After what seemed like an eternity, the street redevelopment in front of my beloved downtown coffee shop is finally complete. It’s almost eerily quiet now that the fleet of excavators, dump trucks and compactors has moved on—most people would’ve simply gone elsewhere for their morning caffeine hit while the chaos was in full swing. As a true stormwater nerd, however, I dutifully braved the noise and dust to observe the refurbishment of the storm sewer, including the addition of small-media filter vaults that bring the system up to Washington State treatment standards. Today, the birds are singing, the catch basins are clean and new, and the coffee is delicious.

Green Infrastructure Evolving

If, like me, you live in an urban environment established before the 1990s, chances are the bulk of your stormwater discharges go untreated. While great improvements to stormwater quality have been made since the inception of the Phase I and II NPDES permitting system, the focus has understandably been on new development. Urban redevelopment projects such as the one I’m describing are costly, disruptive to local businesses and only come around every 20 to 30 years—not an efficient mechanism for stormwater management retrofits. This is where green infrastructure (GI) is meant to fit.

During the last couple decades, small, dispersed bioretention planters have become a standard fix for existing development, popping up at the edge of parking lots, squeezed alongside intersections and taking over inner lanes of street sections in neighborhoods across the country. Ideally, these systems are a cost-effective way to reduce and treat stormwater flows while also providing ancillary livability benefits. However, as stormwater agencies tighten requirements, manage assets, and plan for Total Maximum Daily Load compliance and Municipal Separate Storm Sewer System resilience, many are finding that distributed GI installations aren’t the best strategy, with some opting instead for large regional facilities.

Learning Lessons

A telling example of the difficulty in managing distributed GI networks comes from Portland, Ore., which lies just across the Columbia River from me. In 2018, the city performed an audit of its Green Street program, finding that it lacked the planning structure to prioritize capital spending on Green Street installations relative to established watershed goals. This occurred after at least 2,000 systems were in the ground. Furthermore, the audit found there was no sufficient method to quantify the condition of the units, which implies increased inspection and maintenance costs to keep them working—sure, one raingarden is easy to maintain, but what about 2,000?

I don’t mean to pick on Portland here. Conducting an internal assessment of delocalized GI assets and returning a constructively critical report is a difficult task, and rate payers appreciate city agencies that are transparent and committed toward improvement. Their experience, however, provides a useful lesson to other municipalities trying to establish their own stormwater retrofit programs.

Up here in Washington State, there are many such municipalities, largely because recent permit updates require Stormwater Management for Existing Development plans. This program is point-based, with clearly defined values for different project types and varying implementation deadlines for Phase I and Phase II permittees. With this regulatory driver in place, stormwater managers are encouraged to coordinate with other departments such as transportation or parks to optimize the benefits of the projects and develop cooperative funding structures.

Site Selection Is Key

Space limitation and other design challenges can limit the effectiveness of traditional GI practices. To maximize runoff treatment in a restricted footprint while maintaining the vegetated look and water-quality benefits of raingardens, several Washington cities are utilizing high-rate biofiltration (HRBF). These systems utilize specially engineered filtration media that remove pollutants and sustain vegetation while operating at hydraulic loading rates up to 25 times higher than conventional biofilters. To be used in Washington, these technologies must be certified through the state’s Technology Assessment Protocol—Ecology, the nation’s premier field-testing program for innovative stormwater treatment technologies, which ensures they meet stringent requirements for removal of sediment, dissolved metals and phosphorus.

HRBF installations such as Tacoma’s Point Defiance and Kitsap County’s Whispering Firs are great examples of regional stormwater parks that offer public recreational amenities while treating runoff from hundreds of acres of existing development—precisely the types of multi-sector benefits GI is meant to provide. These are only a couple illustrations in a list that will only grow under Washington’s progressive regulatory structure, and I’m looking forward to the results.

If you’re a true stormwater nerd like I am, come visit some of these great installations, and please let me know if you have similar examples of regional stormwater facilities where you live. If you do visit, I hope you also enjoy the coffee.