Prehistoric nomads once gathered and cooked on land in what is now Ashburn, on about two acres on the banks of Broad Run that will soon become part of a wastewater treatment plant.

Archaeologists who spent weeks recovering artifacts from the site are classifying and dating them to learn more about these ancient tribes, and the Loudoun County Sanitation Authority is planning an exhibit to share their story with the area's current residents.

The finds -- more than 1,500 items -- on the site of the planned Broad Run Water Reclamation Facility, a 50-acre complex off the Loudoun County Parkway near Smith Switch Road, include scrapers and spearheads.

Although it is not unusual to find a stray lance point or other relic in the area, archaeologist Alain Outlaw said the sheer number of artifacts as well as their potential for being dated make the site one of the most significant in the county. Outlaw is the principal archaeologist for Williamsburg-based Archaeological & Cultural Solutions, an archaeological consulting firm that excavated the site in May.

Long before the land on the banks of Broad Run belonged to the Loudoun County Sanitation Authority, it was attractive to settlers; the remains of a 19th-century farmstead are nearby. But those who set up camp thousands of years ago didn't necessarily stick around for long, Outlaw said.

"They made periodic visits to exploit natural resources" such as quartzite, Outlaw said. The rock was used to make such tools as points for spears, primitive drills and scrapers for cleaning hides, he said. In addition, the nomads cooked with fire, leaving behind charcoal and inadvertently preserving wooden objects that became carbonized.

Outlaw estimated that the nomads stayed there sometime between 2900 B.C. and 700 B.C., a span that includes the Late Archaic and Early Woodland periods. More precise timing is expected from carbon-dating results due in early July.

"All the combination of the information we got out of the site makes it valuable to anyone studying prehistory in Loudoun County," Outlaw said. For example, the triangular spear points -- and their similarity to those found in other parts of the country -- can help scientists learn more about the migrations and interactions of prehistoric humans on this continent.

"Prehistory, by necessity, is a comparison to other areas," Outlaw said. "Everything we know is from what we excavate."

Although the sanitation authority has spent about $60,000 to study and excavate the site, project manager Tom Broderick said there had been no discovery, such as burial grounds, that would preclude construction from proceeding. "There are only certain finds that would force us to avoid the site, but we're not finding those," he said.

The sanitation authority's plan for the wastewater treatment plant calls for reconstructing a dam on a farm pond in a wetlands area. After the plant is built, clean water discharged at the facility will be directed through the pond. These restoration plans, which could temporarily dry out the wetlands, require a federal permit, which dictated the archaeological survey.

Construction on the treatment plant is scheduled to begin in July. When it is completed in 2008, the adjacent administration building will include a small exhibit displaying some of the artifacts and explaining their history.

"It's important to share the information," Broderick said. "These aren't going to end up in a box."