BELLINGHAM - City officials have been working for years to reduce the amount of phosphorus draining into Lake Whatcom. This year, officials plan to clean up their own backyard by improving stormwater treatment at Bloedel Donovan Park, which has especially high levels of phosphorus in its soil.
Work is scheduled to begin after Labor Day on a project that is part shoreline makeover and part runoff filtering system. The collapsing bulkhead will be removed, along with some of the lawn along the lakeshore, to make room for a sand-and-gravel beach. While that will help reduce the amount of phosphorus entering the lake from the park, most of the pollution reduction will happen underground.
Crews will dig a trench just off the shoreline and fill it with sandy material. The trench will catch water running off the lawn and direct it into the groundwater. The material in the trench will filter out the phosphorus, said Bill Reilly, the city's stormwater manager.
The sand added to the new beach will be low in phosphorus and will serve as a backup filter for runoff, he said.
"The beach will provide some buffer for contaminants that miss our trench," he wrote Wednesday, April 16, in an email to The Bellingham Herald.
Excessive phosphorus runoff stimulates algae growth, leading to low levels of dissolved oxygen in the lake. The algae can be thick enough to clog the city's water filters, and the low oxygen harms fish.
In a draft report on Lake Whatcom pollution released in early 2013, the state Department of Ecology said the lake would have healthy levels of algae and oxygen if 87 percent of the developed land around the lake released as much runoff as natural forest. Runoff is greater on developed lots because of impervious surfaces, such as driveways and roofs, and lawns that act poorly as filters.
"Lawn and landscape areas have the highest rate of phosphorus loading in the watershed," Reilly wrote.
That is true even if phosphorus-free fertilizers are used on the lawns around the lake, as required by city code.
Bloedel's lawn has especially high levels of phosphorus, according to a letter dated March 22, 2012, to the city parks department from Gwen Stahnke, a turf grass specialist with the Washington State University Puyallup Research and Extension Center. The high phosphorus could be caused by large amounts of fecal waste from Canada geese and other waterfowl, or from decaying organic matter left behind by the sawmill that once stood at the park site, Stahnke wrote.
At Bloedel Donovan, the city expects to exceed the state's goal to reduce phosphorus going into Lake Whatcom by 87 percent.
"We are hopeful, and our modeling predicts, that we can remove approximately 41/2 pounds of phosphorus per year from this project with an efficiency rating of over 90 percent," Reilly wrote.
The most heavily used part of Bloedel Donovan is less than five acres. Correcting the phosphorus problem there does little for the lake as a whole, which has more than 4,000 acres of developed land around it. After planned pollution reductions between now and 2018, the city estimates it will still need to remove 757 pounds of phosphorus a year to meet state goals.
The state will soon set deadlines for the city, Whatcom County and the Lake Whatcom Water and Sewer District to come up with a plan to reach the 87 percent reduction target. Meeting that goal is expected to take 50 years.