The Alberta Energy Regulator has rejected an oilsands tailings pond retirement plan submitted by Suncor Energy.

It says in a decision posted Friday on its website that the oilsands giant's application did not satisfy regulatory requirements and it must submit a new proposal.

Suncor had proposed using a water cap to contain the tailings — toxic ponds of water mixed with fine clay particles, bitumen and other chemicals left behind after its mining and upgrading process — at its northern Alberta facilities.

The AER says its decision that Suncor did not provide "adequate information" about how it would demonstrate the viability of the proposal.

It says the company also failed to adequately describe its alternative plan to retire the tailings ponds by filling them in with a solid material.

New rules introduced last year

In a news release, Suncor acknowledged the AER decision and said it will work with the regulator to move the application forward.

The AER introduced new rules last year that require all tailings ponds to be removed within 10 years of the end of a mine's life, replacing more stringent tailings pond regulations put in place in 2009 that industry said it couldn't comply with.

Alberta Energy estimates oilsands mining projects had created about 220 square kilometres of tailings ponds by the end of 2013.