A proposal to construct sewage treatment works within the area of the scheduled monument required a thorough archaeological investigation to establish the nature and extent of any buried features .
A thorough archaeological investigation was carried out by Gwynedd Archaeological Trust in the summer of 1991 .
A proposal to construct sewage treatment works within the area of the scheduled monument required a thorough archaeological investigation , which was carried out by Gwynedd Archaeological Trust in the summer of 1991 , to establish the nature and extent of any buried features .