Research Projects

Facilitating a Better Understanding of Water Quality of Airside Stormwater Runoff at Airports

Assigned to Jennifer Martin
Last Edited by Jennifer Martin

In accordance with the Clean Water Act, airports must responsibly manage stormwater runoff through a combination of industrial stormwater permitting, MS4 permitting, and state/local post-construction stormwater requirements for development. Permitting requirements for airports can vary widely across the nation, with some airports also subject to municipal stormwater fees. These fees may be reduced via credits for effective on-site management (quantity and quality). Given that water quality is a significant component of these responsibilities, a firm understanding of stormwater quality from various airport land uses will help airports manage permitting requirements and obtaining stormwater fee credits.

Unlike highways, which have had extensive research related to stormwater runoff quality, there are few studies on stormwater runoff quality from various portions and layouts off existing airports and airfields. Yet runoff from runways and taxiways is often compared to that from highways or other high intensity uses, which doesn't appear to be appropriate, especially at airports that do not deice runways and taxiways (due to either climate or airport classification). Preliminary studies indicate that runoff from runways and taxiways is cleaner than most regulatory staff realize, due in part to natural treatment occurring next to these areas and may actually function as Low Impact Development (LID). Runways and taxiways are often flanked by large, grassed areas that help mitigate runoff volume and quality before it leaves the airport property. More data is needed to evaluate the hypothesis that airports can effectively treat runoff with grassed areas and vegetated swales before the runoff leaves the airport property. A positive conclusion could mean additional treatment or best management practices (BMPs) are not required for these airports and, furthermore, that stormwater fee credits may be appropriate based on runoff reduction from these features.

Background (Describe the current situation or problem in the industry, and how your idea would address it.)

It is thought that with more data, a case can be made that the existing airside configuration of many airports containing large grassed areas and vegetated swales could function as green stormwater infrastructure (GSI) features for runoff and pollutant reduction. This, however, may depend on the types of development and activities on airside areas and what percentage of the airfield is pervious surface. More information about GSI/LID can be found here: https://www.epa.gov/sites/production/files/2015-09/documents/bbfs1benefits.pdf . The nature of an airport facility provides a great amount of pervious surface in the form of grassy swales and naturally occurring vegetated filter strips alongside runways and taxiways. The overland flow of runoff on the airside, coupled with these large vegetated areas, is ideal for infiltration.
Currently, airports are sometimes characterized as polluting industrial facilities by environmental regulatory agencies who may compare their airside runoff quality to that of highways or other high-volume roadways, resulting in unnecessary permitting requirements. If data supports the hypothesis that the airside of most airports can be considered GSI, it could potentially save many airports in design, construction and maintenance costs for stormwater best management practices (BMPs), and potentially also result in stormwater credits. However, there is little information to support an airport's contention that airside areas should be considered GSI facilities. Furthermore, many GA airports and small and non-hub airports don't have the expertise or resources to determine this.
The primary goals of this project will be to 1) identify and compile any existing data on runoff quality from various airport land uses and at airports representing different locations and sizes/types, 2) obtain and compile new data on runoff quality at airports to fill data gaps, and 3) compare these data to other typically understood land uses.
An additional benefit of such a data set is that it will support stormwater management decisions at airports. As green stormwater infrastructure becomes increasingly popular, data on stormwater quality (as well as quantity) will help airports determine whether and where GSI BMPs will be appropriate. Conversely, if both water quality and quantity are demonstrably controlled, airports may be able to avoid unnecessary infrastructure projects. Some airports may already have features of their facilities and stormwater management that are effectively GSI. An obvious example is the potential for grassed areas adjacent to runways to count as filter strips either as they are or with modification. Another example is a swale where the design and/or native soils allow for infiltration functioning as GSI even if the airport does not specifically plan for it. Recognizing these structures and having supporting data on runoff quality will be valuable when talking with permitting agencies and stormwater utilities.
This project will dovetail with and support airports in conjunction with previous ACRP projects 02-62 (Green Stormwater Infrastructure Strategies for Airports) and 02-68 (Strategies for Reducing Local Stormwater Utility Fees for Airports).

Objective (What is the desired product or result that will help the airport industry?)

A guidebook that discusses the differences and similarities of pollutants contained in stormwater runoff at airside portions of airports versus highways and GSI from non-industrial areas will be developed. The guidebook would also review differences in data between larger and smaller airports, airports with differing levels of pervious surface, and airports in different regions to define locations and situations where existing vegetated airport areas are functioning as GSI/LID to provide a guideline to airports of what areas may qualify as GSI/LID. This guidebook would be used by airport engineering professionals in order to communicate the nature of the airport environment to environmental permitting agencies as an educational tool when planning for stormwater runoff management at airports.

Approach (Describe in general terms the steps you think are needed to achieve the objective.)

• Research to determine what studies have already been done and what data is available currently
• Identification of gaps in data (US geographic locations not represented, certain pollutants not tested for, types of airport land uses that have been monitored in the past being limited, poor distribution between large and small airports, etc.)
• Identification of airports whose staff may be willing to monitor runoff and development and implementation of sampling at a series of airports to collect data for typical easily measured stormwater pollutants (Total Suspended Solids, Total Phosphorus, Nitrogen, Oil and Grease, Conductivity, pH, etc.)
• Compilation and review/presentation of data
• Create general guidance to assess an airport's likeliness to align with GSI/LID principles (infrastructure, users, acreage, etc…) and how to communicate this to permitting officials.

Cost Estimate and Backup (Provide a cost estimate and support for how you arrived at the estimate.)

Similar research done in a state aviation department that included monitoring, testing, and date collection, analysis and reporting for three general aviation airports over 18 months entailed a contract for $220,000. Considering logistics of equipment and staff, it might be wise to consider phases for this research. A first phase of research and reporting could be set at $500,000. The first phase would help inform subsequent phases for monitoring. A final phase could analyze data collected in prior phases and produce the guidance.

Related Research - List related ACRP and other industry research; describe gaps (see link to Research Roadmaps above), and describe how your idea would address these gaps. This is a critical element of a synthesis topic submission.

The following research is complete or in progress for airport stormwater:

ACRP 02-19
Winter Design Storm Factors for Airport Stormwater Management (Final)
ACRP 02-29
Guidance for Treatment of Deicing-Impacted Airport Stormwater (Final)
ACRP 02-61
Airport Stormwater Management Electronic Resource Library and Training Materials (Final)
ACRP 02-62
Green Stormwater Infrastructure Strategies for Airports (Final)
ACRP 02-68
Strategies for Reducing Local Stormwater Utility Fees for Airports (Final)
ACRP 02-71
Guidebook and Decision Tool for Managing Airport Stormwater Containing Deicers (Final)
ACRP 02-75
Benefit-Cost Analyses Guidebook for Airport Stormwater (Final)
ACRP 02-87
Determining Airfield Pavement Deicer and Anti-Icer Contributions to Airport Stormwater (Active)
ACRP 02-96
Update ACRP Report 99: Guidance for Treatment of Airport Stormwater Containing Deicers (Anticipated)
ACRP 09-08
Balancing Airport Stormwater and Wildlife Hazard Management: Analysis Tools and Guidance (Final)

There is considerable existing research devoted to airport stormwater management, however none that has produced actual data of stormwater runoff at airports from naturally vegetated buffer areas of the airport.
NCHRP 25-25/Task 53 -Stormwater Treatment with Vegetated Buffers http://onlinepubs.trb.org/onlinepubs/nchrp/docs/NCHRP25-25(53)_FR.pdf is the most similar study done under the TRB umbrella, but conclusions and data are focused on highway environments.
A research gap exists for a discussion of pollutant removal performance of the naturally vegetated areas surrounding runways, taxiways, and aprons at airports of all sizes and capacities.

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Idea No. 286