AUGUSTA — A proposal to build a 1-million-gallon, roughly 100-foot diameter concrete tank that would hold a combination of stormwater and sewage on Greater Augusta Utility District land next to the city’s East Side Boat Landing on the Kennebec River is the most affordable option, at the most practical available site in the city, and would be done with an eye on its appearance, district officials assured city councilors Thursday. City officials expressed concern about the visual effect of such a large tank so close to the boat landing, as well as its potential visibility from the Kennebec River and from the downtown area across the river, which has been the focus of extensive redevelopment efforts in recent years. District Trustees Patrick Paradis and Cecil Munson, both former city councilors, and Superintendent Brian Tarbuck met with councilors Thursday to discuss the proposal, in a meeting requested by City Manager William Bridgeo after he heard about the proposed tank.