Groton - The Naval Submarine Base is entering the final phase of an extensive cleanup project that began a dozen years ago to remove more than 100 years' worth of toxic chemicals from nearly all corners of the 687-acre riverfront property. 

"It's the last leg of the marathon," Christopher Zendan, sub base public affairs officer, said last week. 

The cleanup began in 1990, after the base was named to the Environmental Protection Agency's Superfund list of the nation's most contaminated sites, and is now about 90 percent complete, said Kymberlee Keckler, remedial project manager for the federal Environmental Protection Agency's New England office. 

"We've made a lot of progress, especially since it's an open, active base," said Keckler, whose agency is overseeing the cleanup along with the Navy. The cleanup is being done to an industrial-commercial standard, with some contaminated soils capped with pavement or building foundations rather than removed, instead of the higher residential standard. That means deed restrictions will be placed on the land so that, if the property ever ceases to be a military facility, no homes could be built there unless further cleanup is done, Keckler said. 

Sub base officials overseeing the cleanup are hopeful that the base could come off the Superfund list within the next two years. 

"It would be a testament to our commitment to being good stewards of the environment," Zendan said. "We were the nation's first submarine base, and we created this situation on the base with all the pollution and hazards. But now we're much better in managing and remediating and taking our environmental responsibility seriously." 

A proposed plan to remove contaminated soils and river bottom from the 33-acre area known as the lower base - the last major section of the base as yet unaddressed - is in final stages of development. Within the next month, a draft version will be released to the public and comment sought. Due to a delay in completion of the draft plan, a meeting originally scheduled for Jan. 19 will be rescheduled for sometime in February. Once complete, the proposed plan will be made available online and at local libraries. 

After the February meeting, a final cleanup plan will be written, and the EPA and state Department of Energy and Environmental Protection will be asked to give their approval. Work could begin by early next year and be completed by the end of 2013, said Michael Brown, environmental director for the base. 

Mark Lewis, environmental analyst III at DEEP, said his office has been reviewing earlier versions of the draft plan and is in agreement with the overall remedy as proposed thus far. 

Keckler said the lower base is perhaps the most complicated of all the areas previously addressed, because it is active with piers and berths for docking submarines as well as facilities for submarine maintenance, repair, overhaul and administration. Also, testing revealed a variety of different contaminants in the soils, river sediments and groundwater, she said. 

The area has been divided into seven zones, with contaminants identified ranging from lead, mercury, polycyclic aromatic hydrocarbons, or PAHs (byproducts of petroleum processing or combustion), pesticides, heavy metals and antimony. Exposure can be carcinogenic or cause other health problems in humans and wildlife. 

The chemicals, components of battery acids, fuels, paints, flame retardants and lubricants, were dumped or spilled during the maintenance and repair of submarines and other Navy vessels. The base became a Navy yard in 1868 and a submarine base in 1916. 

For six of the seven areas in the lower base, the contaminated soils would be left undisturbed, but monitoring wells and other long-term land use controls put in place to ensure that the pollutants are not migrating into groundwater or the river. That means pavement and building foundations must be kept in good repair, Lewis said. Removing the soils, he said, would be "very costly and very disruptive to the base" because it would involve removing buildings and tearing up pavement in active areas. 

For the area known as Zone 4, about $8 million worth of remediation is being proposed. That would include soil excavation and removal, land use controls, monitoring and dredging of contaminated river sediments. 

"Land use controls would continue as long as we have a base," Brown said. 

Zone 4 is more heavily contaminated than other areas of the lower base because a waste oil pit and incinerators were located there, Brown said. Solvents were also stored there, and fuel distribution lines ran through the area. 

Tracey McKenzie, natural resources manager for the base, said the cleanup plan will be designed to ensure that contaminated soils do not migrate into the Thames River.