Norwich — Two 70-foot-tall utility towers that have stood on opposite banks of the Shetucket River for nearly 100 years are being dismantled as part of a $300,000 power service upgrade to the Laurel Hill and East Side areas, Norwich Public Utilities officials said Thursday.

The two steel towers supported wires that sent 4.8 kilovolts of power from NPU’s transmission lines across the Shetucket River to about 3,000 customers in the two neighborhoods. When the project is completed, four wooden utility poles will be erected on each side of the river to carry power lines with the capacity of transmitting up to 13.8 kilovolts of power.

The transformer currently supplying power to Laurel Hill and the East Side is 70 years old and will be replaced in the project.

The upgrade is designed to improve reliability and power capacity to meet future development needs, including potential development at the former Norwich Hospital property, said Eric McDermott, NPU integrity manager of the electric division.

But until higher capacity of power is needed, a “power down” transformer will be installed on the south side to provide the 4.8 kilovolts of power now being consumed, he said.

The project is expected to be completed by June, when new transmission lines will be strung across the river connected to the new poles. The project required approvals from the state Department of Energy and Environmental Protection and the U.S. Army Corps of Engineers, NPU spokesman Chris Riley said.

NPU first installed single temporary power poles on each side of the river and transferred power lines from the towers to the poles.

Like a Jenga game, crews from Wiese Construction on Thursday worked in a lift bucket to unbolt and drop to the ground individual segments of the rusted lattice-work style tower on the north bank of the Shetucket River, carefully selecting pieces that could be removed first but leave the basic frame stable. Wiese will remove the debris and salvage the scrap metal, Riley said.

The towers are located behind the NPU customer service center at 173 N. Main St. NPU records show they dated back at least to the 1930s and possibly were older, NPU officials said.

While most of the former Norwich Hospital property, 393 acres, lies in Preston and outside NPU’s service franchise area, NPU officials have said in the past they hope to be in competition to serve the proposed future development by Mohegan Gaming & Entertainment.

Nearly 50 acres of the former hospital property are in Norwich and owned by Castanho Development LLC. No formal development plans have been submitted for that portion, but in July, the city Redevelopment Agency agreed to allocate $45,500 of the city’s federal brownfields environmental assessment grant to study three of the decaying, abandoned state buildings on the property — the Lippitt, Pondview and Martin buildings — based on interest expressed by potential developers.

Mayor Peter Nystrom said Thursday there’s no new update on potential development at the property but he remains “in touch periodically” with property owner Carl Castanho.

c.bessette@theday.com