Any vehicle impounded pursuant to this chapter and left unclaimed for a period of 15 days shall be deemed to be an abandoned vehicle, and at the expiration of such period the vehicle shall be deemed to be in the custody of the sheriff, and the sheriff shall deliver the vehicle to a tow truck operator who shall dispose of the vehicle in the manner provided in RCW 46.52.111 and 46.52.112; PROVIDED, That if the vehicle is of a model year 10 or more years prior to the calendar year in which such vehicle is stored, the sheriff is authorized to declare that such vehicle is a public nuisance, and may dispose of such vehicle without notice of sale, and in such case the director of motor vehicles will issue an appropriate bill of sale to the tow truck operator to dispose of the vehicle as he may determine. (Added by § 14 of Res. adopted June 15, 1970).