MARBLEHEAD – The Planning Board will make a May 7 site visit to 121 Green St. to view the 3.67 acres where Redstone Building Corp. wants to build 20 two-bedroom condominium units at Green Street and West Shore Drive.Seven of the 10 townhouse structures will be on the street and three will be built at the back of the lot. Two of the condominium units will be affordable, under a Marblehead incentive zoning bylaw passed in the early 1990s.It is the first use of the law. The Planning Board continued its hearing on the proposal to its May 10 meeting.Under the bylaw, the board has the authority to allow the project to proceed, by granting a special permit, but Attorney Paul Lynch, representing Redstone, said the developer will also go before the Board of Appeals on a height issue and the Conservation Commission for a wetland?s issue.Lynch faced some serious questions from the audience.Fire Chief Jason Gilliland said the plans did not show sufficient access for fire engines.Neighbors questioned the amount and location of parking for guests, the number of floors in the buildings, the presence of arsenic in the wetland from the former town landfill and the fact that Redstone dissolved as a corporation in 2007.Town Counsel Lisa Mead said the arsenic would be addressed by the town clean-up of the former landfill seepage. Lynch said the corporation would be revived by the time the Planning Board approved the plans. He expected other matters to be resolved by the time the Planning Board makes its site visit.