In the U.S., airports have been making upgrades to terminal facilities to address modernization and technology needs and to accommodate growth. Although the outbreak of COVID-19 and its anticipated short- and long-term implications have slowed these efforts, now is an opportune time to discuss best practices in airport infrastructure planning.

When planning for highly visible renovations and improvements, airports should assess the condition and remaining life expectancy of existing underground infrastructure to support redevelopment. This infrastructure includes critical water, stormwater and sanitary sewer systems. For one reason or another, system-wide wet infrastructure condition and capacity evaluations are not always a high priority during the planning or design phase, which can create problems down the road.

In this first blog in a three-part airport water utilities series, we’ll explore sanitary sewer infrastructure needs.

As the U.S. population continues to grow and the nation is hit with more frequent and intense weather events, the need for upgraded wet infrastructure will be increasingly critical. According to the National Climate Report, in 2019, there were 14 weather and climate events that each caused financial losses exceeding $1 billion—and all but one of those events was a storm or flood. Also last year, the average annual precipitation in the contiguous U.S. was nearly 5 inches above the long-term average.

Airport utility infrastructure often is built based on a patchwork of development over multiple years. In most cases, this results in less-than-optimal system capacity and flow. Airport sanitary sewer infrastructure systems need to be assessed from a maintenance standpoint and should also be evaluated to ensure proper capacity to prevent building backups and/or sewer overflows.

Questions need to be asked, like: What happens when critical systems lose efficiency over time (pumps and/or other mechanical flow diversion structures)? What happens if the pipes aren’t properly maintained? Is the inventory of the assets up to date? And, more importantly, what happens when additional gates/bathrooms/concessions are added as part of airport development? This is where system capacity analyses are needed.

Pipes laid 20 to 30 years ago were not designed to take on the current rate of expansion we’re seeing at some airports. Sanitary sewer system pipes, for example, are typically designed to carry a calculated amount of flow—the peak average daily flow—plus account for the natural occurrence of groundwater infiltration. At airports, in some cases the contribution of first flush diversion systems must be accounted for. Those are systems designed to capture the first flush of rainwater from the tarmac and release it into the sanitary sewers, which uses sewer capacity.

Building the system without factoring in the predictive, added flows of new development could lead to sewer overflows, resulting in environmental fines and emergency repairs that can cost up to eight times more than planned maintenance and initial installation expenses.

Here at Woolpert, we are currently working through a sanitary sewer system mapping and assessment project for an existing client that includes airside, landside and terminal systems. The airport plans to add new hotel and office facilities around the terminal. We deployed a network of flow meters throughout the sanitary system to gather capacity data on the existing system as it operates today. After a three-month period of data collection, we used the data to calibrate a Personal Computer Storm Water Management Model (PCSWMM) in order to evaluate predictive flows from the new development. The PCSWMM is a spatial decision support system for water management modeling.

The results of our capacity analysis assisted the planners in identifying a significant bottleneck within the airport’s sanitary system. Eliminating the bottleneck would mean upsizing over 2,000 LF of existing 24-inch pipe at depths over 20 feet near critical infrastructure prior to the construction of the new facilities. If the system was left untouched, the model predicted that even small, two-year storm events would have led to sewer overflows into nearby environmentally sensitive wetlands, which could have resulted in multi-thousand-dollar fines from the EPA for each event.

Performing the capacity analysis proved to be beneficial as the issue was caught in the planning process, enabling planners to make pre-design decisions on ways to divert flows around the existing system and eliminating the need to upsize the 2,000 LF of 24-inch pipe. This decision ultimately saved the airport significant costs in future environmental fines and emergency repairs, while limiting the risks of operational disruptions.

As airports continue to expand and reconfigure their footprints, underground utilities must be assessed, evaluated and properly designed to ensure above-ground operations flow smoothly, long into the future.

In this series in the coming weeks, we’ll evaluate stormwater solutions for evolving airports and assess airport water main integrity and modeling.