Work to replace an 85-year-old bridge over the Allegheny River outside of Tionesta will begin next week.

The Hunters Station bridge on Route 62 south of Tionesta will cost a total of $23.7 million to replace.

According to PennDOT, the bridge sits between the Forest/Venango County line and Hunter Station Road.

“Work will involve construction of a new 1,124-foot-long, four-span continuous composite steel plate girder bridge, along with new concrete and asphalt roadway approaches and updated drainage, guiderail, landscaping and pavement markings, along with other miscellaneous work,” PennDOT said.

The new bridge will be built approximately 100 feet upstream from the existing structure.

PennDOT said that the current bridge was built in 1934, is considered to be structurally deficient and is used by approximately 1,100 vehicles per day.

The project will take over a year to complete and will include an extensive detour next summer.

PennDOT said that the project is expected to be completed by May 28, 2018 with a roughly 44-mile detour that “will not begin before July 5, 2017 and will end by October 31, 2017.”

That detour will utilize Routes 36, 208 and 157.

“At times during construction, motorists will encounter lane restrictions with traffic controlled by flaggers,” PennDOT explained.

The contractor is Mekis Construction Corp. of Fenelton, PA. The contract cost is $23,774,703.87, which is to be paid entirely with federal funds.

PennDOT explained that buoys will be placed in the river as navigational aids to boaters who are using the river during construction. Additionally, provisions will be made to enable recreational canoeists to portage around the work area when necessary.

The project area includes some 52,577 square feet of the Allegheny River. The Fish and Boat Commission has estimated there are 168,720 freshwater mussels 35 in every square meter that are directly threatened with death by crushing or suffocation due to the project. Of those, over two-thirds are federally listed as threatened or endangered.

Five threatened and endangered species northern riffleshell, clubshell, rayed bean, snuffbox, and sheepnose are known to exist in the Allegheny River at the bridge. Some were moved to the Conewango Creek in 2014.

Because the bridge is on the historic register, the department has to mitigate the “adverse effect” of tearing it down. Kiosks with informative panels detailing the history of the bridge, the historical human use of the river in that area, and the mussels, are part of the project.