This report describes the refined delineation of the Wellhead Protection Area (WHPA) of a wellfield of five public supply wells installed in granitic bedrock in Charlestown, Rhode Island, approximately 32 miles southwest of Providence, RI. The Rhode Island Department of Environmental Management (RIDEM) requested technical assistance from the USEPA-New England office to reevaluate the wellfield's existing WHPA boundary with respect to the Charlestown Municipal Landfill, less than one mile upgradient from the wellfield. The Town of Charlestown, which owns the solid waste facility, was considering an areal expansion of the site. Based on the best available information, the refined wellhead protection area is approximately one-tenth the size of that delineated by the RIDEM. In addition, despite these modified size, a portion of the waste cell of the Charlestown Municipal Landfill apparently still lies within the refined WHPA.