Washington Engineering designed upgrades to Outfall 7 at Fort Lewis.

Discharges from the existing system were not meeting the NPDES permit requirements for oil/grease. Hydrological studies were conducted at all three sites to quantify the peak flow and runoff volumes associated with the 6-month/24-hour Water Quality Design storm and various other frequencies.

Outfall 007 had a relatively large amount of land adjacent to the outfall. Improvements at Outfall 007 included construction of an upstream sedimentation basin and a moderate capacity infiltration/detention pond to control discharge quantities through the OWS.

A pre-engineered oil/water separator and by-pass structure was installed at Outfall 7.