After two decades and roughly $70 million worth of work, the environmental cleanup of the Naval Submarine Base is entering its final phase.

Named in 1990 to the Environmental Protection Agency's Superfund list of the nation's most contaminated sites, the base now has two main areas still in need of remediation of the dozens originally identified.

The contamination was caused by the indiscriminate dumping of petroleum products, solvents, paints, metals, tanks that held acids and other materials used on submarines, torpedoes and other equipment over the nearly 150 years the base has been in use by the Navy. All of this left polluted soils, groundwater and sediments offshore in the Thames River.

On Thursday, the Restoration Advisory Board for the cleanup met for an update on the progress made over the past year and a summary of what remains. Richard Conant, environmental program manager for the cleanup, said the two remaining projects - remediation of a freshwater wetlands and removal of contaminated river sediments and other pollutants from the area known as the lower base - should be completed by 2014. The advisory board comprises representatives of the EPA, the state Department of Environmental Protection, the local community, the Navy, Ledge Light Health District and others.

"At some point we will be de-listed," he said, referring to the Superfund list. Testing of groundwater samples and monitoring of completed cleanup sites, however, will continue for several years after the last truckload of polluted soil is hauled away.

Thursday's meeting marked a milestone for Conant, who has been in charge of the cleanup project for most of the time the base has been on the Superfund list. Conant, a civilian employee of the Navy, is retiring at the end of the month.

"This has been a big, complex and successful program, and I consider myself lucky to have been involved," he said at the close of the meeting. Looking toward the final phase, he said he hopes more members of the community attend meetings and take advantage of opportunities for public comment on plans for the remaining work, and that he is pleased that the end is finally in sight.

"We're about to pop out of the woods," he said.

In October, the Navy launched a website where the public can find information about the cleanup in Groton and at its other facilities, and mailings will be sent to local residents and others identified through interviews.

Monitoring over the past year has revealed two problems, advisory board members learned. At Goss Cove near the Nautilus Museum, a gun display has sunk several inches. Action will have to be taken if further settling occurs. In addition, an above-ground storage tank on a concrete slab was built atop an area where contaminated soil was kept in place and capped to prevent leaching. Conant said the tank and concrete slab were placed without proper in-house environmental reviews, and an investigation is under way to determine how that happened and whether the cap has been damaged and will need to be fixed.

Restoration of the wetlands area began over the past year with mowing of phragmites, an invasive species, that will be followed in the coming months with application of an herbicide. It is not a natural wetland, but one created by the Navy when it dumped about 1.2 million cubic yards of material dredged from the Thames River there in the 1950s. But it is being restored as if it were a natural area.

"We're starting to see some of the native vegetation come in," Conant said. "But we may need to do some additional planting of vegetation, and it's going to need continuing management. We're trying to get it to something that will be truly functional as a wetland."

About one acre of the 20-acre wetlands is filled with contaminated soils that will be dug out to a depth of 2 to 3 feet and taken to a hazardous waste disposal site. Sampling is taking place to map out the exact contours of the removal area, and excavation would begin in mid-2012.

Cleanup of the lower base, about 50 acres that includes the active waterfront and submarine berths, is perhaps the most complex part of the entire project, Conant said. It will involve in-river as well as land-based work, and the need for careful planning and coordination to work around the needs of a busy military base.

"We need to continue to support the mission," he said.

A plan for the lower base is expected to be ready by the end of this year. The public will be invited to review the plan and comment before a final plan is developed and work begins. Because of the potential impact on the Thames River, the lower base cleanup could generate more public interest and input than other parts of the project have, Conant said.

"There's such a focus on the river," he said.