The Moulton Niguel Water District has agreed to pay $4.8 million to settle a 3-year dispute with South Orange County Wastewater Authority, which processes a portion of the district’s wastewater, according to a settlement agreement released Monday. Moulton Niguel wanted to terminate funding obligations for a treatment plant run by the wastewater authority, the Coastal Treatment Plant, because the water district has rarely needed the sewage capacity since signing a use-agreement in 1999. Instead, it has been able to rely on other plants and has said its customers shouldn’t have to pay for something they didn’t use.