Importance Of Stormwater Drainage

During the past several years there has been a lot of construction at U.S. airports. As usual, everyone is thrilled when they see above-ground improvements. But what they don’t realize is how important the underground infrastructure is to the airport. This article will explore how some airports are handling their stormwater drainage.

For any work at any airport, safety is the most important goal, closely followed by speed. Any project involving the field itself must meet those two requirements. Handling pipe for a stormwater system as large as 60 inches in diameter can be a problem for both speed and safety. Traditional 48-inch diameter reinforced concrete pipe (RCP) is generally 8 feet long and can weigh up to 9,000 pounds.

Many airports have found the solution to be a lighter-weight alternative that still provides the strength and integrity required by the airport, engineers and the U. S. Federal Aviation Administration (FAA).

At the Seattle-Tacoma International Airport in Washington, known as Sea-Tac, rebuilding the 46-year-old center runway wasn’t limited to just the pavement. To comply with strict FAA criteria regarding drainage within runway safety areas, as well as provide environmental enhancements for runoff, the Port of Seattle, operator of the airport, also elected to upgrade the stormwater drainage system.

According to Chris Coulter, P.E. of the engineering firm HNTB (Kansas City, MO), “There were a variety of overlapping requirements that needed to be met. This included assurances that there would be zero ponding within the Runway Safety Area, zero pipe failures, rapid pipe installation, compliance with FAA grant eligibility requirements, and the pipe would be structurally robust for use within the Runway Safety Area.

“Furthermore, the Port has very strict monitoring requirements for stormwater release, so we needed a product that had proven joint reliability,” explained Coulter. “Our aviation group in the Seattle office was contacted to assist with the stormwater conveyance design for the Runway 16C-34C reconstruction project. The system drains the center of the airfield, which encompasses about 145 acres of both airfield pavement and runway safety area.”

Built in 1969, Runway 16C/34C is the oldest of the three runways at the Pacific Northwest’s largest airport and is 9,426 feet long. The surface is made up of more than 4,000 concrete panels, of which 600 have been replaced during the past 20 years to keep the runway operational. The $95 million total reconstruction project was completed in October 2015.

Big job

Sea-Tac is the 13th busiest U.S. airport, serving more than 42 million passengers and handling more than 332,000 metric tons of air cargo in 2015. Twenty-four airlines serve 81 non-stop domestic and 24 international destinations.

“The runway we were reconstructing had outlived its useful life by about 20 years,” said Coulter, who was the QA/QC construction manager for the project. “So it was long overdue for reconstruction and while doing that much work in a short amount of time, the Port wanted to make sure all bases were covered. This meant that the project would include a whole new stormwater conveyance infrastructure to improve drainage from the paved areas, and bring the infield area to a better state for deviation of any aircraft from the paved surfaces. The runway safety area needs to be able to support aircraft whether it’s on pavement or not. Plus, there’s always a concern about bird strikes, which means there’s no standing water allowed. Period. We designed the system to have the capacity for a 24-hour, 100-year storm and used about 3 miles of pipe that would provide the required hydraulic characteristics.”

The stormwater management system used 16,000 linear feet of 12- to 36-inch diameter pipe, most of which was thermoplastic pipe – SaniTite HP pipe – from Advanced Drainage Systems Inc. (ADS). The company designs and manufactures water management components that include corrugated high-density polyethylene (HDPE) pipe.

SaniTite HP pipe’s stiffness and beam strength minimizes deflection and enhances long-term performance. It meets ASTM F2736, ASTM F2764 and exceeds ASTM D3212 for water tightness with dual-gaskets and a banded reinforced bell. Made from an advanced, engineering grade of polypropylene, its designed service life exceeds 100 years. Burial depth at the airport ranged from 4 to 12 feet.

In 2014 the FAA approved polypropylene pipe for subsurface water collection and disposal at civilian airports. The decision to recognize polypropylene pipe as an equal alternative to other materials enables design engineers and contractors to leverage the benefits of the light-weight, cost-effective and durable solution for water collection and removal under airfield pavements. This action followed the FAA approval of HDPE pipe for under pavement use in all airport areas, including deicing pads, runways and taxiways.

Coulter has more than 18 years of experience, with most of that time spent overseeing pipe being put into the ground at Sea-Tac. “We’ve gone away from RCP (reinforced concrete pipe) out here a long time ago,” he stated. “The ADS pipe comes in longer, 20-foot lengths and that also means a lot fewer joints along the entire system.

“One of the things that was very hard with this project was the limited duration we had to accomplish it. We were doing a lot of work in 180 days.
“Obviously, the pipe was a small monetary part, but a large time-saving component. We could not shut down the whole runway at once because aircraft still had to get through the area safely. There wasn’t a whole lot of time to put pipe in the ground as we were concentrating on paving and grading – that’s the job. The pipe work had to go quickly. We use the term ‘set it and forget it.'”

Southern success

In November 2015, the new stormwater drainage system was completed for the Jackson-Medgar Wiley Evers International Airport (JAN) in Jackson, MS. Key to the required installed efficiency of the project was the use of 13,000 feet of thermoplastic pipe in diameters up to 5 feet. The pipe was used to replace RCP that was failing, and also for new runs. The project was designed and overseen by WEI/AJA, a joint venture between Waggoner Engineering and AJA Management & Technical Services, both of Jackson, MS.

“The project was initiated because the airport was having issues maintaining the airfield,” explained Will Pentecost, P.E., manager of the project for WEI/AJA. “The original concrete pipe had reached its design life. It had been in the ground for well over 60 years and was starting to experience joint failures, causing sinkholes which were safety risks. What they had was a safety issue for maintenance personnel, and the sinkholes could have caused damage to an aircraft if it left the runway. There were some large sinkholes on the airfield where they were losing material through the concrete pipe joints. Also, if the drainage could not be maintained, it would allow water to accumulate and be a concern because birds would congregate there and increase the potential for bird strikes.

“We conducted an evaluation of all the storm drainage on the airfield and compiled a report on the condition of each pipe run and inlet. We then designed a project to meet the airport’s current budget and needs at the time, and to immediately address the worst areas.”
The airport, with two runways, encompasses some 3,300 acres and services approximately 20 commercial aircraft daily. It is also home of the 172nd Airlift Wing of the Mississippi Air National Guard.

“Originally the project was designed using reinforced concrete pipe in order to meet FAA specifications,” Pentecost continued. “But I liked the idea of fewer joints. Generally, in concrete pipe that is where we have the most issues, and on that airfield most of the pipe was fairly deep.”
In addition to meeting long-life and other performance criteria, the pipe would need to provide an efficient means of installation. “Speed was the key,” exclaimed Pentecost. “There are only two runways, so shutting down one for an extended period of time to install the pipe was not a favorable option.”

The bid specifications from Waggoner called for ADS HP pipe to be considered as an alternate. “This did help to keep the prices in line with the budget and added competition to the bidding process,” he stated.

ADS HP pipe is a high-performance polypropylene pipe designed and manufactured by the company for gravity-flow storm drainage applications. It couples advanced polypropylene resin technology with a dual-wall profile design for superior performance and durability. The smooth interior wall offers additional strength and flow. HP pipe has a patented, extended, reinforced bell with a polymer composite band and dual gaskets that add an additional factor of safety within each joint. Pipe sections are 20 feet long and can be easily moved with minimal equipment and crew.

“The ADS HP pipe fit (the specifications) and at the same time the FAA was in the process of approving that pipe,” he continued. “It all just kind of fell together. It was after we advertised the project that the FAA approved the ADS HP pipe. So we included it as an alternate by addendum prior to the bid. For Hemphill Construction this was the first time they used it and they seemed to like it because the pipe was easy to handle and install.”
The system was designed by Pentecost and his WEI/AJA team members for a 25-year storm. They reevaluated the hydraulics of the entire field and resized some areas that had added or expanded buildings and parking lots. The watertight pipe ranged from 24 to 60 inches in diameter and traditional precast structures were also used.

The new pipe was installed as the old RCP was being removed, using the same pathway. Burial depth ranged from 4 to 16 feet with the average being 8 to 10 feet. “In the design process, we were going to specify a granular material for bedding,” explained Pentecost, “but ADS preferred to use a select sandy material instead of having granular material to the spring line of the pipe and another backfill material above it. They preferred a homogeneous material all the way around the pipe.”

FOR MORE INFORMATION:
Advanced Drainage Systems Inc.,
(419) 424-8275, ads-pipe.com

Related Articles

    Find articles with similar topics