there are practical constraints of a technical nature (for example, if the commissioning of a new industrial process or site prevents implementation of measures by an earlier deadline).
ceir cyfyngiadau ymarferol o natur dechnegol (er enghraifft, os bydd comisiynu safle neu broses ddiwydiannol newydd yn atal y mesurau rhag cael eu rhoi ar waith o fewn terfyn amser cynharach).