Steep slope disturbance can result in grave
consequences to watercourses. Erosion and sediment from construction
sites can impair water supplies, the biological integrity of a waterbody,
and the local hydrology. Erosion and sediment impair water supplies
by: increasing nutrient loading, impairing the ability of chlorine
to disinfect the water supply, reducing the storage capacity of
reservoirs, and increasing the treatment costs of any municipalities
that filter their water supply. Erosion and sediment impair the
biological integrity of waterbodies by filling streambeds and threatening
macroinvertebrate habitat. Additionally, erosion and sediment alter
hydrology by reducing the streams carrying capacity and increasing
the likelihood of flooding.
For these reasons, construction activities on steep slopes should
be severely limited. In the event that activities are required in
close proximity to steep slopes, stabilization of the slopes should
first be accomplished by grading to decrease runoff velocity over
erodible soils, and site fingerprinting to minimize disturbance(1).
Improper grading practices disrupt natural stormwater runoff patterns,
resulting in poor drainage, high runoff velocities, and increased
peak flows during storm events(2). For these reasons, permitting
authorities should require a grading plan before approving grading
activities. The plan should identify areas of the site to be graded
and should address alteration of existing drainage patterns, and
practices to stabilize, maintain and protect slopes from runoff.
The grading plan also should include a schedule for grading disturbances
as well as methods for disposal of borrow and fill materials(3).
Site fingerprinting is a low-impact development BMP that involves
clearing and grading only those onsite areas necessary for access
and construction activities. Extensive clearing and grading of sites
promotes off-site transport of sediments and other pollutants(4).
Site fingerprinting and the maintenance of temporary or permanent
vegetated buffers during grading operations provide sediment control
that reduces runoff and off-site sedimentation(5). Destruction
of vegetated buffers on site perimeters and alteration of existing
drainage patterns severely limits the effectiveness of land grading
in stabilizing steep slopes and erodible soils.
EPA recommends periodic inspection of all graded areas and supporting
erosion and sediment control practices, especially after rain events(6).
Early detection and repair of failing control measures are critical
in preventing small-scale eroded areas from becoming significant
conveyances of stormwater runoff and its attendant pollutants(7).
EPA also recommends a Storm Water Contamination Assessment (SWCA)
program to identify primary contaminants of concern for correction
or prevention. The program is applicable in areas that contain materials
or are subject to activities that may contribute pollutants to stormwater
runoff from the site. The program is also valuable in identifying
BMPs to control contamination from high-risk sources on a site-by-site
All photos @Brian Alberghini
By Marc A. Yaggi, Senior Attorney and William
Wegner, Watershed Analyst, Riverkeeper, Inc.
See U.S. ENVIRONMENTAL PROTECTION AGENCY,
CONSTRUCTION SITE STORM WATER RUNOFF CONTROL, LAND GRADING
(last visited January 3, 2009).