The historic Graue Mill is located at Fullersburg Woods Forest Preserve in Oak Brook. (Explore Illinois photo)

The Forest Preserve District of DuPage County’s Graue Mill is expected to reopen to the public in early August after being closed for structural repairs.

Repairs were needed to the historic landmark, located at Fullersburg Woods Forest Preserve in Oak Brook, after an April 2013 flood left 5 feet of water in the basement, worsening problems with the grist mill’s grinding and gear works as well as the mill’s basement subfloor and millrace foundation.

Work began in April and is expected to finish in early August. The District spent $584,670 for the repairs, and the DuPage Graue Mill Corporation, which operates the mill for the District, funded nearly $25,000 in repairs to the grist mill and jib crane assemblies.

“Though these improvements may not change the look of the building, people need to know that the building has been stabilized and better protected from flooding,” said Forest Preserve District Commissioner Jeff Redick, District 2.

To complete the work, crews moved the water wheel and stored it on site while masons removed old mortar in the joints between the stones of the sluiceway walls directly against the mill’s foundation.

The masons then refilled the joints with new grout and made similar repairs to the stone foundation walls above grade on the east and west sides of the mill. They added a concrete wall below grade with additional moisture-proofing underground and installed drain tiles to help prevent seepage into the basement.

In the basement, workers removed and replaced the north portion of the floor added an underdrain and sump pump to further protect from flooding. They replaced old wooden columns with new steel ones and moved the wooden gears so they could install new concrete pedestals.

Finally, they repaired the jib crane and installed a new motor and pedestal to turn the millstones.

The mill was closed to the public during the work, which also required closing the trail and underpass between the mill and York Road.

The Graue Mill and Museum is one of the area’s remaining authenticated Underground Railroad “stations” and the only operating gristmill in the Chicago area.

It was listed in the National Register of Historic Places in May 1975 and was recognized in 1981 as an Illinois Historic Mechanical Engineering Landmark by the American Society of Mechanical Engineers, the only gristmill so designated on a national or local level.