Glenn Unterberger, 65, an environmental lawyer for the federal government who later became a partner at the Philadelphia law firm of Ballard Spahr LLP, died Sunday, Oct. 14, at his Bala Cynwyd home.

Mr. Unterberger's death was cardiovascular in nature, the Montgomery County Medical Examiner's Office said.

Mr. Unterberger was a leading authority in the Philadelphia area on the Clean Air Act of 1970, the federal law that regulates air emissions.

After spending more than a decade as an enforcement attorney at the U.S. Environmental Protection Agency in Washington, he parlayed that knowledge into a job with Ballard Spahr in 1990, and became leader of the law firm's environmental practice in 2006.

Once in the private sector, Mr. Unterberger advised many major companies on compliance with the Clean Air Act and other environmental laws and regulations, Ballard Spahr said in a statement announcing his death.

Although Mr. Unterberger's field of expertise was weighty and detail-laden, he kept things light in the office, the law firm said. He was known for his distinctive writing style, gentlemanly manner, and wry wit.

"You could count on Glenn for certain things: distinguished writing; a calm and thoughtful approach to every situation; and a sense of humor that was dry, exquisitely timed, and very often nuanced. It would leave you laughing out loud at your desk," said Ballard Spahr chair Mark Stewart.

"Glenn succeeded me as 'commissioner' of March Madness activities and he sent some of the most entertaining communications I have read. We have lost a dear friend who excelled at the big and little things in life," said Stewart.

Mr. Unterberger's love for sports, especially basketball, and his penchant for fun were legendary. He organized and informally served as commissioner of the "Old Guys Basketball Association," a group of his friends who have met weekly in Bala Cynwyd for Sunday morning pickup games for the last 25 years.

In addition to sports and law, Mr. Unterberger was passionate about music and, most of all, his family, said his friend Harry Weiss, practice leader of Ballard Spahr's Environment and Natural Resources Group.

Weiss joined the firm as a young associate around the time Mr. Unterberger came to Ballard Spahr from the EPA, where he had served as national legal director for the agency's water and hazardous-waste enforcement. Mr. Unterberger became the go-to resource for regulatory issues for Weiss and other lawyers in the firm's environmental practice.

"Glenn had come from the EPA, where he wrote many regulations, so who better to teach young lawyers not only where to find the regulations, which is hard enough, but what they meant, which was almost impossible?" Weiss said. "His effectiveness was in parsing the words and understanding from a regulatory and a policy standpoint what those words on a page meant and how they could affect clients' businesses.

"I also think about him being a very different kind of lawyer, especially in a big-firm setting: completely ego-free, unassuming, and gentlemanly," said Weiss.

Though he had focused on water and hazardous-waste issues at the EPA, Mr. Unterberger "took it upon himself to learn the Clean Air Act inside and out" when the law underwent reauthorization and large-scale expansion in 1990, Weiss said.

"He became, over the years and up until today, one of the foremost experts in the region and advised countless clients on compliance with that law," Weiss said.

Mr. Unterberger was so well-versed in the law that he could forge solutions to regulatory issues for manufacturing clients that even the regulators had not thought of, Weiss said.

A frequent speaker and writer on environmental law, Mr. Unterberger was active in professional affairs. He was a past vice chair of the Environment Committee of the Federal Bar Association and cochair of the Air Quality Work Group of the Pennsylvania Chamber of Business and Industry. The latter group consists of regulators and business leaders who meet regularly to discuss environmental issues and policy.

In addition to his work at Ballard Spahr, Mr. Unterberger was a fixture in the Lower Merion Jewish community, his family said. He served for two years as president of Temple Adath Israel in Merion Station and was a member of the synagogue's board of directors for 20 years.

He was also a member of the Philadelphia-area cabinet of the Jewish Theological Seminary and was honored with the Shin Award for outstanding service to his community and synagogue in 2007.

Mr. Unterberger is survived by his wife, Alyse, sons Sam and Andrew, and three brothers.

Funeral services will be at noon Wednesday. Oct. 17, at Adath Israel, 250 N. Highland Ave., Merion Station, Pa. 19066. Interment will follow in Har Jehuda Cemetery, Upper Darby.

Shiva will be observed Wednesday and Thursday, Oct. 18, at 6 p.m. at the synagogue, with services at 7 p.m.

Donations in Mr. Unterberger's memory may be made to Adath Israel at the address above or via www.adathisrael.org/donation/memorial-fund.