Environmental giant CDM is in talks about a possible link with transportation engineer Wilbur Smith.

A merger or acquisition if completed would combine two businesses with strong brands in their respective markets and more than 100 years of combined operating history.

Both are based on the U.S. east coast but operate internationally. CDM is a Cambridge, Mass.-based engineering and construction management firm and Wilbur Smith & Associates Inc. is a Columbia, S.C., transportation designer.

The transaction is in “due diligence,” says a CDM spokeswoman, declining to note the nature or timing of any new association.

“This would be a good combination for both firms,” says the spokeswoman, noting that the firms are “complimentary” and have “compatible cultures and values. It’s a strategic opportunity and a broader way to serve clients.”

A Wilbur Smith spokeswoman also confirms the talks, adding that’s “it’s looking good.”

Both firms are 100% employee-owned.

CDM, which specializes in global water and wastewater markets, ranks 21st on ENR’s list of the Top 500 Design Firms, with $720 million in 2009 revenue, more than $101 million performed overseas. Wilbur Smith, which ranks 64th on that list, reports that 95% of its $182.4 million in revenue last year was in transportation.

CDM also ranks among the top ten engineering firms in water supply, treatment and transmission, sewerage, solid waste, soil remediation, clean air and abatement on ENR’s Top 500 Design Firms sourcebook for 2009, based on 2008 revenue.

Wilbur Smith ranks 11th on the list of top highway engineers in the ENR’s 2009 design firm sourcebook.

CDM, which has 4,500 employees worldwide, began as a partnership in 1947.

Thomas R. Camp, one of its three founders, formerly headed the department of sanitary engineering at the Cambridge-based Massachusetts Institute of Technology, pioneering water treatment technologies such as dual-media filters and direct filtration for public water supplies, the company says.

Founded in 1952 by Wilbur S. Smith, who the firm says was the first state traffic engineer in South Carolina, Wilbur Smith has more than 1,200 staff members in about 60 offices around the world.