The region's transportation and works committee heard yesterday from staff that it will cost that much for an environmental mitigation plan needed to obtain provincial and federal water approvals.

Paul Jankowski, manager of design and construction for the region's transportation and works department, told the committee that regional staff have been working with government agencies since early summer to allay problems linked to the sewer project.

"But unfortunately, we're not there yet," he said. "The agencies want more."

Critics say construction of an $800 million section of the Big Pipe in Markham is sucking water out of aquifers on the Oak Ridges Moraine, causing local wells to fail and reducing the water level in tributaries.

Environmentalists, too, are raising concerns over the discharge of groundwater into local streams and rivers. They say the cooler water, which has a different mineral composition, poses a threat to wildlife sensitive to temperature change.

They are demanding the project be subject to a full environmental assessment to determine the impact of pumping billions of litres of water from the ground to lay the sewer.

Jankowski told the committee that the mitigation plan will include measures to heat the cooler ground water pumped into local streams.

Propane boilers will be used to "superheat" about 10 per cent of the groundwater, which will then be mixed with the remaining water before it is finally discharged into local streams.

Jankowski said there isn't the same concern with varying water temperatures in winter.