In addressing the subject of pollution, we must be aware that none of the natural resources, especially water and air resources, is completely pure. Air often contains pollen, dust, volcanic ash, and other particu-lates. In that sense, the air we breathe would rarely be "pure," even without the influence of man.
Likewise, all natural water, including surface water, ground water, and precipitation, contains foreign substances; it is not simply two parts hydrogen and one part oxygen (H20). Some foreign substances occur naturally, and some are there because of cultural contamination (human activity on the land).
Natural water might contain minerals, salts, algae, bacteria, gases, and chemicals and have an unpleasant taste, yet it still might not be considered polluted. Water generally is considered polluted only if foreign substances in the water result in impairment of a specific, designated use of the water. The determination of use impairment is based on the quality of water not meeting established limits for specific constituents (for example, 5 mg/L of dissolved oxygen) and not necessarily on an obvious problem, such as an algae bloom or bad taste and odor.
Water may be contaminated by substances, but not be considered polluted with regard to meeting established standards. A farmer, for example, may fertilize the farm pond at recommended rates in the spring to enhance fish production. This purposeful addition of nutrients to the water and the subsequent minor enrichment do not constitute an act of pollution because the intended use of the water (fish production in this case) is not impaired; rather, fish production is enhanced.
On the other hand, if the water from that same farm pond was discharged to a stream having an inlet pipe for a municipal water supply immediately downstream, the discharge could be considered polluted if it contained a concentration of any substance that did not meet State standards for a water supply. The algae that served as a source of feed for aquatic organisms in the pond could become unwanted suspended solids and a potential problem at the water treatment plant.
In this chapter, pollution refers to a resource that has been contaminated beyond legal limits. Such limits are specifically designated by State agencies, but may be limited to only the water and air resources. However, limits can also be applied to soils and plants to prevent unsafe levels of heavy metals where municipal sludge is being applied. Fish and cattle (animal resources) may also be contaminated to unsafe levels with pesticides or other substances, but specific pollution limits for this resource may not be a part of State standards.
Chapter 1 provides detailed information on the designated use classifications that most States use to establish pollution limits for water. Information on the ways in which each use can be affected by agricultural pollutants and the characteristics of nonpoint source pollution are also included in that chapter.
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