Case Study: Engineered soil maximizes Georgia Tech campus building and grounds

By Don Eberly, Laura Drotleff and Liz Burlingame

Universities have long marketed their degree programs, athletic championships and selective locations. But with the help of advances in stormwater engineering, the Georgia Institute of Technology in Atlanta has been able to add “green” credentials to its list of achievements. An innovative stormwater management project at Georgia Tech has been making a strong case for sustainable investments. As well as diminishing the campus’ reliance on portable water to manage irrigation needs, the project serves as a real-world example about how water conservation methods can make a true difference.

The university’s push for more eco-friendly standards began in 2006, when the new Christopher W. Klaus Advanced Computing Building was slated for construction. Georgia Tech’s goal was to develop a water reclamation system on the site that could collect and store irrigated water from the first flush, or 1.2 inches of each rain event.

Ecos Environmental Designs, a landscape architecture and planning firm, saw an opportunity to embrace the university’s challenge to preserve the site’s native ecology and recreate pre-development hydrology. At the core of the mission, Ecos partnered with ERTH Products and Big River Industries to engineer a soil mix for better bioretention and less water runoff.

Today, the system collects water for about three weeks of irrigation — enough to sustain Georgia Tech’s native landscaping through the typical southeastern drought. The project was also pivotal in earning the facility a coveted LEED Gold Certification from the U.S. Green Building Council.

“It turned out to be a perfect fit,” said Stephen Brooks, Ecos vice president. “We were able to achieve the needed infiltration rates while maintaining a certain amount of moisture, combined with good organic content to support proper soil biology for ample plant life.”

As with most stormwater management systems – and the landscapes and building sites for which they are developed – the solution required a significant measure of collaborative ingenuity.

Approaching the design

At the start of construction, the management of Georgia Tech and those involved with the project found the 6.2-acre site had complex issues to resolve. Although the soil quality was ideal for building support, it lacked the necessary infiltration for adequate stormwater management.

For the bioretention area, crews used 350 cubic yards of specially engineered soil containing a mix of clay topsoil, sand, ERTH food compost and HydRocks. Manufactured by Big River Industries. HydRocks is an expanded clay lightweight aggregate product, manufactured through a rotary kiln process in which selectively mined clay is fired at 2,000 degrees Fahrenheit.

“As a filter medium, HydRocks increases surface area and allows fast, free drainage, helps remove or reduce toxins, and absorbs nutrients for long-term, sustainable water treatment,” said Jeff Speck, Big River Industries’ vice president of sales and marketing. For site developers and stormwater management professionals, it improves soil’s functionality and service life, saving material, labor and transportation costs.

According to Scott King of ERTH products, the engineered soil mix allowed for good surface infiltration of stormwater, while not creating a continuously saturated soil which would be harmful to plant life. Also developed was a “living soil,” containing macro- and micro-nutrients. The living soil breaks down contaminants and provides movement in the soil, which increases infiltration and water-holding capacity.

To mimic a perennial stream condition in Georgia’s Piedmont region, crews planted a mix of native plant species in the bioretention area, providing a drought-tolerant landscape. Any stormwater that does not absorb is captured by the underdrain and sent to two underground cisterns, with a combined 174,149-gallon volume. There, irrigation pumps recycle it through the grounds.

Once the cisterns were in place, Ecos constructed a series of retaining walls made of local, natural granite 25 feet long and 5 feet wide. The walls were set perpendicular to the flow of the bioretention area, serving as a delivery vehicle to infiltrate roof runoff through the bioretention area to the cisterns below.

“The roof’s downspouts were connected to the end of the walls leading to an interior channel, which has a series of openings on the downstream side,” explained Brooks. “Roof runoff passes from the downspout to the walls’ interior, turns 90 degrees, and exits to the landscape. The reinforced channel of the walls withstands the four stories of velocity from the roof, preventing soil erosion.”

Ecos excavated four-foot deep cells between the retention walls, where it laid under-drain pipe that connects to the underground cisterns, and wrapped the area with gravel and filter fabric. The engineered soil mix was then installed in a series of lifts, each watered down to ensure soil settlement until design elevation was reached. The channels were lined with native river rock, broken up by large boulders salvaged during excavation of the building site. Cranes placed the boulders on graded aggregate to ensure that they did not move. The boulders were slightly elevated to absorb grade and encourage pooling behind them, maximizing infiltration time.

In its current state, students can relax on a lawn to the rear of the Klaus building, where hidden drains empty water into the cisterns beneath their feet. Under the sod, the same bioretention mix formulated with Hydrocks was used to capture stormwater sheeting off hardscapes.

The university’s rainwater harvesting system has not only contributed to the facility’s LEED Gold Certification, but it has set a competitive benchmark in stormwater management. Additionally, it has set a new standard for future development projects, as Georgia Tech continues its path of conservation, both by continuing landscape projects to increase the institute’s green space and developing an ecologically based landscape that enhances the living, working and learning environment.

Don Eberly is president/CEO of Eberly & Collard Public Relations, specializing in marketing businesses in the home, garden, design, landscape, and agribusiness industries. Laura Drotleff and Liz Burlingame are also with Eberly & Collard Public Relations. They can be reached through www.eberlycollardpr.com