XR-5® Lines Jet Fuel Tank Farm at Denver Airport

XR-5® Lines Jet Fuel Tank Farm at Denver Airport

When Dallas/Fort Worth International Airport opened in the early 1970's, it was termed the airport of the future. That future is now, and the new Denver International Airport is being termed the Airport of the 21st century. Denver International covers an area roughly half the size of the city of Denver and uses concourses as long as 0.6 mile. The $2.7 billion, 53-square-mile airport represents state-of-the-art technology for environmentally conscious air transportation management.

Denver International serves as the hub airport for two commercial carriers, including maintenance and fueling facilities. Six above-ground, welded, steel storage tanks constructed on concrete ringwalls (Figure 1) make up fuel storage. All are equipped with Phase II vapor recovery technology designed to cut VOC emissions by 95 percent. Each tank is 85 feet in diameter with a capacity of more than one million gallons.

The tank farm is located approximately one mile north of the apron areas where refueling occurs. Underground pipelines convey the fuel from the terminal to dispensing points, while fuel is brought to the facility via underground pipelines owned by a private contractor.

Secondary Containment Facilities

A 5-foot-high concrete wall surrounds the terminal complex. This structure provides compliance with 40 CFR 112, which requires a containment volume sufficient to hold contents of the largest tank for a short period during a catastrophic tank failure. Interior dikes, of similar design and construction to the exterior walls (reinforced concrete), are provided as a fire-spread minimization technique, a common practice.

After considering concrete, clay, clay blankets and unreinforced geomembranes, a reinforced synthetic geomembrane was chosen to overlay the concrete walls and containment area floors.

An ethylene copolymer alloy material, XR-5, manufactured by Seaman Corporation, Wooster, Ohio, was used as the fuel barrier membrane.

When selecting the geomembrane, consultants Robert and Co., Atlanta, and Frazier Engineering, Denver, considered its resistance to puncture, long-term contact with leaked Jet A (commercial jet fuel), and thermal expansion/contraction.

The geomembrane lines the floor of the containment areas to prevent slow or massive leaks from damaging subsoil and groundwater. The geomembrane had been previously tested in constant contact with Jet A for six-and-a-half years with no damage or loss of strength.

The geomembrane exhibits permeability to Jet A using ASTM E 96 or ASTM D 814 as low as 0.01 fluid oz./sq.ft./day, or expressed as a Darcy's Law equivalent, 1 x 10-12 cm/sec. Typical equivalent permeability values for water are 1 x 10-8 cm/sec for concrete and as high as 1 x 10-6 cm/sec for compacted clays, under low overburden, if hydrated.

During final facility installation, the geomembrane was covered by a layer of mesh-reinforced concrete as additional mechanical protection, although many similar systems leave the entire geomembrane exposed.

The geomembrane also was installed as enhanced monitoring inside the concrete ringwall areas. The liner was laid under the tank and attached on the ringwall using a standard batten technique, (Figure 2) which allows access under the liner and minimizes stress points.

Because the geomembrane could be prefabricated and withstand the rigors of installation, each 85-foot-diameter geomembrane tank liner was installed as one piece with no field seams in all six above-ground jet fuel tanks.

Monitoring ports allow a continuous check on the integrity of the tank floor. Because of difficulty in repairing a slow leak in the tank floor, the long-term resistance of the geomembrane to the stored product is paramount.

Finally, the piping galleries are lined with the geomembrane (Figure 3). This represents a 109-foot-wide area of more than 100,000 square feet, in which extensive piping systems exit the fuel storage terminal. Piping areas were particularly vulnerable to puncture during installation.

Geomembrane Installation

The complexity of the construction of Denver International is like no other airport. It is the first nonmilitary airport to be programmed totally on CAD. More than 120 design contracts were issued for the entire complex and more than $500,000 was spent on scheduling software.

A secondary containment system with minimal field installation requirements was critical to the overall project schedule. The geomembrane was factory fabricated and installed by Environmental Liners Inc., Cortez, Colorado. Using factory automated radio-frequency welding, single-piece panels up to 95 feet wide and up to 18,000 square feet were manufactured.

Total field seaming requirements were approximately 3,500 linear feet for more than 550,000 square feet of geomembrane. All field seaming was performed using thermal hot-air welding. MQA/CQA requirements included factory sheet, factory seam and field seam destructive testing. Nondestructive testing for both factory and field seams, along with factory lot mechanical properties, were included in the CQA monitoring program. All field seams were tested using the vacuum box technique.

Project Completion

The geomembrane installation was completed in early August 1993. Final acceptance of the membrane occurred immediately after completion.

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