A potential overhaul of Washington County's public works complex north of Stillwater now includes something "green" that would run underground.

Under study is a new sewer line that would replace drain fields at the county's North Shop. It would link to Stillwater's city sewer about 4 miles away, produce a daily discharge equivalent to that of eight to 10 houses and eliminate any future need for septic systems, according to the proposal.

"That really makes the site sustainable for the next 50 years plus," said Don Theisen, the public works manager.

A new sewer is one of several ideas being discussed for reconstructing the North Shop — the county's central vehicle operations center — into something more environmentally respectable. The county also washes large trucks and Sheriff's Office vehicles at the shop, using an average of 350 gallons of water a day.

Theisen has told the County Board that the complex is now far too small to accommodate the many vehicles serviced there. It was built in 1962, when the county's population was less than 55,000 residents. Now, more than 240,000 people live in the county, bringing a greater demand for public works services ranging from snowplowing to vehicle repair to improved roads and bridges.

Whether the estimated $18 million project moves ahead depends on County Board approval. So far, however, commissioners informally have indicated their support for it.

Meanwhile, Theisen is exploring other sustainable energy features, such as geothermal heating, solar power, and energy rebates and credits. He determined last year that the poor condition of the buildings was resulting in wasteful spending, including $90,000 a year in energy losses because of uninsulated walls.

The North Shop uses more energy than the county's Historic Courthouse in Stillwater, built in 1870, he said.

Making the existing public works structure compliant with current building codes would cost millions of dollars, a county report determined. The building lacks fire-suppression sprinklers and provides less than half the space needed. It has no locker rooms for female employees, cramped conference rooms, substandard heating and ventilating systems and no disability-accessible toilets.

Recent troubles at the 54-acre complex included an electrical fire and a sewage backup. About 85 full-time and seasonal employees work there.

Ongoing design work will help the County Board decide how to proceed, and funding sources include possible state water grants, Theisen said.

In recent years Theisen has led a series of major county building projects, including the $56 million overhaul of the main county campus in Stillwater, completed in 2010. That project included a new courts building, an expanded law enforcement center and renovated offices in the adjoining five-story county office building.

The county also built satellite service centers in Forest Lake and Cottage Grove in 2007.

Conditions at the North Shop and the county's smaller South Shop in Woodbury were widely condemned in the county report, compiled by architects, engineers and builders that the county hired to make inspections.

Kevin Giles • 651-925-5037