Cobb County Government

Chemical Sampling

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Assessing water quality of local streams and rivers is important to protect the natural environment, human health, and ensure a safe drinking water supply. When testing chemical characteristics of water, we compare them to standards set by the State of Georgia in compliance with the Clean Water Act of 1972, for water quality protection.

The Stream Monitoring Program samples 92 sites on 21 streams four times a year. By assessing water quality so frequently, a baseline of stream chemical water quality can be established. Water quality data can then be assessed to see if any parameters are elevated above the standards. If a standard is exceeded and pollution is detected, Stream Monitoring investigates to locate the source and initiate corrective action.

All samples collected by the Stream Monitoring Program are analyzed by certified laboratory analysts at the Cobb County Water Quality Laboratory. Samples collected by the Stream Monitoring Program are analyzed for the following chemical characteristics:

    Biochemical Oxygen Demand

    Biochemical Oxygen Demand (BOD) is the measure of oxygen consumed by bacteria and other microorganisms while they decompose organic matter.

    Chemical Oxygen Demand

    Chemical Oxygen Demand (COD) is a measure of the amount of oxygen consumed during the chemical decomposition of organic and inorganic contaminants dissolved or suspended in water.


    Conductivity is the measure of dissolved ions in water. Conductivity is commonly influenced by geology and urban runoff.

    Dissolved Oxygen

    Dissolved Oxygen (DO) is the measure of how much oxygen is dissolved in water. Aquatic organisms require oxygen for respiration. Dissolved oxygen enters water through photosynthesis of aquatic plants or diffusion with the surrounding air. Consumption of dissolved oxygen in water occurs through respiration, decomposition of organic matter, and different chemical reactions. DO concentrations range from 0-14 mg/L and less than 2 mg/L is not enough oxygen to support most species of aquatic life.

    Fecal Coliform 

    Fecal Coliform bacteria are present in the feces and intestinal tracts of humans and other warm-blooded animals. Fecal coliform are indicator organisms and high numbers of fecal coliform may indicate the presence of other pathogenic (capable of causing illness) bacteria.


    Some level of metals are essential to life but high concentrations of metals are toxic to aquatic organisms. Heavy metals, which include copper (Cu), iron (Fe), cadmium (Cd), zinc (Zn), mercury (Hg), and lead (Pb), are the most toxic to aquatic organisms. Other metals analyzed are Calcium (Ca), Magnesium (Mg), Potassium (K), Sodium (Na), Boron (B), Aluminum (Al), Barium (Ba), and Manganese (Mn).

    Nutrients (Phosphorous and Nitrogen)

    Phosphorus is a natural element found in rocks, soil, and organic matter. Total Phosphorus is the measure of all forms of Phosphorus, dissolved or particulate, found in a sample of water. Nitrogen includes ammonia, nitrite, nitrate, organic and inorganic nitrogen. Total Kjeldahl Nitrogen (TKN) measures the sum of ammonia and organic nitrogen in the water. Nitrate dissolves easily in water and is stable over a wide range of environmental conditions. Nitrite is quickly converted to Nitrate in water by bacteria. An excess of nutrients in a water body can result in excess plant growth and eutrophication, which is the process in which decomposing organic matter depletes the water of oxygen, killing other organisms such as fish.

    pH –pH

    A measure of how acidic or basic water is. pH ranges from 0 – 14. Since pH can be affected by chemicals in the water, it is an important indicator of water that is changing chemically.


    Water temperature governs the type of aquatic life that can survive in the stream. Temperature also influences water chemistry, by affecting the rate of chemical reactions and biological activity, and the dissolved oxygen concentration.

    Total Suspended Solids

    Total Suspended Solids (TSS) are solids in water such as silt or decaying plant and animal matter that can be trapped by a filter.


    Turbidity measures the light-scattering effect of suspended particles in the water, such as silt, sediment, organic material, and plankton. Turbidity appears as cloudiness caused by these suspended particles in the water.
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