A group of neighbors, the Aquarion Water Co. and some town officials are criticizing a proposal by a Virginia firm to construct an energy storage facility off rural Prentice Williams Road in Old Mystic. They say it endangers the aquifer where it is located and the nearby Aquarion Water Co. reservoir, does not conform to the rural zoning in the area, and poses both a fire and safety hazard for neighbors. The state Siting Council and not the town, though, will decide whether to issue the required permit for the project. Scott Connuck, the senior project developer for East Point Energy of Charlottesville, Va., said Friday that last week he met for the first time with neighbors to discuss their concerns. Connuck estimated that the project, which takes electricity from the adjacent Eversource power lines and stores it in batteries for later sale and use, would be worth tens of millions of dollars. He said East Point Energy would be seeking a tax abatement from the town for the project.