An overlay district "is superimposed over [an] existing zoning district and imposes specific requirements in addition to those otherwise applicable for the underlying zone." Schroeder v. Town of Windham, 158 N.H. 187, 191 (2008) (quotation and ellipsis omitted). For example, in the Groundwater Resource Conservation District, an overlay district, "a new excavation site within the Wellhead Protection Area" is an expressly prohibited use unless "it is incidental to a permitted use and with the exception of any existing excavation legally permitted under the excavation regulations of the Town of Hooksett at the time of adoption of this ordinance."
They assert that this interpretation defeats the purpose of an overlay district. See Schroeder v. Town of Windham, 158 N.H. 187, 191, 965 A.2d 1081 (2008) (defining overlay zone as “superimposed over the existing zoning district and imposes specified requirements in addition to those otherwise applicable for the underlying zone” (quotations and ellipsis omitted)). They argue that the ordinance permits only the removal of fill incidental to construction that is lawful without the excavation.