Chalk Hill Road is a local rural road located east of Healdsburg in Sonoma County. The road has a northerly terminus at Highway 128 and traverses southerly over 8.0 miles to its southerly terminus at Faught Road. The existing one-lane, 170-feet long by 18-feet wide bridge is located about 1.5 miles south of Highway 128. It was built in 1915 and is eligible for the National Register of Historic Places.

The existing bridge structure consists of a five span conventionally reinforced concrete open-spandrel arch span of 110 feet and a few short approach spans. The superstructure consists of spandrel beams and a transverse ribbed slab.

The existing bridge is determined by Caltrans as structurally deficient and replacement is best strategy. The County decided to build a new two-lane bridge upstream of the existing bridge and plans to leave the original arch bridge in place.

OPAC is the prime consultant for the design of the new bridge. It is envisioned that several alternative structural types, such as concrete box girder, concrete arch and network arch are potentially applicable for the new bridge.

This project requires surveying, hydrologic and hydraulic studies and geotechnical investigations and engineering as well as structural and civil engineering. Sonoma County PRMB staff will perform the necessary environmental studies and documentation. The design team will provide environmental and engineering support to PRMB.

The scope of work for OPAC included project management, complete bridge design and coordination of their design work with the environmental work performed by County staff.