Erosion and Sediment Control on Atlanta's Hartsfield International Airport Project
by Luke Snyder
One of the five "Borrow Pits" providing over 27 million cubic yards of fill material for the 5th runway embankment.
Hartsfield International Atlanta Airport has been the "world's busiest" airport for the past four years. Last year alone, a recorded 76.8 million passengers traveled via Hartsfield and approximately 80 million passengers are expected to pass through the airport in 2003. That is over 200,000 passengers a day. This increase in traveler growth is one of the reasons Hartsfield International Atlanta Airport is currently undertaking a ten-year, 5.4 billion dollar expansion project.
This master project, called the "Hartsfield Developing Program-Focus On the Future" includes a new Fifth Runway, an International Terminal, a Consolidated Car Rental facility, a proposed south Terminal, and enhanced infrastructure. These additions are designed to accommodate the airport's future growth and reduce air pollution by significantly decreasing ground delays and holding patterns in the air. Delays experienced in Atlanta often cause an Air Traffic Control ripple effect across the country, something the City of Atlanta, Department of Aviation would like to minimize.
To reduce these delays, Hartsfield Airport hired 5R Contractors, LLC to construct a 9,000 foot landing strip. This Fifth Runway is divided into five phases. Phases I and II began on May 15, 2002 and are expected to end in September of 2005. These first two phases are called "The Embankment Project" and require placement of 27 million cubic yards of fill material to support the eventual runway. To accomplish this without damaging the surrounding roadways, generating unnecessary pollution or affecting local transportation, 5R Contractors designed and built a five and a half mile conveyor belt system. The conveyor moves 60,000 cubic yards of soil per shift from five different "Borrow pits" or source locations within the area. First, soil and rock are excavated and loaded into a huge rock crushing machine that feeds directly onto the conveyor system. Then, the soil is transported from the "Borrow Pits" to the embankment site. Here, the conveyor belt distributes the material into four large hoppers. These hoppers drop the soil into dump trucks that precisely relocate the fill material to be manipulated and compacted by the construction equipment. A total of 300 employees are working toward the completion of phases I and II. Phases III, IV, and V will involve pouring the concrete for the runway.
A job of this magnitude, linking so many people and equipment, is bound to have complications. Frank Crumbley, Business Manager for 5R Contractors, says one of the biggest problems is coordination with other projects. The "Embankment Project" is just one of a dozen projects presently taking place. Constant communication between projects is very important; otherwise, valuable time is wasted as a result of overlapping.
Excessive rain has been another time consuming obstacle 5R has had to face. When excavating the runway embankment, obtaining maximum compaction is a priority. To achieve acceptable compaction, the level of moisture in the soil must be plus or minus five percent of the optimum. Therefore, 5R has spent a lot of time disking and adding lime to dry out the fill material before it is incorporated into the embankment.
Lots of rain can also create soil erosion problems. "Erosion control and the environment are important to 5R and the City of Atlanta," says Frank Crumbley. So far, the Hartsfield Developing Program has impacted over 630 acres and diverted two small creeks around the site. Because such large quantities of soil are being moved on the land, the potential for sediment contamination is great. As a result, 5R Contractors have subcontracted WCC Landscape Maintenance to implement numerous erosion control systems.
One hundred and forty thousand linear feet of wire-backed silt fence is to be placed around the perimeter and outer edges of most disturbed areas on this massive project to protect the surrounding environment from soil runoff. The silt fence consists of four-foot metal posts which support a polypropylene fabric, reinforced by 12 gauge wire. This barrier is trenched eight to ten inches into the ground and acts as a filter to collect fine soil particles yet allowing water to slowly pass through.
Another erosion control measure used on this project is slope drains. A slope drain consists of an earthen diversion dike, plastic corrugated pipe manufactured by Crumpler Plastic Pipe, Inc., and a rock spillway. The dike is constructed at the top of a slope and rises a minimum of 1.5 feet above the natural ground creating a containment berm. The berm prevents water from the higher elevated area from spilling over and eroding the slope. The plastic pipe conveys the confined runoff to a lower elevation and onto a spillway which dissipates the water. About 10,000 linear feet of slope drains will be installed to control erosion. In some places, the slope drains feed into detention basins. The detention basins are designed to collect water from the surrounding area and to receive soil deposition. As water runs into the basin, soil settles to the bottom and the clean water on top flows to a natural system. When the project is finished, the basins will serve as collectors of heavy rainfall to prevent flooding. 5R Contractors, LLC have planned to construct eight sediment basins.
Rock is often times used in conjunction with the erosion control systems. Rip rap is used to stabilize slopes, channels, the edges of detention basins, and pipe spillways. Its purpose is to carry concentrated runoff to a stable outlet without erosion. Twenty thousand cubic yards of rip rap will be installed at the Atlanta airport. Filter stone will also be used. It is smaller than rip rap but serves the same purpose and is used in the same erosion control systems. A total of 2000 yards of filter stone is planned for this project.
A more aesthetically pleasing means of erosion control used on this project will be vegetative cover provided by 3.2 million square yards of temporary seeding and 2 million square yards of permanent seeding. The purpose of temporary seeding is to reduce erosion and sedimentation damage by stabilizing disturbed areas where additional grading is not scheduled for a period of two months to a year. Permanent seeding is used where the final grading is complete and no more work is scheduled to be done. Both temporary and permanent seeding are done by broadcasting or hydroseeding onto the soil. In areas where the soil is flat and runoff isn't as big of a concern, the seed is broadcast and then straw is blown on top of it to hold it in place. For sloping areas, the seed is mixed with green dye, fertilizer, lime, and also with wood and paper fiber manufactured by Precision Fiber. This blend is placed in a tank and mixed with water and then sprayed onto the soil. This slurry of ingredients stabilizes the slope and enables the grass to become established.
There are some slopes and ditches where the runoff is so strong that, even with a stand of grass, soil erosion occurs. A total of 300,000 square yards of turf reinforcement mat and 4,000 square yards of ditch liner will be installed to help anchor the grass on these problem areas. The synthetic blanket provides permanent turf reinforcement and stabilizes the embankment foundation. WCC's team of professionals has installed over 100,000 square yards of synthetic, PP-5 slope matting manufactured by Western Excelsior. Without stabilization, the slopes would erode away and jeopardize the environment as well as this very important project.
Throughout the different stages of excavation, the landscape is constantly changing. New slopes appear and disappear. Holes, ditches and mounds come and go every day. Frank Crumbley addresses the issue by saying, "Though this is a complex and challenging project, we are not ignoring proper erosion control maintenance by stopping sediment at its source."
The P.R. Manager for the Atlanta Airport, Lanii Thomas, confirms that the Hartsfield Developing Program is the biggest public works project in the state of Georgia. Georgia also has some of the most stringent regulations on erosion control in the nation. The "Hartsfield Atlanta Airport-Focus On the Future Program" is committed to protecting the environment and progressing towards more convenient travel.
For more information contact Western Excelsior, 901 Grand Ave., Mancos, CO 81328, phone (800)833-8573.
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