Bamboo grasses sprouting from giant concrete boxes that stretch the length of two football fields are helping to remove pollutants from the stormwater runoff at the Port of Tacoma’s West Hylebos Log Yard.
The plants are a key piece of the innovative biofiltration stormwater treatment system designed and built by the Port. The system mimics nature’s filtering processes to remove zinc, copper and other pollutants to improve water quality before it runs into Commencement Bay.
It is the first of its kind used to manage stormwater at a log export terminal.
To date, the system has yielded impressive results, removing more than 92 percent of pollutants:
| Parameter | Influent (mg/L) | Effluent (mg/L) | Permit benchmarks (mg/L) |
|---|---|---|---|
| Turbidity | 58.4 | 9.4 | 25 |
| Total suspended solids | 42 | 3.5 | 100 |
| Copper | 33.9 | 12.5 | 14 |
| Zinc | 57.4 | 8.8 | 117 |
| Chemical oxygen demand | 290 | 85 | 120 |
“We’ve had phenomenal results,” said Anita Fichthorn, water quality project manager.
Debarking activities at log yards leach high levels of pollutants and make stormwater management a particular challenge. When the log yard failed to meet Washington state’s stringent water quality standards in 2010, the Port analyzed six treatment options. Biofiltration emerged as the most cost-effective solution.
“Biofiltration relies on plants, soil and microbes to remove contaminants from the stormwater runoff,” Fichthorn said. “It’s traditionally used to control flow in urban environments and is a relatively new stormwater treatment technology.”
Biofiltration is not new at the Port. The technology was first used in 2010 on smaller scale to treat rainwater flowing off the maintenance shop’s metal roof. The Port built 300-gallon downspout treatment boxes based on designs implemented at other ports with remarkable results: up to 99 percent of metals were removed.
The technology, however, was untested in treating stormwater runoff from a log yard.
The Port worked with Kennedy/Jenks Consultants to conduct extensive pilot tests. The results helped refine the four-stage design ultimately approved by the Washington State Department of Ecology.
The $2.7 million system measures 600 feet long by 45 feet wide. Completed last December, it moves stormwater through four cells. Each targets a particular pollutant:
- In stage one, pea gravel removes solid pollutants.
- In stage two, sand amended with biochar removes fine solids, metals and organic contaminants.
- In stages three and four, the bioretention mix of sand and compost is planted with bamboo and other vegetation to remove the remaining pollutants through biological uptake in the plants.
The log yard system cost less than traditional systems that rely on mechanical filtration or chemical treatment. It’s also flexible enough to support other potential uses at the West Hylebos pier.
The project recently won the American Association of Port Authorities 2014 Comprehensive Environmental Management award. Port officials accepted the award Nov. 13 at the association’s annual convention in Houston, Texas.
“This treatment system underscores our commitment to doing business in a way that protects the environment,” said Jason Jordan, director of environmental programs. “The technology has proven successful at the log yard and could easily be adapted for other applications in the port industry.”
About the Port of Tacoma
The Port of Tacoma is an economic engine for South Puget Sound. A major gateway to Asia and Alaska, the Port of Tacoma is among the largest container ports in North America. The Port is also a major center for bulk, breakbulk and project/heavy-lift cargoes, as well as automobiles and trucks.
