Across Texas, a problem is becoming a solution. Compost has found a place in highway construction.
The Texas Department of Transportation has successfully used compost for several years to control erosion. By doing so, TxDOT has provided a market for municipalities and others to help keep their landfills free of an abundance of waste.
In fact, TxDOT has become the nation’s largest market for compost, said Barrie Cogburn, a field landscape architect in TxDOT’s Design Division.
Over the years, topsoil sources have depleted, Cogburn said. And what is available contains little organic matter, a needed component to help grasses planted along roadways take hold and sustain growth. Without revegetation, erosion begins to occur on rights of way.
In the late 1990s, TxDOT began testing compost as a substitute for topsoil. Cogburn said TxDOT worked closely with the Texas Commission on Environmental Quality (TCEQ) in researching, testing and developing the use of compost.
The compost was tested in some of the state’s worst eroded places, Cogburn said, and it worked. In 1997, specifications were written for using compost, demonstrations were held across the state, and the rest is history.
Cogburn said compost used by TxDOT must comply with U.S. Composing Council standards. Some compost is used in landscaping, but the majority is used in roadway construction.
While TxDOT uses a variety of compost types – wood and yard trimmings, dairy and feedlot waste, and poultry litter – a large portion of its compost is biosolids, or treated sludge, said Cogburn. Sources for the biosolids are municipalities, including Denton, Plano, Austin and San Antonio.
“This is a beautiful solution,” Cogburn explained. “Cities don’t want to put this material in their landfills, and TxDOT has become a market for the composted material.”
In fiscal year 2004, TxDOT used 360,000 cubic yards of compost. In fact, the department laid its one-millionth yard of compost in the spring of 2004.
On flat sections, Cogburn said compost alone is added to help amend the soil. On slopes, where rainfall can wash away soil, TxDOT blends an equal mixture of compost and wood chips. The chips help the compost adhere to the slope and help conserve moisture.
The compost and wood chips are applied in one pass, she said, using a piece of pneumatic equipment. An 18-wheeler has an applicator hose that is controlled remotely.
“The wood chips act as a blanket,” Cogburn said.
In many instances, the familiar green curled wood fiber blankets that dot many roadsides are being replaced with the compost mixture. Cogburn said the cost of the compost is about half the cost of the wood fiber blankets.
While the cost of laying topsoil is similar to that of laying compost, Cogburn said the avoided cost is a dividend.
“By doing it right the first time, we don’t have to keep doing the process over and over,” she said.
When topsoil is used, Cogburn said a contractor has to be paid per visit if the soil is eroding while a project is still under contract. And each time, the contractor has to reapply topsoil, seed, fertilizer, and mulch/and or erosion control blankets.
Another plus is reduced maintenance. By avoiding erosion, less maintenance is required.
Testing on Cracked Concrete
TxDOT is in the midst of trying to solve another problem – cracking concrete – using composted dairy waste. The test is taking place near Stephenville in Erath County.
The research is funded by a grant from the Environmental Protection Agency in an effort to help curb the problem of dairy waste and is being conducted by the University of Texas at Arlington College of Engineering. TxDOT is funding the implementation.
Richard Williammee, PE, materials engineer in TxDOT’s Fort Worth District, said the study compares the effectiveness of dairy waste with biosolids. The compost serves as a layer of mulch along the roadways to help keep moisture in the soil to keep it from cracking and coming through the pavement.
The test plots contain varying thicknesses and lengths of compost to see what works best. Temperature and moisture sensors in the test plots collect data, which continues to be analyzed, Williammee said. Evaluation will continue until mid-2005.
Williammee said the idea for using compost in this way generated itself. TxDOT’s Stephenville District was struggling with cracking concrete, and the glut of potential compost from area dairy cows seemed like a potential solution.
Typically, cracks in the asphalt would be sealed, said Williammee, but this is, at best, a “band-aid.”
The compost, he said, “goes to the root of the problem – trying to keep the moisture in the soil.”
So far, the compost shows promise.
Anand Puppala, an engineering professor at the UT Arlington College of Engineering, said the biosolids have performed better because of high proportions of fiber coming from organic matter in that type of compost.
“Erosion was higher in manure plots because of high proportions of manure used in the test sections. However, at low proportions, we expect the erosion problems will be low,” Puppala said.
Erath County Judge Tab Thompson calls the use of compost a win-win situation. “This is good for agriculture,” he said, “and good for TxDOT to be able to use an industry byproduct.”
Already, TxDOT has begun to implement the idea in three other areas of the state: its Lubbock, Bryan and Corpus Christi districts. The compost is being tested to see how effective it is in a variety of soil types.
Williammee said the compost used in those areas varies. For instance, feedlot and cotton burr compost is being used in the West Texas region. Yard trimmings and biosolids are being used in the other areas.
Getting into the Act
Counties can consider using compost on their roadways and/or becoming a provider of compost.
Rebates are available through TCEQ’s Composted Manure Incentive Program for governmental entities that use compost from the Bosque and Leon watersheds. The rebates, $5 per cubic yard, are offered through August. The rebates are funded by a grant from the EPA, which aims to address the excess dairy manure in the watersheds.
Cogburn said counties also may want to consider being a supplier of compost. Local sources are needed as freight costs to bring in compost can be cost-prohibitive. Suppliers are needed in Far West Texas, in particular, she said.
By Tammy Wishard