Selectmen awarded engineering firm Tata & Howard an additional $11,500 to design a water tower that will hold one million gallons of water in east Marion.

Design costs now total $104,500 for the estimated $1.5 million project, which will tear down an existing tower to make room for the new one.

At the board’s Tuesday meeting, Town Administrator Paul Dawson said the project’s location on land owned by the town and Great Hill Dairy Inc. on Delano Road complicated the process. Despite the increase, the project is still within budget.

“There’s a lot of work related to the design,” Dawson said. “Erection of a new tower, demolition of the existing tower, land swaps, easements, and in addition to all of that, we’re working with the trustees of the Great Hill Reservation to ensure there’s little to no disruption of their business.”

Dawson said the new design would, in part, lay out paths to work around Great Hill’s haying operations and other activities.

In June, Tata & Howard engineers presented the Planning Board with the initial plans. Town Meeting voters approved the project, with associated expenses, in 2013. Engineers said the tower is overdue for replacement.

Built in 1965, the existing water tower holds two million gallons of water used by homeowners. Also, the tower is a source of water pressure in the event of a fire.

Selectman Steve Cushing asked if additional cost increases could be expected.

“I don’t see anything on the horizon,” Dawson said.

The town will start advertising bids for contracts to take on the project in late December. Dawson said the water tower should be operational by August 2015.