A nature site being developed on what was once an illegal landfill along the Trinity River and Loop 12 in south Dallas has been planned as a showcase LEED© Gold sustainable project (U.S. Green Building Council Leadership in Energy and Environmental Design).
As owner, Dallas city administrators chose the site that is reclaiming 120 acres of the Great Trinity River Corridor. Factors in choosing this site over others included its location high enough off the flood plain, yet close enough to the river for interpretation; and it is providing the city an opportunity to turn a community eyesore into an asset, according to Catherine Horsey, LEED AP, former director of the Trinity River and Dogwood Canyon Audubon Centers.
Audubon has a long-term operating agreement for the interpretive area. Brown Reynolds Watford Architects, Inc. serves as the architect-of-record with Antoine Predock Architect PC as the design architect. Lopez-Garcia Group Inc. of Dallas provided civil engineering services. Jaster-Quintanilla (JQ) created the structural design of the bridges and four site structures.
"The Deepwood Landfill site comprised 1.5 million tons of mostly construction debris illegally dumped over a 15-year period," said Horsey. Following the criteria of the TCEQ's (Texas Commission on Environmental Quality) requirements and the goal of reducing erosion and returning this land to nature for the use of future generations, Brown Reynolds Watford Architects, Inc. and Terracon Consulting Engineers & Scientists devised a plan that would consolidate the waste into capped rolling hills replanted with tall prairie grass and hardwood trees once dominant on the Texas Blackland Prairie. At the base of the hills, a series of cascading wetland marshes and ponds captures and polishes runoff from adjoining neighborhoods and prairies before returning the cleansed water to the river. Rodman Excavating performed this remediation work.
"They consolidated the debris, graded the ponds, covered the debris piles, and vegetated the ponds," said Horsey.
The 21,000-square-foot center will include classrooms, exhibits on the various habitats found on the site, a floodable scale model of the Trinity River, and a great hall for community events. Special exterior architectural features include sloped curtain walls; integral, green-colored concrete; windows sized to illustrate Fibonacci's sequence (also known as the "golden ratio"); a vegetative roof; and 48-foot cantilevered canopies. Natural textures are cast into the exterior tilt-wall panels with custom rough-sawn board and into the exterior soffits with EPDM rubber roofing cut in the shape of feathers. The architect's goal was to include many natural elements into the design.
"The vegetative roof adds about 100 pounds per square foot more weight than a regular roof. Instead of just a metal deck, we designed a concrete deck on the roof and a drainage system over that," explained JQ's Tom Scott, P.E., LEED AP. The drainage system includes a manufactured plastic product of the type used for rooftop gardens and a 6-inch thick layer of lightweight soil.
"At 48 feet, the cantilevered canopies are unusually large," Scott continued. "The engineering was not so much a problem of strength as of deflection. We calculated the beams to be cantilevered up just enough to level out once the weight of the roof is added."
General contractor SEDALCO began construction March 31 on the 21,000-square-foot building, a roadway of about one mile, utilities, and approximately three miles of nature trails, wooden bridges and retaining walls.
Then the floods of 2007 struck. Four months into the project, SEDALCO had lost 44 days due to rainy weather, from June 18 until July 9. The Trinity River stayed at a flood stage most of those 44 days, according to Jared Hicks, assistant project manager for SEDALCO. The river got within 70 feet of the building, which was about 10 feet below the top of the finished floor. The building is typically about 450 feet from the river bank.
NTEX Erectors of Arlington has been subcontracted to erect the concrete tilt wall building exterior and the structural steel. David Prendergast and Marrk Scoggins are partners in the two-year-old business.
"We rented the 200-ton Link Belt HC 258 crane primarily because of its reach capability and the operator," Prendergast explained. "He is good at his job, and we have to be very careful not to mar or chip these panels. They have a very detailed design and they will not be painted like most other tilt wall buildings. The exterior concrete will be left just as it is, so any patches would remain highly visible."
Cooperating For Nature
The contractor has embraced the green concept, cooperating with naturalists in ways that were not seen in the construction industry only a few years ago.
The site has begun to yield its share of surprises. Dr. Omar Bocanegra, U.S. Fish and Wildlife biologist, sighted a lilypad forktail damselfly, generally seen in West Texas, so he was ecstatic when he spotted this one in the southeast portion of Dallas.
"We will be draining the ponds in order to construct walkways and bridges as part of the nature trail," SEDALCO project manager Patrick Farr explained. "Omar has agreed to come out and harvest a few of the insects that live in the pond and preserve them in a living state for 30 to 45 days and repopulate the pond as it is refilled. Once we drain the pond, it can stay dry for only one month."
"The interface between manufacturers and contractors has not yet become seamless in transitioning into the LEED concepts," said Farr. "With respect to implementing the architects' and engineers' design, carrying the design concept into the marketplace is a pretty big challenge, especially when comparing public entities to private entities.
"A city cannot sole-source a particular vendor; they have to leave it open to the marketplace. The engineer will identify potential vendors for a given item of mechanical equipment, for instance. Manufacturers list the operating performance level of their equipment as meeting certain specifications. As long as they have met those requirements, they feel that they have met the specs. But they may not meet LEED specifications. Whether or not it meets the requirements of LEED is left to be determined by the contractor and the architect."
Structurally, locating LEED-friendly materials has been much easier. Chaparall Steel in Midlothian, in the southern portion of the DFW metroplex, is a major steel recycler. Their steel is almost 100-percent recycled, according to Scott, so that is an advantage for a project that requires 95-percent recycled content for the structural steel beams, roof deck and concrete reinforcing. And they are well within the 500-mile radius required for LEED's "locally manufactured" products.
Jaster-Quintanilla specified fly ash as a component in every concrete mix for this project. Fly ash is a by-product of coal burned in electric power plants. Instead of being sent to landfills, using fly ash as partial replacement of cement significantly reduces the need for cement production, which is a contributor to CO2 in our atmosphere. Altogether on this project, the use of fly ash has reduced the amount of cement needed by about 40 percent, according to Scott.
Tracking and accounting recyclables is another important aspect of LEED for contractors. Shelley Wheeler of Waste Management (WM) met with SEDALCO before the project began and participated in the formation of a waste management plan.
"We identified the project recyclables and set up a recycling network where each product is tracked on its own separate account," said Wheeler, who is currently working on her LEED certification as well.
This project is recycling wood, concrete, steel, and paper/cardboard products. Plastic and gypsum drywall are two materials that will not be recycled here. This project will not yield enough plastic to make recycling worthwhile, according to Wheeler.
"There is no market in this area [Dallas] for the gypsum drywall," she added.
In some areas, drywall, also called sheetrock and gypboard, is pulverized and mixed into landscaping mulch. Because the soil in Dallas and much of the surrounding area is heavy in calcium, adding gypboard can be detrimental, according to landscaping industry sources.
"Waste Management had an infrastructure in place which worked into LEED requirements nicely," said Greta Calvery, Waste Management community and municipal affairs manager. "Our drivers are trained to observe that recyclables are properly separated and not contaminated with other trash to prevent being dinged for 50-percent trash at the recycling facility. That would be real damaging to a LEED program."
The Trinity River Audubon Center will serve as a gateway to a myriad of opportunities for citizens from the entire Metroplex, including nature viewing, hiking, biking, picnicking, and Trinity River access.
When completed in 2008, the Trinity River Audubon Center will include these other significant sustainable features recommended by the U.S. Green Building Council:
On-site waste water treatmentRainwater collection systemPermeable parkingOn-site environmental educationIndoor air qualityEnergy efficiencyWater efficiencyDaylighting"Night sky" light pollution reduction
|Site prep||Maroney Excavation, LLC|
|Concrete placement||Excel Inc.|
|Tilt-wall erector||NTEX Erectors|
|Steel erector||NTEX Erectors|
|Plumbing||Curtis Mechanical Contractors|
|Roofing||Sta-Dri Company, Inc.|