Into each construction job, some rain must fall. When that happens, the first task at hand is likely staying upright and not ending up with a shirttail full of mud. Another priority: keeping the site from eroding away. Silt fences, straw and hay bales, and rock- or sand-filled berms are commonly used as temporary sediment dams during construction. Some firms also use spray-on tackifier products to cover large areas of disturbed soil. In many cases, however, these erosion and sediment control methods are only moderately effective; in addition, because they must be removed before final grading and landscaping, they are time- and labor-intensive. In many parts of the nation, compost is now being touted as the better alternative for temporary erosion control. “A compost filter berm costs about $2 to $3 per linear foot installed, roughly the same as a silt fence,” points out Green Horizons’ Rod Tyler from his Grafton, OH, office. “Yet compost is five-to-one better at stopping erosion. Why not use a compost berm? It’s annually renewable, all organic, 100% recycled, and it works better!”Compost’s Correlation and Composition
A healthy soil profileThis roadside compost berm keeps the sidewalk clear as new grass grows Basically, compost is decomposing organic materials. In a natural setting, leaves, conifer needles, twigs and wood, dead animals, and insects can be compost’s building blocks. Add moisture, time, microorganisms, and heat (the microorganisms throw off a lot of heat as they work), and these disparate elements transform into a rich, nutrient-filled product that feeds the surrounding plants. During the course of its life, compost becomes a “parent” of topsoil. As the drawing shows, the top layer (about 2 in.) of a healthy soil profile, called the “O” horizon, is organic material. Because of its composition–materials in the process of decay–this layer is characterized by large particle size, which creates pore spaces that fill with the air and moisture plants need to thrive. The warmth the “O” horizon creates helps seeds germinate. Topsoil, the “A” horizon, is filled with beneficial bacteria, fungi, and small animals and insects. It eventually contains organic matter as time, water, and burrowing creatures move through it and the “O” horizon, making it darker and more nutrient-filled than the lower soil horizons. Reaching 10 in. in depth, this horizon is filled with roots; the greatest percentage of a plant’s roots remains in the A horizon. Because of its mixture of soil and organic matter, this layer’s particle size (albeit smaller than the one above) also creates all-important pore spaces. Subsoil, or the “B” horizon, contains fewer organisms and less topsoil. Although a few deep roots reach it to glean the various elements located there, plants don’t thrive in this horizon, which reaches about 30 in. below the surface. This horizon is more compressed than those above, resulting in small particle size and few pore spaces. Reaching approximately 48 in. down, the lowest layer, or “C” horizon, is the other “parent” of soil, so called because it’s the weathered rock and soil from which the A and B horizons are formed. Further compressed by everything above it, the C horizon contains less living matter and offers scarce pore space. There’s virtually no pore space below it, either, as below it (not shown) is bedrock.Excavation disrupts this soil profile, virtually eliminating the first two horizons and breaching well into the third. (For huge structures needing to be well anchored, crews also drill into the bedrock.) Stripped of the water-using layers above, the C horizon easily yields to erosion; when construction is complete and the landscape phase is underway, an application of topsoil alone might not give plantings the correct nutrients and medium they require for vigorous growth. Without a blanket of organic material, weather conditions may even wash or blow away some of the topsoil before the plantings take root.“Where before you may have had undifferentiated soil, with organic matter and biological activity you begin to cement those particles together and create humus. Humus does not erode nearly as easily as raw soil–and raw soil is what you usually have on a construction site,” notes Richard Pete, president of Planet Green in Charlotte, VT, which offers a pelletized compost mulch. With his degree in plant science, he encourages landscapers to understand the carbon cycle of the soil. “Just a small understanding of biological processes and soil biology can save a lot of money.”Compost: The Gift That Keeps On GivingThe hydroseeding process did not do an adequate job for this slope. Seed injection was later used.Because of its water-retaining properties, compost not only makes a good topsoil cover but also makes an excellent berm to stop erosion. In addition, unlike silt fences, hay bales, and rock- or sand-filled berms, compost need not be removed from the site; because of its benefits for the soil, it’s actually better to leave the compost there. In both his capacities as a businessman (Maine’s New England Organics) and as an industry advocate (a US Composting Council member), Chris Bales is an enthusiastic proponent of compost berms. “Composted berms will adjust to the lay of the land and settle with the ground, not like the fabrics sometimes used,” Bales says. “Compost berms are also continuous, not jointed like hay bales. After construction, you can work it in or remove it, but that’s not usually done. You can just leave it, if it fits into the landscape–say, if the site’s surrounded with wood. Up here, we see it as turtle-, or ‘critter-,’ friendly.”Since compost evolves from a variety of organic materials, different areas of the nation use whatever’s most available locally. “Maine’s a forested state, with forest-product industries, and bark is one byproduct. We’re using this for erosion control purposes,” Bales reports. “Not landscape bark, though; the byproducts of making logs and lumber have a lower pH.” He adds, “Berms don’t really have to be that big. Maine puts berms along the roads next to lakes; people can walk over them.” In addition to controlling erosion, Bales says these roadside berms “tie up some of the contaminants from the asphalt.”Bales notes a recently published University of Connecticut study conducted for the New England Transportation Consortium (Demars, Long, and Ives: “Use of Wood Waste Materials for Erosion Control,” Project #97-3). Four materials (straw/hay bales, composted wood mulch, and fabric; soil was used as an experimental control) were studied for their erosion control properties. The materials were used as both a slope treatment and a barrier. “In all cases, wood mulch did the best–a factor from two-to-one to four-to-one more effective,” Bales says proudly. The New England Transportation Consortium (NETC) plans to make its research materials available on the Web; those wanting in-depth results from Project #97-3 should periodically visit NETC’s site at www.cti.uconn.edu/ti/Research/netc_home.htm for updates.Compost’s Wide Availability“Compost happens” in the wild, but as Chris Bales’ tale illustrates, civilization also creates a wealth of compostable material. Yardwaste (leaves and grass clippings), wastewater sludge, various paper products, and some animal manures can also be converted into nutrient-rich compost. This particular municipal wastestream can be a potential gold mine of erosion-combating compost.In the past, yardwaste usually went into landfills; with landfill space rapidly becoming scarce, however, more communities are banning yardwaste from “regular” refuse pickup. According to a US Composting Council (USCC) fact sheet, states are setting aggressive recycling goals. The USCC estimates that “adding composting to traditional recycling can divert as much as 70% of the wastestream.” Atop these state restrictions, EPA has noted that composting can play a key role in diverting organic waste from landfills and that applying compost to combat nutrient runoff helps prevent natural-water pollution.The mandates are there, but what about real-world solutions? “States don’t create the market for what their laws create,” Rod Tyler says. “You can’t put yardwaste in landfills, but states haven’t made a market for reusing the stuff.”In temperate states, yardwaste is a partial-year concern; in warmer states, however, yardwaste is generated year-round. With this fact likely in mind, Florida set a goal: 30% less solid waste would enter landfills by 1998. The Solid Waste Authority (SWA) of Palm Beach County, www.swa.org, met that goal two years early, and it currently recycles 50% of its waste. In addition, the SWA found a market for its yardwaste. “We make so much compost, we sell it to nurseries and citrus growers,” SWA Public Information Officer Linda Hodgkins says. “We also give it free to the public we serve and to the Florida Department of Transportation, which uses it along roadsides.”SWA’s $15-million composting plant in West Palm Beach began operating in September 1991 as a pilot program to recycle yardwaste and wastewater sludge into compost. Three years later, the facility expanded from a four-bay to a 36-bay system, which daily processes more than 300 tons of waste. In fiscal year 1997-98, when the facility exceeded Florida’s goals, it turned 55,984 tons of wastewater residuals and 48,929 tons of screened yardwaste into 73,605 tons of organic compost. The SWA also has plans to further expand its recycling success.“We are going to build a recalcination plant here,” Hodgkins adds. “Water treatment plants go through a lot of lime during their process, and instead of disposing of this lime, we will reclaim it, and the treatment plants will buy our [recycled] lime.”Deep in the Heart of TexasIn addition to controlling erosion, roadside berms tie up some of the contaminants from asphalt.Although Texas homeowners produce a hefty amount of yardwaste, the Lone Star State is most concerned with keeping feedlot and dairy waste out of its watersheds. Texas’s Senate Bill 1, made law in 1997, mandated protection and preservation of the state’s valuable groundwater supplies. In response, the Texas Natural Resource Conservation Commission (TNRCC), in conjunction with the Texas Department of Transportation (TxDOT) and the Texas State Soil and Water Conservation Board (TSSWCB), developed a composting program that could reduce the animal waste, thus saving the watersheds while helping battle drought and erosion problems.The working theory: Although in its “raw” state cattle manure could leach into groundwater and pollute Texas waterways, that same manure, when worked with yardwaste, could become a nutrient-rich, moisture-retaining compost. Retaining soil moisture was another large concern for the agencies, because in some areas the state has suffered greatly from recent multiyear droughts.Realizing public support would benefit the program, TNRCC and TxDOT worked together to demonstrate compost’s benefit along Texas roadsides; it was hoped the public and potential contractors would quickly recognize compost’s potential. To create this compost, however, not just any organic waste would do. “We work with citizens’ yardwaste,” says TxDOT Landscape Architect Barrie Cogburn. “Many cities and private entities collect it. However, we have a specification written, telling them what yardwaste can and can’t be. We also have specifications for feedlot and dairy-industry manure.”TNRCC and TxDOT presented their demonstration in May 1999 in Big Spring, TX, at a highway overpass built in 1968. TxDOT tried five times since construction of the overpass to establish vegetation on the steep, severely eroded site; if compost could work its magic there, it would work anywhere.The compost, created from feedlot manure, cotton burrs, and yard-trimming wood chips, was applied at a 3-in. depth. Incorporated because they reduce water and wind erosion, wood chips were blended with the compost at a 3:1 ratio (three parts compost, one part wood). Six weeks later, thick grass was growing on the long-barren site.Cogburn explains how costly erosion can be to a state. “Topsoil sources have become depleted over the past few years, leading to severe erosion on many projects. If erosion occurs while the project is still under contract, the contractor must reapply topsoil, seed, fertilizer, mulch, and/or erosion control blankets and cannot leave the project until sufficient grass growth occurs. If erosion results on existing highway sections, [TxDOT] maintenance is left to deal with the resulting problem.” Noting the excellent results on the Big Spring project, she says that with compost, “poor soils can be amended, revegetation can occur, erosion is avoided, and TxDOT saves time and money.” Considering that Texas contains 1.3 million ac. of highway right-of-way, the potential cost savings could be substantial. In addition, TxDOT’s use of compost would create a huge market for the product, spurring the composting industry to remove large volumes of organic material from high-impact watersheds.There’s another financial bonus to this project. “EPA will give TxDOT a rebate if we use the feedlot waste, because they want to keep it out of the watershed,” Cogburn says. Further information on the project is available on the Internet (see sidebar). California’s Gold Rush for CompostThe Big Spring overpass before (above) and after (below)Studies conducted by the California Department of Transportation (Caltrans) and the University of California, Davis also revealed that compost made from municipal yard trimmings and other organic materials is excellent amendment material for roadside erosion control. As their data documented, composts vary in physical and chemical characteristics, and more research has been suggested.One such research project is Caltrans’ compost demonstration, currently underway at Brockway Summit, Placer County. The demonstration site was constructed in the fall of 1998 on State Highway 267, at the Lake Tahoe Basin’s north end. This project involves a long series of southwest-facing road cuts totaling 9 ac.; the cuts display 2:1 horizontal-to-vertical slope angles. The parent materials are volcanic mudflows cut to 5-8 m below the previous soil surface.The site’s existing erosion control specification was modified to create three additional treatments (zero control, compost, and compost plus specified), each designed to contrast the performance of various slope amendments. The four treatments specified were all repeated on three separate slopes. As of the 1998-99 winter (the latest published data), the slope amendments showed only small areas of slippage. According to the report, plant growth and soil nutrient content will be monitored for several years after application (see sidebar).In the meantime, other composting methods are slowly gaining acceptance in California. Noting that native plants are the ones most likely to thrive in the climate (as opposed to plant varieties from other areas), URS Corporation Vice President Carol Forrest encourages the native regrowth method. “This is not new; it’s been around 20 years, although it’s not widely used,” states Forrest. “You have to want the native plants there to do this; if you have a good growth of native, this is the way to go.” Using the native regrowth method requires clearing and grubbing the site of its existing vegetation, then placing the materials in a chipper. The chipped material is then combined with enough topsoil to result in a 3- to 6-in. layer and stockpiled until it’s needed during the regrading process. “When you’re regrading, put this mixture onto the slope. The existing vegetation will grow back. It’s effective and inexpensive–no irrigation, seed, or fertilizer,” Forrest says. “Contractors have been resistant to handling the stuff twice, but vegetation, both green plantings and woody, is the erosion control. The different heights of plants–the canopy–keeps the rainfall from smashing the ground.”Getting Into CompostMany states are creating guidelines and specifications for compost, especially for that used on state-owned sites. “Erosion management is dictated by the state. Maine runs workshops and certifies contractors–this is voluntary training–but you must have an erosion control plan and have someone on the project to write the plan, then you must follow it,” Chris Bales explains. Once you have the information you need about compost and a materials source, all that remains is applying the compost to your site–and various equipment manufacturers have made this a less labor-intensive step. Finn, located near Cincinnati, OH, calls its Bark Blower “A Smarter Way to Work.” The multimodel line ranges from the 1.5-yd.3 (hopper capacity) Model 302 tow-behind to the 36- to 40-yd.3 Model 1240, which is available in either truck- or trailer-mount. Finn states that its products allow 20-30% material savings, depending on the material and its moisture content, because blown material offers a more even, consistent surface than could be achieved by hand-raking. As to the machines’ versatility, one project used a Bark Blower to deliver product to a rooftop garden–six stories up. Rod Tyler agrees that blowing is the way to go. “You can add compost just after the rough grading. By blowing it on, you end up with more even soil, eliminating the fine-grading step, which is usually done by hand.”Another supplier, Rexius, located in Eugene, OR, sells hoses, blowers, and mulch spreaders. “Our customer base is an even split of various markets–contractors, landscapers, et cetera,” says Rexius’s Dan Sutton. “Many are getting involved in erosion control projects, and some have purchased our Express Blower patented seed-injection system, which allows you to blow-apply compost and seed at the same time.” The four current Rexius models range from 20- to 90-yd.3 capacities. The machines offer dry or moist application, with the ability to deliver products with a moisture content between 0 and 60%. Depending on the model, Express Blowers cost between $119,000 and $272,000–”and that includes a brand-new truck chassis,” Sutton adds.Since seeing them in action, Bales is a fan of Rexius’s products. “In Portland, a local contractor composted the street medians. Because the city wanted wildflowers in the medians, the company mixed the seeds right into the compost mix and applied it all at once.”Conclusion: Compost!Many advantages make compost an attractive choice for both temporary and continuing erosion control. Not only is it a highly effective erosion control medium, it’s also the premium choice for enriching depleted soils. And considering that compost can be made from America’s wastewater and yardwaste (which, unlike many of our natural resources, are abundant), creating and using compost is an environmentally smart idea that everyone can “dig.”
