Tetra Tech Inc. said Wednesday that its third quarter net income jumped 93 percent on improved operating margin, tax benefits and strong cash generation.

After the markets closed, the Pasadena engineering company reported net income of $31 million (51 cents per share) for the quarter ended June 28, compared with $16.1 million (27 cents) a year ago.

Revenue fell 2 percent to $551 million, but after subtracting subcontractor costs it was up more than 7 percent to nearly $357 million. Cash generated from operations soared 262 percent to $60.8 million, bolstered by a nearly $40 million cash refund related to an IRS settlement in the previous quarter.

Analysts surveyed by Thomson Reuters on average expected the company to report a profit of 30 cents per share on revenues of $348 million.

The company’s backlog of work is up 8 percent to $1.7 billion.

“We were successful in winning several key new orders, and completed three acquisitions in the quarter,” Chief Executive Dan Batrack said in a statement. “The company remains on track for a solid fiscal 2009.”

For fiscal 2009, Tetra Tech raised its guidance and now expects net income of $1.40 to $1.43 per share, which includes 22 cents in tax benefits. Revenue is expected to range from $1.35 billion to $1.38 billion. Analysts have been expecting earnings of $1.22 per share on revenue of $1.39 billion.

Prior to the announcement, Tetra Tech shares closed down 52 cents, or 1.7 percent to $30.09 on the Nasdaq.