Former Drinker Biddle & Reath corporate partner Samuel Mason has been tapped to serve in the newly-created position of general counsel at global environmental, health and safety consulting firm Environ Corp., a longtime client.

Mason said he’s served as outside counsel to the privately-held, Arlington, Va.-based company for more than a decade, starting when it was still a relatively small operation.

But Environ has expanded aggressively in the past decade, including mergers with Massachusetts-based epidemiological consulting firm Applied Epidemiology Inc., Tennessee-based wastewater treatment consulting firm the Advent Group, Illinois-based forensic architecture consulting firms Boelter Associates Inc. and Gustitus Group Inc., and Brazilian environmental consultancy firm Arquipelago Engenharia Ambiental.

Environ now employs 1,000 consultants across 88 offices in 19 countries, including China, Germany and South Africa.

According to Mason, the significant expansion in recent years is what drove Environ to the conclusion that it needed full-time, in-house counsel.

Mason said that when the company approached him about the position, he decided he was ready to make a change after 35 years in private practice, 15 of which he spent at Drinker Biddle as a partner in its corporate practice.

“At this point I feel it would be very interesting to work with one client and to be more immersed in everything they do,” Mason said, adding that he was also eager to join Environ’s management team, with which he has become well-acquainted over the years.

Mason said one of the things that attracted him to the new role was that it allowed him to remain in Philadelphia, just a few blocks from Drinker Biddle’s offices, despite Environ being based in Virginia.

According to Mason, the company has a decentralized management structure in which its chief executive officer is based in San Francisco, while its chief financial officer is based in Arlington and its chief operating officer works out of the company’s office in Newark, N.J.

Mason said Environ also houses some management functions in its Chicago office.

Mason, a corporate transactional lawyer, said the bulk of his work as Environ’s outside counsel involved international mergers and acquisitions, corporate governance and financing matters.

As Environ’s GC and the company’s only in-house lawyer, Mason said, he’ll still continue to handle the bulk of the business law matters himself, but will have “more of a supervisory role” with regard to other areas of law.

“As inside counsel, I’ll be coordinating work for Drinker and for foreign outside counsel,” Mason said.

According to a press release, Mason will report to COO Thomas R. Vetrano and will also provide counsel to Environ’s board of directors and global management committee.

Mason said there are currently no plans to build an in-house legal department at Environ, but noted that it’s not out of the question as the company continues to grow.

Overall, Mason said his job, like any GC’s, will be to manage the company’s legal functions as efficiently as possible and having a deep familiarity with both Drinker Biddle and Environ will be a significant benefit to that end.

“I think when you take on any particular matter, whether it’s litigation or financing, you have to think about the most efficient way of handling it and the most effective way,” Mason said. “There should be communication between inside counsel and outside counsel as to how to handle a matter.”

Mason said he’s confident both his former firm and his new employer “are acutely aware that if there’s a $100,000 matter, you don’t want to spend $100,000 dealing with it.”

Robert C. Juelke, chair of Drinker Biddle’s corporate and securities practice group, said that while the firm was sad to lose Mason as a partner, his new role will help the firm strengthen its relationship with a longtime client.

The past few years has seen a good deal of lateral movement between firms and their clients.

By far the most high-profile, firm-to-client move in recent memory came earlier this month when longtime Reed Smith global managing partner Gregory B. Jordan announced he would be leaving the firm to serve as GC of PNC Financial Services Group.

Jordan will now serve as executive vice president, GC and head of regulatory and government affairs at PNC.

Last year, Buchanan Ingersoll & Rooney Chairman Thomas L. VanKirk left the firm to join client Highmark Inc., Pittsburgh’s largest health insurer, as its executive vice president and chief legal officer.

Also last year, Rachel Allen left Jones Day in Pittsburgh, where she had been a partner in the firm’s corporate practice, to join ALung Technologies Inc., a Pittsburgh-based company that makes respiratory support devices.

Lawyers have also been returning to private practice from in-house life recently.

In August, for example, Thomas Zielinski, who served as executive vice president and GC at Coventry Health Care since 2001, joined Morgan, Lewis & Bockius in Philadelphia as a litigation partner earlier this year.

Last month, senior vice president and deputy GC of Aramark Corp., John C. Ryan, rejoined Duane Morris in Philadelphia,

Zack Needles can be contacted at 215-557-2493 or Follow him on Twitter @ZNeedlesTLI.