com