The Danbury Environmental Impact Commission has held a hearing on plans by a car dealer to build near Danbury Municipal Airport.  A Mercedes-Benz sales and service facility has been proposed for a construction storage yard between the airport and Route 7 at the northwest corner of Miry Brook and Sugar Hollow roads.  Curry Automotive is also seeking parking for 85 vehicles on the second-story roof.  The 2.5 acre site is near the environmentally sensitive Kissen Brook.  No direct discharges to wetlands are proposed.  Drainage and stormwater improvements are planned for the site.  A concrete building and shed on the propertywould be demolished, and a retaining wall would be constructed. A special exception is needed from the Planning Commission, a permit from the Zoning Commission, and approval from the Federal Aviation Administration.