Mystic - About 70 residents turned out Tuesday night to hear Toll Bros. outline its plan to solve a drainage problem on their 48-lot Old Mystic Estates subdivision that at times has flooded nearby properties.

The presentation took place during a Stonington Planning and Zoning Commission public hearing that was expected to be continued to a later date.

Toll Bros. attorney Tom Collier said the company has now sacrificed one building lot in order to solve the problem by constructing three large retention basins that will retain water on site and allow it to evaporate and slowly soak into the ground, reducing the impact on surrounding properties, including the Whitehall Pond condominium project across Route 27. He said other options the firm considered are not viable.

He said Town Engineer Larry Sullivan discovered the drainage problem shortly after Toll Bros. purchased the property off Pequot Trail, Route 27 and Jerry Browne Road in December 2010 from the original developer, the Meehan Group.

"Deficiencies in the original engineering have been discovered. Our hope is the applicant has found a solution to this problem," acting commission Chairman John Prue said as the hearing got underway.

Collier said 75 to 80 percent of the existing drainage plan would remain; the proposed change is designed to only correct the error in the originally approved plan. He said the new plan exceeds design standards, reduces the water that flows off the property and has been reviewed and approved by Sullivan.

Collier pointed out to the commission that other problems the town has cited with the project, such as significant erosion problems onto adjacent properties, are not the subject of the hearing. Those problems have angered neighbors.

The commission asked many detailed questions of the Toll Bros. engineers.

Commission member Frances Hoffman said the original error was not noticed by Toll Bros. when it bought the property, so she wants to make sure the new plan will be effective.

Collier pointed out that the town approved the original 2004 drainage plan and said developers in troubled projects in other communities often leave towns with a "barren lunar landscape."

"But Toll Brothers is trying to fix the problem," he said.

The hearing was continuing late Tuesday night, and residents had not yet had the opportunity to speak.

j.wojtas@theday.com