This is due to the small number of landfill operators who had already submitted returns and paid before the end of June 2018 (most of them submitted and paid in July 2018).
Mae oherwydd nifer fechan y darparwyr a oedd eisoes wedi cyflwyno ffurflenni ac wedi talu cyn diwedd mis Mehefin 2018 (cyflwynodd a thalodd y rhan fwyaf ohonynt ym mis Gorffennaf 2018).