Environmental Engineering FOURTH EDITION

Nonpoint Source Water Pollution 243

at the site may exceed the local need for crop fertilizers. Converting the animal

waste into a commercial product (e.g., methane, dry fertilizer, or soil conditioner)

is an option, but may not be economically self-sustaining for small- to medium-sized

facilities.

Erosion and sediment control includes a wide variety of agricultural practices

designed to protect the soil from being suspended and transported by water or wind.

Conservation tillage, conservation buffers, and grazing management (discussed ear-

lier) are all part of the attempt to reduce or eliminate soil erosion in agricultural areas.

Other approaches include terracing and contour farming, diverting runoff into reten-

tioddetention basins, maintaining natural or constructed wetlands (which act as a

sediment trap), conditioning soil to increase infiltration rates, maintaining wind buffers,

and creating a site-specific erosion control plan that accounts for the specific needs of

a particular agricultural site.

Construction Nonpoint Source Pollution

Erosion of soil at construction sites will not only cause water quality problems offsite,
but may be regarded as the loss of a valuable natural resource. Homebuyers expect a
landscaped yard, and lost topsoil is often costly for the contractor to replace. Builders
of houses, highways, and other construction view soil erosion as a process that must
be controlled in order to maximize economic return. Under the USEPA’s 1999 storm
water management regulations, construction activities that disturb one acre or more
are required to have NPDES storm water permits (see discussion of Urban Nonpoint
Source Pollution).
Controlling nonpoint pollution at construction sites involves careful planning prior
to, during, and after the construction process. prior to construction the site should be
evaluated to identify natural features that will affect drainage and soil erosion. An
erosion control plan should be developed to identify specific mitigation techniques
that will be used during construction, and long-term storm water and erosion control
features that will become part of the final constructed site. Environmentally sensitive
areas, including steep slopes, critical wildlife habitat, and natural waterways such as
wetlands, ponds, and intermittent streams, must be identified, and clearing in those
areas must follow local construction and erosion control ordinances. Construction
traffic, particularly heavy equipment, should be kept away from the root zone of trees
and other vegetation that you want to preserve. If the site will have a septic system,
construction traffic should be directed away from the absorption field to avoid soil
compaction.
The next step in reducing sediment pollution from construction sites is to install
erosion control devices prior to cleating the site. There are many possible techniques for
controlling erosion and reducing sediment transport during construction. One approach
is to cover the soil using biodegradable mulch, plastic mesh, reseeded vegetation (or
existing vegetation), or other materials that prevent precipitation from landing on bare
soil. Sediments can also be trapped on-site using sediment traps, catch basins, veg-
etation filter strips, silt fences, straw bales, or gravel roadways. Storm water can be