The Board of Selectmen unanimously approved an agreement this week for wastewater treatment that town officials said would allow the sewer project for the Old Lyme beach communities to go out to bid before the end of the year. The agreement voted at a special meeting last Tuesday established the terms of service that the New London wastewater treatment plant would provide to Sound View neighbors and residents of the private beach associations Old Colony Club, Old Lyme Shores and Miami Beach. Residents of Sound View and the neighboring chartered beach associations would have to pay that amount — which includes the cost of treatment, the so-called initial connection cost and capital costs — in addition to the cost of sewer construction. The construction of sewers on the Old Lyme shoreline is a project that has been under discussion for more than a decade and is intended to replace the area’s septic systems to solve a water pollution problem identified by the Connecticut Department of Energy and Environmental Protection — a problem that many in the neighborhood dispute, pointing to a lack of up-to-date data on water pollution, to cheaper alternatives, and to the cost burden for less-well-off residents. DEEP committed to paying up to 50 percent of the estimated $53 million project cost through a grant and a forgivable loan from the Clean Water Fund to reduce the burden on residents.