Two environmental groups are trying to stop Dominion Virginia Power from building a third nuclear reactor at its North Anna Power Station in Louisa County.

In a petition filed with federal regulators, the Blue Ridge Environmental Defense League and the People's Alliance for Clean Energy argue the two reactors at the station use excessive water.

They estimate more than four billion gallons of water would be evaporated annually cooling the new unit, compounding area drought conditions. The petition also points to geological and waste-related concerns.

In January, federal regulators accepted Dominion's application for a full review of a possible third nuclear reactor at North Anna.

The Nuclear Regulatory Commission already approved an early site permit for the reactor, expected to cost billions of dollars.