The objective of this research project was to compare the performance of conventionally-treated highway embankments with performance of roadsides treated with three types of compost (biosolids, yard waste, and bio-industrial byproducts). Conventionally prepared embankment areas consisted of compacted subsoil, or subsoil amended with topsoil. Key performance indicators were

1. erosion control
2. runoff quantity
3. runoff quality
4. growth of desired cover crop, and
5. weed growth.

Key findings for un-vegetated test areas are as follows:

• Initiation of runoff from construction areas treated with the compost blankets was delayed significantly, taking 4-10 times longer than runoff from unprotected areas.
• The total volume of runoff from compost-treated areas was less than 1% of the runoff from conventionally prepared construction areas.
• The total mass of interrill erosion from compost-treated areas was less than 0.02% of that from unprotected construction areas.
• Although the composted organics contained higher concentrations of nutrients and heavy metals than the native subsoil or topsoil, the total masses of N, P, and K and eight metals in runoff from composted areas was less than 7% of those in runoff from conventionally prepared areas. Similarly, the total masses of adsorbed nutrients and metals in material eroded from composted areas was less than 2% of that measured in solids eroded from unprotected soils.

Two peer-reviewed journal articles reporting the results of this work are cited below.

This article is not available online, but you may contact Dr. Tom Glanville for a copy.

Partial abstract: This article evaluates interrill runoff and erosion between three types of compost (biosolids, yard waste, and bio-industrial byproducts) and two soil conditions (existing compacted subsoil (control) and imported topsoil) on a 3:1 highway embankment. Composts were applied as 5 and 10 cm blankets on the surface of the control, and topsoil was placed on the surface of the control at a depth of 15 cm. Treatments were replicated six times over a two-year period for both bare soil and six weeks following planting of an Iowa DOT-specified cover crop. Rainfall was applied at an average intensity of 95 mm h-1 using a rainfall simulator, and sampling was conducted for 1 h after runoff began. All compost treatments were effective at reducing interrill erosion rates under the conditions simulated in this study. In addition, the three compost media required 30 min or longer to produce runoff, while the two conventional soils produced runoff within the first 8 min. On unvegetated treatments, the steady-state interrill erosion rates of all three composts were 3% to 24% of the two soils' rates. On vegetated treatments, the steady-state interrill erosion rates were 0.1% to 30% of the rates of the two soils.

This article is not available online, but you may contact Dr. Tom Glanville for a copy.

Partial abstract: Test areas treated with 5 and 10 cm deep blankets (unincorporated) of three types of compost (biosolids, yard waste, and bio-industrial byproducts) were constructed on a new highway embankment with a 3:1 sideslope and subjected to simulated rainfall intensity of approximately 100 mm h-1. Tests showed that runoff from unvegetated plots treated with compost contained significantly greater concentrations of soluble and adsorbed Zn, P, and K, and adsorbed Cr and Cu, than runoff from the two areas treated with conventional runoff and erosion control methods typically used by the Iowa DOT. However, the resulting total masses of individual quantifiable soluble and adsorbed contaminants in runoff from conventionally treated areas were at least 5 and 33 times greater, respectively, than those in runoff from compost-treated areas, because the significantly greater infiltration capacity of the compost-treated areas resulted in much less runoff from those areas. Based on these results, blanket applications of compost can be used to reduce runoff and erosion from construction sites without increasing nutrients and metals in stormwater runoff.

Partial abstract (follow link for complete): This project examined a common, but poorly understood, problem associated with land development, namely the modifications made to soil structure and the associated reduced rainfall infiltration and increased runoff. The project was divided into two separate major tasks:

1. testing infiltration rates of impacted soils, and
2. enhancing soils by amending with compost to increase infiltration and prevent runoff.

The first part of this project examined this problem by conducting more than 150 infiltration tests in disturbed urban soils and by comparing these data with site conditions. A complete factorial experiment fully examined the effects, and interactions, of soil texture, soil moisture, and compaction. In addition, age since development was also briefly examined. It was found that compaction had dramatic effects on infiltration rates through sandy soils, while compaction was generally just as important as soil moisture at sites with predominately clay soils. Moisture levels had little effect on infiltration rates at sandy sites.

The other series of tests examined the benefits of adding large amount of compost to a glacial till soil at the time of development. Compost-amended soils were found to have significantly increased infiltration rates, but increased concentrations of nutrients in the surface runoff. The overall mass of nutrient discharges will most likely decrease when using compost, although the collected data did not always support this hypothesis. In addition, the compost-amended test plots produced superior turf, with little or no need for establishment or maintenance fertilization.

This document is not available online. However, this report [pdf, 183k, 10pp] discusses some of its findings.

Partial summary: This report documents the testing of yard debris composts as a means of controlling soil erosion. Parallel test plots were constructed at two sites in the Portland Metropolitan area. Composts tested were: mixed yard debris compost - medium grade, mixed yard debris compost - coarse grade, and leaf compost. The composts were tested both as uniform slope cover and as barriers at the base of the test plots. These applications were compared with conventional and untreated plots. Runoff samples were analyzed for basic erosion indicators - settleable solids, total solids, total suspended solids, and turbidity. In addition, samples taken during the first and last storms were analyzed for heavy metals (including phosphorus), total organic nitrogen, nitrate-nitrite and chemical oxygen demand. Based on the results, all three yard debris composts are at least as effective as the conventional erosion control measures currently specified. The erosion control effectiveness of the composts, measured in terms of soil loss (suspended solids), was better than that measured from the sediment fences and similar in most cases to that effected by the hydro-mulch.