PORTLAND (AP) — Three areas in Portland Harbor have been identified as possible disposal sites for dredged sediment from the city’s waterfront.

The Portland Harbor Non-Federal Dredge Workgroup will outline its proposal and provide other details about plans for so-called confined aquatic disposal cells to the Waterfront Alliance, a group of Portland and South Portland marine interests on Tuesday.

The cells are holes dug into the harbor bottom, filled with dredged material, and capped. They would contain dredged material from Portland Harbor’s public and private piers, slowly being choked by mud.

Bill Needleman, waterfront coordinator, told the Portland Press Herald (http://bit.ly/1s9dC9Q ) the cells are environmentally safe and cheaper than other sediment disposal options. He says dumping a cubic yard of sediment at sea costs about $22 compared to $100 for land disposal.