25 October 2004
Most Appropriate Uses. Soil amendments increase the soil's infiltration
capacity and help reduce runoff from the site. They have the added benefit of changing
physical, chemical and biological characteristics so that the soils become more effective
at maintaining water quality.
Cost Data. Compared to the costs of traditional lawn preparation practices,
enhancing native soil with soil amendments may have increased upfront costs.
However, the cost of using amended soils can be at least partially offset by reductions
in the required volume of stormwater ponds or other detention or retention practices.
Tilled Compost-Amended Turf (TCT) practices, besides requiring greater site
preparation, require larger volumes of material to be delivered to the site as well as
methods to ensure that the amendments are well mixed with the existing soil.18 The
following cost estimates are based upon 1996 prices in the Seattle, Washington
metropolitan area. Potential soils analysis costs are not included, but can cost as much
as 5 per sample.
Table 8-1. Costs Associated with Soil Amending19
Average Cost (1996 U.S. dollars)
Soil and Site Preparation
61 per square foot
per cubic yard
5 to 10 per square foot
Maintenance Issues. In some jurisdictions across the country, soil
amendments may be inspected as part of the sediment control plan for a site, usually
upon site completion. Routine inspection of amended soils should evaluate factors that
may affect the soil's infiltration capacity, aeration and organic content. Typical post
construction concerns include areas subject to compaction, hydric or waterlogged soils,
poor cover conditions, increased development, and a decrease in organic content. In
addition, a routine soil infiltration rate analysis of amended soils in potential problem
areas is recommended.
Corrective Actions. Corrective actions for soil amendments involve
restoring the infiltration capacity of the soil. Reductions in infiltration capacity typically
result from compaction or extensive root matting of groundcovers, such as grasses.
The first step of corrective action should be extensive mechanical aeration. If this does
not restore the infiltration rate, organic amendments should be disked into the soil for a
depth of several inches and the site restabilized.
BIORETENTION. Bioretention areas typically have porous backfill under the
vegetated surface, and an underdrain that encourages infiltration and water quality
filtering while avoiding extended ponding.
Chollak and Rosenfeld, 1998.