SOUTH PORTLAND — The city is seeking a new director of parks, recreation and waterfront after Rick Towle recently resigned from the post following an internal investigation.

Towle was placed on administrative leave Oct. 31 while the city’s human resources department investigated “concerns” related to his performance, City Manager Jim Gailey said Thursday. The investigation took about a month and no disciplinary action was taken, Gailey said.

Towle, who started working for the city in June 2012, submitted a resignation letter to Gailey on Dec. 1.

“During the past 18 years the focus of my professional life has been on the needs of those communities I have served each day. Many positive moments have helped shape my career in public service,” Towle wrote. “However, after much consideration recently, I have decided to take my career into a new direction.”

Towle was parks and recreation director in Talbot County, Maryland, from 2004 to 2012; and in Biddeford from 2000 to 2004. He was recreation director in Old Orchard Beach from 1997 to 2000, according to his profile.

Towle couldn’t be reached for comment. Gailey declined to discuss Towle’s departure any further, saying it was a personnel matter. Towle’s annual salary was $94,000.

Towle was a key player in developing plans for the new $15.7 million municipal services facility now under construction at the site of the existing solid waste transfer station on Highland Avenue. The new transfer station is set to open in a few weeks, Gailey said.

The project came under scrutiny in October, when city officials reconsidered plans to install a wood-chip biomass heating system in the municipal services building in favor of a natural gas system.

Last summer, Towle had promoted the wood-burning option, providing data that showed it would be more costly to install – $1.6 million compared to $200,000 for a natural gas system – but cleaner-burning and less expensive to operate over time.

In November, the City Council redirected city staff to pursue a natural gas option after learning that it burns cleaner than wood, that the system would be easier and less costly to maintain, and that Unitil would extend the gas line along Highland Avenue, making installation even less expensive than anticipated.

The open director’s job is advertised statewide and nationally, Gailey said, including on the Maine Municipal Association’s website. The application deadline is Jan. 22. Sarah Neuts, parks superintendent, is serving as acting director.