Use of Compost and Shredded Wood on Rights of Way

Problem Statement

Highway construction has historically been viewed as a major contributor of non-point source pollution. Non-point source pollution – or pollution such as surface runoff that cannot be linked to a particular source – is cited as being the most prevalent cause of contamination in receiving waters in the United States.

Damage control for erosion at construction sites can include erosion control nets, open-weave geo-textiles, geo-synthetic mattings, erosion control blankets, loose mulches, hydro mulches, and chemical soil binders. Most are designed to absorb the kinetic energy of rainfall by minimizing its contact with the soil and reducing water velocity. The performance of common sediment control methods such as fences, straw bales, and sediment ponds depends on the quantity of site erosion and maintenance.

State recycling legislation and the possible ban of vegetative materials from Texas landfills, combined with a nationwide expansion of waste-reduction mandates and controls on debris-burning, prompted the Texas Department of Transportation (TxDOT) to investigate the recycling of roadside refuse from right-of-way clearing operations. Additionally, the Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991 encourages the environmentally safe use of compost along the rights-of-way of federally funded highways.

Objectives

The Texas Transportation Institute (TTI) conducted study 0-1352, "The Use of Compost and Shredded Wood on Rights-of-Way," for TxDOT, the Texas Commission on Environmental Quality (TCEQ), and the Federal Highway Administration (FHWA). The purpose of the study was to determine the performance of compost and shredded wood as erosion control materials for use on highway rights-of-way based on literature reviews and field tests.

Findings

The application of mulch – either compost or shredded wood – appears to be an effective erosion control method, and the mulch does not need to be removed after construction. Left in place, the mulch can provide a soil amendment to encourage the establishment of vegetation. Compost may also chemically bind some toxic substances, which suggests that it may have some application in bioremediation.

Some potential advantages of using compost or shredded wood for erosion control:

• Compost may, if incorporated, beneficially alter the texture and structure of the soil in a manner that resists erosion.
• Compost and/or shredded wood can be left in place after construction.
• Using wood chips and compost uses debris that might otherwise be placed in landfills or burned.
• Use of wood chips and compost on rights-of-way provides environmental benefits.

Several research groups in the United States and worldwide have demonstrated the potential of compost as an erosion control material. Compost, in a sufficiently dense mat can provide a physical barrier between rainfall and surface soil, dissipating the impact energy of rainfall and minimizing erosive forces.

TTI tested three materials in six test plots. The test materials were:

• Compost, consisting of mixed yard debris and municipal sewage sludge
• Shredded wood with a polyacrylamide tackifier (TERRA TACKJ SC)
• Shredded wood with a hydrophillic colloid tackifier containing germination stimulant (RMB Plus)

There were three sand plots and three clay plots, on a 1:3 slope in a simulated highway environment. Rain simulations for 1-year, 2-year, and 5-year storm events tested for sediment loss on the plots. The percentage of vegetative cover was captured using the Vegetation Coverage Analysis Program.

The compost produced 92% vegetation cover on sand and 99% vegetation cover on clay. The test plots lost 3.88 kg/10m5 of sediment on the sand plots and 0.34 kg/10m5 on the clay plots. Wood chips with TERRA TACKJ SC produced only 48% cover on sand while producing 95% vegetation cover on clay. These plots lost sediment at a rate of 11.27 kg/10m5 on sand and 0.15 kg/10m5 on clay. Wood chips with RMB Plus produced only a 57% vegetation cover on clay and a 50% vegetation cover on sand. The plots lost sediment at a rate of 10.97 kg/10m5 on sand and 0.30 kg/10m5 on clay.

The results obtained for compost met the minimum performance standards required by TxDOT for soil retention blankets. Wood chips with TERRA TACKJ SC would qualify as a material for use on clay with slopes of 3:1 or less. The wood chips with RMB Plus did not meet any TxDOT standard.

Implementation

Test results exceeded expectations and are most encouraging.

Certainly, the potential cost savings of using compost or wood chips with tackifier rather than rolled materials are significant. However, cost-effective application methods and quality-control issues must be resolved before recommendations can be made for general application.

Debris from right-of-way clearing operations may provide a cost-effective source of wood chips.

The contents of this summary are reported in detail in The Texas A&M University System - Texas Transportation Institute Research Report 1352-2F, "The Use of Compost and Shredded Wood on Rights-of-Way for Erosion Control," Beverly B. Storey, Jett A. McFalls, and Sally H. Godfrey, Preliminary Report Dated - November 1995. This summary does not necessarily reflect the official views of the FHWA, TCEQ, or TxDOT.