SEARSPORT — Two groups opposing the development of a liquefied propane gas tank and terminal at the Mack Point port facility have announced their intent to sue the U.S. Army Corps of Engineers to force the agency to complete an environmental impact statement.

The Islesboro Islands Trust and the Searsport-based Thanks But No Tank groups jointly filed through an attorney a 60-day notice of intent to sue. The groups would assert in court that the Army Corps, which is responsible for reviewing certain large-scale maritime projects, violated the National Environmental Policy Act and the Clean Water Act.

Attorney Steve Hinchman, representing the two groups, said the notices were sent Thursday, March 21 to the Army Corps Boston and Washington D.C. offices, as well as to the Environmental Protection Agency and the Maine Department of Environmental Protection.

The Army Corps has 60 days to withdraw its original permit, and if it does not, the groups are prepared to seek that in court, he said.

The groups say the violations came when the Army Corps issued its approval for the 23-million gallon LPG tank, proposed by Denver, Colo.-based DCP Midstream. That approval came in May.

The Army Corps review essentially focused on documents filed by the company, rather than conducting its own study of possible environmental impacts.

The Searsport Planning Board is in the midst of reviewing the project for what would be the final permit the company needs to build the 14-story-high tank.

Earlier this month, the Islesboro Select Board voted to ask the Army Corps to complete a full environmental impact statement on the project. Belfast’s city council joined the island town in voting to request the same review.

Stephen Miller, executive director the Islesboro Islands Trust, was quoted in the announcement saying the Corps “failed its duty to provide federal, state and local decision-makers with the information necessary to properly weigh the potential economic and environmental costs and benefits of the proposed action.”

Miller concluded that Army Corps should withdraw its earlier approval “and wholly re-do its analysis.”

Islesboro Islands Trust and Thanks But No Tank also assert that a terminal through which LPG would be imported is not needed, and that “more cost-effective and less environmentally damaging practicable alternatives are available to meet Maine energy needs.”

Opponents have cited the change in market conditions since the tank was first proposed that suggest that importing the gas via ship is not economically viable. Domestic sources of propane and natural gas and other factors suggest, opponents say, that the facility is more likely to be used to export gas via ship, which would pose different environmental and security threats.

Tara Hollander of Stockton Springs, who is a member of the Thanks But No Tank group, also is quoted in the release: “No company—including DCP—is using the marine import facilities that exist today to bring in foreign LPG. In fact, there is a glut of domestic LPG which costs at least a dollar less than imported LPG.”

Hinchman said the Army Corps, as lead agency charged with ensuring compliance with the National Environmental Policy and Clean Water acts, must take “a hard look” at the need for the project and at alternatives.

The notice also argues that the Army Corps “failed to consider the grave consequences for Penobscot Bay if the Searsport terminal is used to export LPG.”