Napa River Flood Protection Project

"Increasing Public Safety and Restoring the Environment"

Can a community provide 100-year flood protection and restore the environment?

Since 1998, MWH has played an integral role in the $250 million Napa River Flood Protection Project in Napa, California. Led by the Napa County Flood Control & Water Conservation District (NCFCWCD) and the United States Army Corps of Engineers (the Corps), this extensive environmental construction project will provide 100-year flood protection for the majority of the City of Napa.

The overall effort includes the creation of river terraces, flood walls and levees along seven miles of the Napa River. Additionally, the project creates over 400 acres of wetland habitat as well as the construction of several new roadway bridges, relocation of railroad tracks and recreational trails. Since project inception, MWH has supported a wide range of activities including project controls management, environmental remediation, permitting, design services and construction.

Resolving a Complex Contamination Problem

Most recently, MWH completed the remediation and flood terrace construction of a 2000-foot length of the Napa River where former bulk oil storage impacted soils and groundwater. During this two-year project, MWH excavated 325,000 cubic yards of soil and constructed a series of river terraces along the entire 2000-foot length as part of the Project’s overall flood protection design. Approximately half of the excavated soil (147,000 cubic yards) was contaminated. This equated to 236,000 tons of contaminated material, and took about 8700 truckloads to transport to a disposal site in Stockton, about 50 miles east of Napa. The project included the construction of extensive sheet piles, a site-specific 1,000 gallons per minute water treatment plant and a comprehensive soil sampling mechanism with regulatory oversight.

MWH continues to provide overall project controls support services to NCFCWCD through completion of the Flood Project in 2007.