Log Yard Stormwater Treatment System

Client: Hampton Affiliates

Location: Willamina, Oregon

When the Oregon Department of Environmental Quality lowered the National Pollutant Discharge Elimination System (NPDES) stormwater permit benchmarks, Hampton Affiliates (Hampton) and many industrial facilities in Oregon had to modify their stormwater systems to comply with the new permit.

After an initial assessment of Hampton’s lumber mill and log yard in Willamina, MFA presented several alternative designs for treating stormwater at the site. The alternative stormwater treatment systems differed in the amount of space and the level of operation and maintenance required, as well as in the capital and long-term costs.

MFA reviewed the advantages and disadvantages of each alternative with Hampton, providing technical and budgetary information that Hampton needed to select a system that best met their needs.

The final design included modifications to the stormwater pipe network to route stormwater from several outfalls into a new pump station to be design by MFA. The new pump station conveys stormwater from a large part of the site into an on-site, passive stormwater treatment system. The treatment system includes a settling pond with a pretreatment forebay where settleable solids are removed via sedimentation. Pretreated stormwater then flows into an open sand filter, where the remaining pollutants are filtered prior to discharge.

MFA provided the following services for Hampton:

• Conceptual design layouts and budgetary estimates for several alternative treatment systems, including a discussion of advantages and disadvantages of each alternative
• A final design of a pump station, settling pond, and open sand filter to treat stormwater prior to discharge
• High probability of meeting NPDES benchmarks