The Castlebar Environs Sewerage Scheme was developed to provide an up to date and modern system for the collection and disposal of wastewater from Castlebar and its environs in compliance with the Urban Wastewater Treatment Regulations.The schemes provided for the collection and transfer of all wastewater to an upgraded Treatment Plant at Knockthomas where it is pumped for treatment before discharge via an outfall downstream of the confluence of the Castlebar and Manulla Rivers.