As the debate rages over a proposed oil pipeline in northern B.C., energy giant Kinder Morgan is quietly working on plans to double the capacity of its pipeline into Metro Vancouver.

The oil company owns the Trans Mountain pipeline that runs from Edmonton to a terminal in Burnaby, and wants to meet China's growing demand for oil by twinning the line to bring in 700,000 barrels a day. The company will decide later this year if it will make an application for the project with the goal of completion in 2016.

The expanded capacity would dwarf the estimated 525,000 barrels per day that would be carried by Enbridge's proposed Northern Gateway pipeline into Kitimat.

The Union of B.C. Indian Chiefs issued a letter Tuesday urging Prime Minister Stephen Harper and Premier Christy Clark to reject both Kinder Morgan and Enbridge's proposals.

Representatives from the Tseil-Waututh First Nation in North Vancouver say they fear an oil spill and are opposed to Kinder Morgan's plans to increase tanker traffic in Burrard Inlet.

"The risk of having that much oil floating through our inlet, it's too great a risk to take," council member Carleen Thomas told CTV News.

The Tsleil-Waututh say oil from a mystery spill was spotted on the shores of their reserve a few weeks ago, and residue from a crude oil spill that dates back to the 1950s can still be seen on rocks at the water line.

"[I have] a heavy heart. Our inlet is in peril, it's dying and we've been trying f or years and years and years to bring the health back to this inlet and our community," director of treaty, lands and resources Ernie George said.

Apart from more tanker traffic, Kinder Morgan also wants bigger tankers in the inlet, and the company told investors in a presentation that would mean dredging the channel to widen it. CTV News has learned that Port Metro Vancouver is testing sediment at the Second Narrows channel in preparation.

Environmentalists say that dredging comes with its own risks.

"Dredging can be quite harmful. There's a lot of toxins, heavy metals well above acceptable limits that are at the bottom of the inlet. When you disturb that, you're mixing that into the ecosystem," Ben West of the Wilderness Committee said.

Kinder Morgan hasn't applied for a permit to dredge yet.

It is currently accepting bids from companies interested in buying oil that would be supplied by the pipeline in an effort to build a strong business case for the expansion.

In an email statement, the company said that the advantage of expanding the Trans Mountain pipeline is that the project has an existing footprint and capacity could increase incrementally.

"Safety is our utmost priority, and we have demonstrated a safe operating history. The Trans Mountain pipeline has been safely and efficiently moving petroleum products from Alberta to the west coast and interior region of B.C. for almost 60 years," the company said.

-With a report from CTV British Columbia's Mi-Jung Lee.