Infiltration Through Disturbed Urban Soils and Compost-Amended Soil Effects on Runoff Quality and Quantity

Abstract

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. Because of the large amounts of variability in the infiltration rates found, it is important that engineers obtain local data to estimate the infiltration rates associated with local development practices.

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. The sorption and ion-exchange properties of the compost reduced the concentration of many cations and toxicants in the infiltrating water, but nutrient concentrations significantly increased. In addition, the compost-amended test plots produced superior turf, with little or no need for establishment or maintenance fertilization.

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2000
EPA# EPA/600/R-00/016
NTIS# PB2000-102012