Arlington Outdoor Lab just purchased 15 acres adjacent to its Fairfax County site where students will study geology and outdoor education. (Bob Schrider/Arlington Outdoor Lab)

More than 9,000 Arlington students every year head out to the 210-acre Arlington Outdoor Lab in Broad Run, where they learn hands-on science and the wonders of the natural world.

Now, thanks to a timely purchase, they will have another 15 acres to roam, and a big boulder to examine. The Arlington Outdoor Lab just bought the land adjoining their property for $150,000 from Glen Gates, said Michael Nardolilli, president of the lab.

“It’s important because it provides a buffer to encroaching development that’s been creeping out I-66 and threatens to ruin the outdoor experience of thousands of schoolchildren,” Nardolilli said. “It’s been identified by the Nature Conservancy as a primary conservation area to help preserve the biodiversity of the Bull Run Mountain chain.”

The land, on top of Biscuit Mountain, provides wonderful views of the surrounding countryside, Nardolilli said, and will help avoid overuse of the existing property.

The lab is open every school day and for three one-week camps in the summer. There are also two open houses that typically draw more than 100 visitors, and Scouting groups also use the land.

“As the school system increases its population, the real question for the Outdoor Lab is do we increase the amount of land or do we have to start rationing its use?” Nardolilli said. “We want to make sure we don’t love it to death.”

The volunteer group that runs the lab is also looking to acquire or protect more of the watershed of Trap Run. The lab owns 70 percent now, but environmentalists worry about pollution in the stream.