Washington Revised Code Title 70A. Environmental Health and Safety § 70A.200.120. Transported waste must be covered or secured

(1) By January 1, 1994, each county or city with a staffed transfer station or landfill in its jurisdiction shall adopt an ordinance to reduce litter from vehicles. The ordinance shall require the operator of a vehicle transporting solid waste to a staffed transfer station or landfill to secure or cover the vehicle's waste in a manner that will prevent spillage. The ordinance may provide exemptions for vehicle operators transporting waste that is unlikely to spill from a vehicle.

The ordinance shall, in the absence of an exemption, require a fee, in addition to other landfill charges, for a person arriving at a staffed landfill or transfer station without a cover on the vehicle's waste or without the waste secured.

(2) The fee collected under subsection (1) of this section shall be deposited, no less often than quarterly, with the city or county in which the landfill or transfer station is located.

(3) A vehicle transporting sand, dirt, or gravel in compliance with the provisions of RCW 46.61.655 shall not be required to secure or cover a load pursuant to ordinances adopted under this section.