By STEVE KARNOWSKI
MINNEAPOLIS (AP) — The Minnesota Supreme Court hears oral arguments Wednesday on an attempt by environmental groups to cancel a key permit for the long-stalled PolyMet copper-nickel mine. They say regulators should have included “end-of-pipe” limits on discharges of mercury and sulfates in PolyMet’s water quality permit. And they say the state improperly tried to suppress the concerns of the federal Environmental Protection Agency, resulting in a weaker permit. The Minnesota Pollution Control Agency and PolyMet counter that the permit meets the legal requirements. It’s one of three major permits issued to PolyMet four years ago that remain on hold due to legal challenges.