Evaluating the impacts of aircraft deicers in runoff from General Mitchell International Airport, Milwaukee, Wis.

Science Center Objects

Chemicals used to deice planes at General Mitchell International Airport in Milwaukee may be entering nearby streams in concentrations that may be harmful to aquatic life. This project will investigate the toxicity of decing chemicals, evaluate their impact on receiving streams, and assess changes in water quality in response to the implementation of deicer management at General Mitchell Airport.

Photgraph of USGS employee surveying snowbanks at General Mitchell International Airport

The USGS surveyed snowbanks at General Mitchell International Airport during an investigation of the effects of aircraft deicing chemicals in snow runoff.

Problem

Milwaukee County is involved in an effort to reduce runoff of deicing chemicals from General Mitchell International Airport (GMIA) to Wilson Park Creek. Ethylene glycol, propylene glycol, and acetate-based deicers are used during cold weather periods for purposes of deicing and antiicing aircraft and pavement. Glycol, acetate, and deicer additives can reach concentrations in receiving streams that may be harmful to aquatic life.

Objectives

The overall goals of the project are to evaluate changes in water quality in Wilson Park Creek due to implementation of deicer management at GMIA, to investigate chemicals causing toxicity to aquatic organisms, to evaluate the impact of organic deicer loading to receiving streams, and to fulfill obligations stated in the Wisconsin Department of Natural Resources (WDNR) stormwater permit for GMIA. Specific objectives are as follows: (1) monitor surface water at four sites in the Wilson Park Creek watershed and one site in the Oak Creek watershed for water quality and flow during dry weather and runoff conditions. This monitoring is to be conducted before and after implementation of deicer management, (2) determine changes in water quality and toxicity levels in Wilson Park Creek due to implementation of deicer management, (3) conduct investigations to identify additives in deicer and antiicer formulations that are responsible for toxicity to aquatic organisms in the receiving stream, (4) investigate controlling factors in the formation of biofilms downstream from deicer discharges, and (5) develop a reliable sensor system for in-stream assessment of deicer content.

Approach

Flow is measured and samples are collected at one site upstream from airport runoff and four sites downstream. Assessments of water quality are made on a yearly basis. Comparisons between pre- and post-management data are made as the deicer management system at GMIA evolves to quantify the level of changes in water quality. Aquatic toxicity of deicers is evaluated as new formulations come to market, the formation of biofilms in the receiving water is evaluated, optical properties of water are being used to estimate deicer content in water in-situ, and sampling is conducted at the five monitoring sites to determine the level of deicer components in the receiving stream.

Photo showing benthic biofilm growing in stream receiving airport deicer and anti-icer runoff

Benthic biofilm growing in a stream that receives airport deicer and anti-icer runoff.

Progress

Deicer runoff management is evolving each year at GMIA based on resources and available technology. An extensive runoff monitoring program has been in place since November 1996 that allows for evaluation of the effectiveness of management practices. Flow, dissolved oxygen, water temperature, and rainfall are being monitored continuously. Water-quality constituents are sampled selectively during deicer application events, baseflow, and a summer rainfall event each year. Glycol, biochemical oxygen demand, deicer additives, chloride, optical properties of water, selected nutrients, and suspended solids analyses are being conducted. Microtox and bioassay analyses are being conducted for toxicity assessment. Snow banks within the airport have been monitored for four years to determine the quantity of deicer stored within the snow banks. Deicer formulations have been investigated to determine the additives responsible for aquatic toxicity. Biofilms have been investigated to better understand controlling factors in the formation and growth of filamentous bacteria and other organisms on the streambed in the receiving stream. Optical properties of water (fluorescence and absorbance) have been investigated as low-cost surrogates for estimating deicer concentrations in streams. Optical sensors are being optimized for field application.

Plans

Continued monitoring and evaluation of changes in deicer concentrations will be conducted as decier management practices continue to evolve. An optical sensor will be installed in a permanent station at the primary outfall for realtime estimation of deicer content in the stream. A manuscript will be written documenting biofilm prevalence and factors that influence the growth of biofilms downstream from the airport. A manuscript will be written on the use of optical properties of dyes in deicers that allow for estimation of deicer content in water.