Tetra Tech Inc. said Tuesday that it has completed the purchase of consulting firm ARD Inc.

The Burlington, Vt.-based ARD provides consulting and technical services for international aid agencies and other government clients. The company, which has more than 25 offices and 760 employees around the world, had annual revenue of about $110 million over the last 12 months.

This is the second recent acquisition for the Los Angeles-based engineering consulting firm and is part of its global expansion effort.

In April, Tetra-Tech purchased New York-based Delaney Group, an engineering firm that specializes in renewable power projects such as wind power facilities.

Terms of the deals were not disclosed.

ARD will become part of Tetra Tech’s resource management division and is expected to add 2 cents per share to Tetra Tech’s 2008 earnings, the company said. Tetra Tech shares fell 26 cents to $22.07 in morning trading Tuesday on the Nasdaq.