Environmental giant CDM, Cambridge, Mass., is in talks about a possible link with Columbia, S.C.-based transportation engineer Wilbur Smith & Associates. A merger or acquisition, if completed, would bring together two businesses with strong brands in their respective markets and more than 100 years of combined operating history. The firms are in “due diligence,” says a CDM spokeswoman, declining to confirm the nature or timing of any new association. However, she says the combination “would be a good for both firms,” noting they are “complementary.” Both firms are 100% employee-owned. CDM ranks 21st on ENR’s list of the Top 500 Design Firms, with $720 million in 2009 revenue. Wilbur Smith, which ranks 64th on that list, reported $182.4 million in revenue last year.