Drainage field disposals should only be used when percolation tests indicate average values of Vp between 15 and 100 and the preliminary assessment of the trial hole tests has been favourable.
Dylid ond gwaredu i gaeau draenio pan fo profion trylifo'n dangos ffigyrau cyfartalog o Vp rhwng 15 a 100 a bod yr asesiad rhagarweiniol o'r profion tyllau prawf wedi bod yn ffafriol.