4.2 Amending Construction Site Soils

Naturally occurring (undisturbed) soil and vegetation provide important stormwater functions including: infiltration; nutrient, sediment, and pollutant adsorption; sediment and pollutant filtration; storage; and pollutant decomposition. Figure 4.1 illustrates the typical soil maturation process over the course of a four-year period. These functions are largely lost when development strips away native soil and vegetation and replaces it with minimal topsoil and sod or other plantings. Not only are the stormwater benefits lost, but the landscapes themselves can become pollution-generating pervious surfaces if pesticides, fertilizers, and other landscape and/or industrial/household chemicals are used for maintenance (Ecology, 2012b).

Installing amended soils can regain greater stormwater functions in the post-development landscape and help preserve the plant and soil system more effectively. This type of approach provides a soil/landscape system with adequate depth, permeability, and organic matter to sustain itself and to continue working as an effective stormwater infiltration system (Ecology, 2004).

Figure 4.1 - Soil Maturation Process
Typical soil maturation process over the course of a four-year period. Source: Courtesy of the University of Arkansas Community Design Center.