No hyphen required

Question: In the following sentence, should the words “on site” be hyphenated?

They removed the trees and dumped them on site.

Answer: No. You use hyphenation when two words appear as a single adjective before a noun—such as well-known expert or on-site trees—or when the compound is listed as a hyphenated word in the dictionary.

More examples of when—and when not—to hyphenate:

• She has a part-time job.   
• He works part time.
• He accepted an out-of-court settlement.
• They settled out of court.