Water Quality

Water quality can be defined as the current status or condition of the water in a specific aquatic ecosystem.  It is much easier to describe what poor water quality is than to describe what conditions are considered good water quality.  Many of the lines between good and poor are stream specific.  Each watershed has some natural buffering capacity. This allows the water to adapt and compensate for normal changes in the environment such as leaching from the soil or the occasional heavy rain.

MoDOT is responsible for implementing control measures to prevent the excessive release of sediment and pollutants into nearby waterways whenever one acre or more of land is disturbed for roadwork.  Links to Water Quality legislation, policies, and guidance is located on the Federal Highway Administration’s website.

Water Pollution

Pollution occurs when conditions exceed the watershed’s ability to compensate for the changes. Polluted water may be discolored, possess a coating on the bottom of a stream, or may show no visible sign at all of pollution.  There are many different kinds of pollution.  The two major categories are point source and nonpoint source.

Point Source Pollution

Point source pollution comes from a defined, specific source such as a discharge pipe from a factory, a municipal sewage treatment plant, or a power generating station.  The state’s Clean Water Laws as well as the federal Clean Water Act have made great strides towards identifying, controlling and cleaning up point source pollution. 

Non-Point Source Pollution

Now that much of the point-source pollution is being controlled, problems are arising that were previously overshadowed.  Non-point source pollution (NPS) is being recognized as a major factor in the deterioration of today’s watersheds.  Section 319 of the Federal Clean Water Act covers NPS pollution.

The most common types of non-point source pollution agriculture, erosion and sedimentation, and acid rain.  Agriculture is a very serious source of NPS because there are so many kinds of pollution generated.  The two most likely pollutants from agriculture are nutrients and sediments.  Many of the pesticides and fertilizers used today have a tendency to be washed off of plants and filter into waterways through runoff, increasing nutrient loads.  Nutrient and sediment levels increase when unprotected streams run through livestock pastures.

Erosion and sedimentation are also very common pollutants.  Often excess amounts of solids enter waterways because of run-off.  Construction sites, fallow fields, and other areas of unprotected soil are extremely prone to large amounts of erosion.  Poor forest management practices, such as clear cutting a hillside can also result in increased erosion. One method of decreasing erosion and sedimentation is with the protection and establishment of riparian buffers.

Acid rain or acid precipitation is becoming a common pollution source.  Car exhaust as well as other discharges spouts compounds into the air.  As clouds form and water vapor mixes with the gases, acids are formed.  Sulfuric and nitric acids are the two most commonly found.  When the clouds release the water as precipitation, these acids are carried down to earth and drain into waterways.

a stormwater drain under the highway


Stormwater picks up excess pollutants along the way that is a leading cause of Missouri’s water quality problems. Each of us contributes to this problem without even realizing it. Fortunately, there are ways in which we can all help to lower the amount of pollutants reaching our waterways and groundwater.

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