PORTLAND (AP) — An environmental group says one of the two pipelines from Portland to Montreal has surpassed its life expectancy, based on court documents filed in a tax dispute in New Hampshire.

Owners of the Portland Pipe Line agreed with a 60-year lifespan assessment for purposes of a tax case in the 1990s. The National Wildlife Federation says that based on records from that court case that an 18-inch pipeline built in 1950 is four years beyond its anticipated service life.

A pipeline spokesman accused the group of a deliberate attempt to mislead the public.

Jim Merrill said the 60-year figure came from the projection of economic viability based on market conditions at the time and had nothing to do with the length of time the pipeline can be operated safely.