MACHIASPORT – A representative of the U.S Army Corps of Engineers will be here Monday to explain the latest delay in a six-year effort to clean up the contamination from a former Air Force installation.

As a result of concerns raised by the state Department of Environmental Protection, the corps will conduct additional water monitoring and soil sampling before developing a long-term plan, according to a project update the corps released last week.

At issue is trichloroethylene, or TCE, a carcinogen detected in 15 Machiasport wells in 1995.

The source of the contamination is the former Air Force tracking station on Miller and Howard mountains, an installation that closed in 1984.

The corps is responsible for the cleanup of former military sites but works under a memorandum of understanding with the DEP. And DEP has taken issue with the five cleanup proposals the corps outlined in a draft report on the project last March.

According to DEP, the corps’ proposals are short-term responses, not long-term cleanup plans.

“The end goal is remediation of the aquifer – getting the TCE out of there,” said Iver McLeod, project manager for DEP’s Bureau of Waste Management and Remediation in an interview last May.

DEP finds acceptable only two of the five options outlined by the corps, and both require additional components, according to department’s comments on last year’s study.

Constructing a new water supply for residents whose wells are affected by the contamination or connecting affected residents to the Machias Water Co. – some 10 miles away – would meet the DEP requirements but would require the corps to establish a buffer zone around the affected area.

The buffer zone would have to be large enough to contain any TCE that travels from the existing site and be subject to monitoring. And there would have to be a contingency plan to address what will happen if the contamination moves, according to the department.

In addition, there has to be a way – either through deed restriction or town ordinance – to ensure that current and future landowners don’t drill wells within the buffer zone, according to the department.

The corps responded to DEP’s comments in the latest update on the project, saying that the buffer zone approach would create an area 15 times larger than the site that was analyzed in last March’s draft study.

The corps is proposing to address DEP’s concerns by:

. Gathering more information on the size of the contaminant plume by installing monitoring wells around known and suspected areas of contamination;

. Sampling soils in an attempt to locate the source of the contamination; and

. Studying the water to understand better the nature of the fractured bedrock and how it affects migration of the TCE.

As that work is going on, the corps proposes to examine options for cleaning TCE out of the aquifer or speeding up the process of natural attenuation.

According to the corps update, the initial study assumed it was impossible to remediate TCE in fractured bedrock. But the agency has since learned that it has been possible at other sites through the use of a variety of technologies.

While the additional work is being done, the corps proposes to continue to supply bottled water and carbon filters to the homeowners whose wells test higher than 5 parts per billion TCE – the level of TCE contamination the federal government considers to be a health risk.

Continuing the filter program was one of the corps’ long-term plans that DEP found unacceptable. The other two proposals were drilling replacement wells for the homeowners or connecting them to the water supply at the Down East Correctional Facility.

The prison well already tests positive for up to 2 parts per billion TCE and the department said drilling more wells in the area could cause the TCE to migrate to a larger area.

The corps’ project director will discuss the new plan with town selectmen at 7 p.m. Monday, Feb. 25, at the Machiasport town office. Before the meeting, the corps will conduct a poster board session in which residents can review project information and ask questions.