Chalfont Borough Council has approved a new Stormwater Management Ordinance. Several other municipalities have adopted similar ordinances, required by the Pennsylvania Department of Environmental Protection.  They require anyone adding a patio, shed or other impervious surface to contain stormwater on the site, although Chalfont is letting property owners with projects up to 1,000 square feet to do it on the honor system.  Some townships and boroughs are letting people with small projects plant a couple of trees, but Chalfont resident and engineer Bob Showalter says compliance will be costly.