Landfills do fill up and then become valuable open space in the urban areas, look no further than Alton Baker park.  As to running out of land, look to the east.  Lots of land east of Highway 97.  Several years ago a couple of private venture landfill operations were openned in eastern Oregon (all meeting EPA regulations) and offering much cheaper dumping fees than the government sites.  Lane County theatened local haulers that they would be banned from using the Short Mt. facilities if they dared to ship any refuse to these private sites.  The myth that there is no place to put the waste is a media invention.