Storm Water Capture and Reuse at San Diego International Airport

Storm Water Capture and Reuse at San Diego International Airport

The San Diego International Airport.

Over the past few years, San Diego International Airport has implemented several water reuse and conservation programs that are saving potable water, reducing runoff, and protecting the environment. These projects have been recognized with several Environmental Excellence Awards from the Industrial Environmental Association. In this interview, Richard Gilb, one of the airport’s managers for environmental affairs, tells Municipal Water Leader about the details of its ambitious projects.

Municipal Water Leader: Please tell us about your background and how you came to be in your current position.

Richard Gilb: I have a bachelor of science in geology from the University of Cincinnati and a master’s in public health from San Diego State University with an emphasis in environmental health. My master’s thesis involved storm water pollution. I’ve been working with storm water since the early 1990s, and I have 30 years of experience with storm water, solid waste, hazardous materials, and site assessment and mitigation. I spent 10 years with the County of San Diego Department of Environmental Health and 2 years with the Port of San Diego. For the last 17 years, I’ve been a manager at the airport, managing all aspects of regulatory compliance, whether related to air, water, waste, or endangered species.

Municipal Water Leader: Please tell us about San Diego International Airport.

Richard Gilb: San Diego International Airport is about a mile north of downtown San Diego and sits on 661 acres— just over a square mile. It is not directly on the San Diego Bay, but it’s across the street from it. We have one runway, which is the busiest single runway in the United States. We have 51 gates and had over 25 million passengers last year. Before the COVID‐19 pandemic, we had aircraft landing or taking off about every 3 minutes, and 68,000 passengers passing through the airport every day.

The San Diego County Regional Airport Authority, which owns and operations the airport, has a little more than 400 employees, while around 9,000 additional people work for airlines, concessions, or other operations at the airport. We drive a $12 billion local economic engine. (These numbers are all prepandemic.)

We have about 20 acres of endangered species habitat on our land. We also have the first and only Leadership in Energy and Environmental Design (LEED) Platinum airport terminal in the world.

Municipal Water Leader: Where does the airport get its potable and nonpotable water, and where does it send its wastewater?

Richard Gilb: Almost all the potable water in San Diego is imported; only 17 percent is local. All the water the airport uses is potable, but approximately 80 percent of it is used for nonpotable purposes. There is no recycled water source in the vicinity of the airport. That’s why we’re trying to change our operations a little. After the California drought began in 2015, we wrote a water stewardship plan, which is now part of our sustainability efforts. Some of the high-level goals in that plan are to eliminate storm water discharges by 2035 and to use no potable water for nonpotable applications by 2035. By eliminating storm water discharges, we mean that we’ll capture the water from 2‐year storm events, which for us is about a half inch of rain in 24 hours. Capturing and reusing storm water will help us eliminate the use of potable water for nonpotable purposes.

Our wastewater goes to the Metropolitan Wastewater District, an arm of the City of San Diego, which performs advanced primary treatment before it discharges the treated water into the ocean through a deep-water outfall.

Municipal Water Leader: Please tell us about the storm water control challenges the airport faces and the actions it has taken to address the issue.

Richard Gilb: A couple of things were coming together all at once in 2016. The drought was still hitting us, and there were some new permitting requirements under our municipal separate storm sewer systems (MS4) permit that required the assessment of water quality impacts through a hierarchy of treatment controls for storm water discharges from new developments. We were also about to build a new parking structure. According to the permit, we had to keep storm water on site, which means that we needed to infiltrate it or capture and reuse it.

Infiltration is not ideal for us because the whole airport sits on a mudflat that has been filled in with bay mud, and its infiltration rates are poor. We decided that we might be able to pull off capture and reuse with this new parking structure. In order to capture the water from a 2‐year storm on a 7.6‐acre parking structure, we needed about 100,000 gallons of storage. There were going to be storm drainpipes under the structure itself anyway, and by increasing their size from 24 inches in diameter to 36, we were able to create that volume of storage.

This system was commissioned in 2018 when the parking structure opened. If we get an average amount of rain, we should be able to capture 2 million gallons of water a year. The storm water runoff that requires treatment is initially held behind a weir within the storm drain system. Larger storms will overtop the weir, but the water from small storms is held behind it and is pumped into an oil/water separator. Then it goes into a wet well to make the pumping a little more efficient. It goes through a series of high-rate media filters; is treated with ultraviolet light; is stored in an 8,500‐gallon tank; and then is pumped to a central utility plant, where it’s used in the cooling towers for our heating, ventilation, and air conditioning system. Those cooling towers use an average of 35,000 gallons of city potable water every day to cool the terminals. The central utility plant uses an average of 16 million gallons a year. If we can use reused rainwater for that, we can save 2 million gallons of potable water a year.

One of the other benefits of capturing and reusing rainwater on site is that it helps avoid getting wrapped up in any total maximum daily loads (TMDLs) applicable to San Diego Bay. We are not currently facing any TMDLs, and we want to keep it that way.

The San Diego International Airport and the San Diego Bay, seen from above.

Once we installed water capture and reuse infrastructure in this parking structure, we started drawing up a master plan for storm water capture. We worked with the engineering firm AECOM, using the U.S. Environmental Protection Agency’s (EPA) Storm Water Management Model, and tried to identify the areas of the airport facility from which we could efficiently and cost-effectively capture and reuse rainwater. We decided that we were able to build a system that could capture rainwater from approximately 200 of the 661 total acres of the airport’s footprint.

The system that was proposed for the 200 acres involved two large underground basins or cisterns, initially envisioned at 3 million gallons each, and an open-bottom infiltration area that would have covered about 10 acres and given us another 3 million gallons’ worth of storage. Even though our infiltration rates are poor, we do have some infiltration capabilities, particularly if water is spread over a large enough area over a long enough time period.

We are now planning to build a new terminal, and because we’re a highly developed facility with little free space, we need to first get some other structures out of the way. These relocated facilities are subject to the MS4 permit’s requirement that new developments need to capture or infiltrate storm water on site. To comply with the regulations, we are about to complete the construction of the first 3‐million-gallon cistern, which is located on the north side of the airport. Eighty acres of airport property should drain into it in its final form. We hope to use the water it captures to wash cars at the rental car facility right across the street, where approximately 4,000 cars are washed every day (the figure comes from before the pandemic).

The second 3‐million-gallon system will be on the south side, near where we want to build the new terminal. That water will be pumped to the same treatment system at the central plant described earlier. The treatment system is oversized, so it can handle more water. As I mentioned,

The San Diego International Airport has the busiest single runway in the United States.

we’re currently only getting about 2 million gallons of rainwater a year off the parking structure’s capture and reuse system, and the central plant is consuming approximately 16 million gallons of potable water annually, so we want to increase the amount of captured storm water being used to offset the potable water. We’re pretty sure we can increase it by at least 5 million gallons per year. We’re also thinking that we’d like to double plumb the new terminal so that we can use some of this water to flush toilets.

That’s the grand scheme for storm water. There are some issues in front of us. Currently, there is no authority that is willing give us a permit to use captured storm water to flush toilets, but the State of California is moving in the direction of allowing these types of uses. Without a new permitting process to flush toilets, we would need to carry out E. coli testing on an almost-daily basis just to flush toilets with storm water, which would probably be cost prohibitive.

One of our sustainability measures related to greenhouse gas emissions is that, when a plane pulls up to the gate, it plugs into our power system so that it doesn’t have to run its own little jet-fuel-powered engine on the back of the plane. We also provide air conditioning that can be pumped into the plane. The air conditioning units we use to do this are fairly large. They hang off the jet bridges and create condensate. During the 2015 drought, we realized that we could capture this condensate, so we took a hose and a pump and ran it into a 55‐gallon drum. We now use 275‐gallon totes to capture condensate from 16 jet bridges (down from 19 before the pandemic). Most of the condensate is used to wash sidewalks, but we’ve also developed wash facilities to clean trash cans or floor mats. Once it gets too greasy, the water is discharged to the sanitary sewer. The current system is labor intensive, since we have to move the water from the drums and totes after capturing it. We hope that, in our new terminal, we can come up with a better system.

The condensate water from the air conditioning units is extremely pure. Last August, we worked with Ballast Point Brewing to make SAN Test Pilot, a beer brewed with condensate that was collected on airport property. It was sold at Ballast Point’s locations in December 2019.

Municipal Water Leader: Is flooding from storm surge also a problem for the airport?

Richard Gilb: Not really. We’re subject to the California Coastal Commission, which requires all new development to consider the potential effects of climate change. Through our climate resiliency plan, which is part of our sustainability management program, we require all our critical infrastructure to be at an elevation of 14 feet above sea level. This applies to generators and any sort of electrical connection. We have looked at flooding at the airport based on what the state is predicting by the year 2100— approximately 5 feet of sea-level rise—and we think we can manage most of the expected flooding issues. Localized flooding will likely close the roads to the airport before affecting the facilities of the airport itself. Since we’re not right on the San Diego Bay, we’re trying to collaborate with the City of San Diego, the Port of San Diego, and even the Navy on long-term efforts. We are all in this together.

Municipal Water Leader: Is there any concern about precipitation runoff from the airport that contains jet fuel or other specific pollutants?

Richard Gilb: Yes. Because we’ve been subject to the MS4 permit since the mid-1990s and are also subject to the state general industrial permit—much like the EPA’s multisector permit—we have to sample at least four storm events at every outfall every year. Over the last 20 years, we have realized that our main issues concern heavy metals like copper and zinc. Those materials come off the tires and brake pads of aircraft in the touchdown zone on the runway and from all the vehicles that are moving around. We also have a lot of chain link fencing around the facility, which sheds metals as well. We’re trying to eventually retrofit it with vinyl or enamel covering to help with this problem.

Jet fuel is not really an issue, even though we generally have half a million gallons of jet fuel moving around the airfield every day (the figure comes from before the pandemic). We’ve only had three major spills in the past 25 years. Only one airline at our airport does any deicing, and it is a fairly minor process—not like the major deicing efforts needed at other airports. It’s done right at the gate with a device similar to those used to spray pesticides. The excess chemicals are swept up with a little zamboni.

Municipal Water Leader: What is the motivation for reducing the nonpotable use of potable water? Is that primarily to reduce the cost of purchasing water, or are there environmental reasons?

Richard Gilb: It is to be good environmental stewards.

Municipal Water Leader: When did the airport establish a formal sustainability policy, and why?

Richard Gilb: It was first adopted by the airport authority board in 2008 and has been tweaked slightly since then. The board and my department pushed for the policy because sustainability is a way to future-proof yourself from regulations. Our policy states that all our new structures have to be at least LEED Silver certified, but every project we’ve done so far has been LEED Gold or better.

Municipal Water Leader: What advice do you have for other airports around the nation that are dealing with similar storm water, conservation, and water reuse issues?

Richard Gilb: Take the time to come up with a plan for what you think you can do and what you would like to do. That certainly helped us. We try to sit down at least once every 4 months and see where we are. It helps to get in front of our engineers and design teams and remind them that we have these goals. There’s a lot of discussion between airports, so just keep your ear to the ground. If somebody else is doing it, there’s no reason why you shouldn’t at least evaluate it.

Richard Gilb is the San Diego International Airport’s manager for planning and environmental affairs. He can be contacted at rgilb@san.org.