When the well to be plugged may safely be used as an underground source of drinking water well and such utilization is desired by the landowner and is authorized by the operator, the cement plug normally required at the top of the surface casing may be waived, and the well need not be filled above the required sealing plug set below underground source of drinking water: Provided, That written authority for such conversion is supplied by the landowner and authorization is obtained by the landowner from the state department of ecology and filed with the supervisor. Approval by the supervisor of the plugging accomplished or notice from the department of ecology of approval of the landowner's authorization as provided herein shall relieve the operator of further responsibility under the Oil and Gas Conservation Act and the supervisor shall release the bond once a water well has been satisfactorily completed.