Residents concerned about construction at Marshfield Airport have begun organizing under the name Marshfield Citizens Against Airport Pollution, and communicating via a Facebook page. Christine Beagan, one of the organizers, said in an interview that residents are worried the runway reconstruction could allow larger aircraft to use the airport. They are concerned about noise, pollution, and harm to wetlands, she said. Airport manager David Dinneen has said the project extends the runway to make it safer for existing flights and to meet Federal Aviation Administration standards, not to expand into new types of service. Beagan said about 30 summer and year-round residents are working on the issue, and that 20 to 25 of them attended the Feb. 4 Conservation Commission meeting for an airport discussion. Her husband, Hugh Beagan, said residents have hired a lawyer to look into whether the airport has received all the required approvals from the Massachusetts Department of Environmental Protection.