A public hearing is scheduled Wednesday on a $19 million proposal to extend Sunport Boulevard westward to Broadway, across part of a South Valley Superfund site. Sunport — a key entrance into the Albuquerque airport — now ends at Interstate 25. The proposed extension would take the road to Broadway, a distance of about a half mile. It would be a four-lane divided highway, with access to local roads. Bernalillo County, which would build the project, contends the work won’t interfere with cleanup of the Superfund site, which was contaminated by a variety of firms that worked on weapons and aircraft. An environmental assessment prepared by URS Corp.