BioCycle August 2004, Vol. 45, No. 8, p. 49
Revised specifications and successful highway projects set the stage for compost-based solutions for erosion and sediment control and storm water management.
Dan Emerson and Nora Goldstein
THE NORTH shore of Lake Superior, extending from northern Minnesota into Canada, is considered one of the most scenic areas in North America. The shoreline along U.S. Highway 61 (the fabled subject of an early Bob Dylan song), a few miles north of the port city of Duluth, is the site of two innovative projects using compost-based erosion control systems to stabilize slopes and restore vegetation after road construction. The Minnesota Department of Transportation (MnDOT) received a $25,000 grant from the Great Lakes Commission (GLC), along with assistance from the Federal Highway Administration, to fund the first restoration trial as part of a 3-mile road reconstruction project in Grand Marais, done in the fall of 2003. The second project, the Silver Cliff Creek Trail in Two Harbors, involves construction of a bike and walking path along an abandoned road corridor (part of Hwy. 61) that has been deemed historic. That project was still in active construction as of late July.
“The soils in this area are very thin, and typically, too little topsoil exists or remains after construction to fully restore the vegetation over the whole project,” explains Dwayne Stenlund, erosion control specialist with the Minnesota Department of Transportation. “The Grand Marais project involved applying leaf and grass clipping compost to clay and rock outcrop soils. Based on the Universal Soil Loss Equation, 1:6 slopes with these soil types have the potential to lose 5 to 61 tons/ac, 0.5 to 6.7 when blanketed, e.g. with mulch or straw matting, and 0.3 to 3 ton/ac when compost blanketed. On 1:2 slopes, the numbers are 95, 19, and 4, respectively. Basically, the compost is what we are using as topsoil, which is why it is so important to have a specification that defines finished compost material. That material needs to be ready from day one in terms of growing plants.”
A new seed mix, designed with the assistance of the Minnesota Department of Natural Resources, along with organic based, slow release fertilizers, were injected into the compost at the time of application. In all, a two-inch compost blanket was applied to just under an acre of this exposed surface; another half-acre or so received a compost topdressing. In addition, 3,000 linear feet of contained filter berms – known in the MnDOT specifications as ‘compost logs’ and in the marketplace as Filtrexx “Soxx” – were installed in ditches and slopes, around culvert ends, and perimeter controls above wetlands and storm water ponds. “There has been no observable movement of compost due to heavy rains or snow, and this past spring it all greened up right away,” reports Stenlund. “In one area, sod was laid down – some over soil topdressed with compost. It’s all green where the sod was put down on the compost, as compared to the areas where it was put down directly on the soil.”
MnDOT’s successful use of compost on the difficult site represented something of a breakthrough, since, as noted in a GLC report on the project, “almost no known effective sediment and erosion control BMPs (best management practices) exist for work on shallow topsoils with high rock content due to construction activities. Revegetating these topsoils has proven difficult due to tied-up nutrients in the clay fraction, low organic carbon content, poor water infiltration, short growing season and cool temperatures. After construction, sensitive design considerations require landscaping for aesthetics.”
The Silver Creek project at Two Harbors involves stabilization of a half-mile of rocky, Lake Superior slope with “huge drainage issues,” according to Stenlund. This is the first project MnDOT has let with compost application included in the written specs (see below). Windscapes, a St. Paul landscape and erosion control company that did the compost installation on the Grand Marais project, installed compost logs around the perimeter and for ditch checks and inlet protection prior to construction getting underway. Prefilled socks were left on-site (covered and on pallets) for use by the construction contractor as needed. Once construction is completed, a 2-inch compost blanket will be applied, requiring about 500 cy of compost. The rocky soil won’t allow the construction of retention ditches, so compost-based “living ditches” will fulfill the same function. “It will be pretty cool,” Stenlund promises. The project should be completed by the end of August.
Last fall’s Lake Superior shoreline project was not MnDOT’s first, high profile compost application. In the summer of 2002, as part of the preparations for a major Professional Golfers Association (PGA) event at Hazeltine National Golf Course in the Minneapolis suburb of Chaska, its highway crews used a compost blanket to stabilize and green-up an eroding slope along state Highway 41, near the golf course. Stenlund specified installation of geo-cell materials filled with a compost, topsoil and seed blend. A bridge prevented normal equipment access to the steep slope, so a pneumatic blower and hose supplied by WindScapes were used to apply the material. “They (Hazeltine officials) said ‘It better be green,’ in time for one of the sport’s biggest, annual events, where the competitors included Tiger Woods. It turned out tremendously well; everyone was pleased.” (BioCycle first covered MnDOT’s use of compost in an article, “Highway Department Taps Compost To Create Wetlands,” December 2002.)
One innovation tested in the Grand Marais project was the use of compost grouting – injecting a compost/seed mix into riprap to trap sediment and facilitate vegetation (instead of the traditional approach of filling riprap with a slurry of cement and sand). This was done at the toe of the slope that discharges directly into Lake Superior. Windscapes blew the compost mix into the voids of the riprap. “What is historic in this area is the view, and we didn’t want to wait ten years for natural vegetation to eventually grow over the riprap,” says Stenlund. “With the compost grouting, boaters can look up from the lake and see green, and eventually, shrubs and bushes will grow in as well.”
MnDOT wrote a specification for Compost Grouting, calling for a particle size that passes a 0.75 inch sieve. Notes the specification: “Compost used for grouting shall be pneumatically applied with blower equipment in a noncompacted layer to fill voids of riprap, fractured bedrock or other hard armor to a minimum of 2-inches depth, or as directed by the project engineer. …Approximately three-quarters of the riprap void depth shall have the fertilizer application, with the remaining one-fourth topdress lift to have the seed, at rates per acre indicated in the plan.” MnDOT’s other compost specifications include Compost Grade 2 Special (a general compost spec), as well as one for Erosion Control Compost and a Compost Log, which is essentially a contained compost berm. (The “log” spec states the compost filler must pass a 2-inch sieve with a minimum of 70% greater than the 3/8-inch sieve, and that the geotextile material used should photodegrade in situ.) The MnDOT spec allows manure-based composts, but to date, only yard trimmings compost has been used for the agency’s projects.
Since not all contractors have experience in applying compost in various settings, Stenlund notes the importance of writing detailed, unambiguous specifications, to ensure that quality finished compost is used and properly applied. He cited the example of a “massive” soil failure on a slope along U.S. 610 in the Twin Cities suburb of Anoka. Rather than loosely spreading the 2-inch compost layer to provide a growth medium, the inexperienced contractor used heavy equipment, which compacted the material into a smoothly packed, erosion-prone surface. “It didn’t have the properties of compost anymore and became just like any other compacted, erodible soil,” he recalls. “Instead of the compost acting like a sponge, it became hydrophobic.”
The erosion control, grouting and compost log specifications require that the contractors be a certified Filtrexx Installer as determined by Filtrexx International, LLC. Four Midwest certified installers, including Windscapes, are included in the specifications. “If we are spending a little more on an erosion control technology, it better work the first time,” adds Stenlund. “That’s why we are very interested in having certified installers. There are more ways to do it wrong than to do it right.”
STEADY GROWTH FOR INSTALLER
Windscapes has become the largest compost applicator in Minnesota, primarily in slope stabilization and silt fence replacement projects, according to Dave Johnson, company vice-president. Within the past two years, he says, Windscapes’ use of compost for these applications has grown five-fold, from about 2,000 cy to approximately 10,000 cy/year. The company was one of the first Filtrexx installers, and became certified when the program was started by Rod Tyler, Filtrexx’ founder.
While Windscapes originally specialized in terraseeding, “compost for erosion control has become our main focus,” Johnson says. Erosion control projects have grown to account for about 40 percent of Windscapes’ business, with another 40 percent for compost terraseeding, and the remaining 20 percent mulch applications, he estimates. “We’ve been expanding the business by finding new, innovative uses for compost in all aspects of the business, both in our landscape and blower-truck divisions,” Johnson notes. To apply the organic material, the firm uses two Express Blowers, a TM-30 and an EB-40 model.
Chuck Joswiak, a Windscapes manager, notes that for a company located in the frigid north, one of the major pluses of using the Filtrexx socks and other synthetic, compost-holding tools has been the ability to use them in the winter, when frozen ground would prevent the use of erosion control measures that involve digging. “It’s expanded from a seven-month business to a year-round business,” he says. So far, having an adequate supply of compost when needed has not been a problem, according to Johnson, partly because “we’ve been proactive in working with our compost manufacturer (NRG Processing Solutions), prebuying our compost for the whole season.”
Using compost in tandem with other BMPs has been key in the company’s growth, Joswiak notes. “One thing we’ve been trying to preach all along is that it is just another tool you can add to your toolbox.” On steep, hillside stabilization projects, Windscapes has used compost along with geosynthetic erosion control products. “There’s a place for all of the tools,” he adds.
Through testing, trial and error, Windscapes crews have made a few adjustments along the way for better erosion control results. One example is varying particle sizes depending on the application. Obviously, larger particles can provide more stabilization against the hydraulic pressure of moving water because they interlock together better, but smaller particles can be better for rapid growth and development of plants. One thing that has surprised Johnson in working with compost is its absorption rate – “how much water it absorbs in a heavy rainfall, and how it slows down runoff.” He notes the importance of varying the coarseness of compost, based on the severity of a slope. “It’s not a one-product-fits all situation. On a terraseeded lawn we might use half-inch material; on a small, 4:1 slope, we may use 3/4th-inch material. On a steeper, 2:1 slope, we might use a 2-inch screened product. There’s quite a variance.”
Educating customers on the uses of compost has been part of Windscapes’ mission. While inroads are being made in some arenas, e.g. with MnDOT, much more education needs to be done, adds Joswiak. “The problem is that a lot of contractors who are dealing with EPA Phase II storm water compliance don’t know about products like ours so they go with what they know. In some cases, the watershed or soil and water conservation district officials are recommending our products to contractors based on performance, which is great.”
Because compost-based BMPs may have a higher installation price in some applications, education also needs to be done on the potential cost-avoidance by using these products. “A site excavator may not need to put down a few inches of good soil because we are improving the soil conditions in our application, as well as doing the seeding and stabilization – all in one step,” he explains. Establishment of good vegetative cover after the first compost application also eliminates the need for additional site work. “People rarely figure in the cost of doing it more than once,” he notes.
Still, getting the cost of compost-based BMPs down a bit will definitely help market acceptance. Factors that impact costs include transportation of compost to job sites and speed at which compost can be applied. Transport economics are improved when a back-haul can be built in, notes Joswiak, but sometimes Windscapes doesn’t get enough advanced notice to arrange that. One solution is to find sources of compost more local to where the jobs are, versus having to haul it from the Twin Cities. Another is to find a place to stockpile compost products nearby, where the material can be kept dry. “If there is a rainstorm the night before we are supposed to start the job, it takes three times as long to get the compost out of the blower truck,” he says. “We are working with NRG to locate a storage facility where we could haul 10,000 to 12,000 cy and keep it dry. Being able to rely on economical access to dry compost will make us more competitive.”
Windscapes also is working to beef up the capacity of the blower system on the trucks so that product can be applied more quickly, again improving the economics. “The daily operating costs of a truck are so high that when you average it on a cubic yard basis, the more you put out per day, the cheaper you can do the job,” Joswiak adds. “And with cost as a market entry barrier, that is going to be key to our success.”
MnDOT requirements being placed on competing products to improve their performance also improves the competitiveness of compost-based systems. “In Minnesota, some companies charge very little to install their products, such as erosion mats,” he explains. “But DOT officials and others are starting to see that the installations are not being done properly and the products are failing. To do it properly raises the cost of the installation. Once that happens, a compost blanket becomes more appealing. And the fact that we can put down two inches of good organic substance and seed it in one application – and have vegetation established and weeds suppressed – is appreciated by increasing numbers of engineers and DOT officials.”
To obtain compost when needed for its projects, MnDOT has a list of about eight area suppliers who have been certified as meeting the department’s specifications. Minneapolis-based NRG Processing Solutions (a subsidiary of NRG Energy) is the largest of those, and the one Stenlund has used the most often. In an area that frequently requires delivery of large amounts of material, often on short notice, “NRG has been the most flexible,” according to Stenlund, although he would like to line up more local compost suppliers. Distance is a problem with some of those on his list. One supplier, Creekside Topsoil, is located in Hutchinson, about 70 miles west of the Twin Cities. Another, Mississippi Topsoil, is 60 miles to the north near St. Cloud. He knows there are local compost suppliers throughout the state that could meet the MnDOT specs, “but haven’t gone through understanding the specifications and standards process. They can all meet our specs at the time of delivery, but it’s helpful to have a pre-approved list of vendors, so contractors know who they can go to,” Stenlund explains.
NRG Processing Solutions, which was formed in 2000, is one of the largest composters in the Midwest, with 11 compost sites in the Twin Cities area producing over 100,000 cubic yards/year of product. The company receives more than one million cubic yards of green waste annually, according to marketing director Mary Williamson. NRG officials don’t have any way of knowing how much of the compost it produces is used for erosion control, and how much for other functions, she notes, adding that NRG sells several types of soil blends using compost, and some hardwood mulches. NRG’s compost operations primarily use half-inch screens, but switch to 3/8th inch mesh for certain purposes, such as incorporating sand into a blend.
Williamson reports that, along with erosion control, water filtering is a developing niche, with local governments requiring contractors and developers to install filtering systems around parking lots and other large developments before water enters storm sewers and winds up in lakes – a major issue in Minnesota, the land of 10,000 lakes. Green roofs on top of flat-roof buildings represent another emerging compost application.
Ginny Black, a compost specialist with the Minnesota Office of Environmental Assistance (MOEA), has noted increasing interest in using compost as a tool to comply with federal Phase II storm water regulations, but she isn’t aware of any cities that have designated it as a BMP, as of yet. Black adds that at a recent compost workshop hosted by MOEA for contractors and local government officials, attendees were surprised at the water-holding capacity of compost. “It opened a lot of eyes.”
MnDOT’s inclusion of compost BMPs in its road construction specs will be a major factor in increasing the use of compost among contractors and landscapers, Black adds. “It perks up their ears when they hear MnDOT uses it; they rely quite a bit on MnDOT’s specs. Many smaller cities use the specs, since most cities don’t have staff resources to develop their own.”
Minnesota DOT Advances Compost Use For Erosion Control
BioCycle August 2004, Vol. 45, No. 8, p. 49