The department of transportation shall construct and maintain recreational vehicle sanitary disposal systems in the following safety rest areas lying along highways which are a part of the interstate highway system:
(1) Gee Creek safety rest area, northbound and southbound on Interstate 5 in Clark county;
(2) SeaTac safety rest area, northbound on Interstate 5 in King county;
(3) Silver Lake safety rest area, southbound on Interstate 5 in Snohomish county;
(4) Winchester Wasteway safety rest area, eastbound and westbound on Interstate 90 in Grant county;
(5) Sprague safety rest area, eastbound on Interstate 90 in Lincoln county;
(6) Selah Creek safety rest area, northbound and southbound on Interstate 82 in Yakima county;
(7) Indian John Hill safety rest area, eastbound and westbound on Interstate 90 in Kittitas county;
(8) Smokey Point safety rest area, northbound and southbound on Interstate 5 in Snohomish county;
(9) Schrag safety rest area, westbound on Interstate 90 in Adams county.