Apportionment of oxygen demand contributions from aircraft and pavement deicer freezing point depressants in airport runoff, Milwaukee, Wisconsin, 2005-2022.

Aircraft anti-icers and pavement deicers improve the safety of airport operations during winter precipitation events. Runoff containing these products can contribute elevated biochemical oxygen demand (BOD) to receiving streams. We monitored runoff from Milwaukee Mitchell International Airport at one upstream site, three outfall sites, and one downstream site from 2005 to 2022 for BOD, chemical oxygen demand (COD), and freezing point depressants used in deicing and anti-icing fluids to determine the primary sources of BOD and COD in the receiving stream. The greatest concentrations of BOD, COD, and freezing point depressants occurred at the primary outfall, which drains the main terminal area, and the secondary outfall, which drains cargo operations. The greatest loadings occurred at the primary outfall; loadings were an order of magnitude less at the secondary outfall due to a small drainage area with relatively low flow volumes. At the three outfalls, median concentrations of five-day BOD (BOD5) and COD were 100-1,300 mg L-1 and 200-2,100 mg L-1 respectively. Apportionment computations indicated that propylene glycol from aircraft deicers and anti-icers was responsible for at least half of the BOD5 and COD concentrations and loadings. Acetate from pavement deicers contributed another 7%-15% at each site. These findings suggest that management actions in the primary outfall drainage area that target propylene glycol-containing deicers have the greatest potential to decrease BOD5 in airport runoff. This work demonstrates the usefulness of BOD and COD apportionment for identifying the deicing products and locations within an airport to prioritize for reduction or recovery and treatment.