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Water Quality Field Screening Program


An on-going field screening program is being used to detect illicit discharges and improper disposals into the storm water system. This program is implemented to satisfy the requirements stated in the NPDES Permit. The Water Quality Staff uses a grid method according to the original permit application.  Within this method all industrial land use areas and heavy commercial land use areas were placed on a .25 mile grid system, and all other land use areas were fitted with a .5 mile grid system. This totaled to 578 field screening sites.


Field screening involves testing chemical characteristics such as:

  • Temperature
  • pH
  • Conductivity
  • Dissolved Oxygen
  • Phosphates                                                                                           
  • Chlorine
  • Detergents
  • Phenol
  • Copper
  • Ammonia
  • Hydrogen Sulfide

These chemical characteristics are tested using various CHEMet test kits and a multiprobe that records the following parameters: dissolved oxygen, connductivity, pH and temperature.

Concrete Drainage Ditch Staff Member Conducting Field Screening 

Physical indicators used include:

  • Odor
  • Color
  • Turbidity
  • Floatables
  • Damage at outfall area
  • Deposits/Stains at the outfall area
  • Abnormal vegetation in channel or outfall
  • Poor pool quality
  • Algae growth

Each site tested involves Water Quality staff conducting two sampling events in one day.  A 4 hour time interval must pass before the second sampling event can take place.  This is shown as a.m./p.m. sampling events.

The overall site characterization, or likelihood of a presence of an illicit discharge, is categorized as:

  • Unlikely
  • Potential
  • Suspect or
  • Obvious

An unlikely characterization is described as having less than 2 of the above indicators.  Potential characterization is the presence of 2 or more indicators. Suspect characterization is described as having the presence of one or more indicators with a severity of 3.  An obvious characterization is the observable and unmistakable presence of an illicit discharge.

For further information on the Field Screening Program, see the Standard Operating Procedure (SOP).

Back to Illicit Discharges & Improper Disposal

To preserve and enhance the quality of the physical environment and infrastructure through prompt, cost effective and courteous delivery of services which protect the health, safety and welfare of citizens.

Justin Holland, Administrator
1250 Market Street
Chattanooga TN 37402 (map)
(423) 643-6311



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