MARBLEHEAD – In an unusual turn of events, a developer and a group of abutters found themselves raising the same question about a proposed zoning bylaw Tuesday evening.During the Planning Board’s 90-minute public hearing on Article 40, which adds a Smart Growth District to the town’s development options, neighbors of the former YMCA property in downtown Marblehead expressed concern about the mixed-use aspect of the proposal.The YMCA parcel on Pleasant Street measures just under one-third of an acre. Developer George Wattendorf, who owns it, plans to build above-ground without excavating or blasting and put indoor parking on the first floor of his building.However, the alternate proposal mentioned by consultant Angus Jennings of Concord Square Planning and Development Tuesday evening described a building with underground parking and a commercial use on the first floor."This is the opposite of what we want and what they want," Wattendorf said. He noted that his plans also include a roof design that hides the air conditioning units and Jennings’s proposal mentioned a different roof design."We’re very concerned," said Jayne Mace, a Pleasant Street abutter who said she feared the effect that blasting could have on the nearby buildings.Jennings and Planning Board members said the change from an earlier design was in response to a letter from the Chamber of Commerce, stating that Marblehead needs more retailers downtown.Board members assured the crowd of 30 that the bylaw gives the Planning Board the flexibility to ignore the requirement for commercial space in a Smart Growth development."We’re not approving any site plans," Chairman Philip Helmes said. "The concerns you raise are valid concerns and they will be addressed."Board members, Smart Growth Committee member Judy Jacobi and Town Planner Becky Curran all pointed out that Smart Growth is a way of implementing Chapter 40R, a state law that gives local boards control over affordable housing proposals. Chapter 40B, the state law Marblehead has dealt with up to now, could allow a much larger housing proposal on the YMCA property with much less local control, Curran said.