Renovating the Dallas/Ft. Worth Airport Fuels Complex

Take a look at the project that transformed an archaic airport jet fuel storage and distribution system into a world class, state-of-the-art facility—the Dallas/ Fort Worth International Airport. Burns & McDonnell’s John Bagnall, PE, John Park, PE, and Gary Austerman report.

Renovation of the DFW aircraft fueling system began after a 1989 study of several fuel piping failures. This study eventually led to the $25.2 million project, referred to as the DFW Fuels Complex Renovation. This project transformed the archaic airport jet fuel storage and distribution system into a world class, state-of-the-art facility complying with the latest environmental regulations.

Burns & McDonnell Engineering Company (Kansas City, Missouri) was commissioned by the DFW Airline Fuel Committee (a consortium of the major airlines utilizing DFW) to master plan and design the new aircraft fueling system. The DFW International Airport Board managed the two-year construction of the project.

Aging and growing pains
By 1989, the fuel system had experienced several failures of rubber expansion joints and structural failures at mitered joints on the main suction piping headers (also known as the “High Line”). The system operator had to perform hourly inspections of the main piping headers around the clock to avert catastrophic failures that could compromise the jet fuel supply to one of the busiest airports in the world and cause huge environmental problems.

The fueling system was “modeled” using state-of-the-art piping stress and fluid hydraulics software, and a detailed analysis was performed by Burns & McDonnell. The engineer’s study revealed several flaws in the system, including over-pressurization of pump headers, oversized pumps and misapplication of materials. The suction piping was moving so much that pipe supports were physically damaged and the piping joints were being over-stressed, resulting in the pipe failures. Several recommendations, both short-term and long-term, were presented.

In the meantime, the airport, which is the major hub for American Airlines, had begun to experience rapid growth due to the opening of trade with Mexico and South America. Also, the state and federal environmental regulations had changed drastically since the original design in the early 1970s. A comprehensive airport fuel master plan was developed in 1994 to answer all of these concerns, and address growth through the Year 2010. This document became the roadmap to the DFW Fuels Complex Renovation Project. It established the scope, budget and schedule for the project, which was finished in May 1999—on time and under budget.

The renovation involved many environmental protection measures to assure that the system could be operated safely and in compliance with all federal, state and local environmental regulations. Such items as impervious membrane liner systems in tank diked areas, leak-detection provisions, secondary containment beneath the tank bottoms, concrete-curbed containment of all equipment areas and a controlled, segregated stormwater drainage system were included in the design. Ease of operation and maintenance were also taken into account in the design.

Fuel containment
The project design incorporated several means of ensuring that fuel is not released to the surrounding environment. These measures range from construction materials selection and testing to secondary containment of storage tanks, equipment and piping systems.

Storage tanks—Before the renovation, the facility had three 76,000-barrel and six 30,000-barrel aboveground tanks for storing Jet A fuel. The 76,000-barrel tanks were retained, but all of the 30,000-barrel tanks were removed—they were older, inefficient and incompatible with the planned new system. Three new 80,000-barrel tanks were constructed. Total gross capacity of the six tanks now in use is over 19 million gallons. The photograph on this page shows these six tanks.

The six tanks in use are vertical, single-wall, carbon steel, with cone-style roofs. Each tank is approximately 100 feet in diameter by 56 feet high. The three 76,000-barrel tanks are on “ringwall-type” foundations (approximately two-foot wide footing–type foundations in annular ring configurations underneath the tank shells). The tank bottoms are in direct contact with the ground (except at the ringwall).

A design decision, primarily based on construction economics, was made to place the three new tanks on solid concrete mat-type foundations due to the poor soil conditions. Inherently, these concrete mats serve as secondary containment for the tank bottoms. Additional means of providing containment for aboveground tank bottoms (not used at the DFW project) include installing an impermeable membrane liner system beneath the tank bottom or installing an actual double-bottom tank.

All six tanks are equipped with internal floating roofs, which ride on the fuel surface (see Photo 1). These roofs have primary and secondary “wiper” seals in contact with the tank shell to maintain a vapor seal and dramatically reduce evaporative fuel emissions into the environment. A study during design revealed that, without these internal floating roofs, approximately ten times as much fuel would evaporate and be released into the environment.

Underground tanks and vessels—These include a waste fuel/water storage tank, a fuel reclaim tank and two oil/water separators. The waste tank stores an unusable fuel/water mix, which originates from sumping of tanks and fuel filters, fuel pipe low point drains and fuel valve pits and vaults located throughout the fueling system.

Photo 1: Underside of storage tank’s internal floating roof, with support legs and 24-inch fuel suction pipe. In upper foreground is roof floatation pontoon. Courtesy of Burns & McDonnell

The fuel reclaim tank (see Photo 2) receives fuel from automatic air vents and thermal/pressure relief valves at the into-hydrant pumping station located within the fuels complex. Fourteen 150-horsepower pumps, filter separator vessels and associated valves and piping are located at this pumping station.

Photo 2: Curbed concrete spill containment above the underground jet fuel reclaim tank. Courtesy of Burns & McDonnell

The reclaimed Jet A fuel is used as an energy source for the facility’s emergency power generator, heating boiler for the operations and maintenance building and for fueling diesel-driven trucks, which can run on Jet A. Two 10,000-gallon oil/water separators process potentially contaminated stormwater runoff from the fuel equipment and tank diked containment areas as well as from fuel truck parking positions at the facility.

Tank diked areas
Originally, the three 76,000-barrel fuel storage tanks were each located in separate adjoining diked containment areas. However, none of the individual containment areas was large enough to contain the contents of a full tank in the event of a leak or tank failure, so a berm spillway had been constructed between the individual diked areas. The diked areas consisted of earthen berm walls with concrete cover and clay/gravel-covered floors. The concrete cover on the earthen berm walls had failed in many locations and the integrity of the clay/gravel floors was questionable.

The renovation included modifying the diked containment areas to consist of three adjoining areas, each with one 76,000-barrel tank and one 80,000-barrel tank. Each diked containment area will contain a potential spill equal to the largest tank volume plus additional capacity to contain precipitation from a 25-year, 24-hour rainfall. (See Photo 3).

Photo 3: Finished tank diked area with gravel over impermeable membrane liner (foreground) and concrete-covered earthen berm (center). Courtesy of Burns & McDonnell

The original earthen berm dike walls were extended and the new containment areas were lined with an impervious membrane liner material. This liner material was extended over the tops of the earthen berm walls. The walls were then covered with concrete to maintain stability. (See Photo 4).

Photo 4: Finished concrete cover over earthen berm wall and impermeable membrane liner. Courtesy of Burns & McDonnell

A cellular confinement system or “geoweb” was used on the wall slopes to facilitate pouring of the concrete cover and allow a uniform concrete thickness to be maintained. The “geoweb” consists of a plastic lattice framework with individual diamond-shaped pockets approximately six inches x six inches x four inches deep. The concrete was poured into these pockets and tooled smooth on the upper surface.

The impermeable membrane liner on the floors of the diked areas was covered with at least four inches of gravel. A protective felt or “geofabric” was installed between the liner and gravel to prevent puncturing or abrading the liner.

Penetration liners for concrete tank foundations, pipe support and equipment foundations, pipe/conduit risers and other items were sealed with liner skirts or boots with stainless steel anchors and clamps (see Photo 5).

Photo 5: Partially completed diked area with impermeable membrane liner and piping penetrations (foreground). Complete diked area is in background. Courtesy of Burns & McDonnell

Equipment areas
All fueling equipment and piping manifold areas with bolted or screwed pipe connections are equipped with curbed concrete slabs to contain minor spills and potentially contaminated stormwater runoff. The larger concrete pads have trenches that drain to one of the two oil/water separators. The smaller concrete-curbed areas are equipped with a “daylight” drain through the curb with a shutoff valve. In these areas, the facility operator can verify that the collected stormwater following a rain is clean before opening the “daylight” valve and draining the water to the adjacent site.

Underground piping systems
Buried piping systems at the site include pressurized fuel piping, gravity drain waste fuel piping, storm drainage piping and fire-protection foam and water piping. All steel piping (fuel and fire protection) is externally coated and protected by an impressed current cathodic protection system. The underground pressurized fuel piping has butt-welded joints that were 100 percent radiographically inspected (x-rayed), which is typical for aircraft fueling systems. The smaller bore gravity drain waste fuel piping is double-wall, welded steel (one-inch diameter) within fiberglass containment pipe (three-inch diameter).

Both the pressurized fuel pipe and gravity drain waste fuel pipe were subjected to a pressure test following installation. Storm drainage piping serving equipment and diked containment areas, which could be subjected to a jet fuel spill, is heavy-wall PVC with Jet A-resistant solvent-welded joints.

Leak detection
Leak-detection means were provided in the various system components, including the new storage tanks, underground tanks/vessels and buried fuel piping. The new 80,000-barrel storage tanks are on full concrete mat-type foundations as described earlier. These foundations (and the steel tank bottoms) are sloped to the tank center with radial grooves cut in the concrete to allow drainage to this location. A sump is provided in the foundation at the tank center with a drainage pipe extended to outside the periphery of the tank. A visual monitoring or inspection port connected to this drainage pipe allows the system operator to periodically check for tank bottom leaks.

The three older 76,000-barrel tanks have the impervious membrane liner system attached to them in a way that precludes fuel from seeping underneath the tanks between the ringwall-type foundations and the tank bottoms in the event that a spill were to occur and fuel were to “pond” in the diked containment area to a level above the tank bottoms.

The underground fuel reclaim tank, waste fuel tank and oil/water separators are all of double-wall construction with leak-detection probes installed in the interstitial space between the inner and outer tank shells to detect a leak and alarm the central fuel system control room. The double-wall gravity drain waste fuel piping is similarly equipped, with leak-detection probes installed at buried piping system low points, which can alarm the control room personnel. All of the buried main fuel piping was installed with provisions for periodic pressure testing and the potential addition of a future pressure/volume type leak-detection system.

No leak-detection is mandated for most aircraft fueling hydrant systems—only periodic pressure testing is required. Requirements vary from state to state. Due to the extensive piping network, dynamic nature and transient operation of these systems (varying flows and pressures) and the fact that they have very little downtime throughout a 24-hour day, it has been considered extremely difficult to economically and practically implement available leak detection methodologies for these systems. However, studies and research have been underway to determine the most feasible approach to airport fuel system leak detection.

The use of double block and bleed valves allows positive isolation of buried piping segments for pressure-type integrity testing. These valves have dual seals with a bleed port between them, which can be opened and drained to verify seal integrity. If fuel or product continues to drain from the bleed port while the piping is under pressure, it is an indication that the valve is not holding and thus a piping pressure test would not be accurate. As part of the DFW renovation project, these double block and bleed valves have been installed to permit positive isolation and testing of buried piping segments.

Segregated storm drainage system
Storm water drainage for the renovated facility includes runoff from equipment and tank diked containment areas and the site in general. The storm drainage piping from tank diked containment areas is normally closed by valves at locations immediately outside the individual containment areas.

Following a rain, and verification by the system operator that the accumulated water is satisfactory for discharge, these valves are opened and contained areas allowed to drain. Stormwater from facility equipment areas, tank diked areas and the tank truck/refueler vehicle parking area, which could contain fuel, enters an underground gravity drainage system routed to the new oil/water separators. Processed water effluent leaving the oil/water separators is pumped into the airport industrial waste sewer system for final treatment prior to release into the surrounding natural watershed.

Stormwater from the general site, including the general vehicle parking areas, is collected by area inlets and conveyed by an underground gravity drainage system to a new controlled release detention basin. The stormwater retention basin has an impervious membrane liner on its floor and a concrete cover on its side slopes. The concrete on the side slopes was installed with a cellular confinement system similar to the tank diked containment area berm walls, described earlier.

Following verification by the system operator that no hydrocarbon sheen exists on the basin content’s surface, this water effluent is allowed to discharge to the original storm drainage outfall into the airport storm drainage channel. This controlled, segregated drainage system assures the cleanliness and quality of the DFW Fuels Complex stormwater discharge and meets or exceeds all of the current relevant codes and regulations.

Environmental vigilance
The day-to-day operation of the DFW Fuel System Complex involves assuring that the surrounding environment is protected from contamination. The facility must have an SPCC (Spill Prevention Control and Countermeasures) plan in place. All operators are made aware of the procedures to be followed in the event of a mishap.

The oil/water separators operate automatically, but must be monitored and maintained on an ongoing basis. Effluent from the oil water separators is sampled and analyzed frequently to ensure satisfactory operation of these units. As the waste or reclaim tank capacity is reached or the oil/water separators’ held oil volume increases, unusable fuel/water is hauled offsite for disposal. Reclaimed fuel is transferred. The entire fuels complex is visually inspected daily for satisfactory condition.

Alarms are announced and responded to through the 24-hour manned, central fuel system control room. These alarms range from tank high level and oil/water separator malfunction, to detection of fluid at a leak-detection probe. With the secondary spill containment, the leak-detection provisions, the segregated storm drainage system and the operating practices in place, the result is a safeguarded, “environmentally friendly” facility. This is in stark contrast to the facility’s previous beleaguered condition.

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