Plans by the Pennsylvania Turnpike Commission to route the Southern Beltway across Canonsburg Lake may actually be a good thing -- at least for the lake.

Stricken by years of silt buildup, the dwindling lake is in need of major rehabilitation costing millions of dollars. That could be partly paid by the Turnpike Commission in conjunction with the beltway project.

The 12.5-mile beltway section between Interstate 79 and the Mon-Fayette Expressway is the easternmost part of the project that will eventually create a 32-mile toll road between Pittsburgh International Airport and the Mon-Fayette Expressway near Finleyville.

One of the nation's largest road construction projects, the beltway is designed to provide easier access to the airport and to ramp up development in the Mon Valley.

The first six miles of the beltway, from the Route 60 Expressway to Route 22 near Burgettstown, opened in October 2006, and there is believed to be enough funding now for the $700 million beltway section between Route 22 and I-79.

Current proposals have the Southern Beltway straddling Canonsburg Lake on its way to the Mon Valley Expressway. At first glance, throwing a highway bridge across a lake already suffering environmental damage was not a good idea. But there are pro-lake incentives.

The 76-acre lake in North Strabane and Peters was built by Alcoa in 1943 as a water source for the Canonsburg Forging plant during World War II. It was given over to the state in 1958 and has been gradually filling with silt. Rapid development in the area has accelerated the rate of runoff into the lake from Little Chartiers Creek, reducing the maximum depth from 34 feet to 18 feet in recent years.

Costs to restore the aquatic system and dredge the lake range from about $2 million to $5 million, 65 percent of which may be paid by the U.S. Army Corps of Engineers, which is studying the project.

The remaining 35 percent of the cost is to be borne by local government, grants or from funds raised.

To mitigate the damage caused by the construction of bridge pylons near the southern section of the lake and for a right of way in the area, the Turnpike Commission is expecting to pay the state Fish and Boat Commission, which controls the lake, millions of dollars.

"I would think you're talking about seven figures," said Turnpike Commission spokesman Joe Agnello.

Formal negotiations between the two state commissions are probably several years away, according to Gary Moore, legislative liaison for the Fish and Boat Commission.

He said the final route of the beltway must first be determined, along with a final design. The route that traverses the lake is the Turnpike Commission's preferred plan. There are several other options, including one that would have put the highway through the Glencannon housing development in North Strabane. That option would have displaced hundreds of residents.

"This is what we think is the best route," Mr. Agnello said of the lake route.

The Turnpike Commission is gathering public comment until Friday on a draft environmental impact statement that lays out the preferred route. The commission is expected to make a final decision later this year or early next year. At that time, there will be more public meetings to gather input.

The new road would extend east from I-79 in Cecil, where a connection would be built between the Bridgeville and Southpointe interchanges, crossing over Cecil Henderson Road, the Montour Trail right-of-way and West McMurray Road. It would cross Canonsburg Lake, then Route 19, before passing south of the Boone Reservoir and running parallel to Waterdam Road. It would continue from there across Linden Road into Nottingham, ending with a connection to Route 43 in Union.

Interchanges are being proposed in Cecil at Morganza Road, along Route 19 near the Waterdam Plaza, and with Sugar Run Road in Nottingham.

A recent hearing in Canonsburg drew more than 300 residents, who learned that about 96 residential properties and three businesses will be torn down to make way for the highway.

Many affected residents already knew they would probably have to sell their homes, but they say the local real estate market and development have remained in limbo for years, while the Turnpike Commission makes a final decision. Property negotiations aren't expected to begin for about three years.

The commission negotiated with North Strabane and Peters to tweak the design to minimize disturbance to two housing developments that are now under way, and to stay near the Peters border with North Strabane so it didn't impact "significant portions" of Peters.

"The thing is, who wants a road in their backyard?" said Frank Siffrin, manager of North Strabane.

The commission also has been in talks with the Canonsburg Lake Restoration and Improvement Committee, a group of residents devoted to rehabilitating the lake.

The group's project manager and chairwoman, Debra Valentino, said her committee has worked for years with the Turnpike Commission to hammer out placement of the pylons to cause the least disruption to the main body of the lake.

"They're working with us and they've pledged to continue working with us," she said. "They made a number of concessions."

Mr. Siffrin said he believes the project probably won't be completed for at least 10 years. Planning for the beltway began a decade ago, and it's unclear where the $700 million will come from to build the I-79/Mon-Fayette Expressway section.

To comment on the Southern Beltway project, submit written comments by 4 p.m. Friday to Pennsylvania Turnpike Commission, David P. Willis, P.O. Box 67676, Harrisburg, PA 17106-7676, or to the U.S. Army Corps of Engineers, Regulatory Branch, Scott A. Hans, William S. Moorhead Federal Building, 1000 Liberty Ave., Pittsburgh, PA 15222.