ROCKLAND, Maine — The company that wants to build a natural gas fired plant on property where City Hall is located is expected to submit a more detailed plan by the end of January.

City Manager James Chaousis said Friday that a purchase and sales agreement needs to be tentatively agreed to by Jan. 28 or the option held by Rockland Energy Center LLC would expire on the approximate 18 acres where City Hall and the adjacent public services garage are located.

City administrators met with Rockland Energy officials Oct. 27.

Assistant City Manager Audra Caler-Bell said Rockland Energy Center LLC is still interested in proceeding with the plant on the site located on Pleasant Street.

Rockland Energy and the city signed an option agreement Aug. 1 for the approximately 18 acres of adjacent city-owned parcels. The City Council had voted May 1 to authorize the city manager to negotiate and execute the option.

At that time, the company said it was interested in constructing a $200 million plant that would generate electricity to be sold on the power grid and steam that could be used by local industries.

The assistant city manager said city officials met with Rockland Energy last month to relay the concerns citizens had about issues such as emissions and noise. She said the city also informed the company that when it does submit its formal plans, the city will be hiring an independent party to review the proposal. She said the city would expect Rockland Energy Center to pay for that cost, and the company is amenable to that arrangement.

Any sale is contingent on subsequent votes of the Rockland City Council and a public referendum after a purchase and sales agreement is reached with Rockland Energy Center.

The manager said Friday that, if the project progresses, the City Council would have to decide whether that referendum would be held in June or November.

The sale also would be contingent on Rockland Energy obtaining all permits needed for the natural-gas-fired power plant, as well as approval from the Public Utilities Commission of long-term contracts to sell electricity generated from the plant to either Emera Maine or Central Maine Power.

The company has been developing engineering plans and financial models since the option was signed, Caler-Bell said.