Grand Rapids’ Gerald R. Ford International Airport (GFIA) is Michigan’s second largest air carrier airport, serving over 2.3 million passengers each year. In the winter, the airplanes get sprayed with a deicing solution for safety and compliance with Federal Aviation Administration standards. At GFIA, de-icing fluids (propylene glycol) mixed with snowmelt would run off from the airfield before entering a nearby stream, known locally as Trout Creek.
Propylene glycol is an organic compound (a sugar) commonly used as a food additive and in personal hygiene products. It is biodegradable and does not “linger” in the environment. However, the de-icer presents two challenges in a natural water system because it:
- Competes with other organisms for dissolved oxygen as it degrades.
- Provides a food source for algae, fungi, and other aquatic organisms, allowing them to multiply to nuisance levels under ideal conditions.
In Trout Creek, fast-growing aquatic organisms created a nuisance biofilm. This was a problem for residents living along Trout Creek. Their odor complaints prompted the Michigan Department of Environmental Quality (MDEQ) to include within GFIA’s 2010 National Pollutant Discharge Elimination System NPDES permit a requirement to remove the airport’s contribution to the nuisance biofilm by October 1, 2015. GFIA’s NPDES permit called for continued seasonal collection of de-icing fluid, stormwater testing, and reporting.
This $20 million project features a Natural Treatment System (NTS) for treating de-icing fluid runoff at GFIA. The NTS is composed of multiple treatment cell pairs with siphon/dosing chambers, leveling structures, and other engineered components. The treatment cells regulate flow, remove suspended sediment, have inlet grates to stop water-borne debris, and use log booms to collect floating objects.
The NTS starts at the airfield where buried pipes collect the deicing fluid laden stormwater. Pipes as large as 108 inches in diameter carry runoff to a series of engineered treatment cells. There, naturally occurring bacteria remove pollutants as the water percolates through an engineered soil matrix. Next, the stormwater flows through an open channel lined with rocks where the water receives further treatment and aeration before it flows into the Thornapple River through a diffuser. The diffuser mixes the treated runoff with river water as it flows downstream.
Before this project, community members voiced concerns to GFIA and the MDEQ regarding earlier efforts to control a nuisance biofilm in Trout Creek. The NTS is among GFIA’s most significant environmental undertakings and will protect the environment for future generations. With the help of the public, regulators, scientists, engineers, and stakeholders, GFIA is proud of its increased environmental stewardship and its efforts to be a good neighbor.
The cornerstone of this project’s success was the Stakeholder Advisory Committee, assembled by GFIA to engage interested parties in the project. The Stakeholder Advisory Committee met with GFIA and the design team often, including a design charrette, where it provided feedback on the various problems and solutions posed by the experts. The charrette identified ten viable design concepts. GFIA’s award-winning public education, outreach, and stakeholder involvement efforts involved producing public education materials, delivering presentations, providing information on its website, conducting airport tours, utilizing social media, and providing information in its quarterly newsletter.