Concentration-Time Study For Water Treatment Plants
- Who must keep a CT study on file?
- When should I complete (or update) the CT study?
- Who may submit the CT study?
- How do I prepare a CT study?
- What information is required in the CT study?
- How do I submit the completed CT study?
The CT study is an evaluation of a water treatment plant’s disinfection process based on the concentration (C) of the disinfectant and the theoretical contact time (T) of the disinfecting chemical during the treatment process. The purpose of the CT study is to:
- identify the number of disinfection zones at a water plant;
- determine the effective contact time, or T10, that is provided in each zone;
- determine if disinfection requirements are being met; and
- provide parameters used to determine daily compliance with disinfection requirements.
The information obtained in the CT study is used to complete surface water monthly operating reports (SWMORs) for surface water systems and groundwater systems under the influence of surface water (GUI) and 4-log groundwater monthly operating reports (4-log GWMORs) for groundwater systems.
Who must keep a CT study on file?
Every treatment plant that uses surface water or GUI must have a current, TCEQ-approved, CT study on file.
If your groundwater system is achieving 4-log inactivation as an option to comply with the groundwater rule, then you must have an approval letter on file and meet all the requirements stated in that letter.
When should I complete (or update) the CT study?
You must submit a CT study to us for review and approval:
- When a new plant that has been approved for construction by our Plan Review Team is approximately 90 percent complete or three months from startup.
- Any time a treatment plant undergoes renovation, a revised CT study is required if significant changes to the plant's disinfection processes occurred. You must not make significant changes to your treatment plant's disinfection processes without first getting our written authorization. [See 30 TAC 290.39(j)] Significant changes to disinfection processes include any of the following:
- changing the type of disinfectant;
- moving any point of disinfectant addition or monitoring;
- changing physical facilities which changes the contact time to be more or less effective;
- changing the approved capacity of the plant; or
- any other change that we consider significant.
- When we require a CT study as a condition to the granting of an exception request.
Who may submit the CT study?
As the licensed operator, you may complete the CT study yourself or hire a Texas-licensed professional engineer to do it for you. Tracer studies must be prepared under the supervision of a Texas-licensed professional engineer.
How do I prepare a CT study?
To prepare a surface water CT study, use the Surface Water CT template , or calculate the effective T10 time. To calculate the effective T10 time, use either of these methods:
- Use the theoretical contact time and estimated baffling factor, as described in Selection of Baffling Factors and Operation Conditions for T10 Calculations ; or
- Use the baffling factor determined by empirical testing of the system in a tracer study, as described in the EPA's Disinfection Profiling and Benchmarking and Technical Guidance Document .
To prepare a groundwater CT study, use the Groundwater Minimum Specified Residual (GWMSR) Spreadsheet .
What information is required in the CT study?
For a surface water or GUI system, include this information:
- a cover page with the reason this CT study is needed and the submitter’s contact information, and
- the Surface Water CT template , completed according to the CT Template Instruction Manual .
For a groundwater system, include this information:
- a cover page with the reason the CT is needed and the submitter’s contact information,
- the Groundwater CT Study Template ,
- a schematic and description of the plant with specific details of each unit including, but not limited to:
- the dimensions of the unit,
- the minimum and maximum water levels of the ground storage tanks,
- the disinfectant injection points, and
- the location of the monitoring points.
How do I submit the completed CT study?
Submit your completed CT study one of these ways:
Texas Commission on Environmental Quality
Technical Review and Oversight Team, MC-159
PO Box 13087
Austin TX 78711-3087