An attorney for environmentalist groups argued Thursday before the Minnesota Court of Appeals why they think the state erred in granting water permits for Enbridge's controversial new pipeline.

The Minnesota Pollution Control Agency (MPCA) granted the permits to Enbridge in November, one of the last approvals the company needed to start construction on the $3 billion replacement for its Line 3.

The appellate court has 90 days to rule; the pipeline is 60% complete and is slated to ship oil in the fourth quarter.

The appeals court also is expected to rule on a separate challenge to Line 3 as early as next week. That appeal by pipeline opponents takes aim at the pipeline's approval by the Minnesota Public Utilities Commission (PUC), the state's primary pipeline regulator.

The 340-mile pipeline will cross 212 streams and affect more than 700 acres of wetlands, necessitating water quality reviews from both the MPCA and the U.S. Army Corps of Engineers.

The two water quality permits are intertwined. Pipeline opponents have challenged the Corps permit for Line 3 in federal district court in Washington, D.C.

Environmental groups Friends of the Headwaters and the Sierra Club; the Indigenous environmental group Honor the Earth; and the Red Lake and White Earth bands of Ojibwe have appealed the MPCA's permits. They argue that the MPCA refused to consider water quality risks from the pipeline's operation, not just its construction. They also argue that the MPCA did not adequately consider the pipeline's longer-term environmental impacts — particularly on the biology of aquatic life.

They also contend that the MPCA failed to consider the pipeline's impacts on tribal treaty rights. Ojibwe tribes have treaty rights to hunt, gather and fish on state lands traversed by the pipeline.

The MPCA rejects those claims, calling its Line 3 authorization its most "stringent" water quality permit ever, and ordering Enbridge to do extensive mitigation of streams and wetlands that Line 3 crosses.

Before granting the water quality permit, the MPCA held a contested case hearing on Line 3 — a trial-like proceeding before an administrative law judge — and then adopted the judge's recommendations.

Calgary-based Enbridge says the new pipeline is needed because the current Line 3 is corroding and it will be a safety improvement. However, the pipeline will partly follow a new route, and opponents say it opens a new region of Minnesota lakes and rivers to oil spill degradation, as well as exacerbates climate change.