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| METHOD STATEMENT FOR DISINFECTION/CHLORINATION OF DOMESTIC WATER TANKS |
Table of Contents
1.0. Scope
2.0. Purpose
3.0. References
4.0. Definitions
5.0. Responsibilities
6.0. Equipment and Procedures
7.0. Method of works
8.0. Procedure for Disinfection/Chlorination of Domestic Water Tank
1.0. Scope
This method Statement details for the Disinfection & Chlorination of Domestic Water Tanks - [Project Name]
2.0. Purpose
The purpose of this procedure is to define the inspection, testing method, and criteria for Disinfection and chlorination of Domestic Water Tanks and piping to confirm the specified requirements of project specification documents and to achieve completion of the specified scope of work.
3.0. References
Project Specification Section:
This Document has been preferred with the following documents:
1.1. Approved Method Statement
4.0. Definitions
CLIENT: Client Name
CONTRACTOR: Contractor Name
ITP: Inspection and Test Plan
MSS: Method Statement Submittal
SE: Site Engineer
QC: Quality Controller
5.0. Responsibilities
5.1. The SE shall be responsible for the following:
5.1.1. To ensure Disinfection/Chlorination of Domestic Water Tanks and piping is carried out according to the required Project Specifications as well as by the approved Method Statements
5.1.2. Ensuring that all parties who are required to make any kind of test or inspection are suitably informed as to the overall program of works and daily inspection testing requirements.
5.1.3. For checking and performing the as per the Specification + schedule.
7.0. Method of works
7.1. Procedure:
Tank & pipes shall be filled a few feet (quarter-full) with treated potable water. Calculate and Add Disinfection chemicals based on tank volume. It is recommended to use the table below to prepare a free chlorine concentration of 50 mg/L (parts per million or ppm). Mix thoroughly while filling the tank to normal operating level.
To disinfect connected plumbing lines and fixtures, open all taps until a chlorine smell is apparent at each outlet. Close taps and allow the chlorinated water to sit for at least 12 hours to ensure adequate time for disinfection
7.2. Test Equipment:
Water Analysis Test Kit:
pH testing paper :
Cl Test paper:
Temperature test meter:
8.0. Procedure for Disinfection/Chlorination of Domestic Water Tank
8.1. Pre-Checks
8.1.1. Select the workers and screen for competency and Physical fitness to perform the activity.
8.1.2. Ensure HSE induction, First Aid, and working in Confined space training are provided before engaging them to work
8.1.3. Ensure all workers at the site wear safety shoes, helmets, full-body harnesses, and gloves during tank cleaning works.
8.1.4. Ensure Fully Equipped First Aid Box should be made available at each location.
8.1.5. Ensure Emergency contact details are listed.
8.1.6. Ensure the confined space permit is implemented before starting tank cleaning works.
8.1.7. Ensure all tools and equipment for the cleaning work are well maintained. Do not use units/parts that are in poor condition.
8.1.8. Ensure & inspect the tank before entering for its safety. Follow the Confined space permit Ensure the weather condition is normal before starting to climb. Do not Work under abnormal weather conditions i.e., storms, wet conditions high winds, etc.
8.2. Accessible for Cleaning & Disinfection
8.2.1. Empty the Tank.
8.2.2. Scrub or pressure hose the Tank interior walls to remove all dirt (using approved Cleaning Chemicals if necessary).
8.2.3. Rinse the Tank and drain the
8.2.4. Wastewater through the drain.
8.2.5. Apply Disinfectant to all internal Tank surfaces.
8.2.6. Allow the Disinfectant to set for a minimum of 30 minutes or in line with the supplier’s recommendations.
8.2.7. Rinse the Tank and drain the Wastewater.
8.2.8. Refill the Tank with potable water.
8.2.9. Not accessible for Cleaning
8.2.10. Notify the Responsible Person to implement the recommended provisions or safety control measures to make the Tank accessible and safe for Cleaning.
8.2.11. Once the Tank is assessed as accessible and safe, follow standard procedure for Cleaning and Disinfection.
8.3. Water Tank Storage Cleaning and Disinfection Guidelines
Using a calibrated thermometer, measure and report the following:
8.3.1. Ambient (external temperature).
8.3.2. Tank room temperature.
8.3.3. Stored water temperature (The temperature of the tanked water shall be monitored via the drain point if practicable).
8.3.4. Visually inspect tank room for bird and/or rodent infestation and state amount.
8.3.5. If insulation allows for inspection of the external condition of the tank walls, inspect for corrosion pitting, and leaks.
8.3.6. Visually inspect the internal walls of the tank for signs of scale deposition, corrosion, and slime deposits.
8.3.7. Visually inspect the tank and associated valves/pipework for leaks.
8.3.8. Visually inspect the bottom of the tank for sludge deposition and state amount.
8.3.9. Visually inspect the internal walls of the tank for corrosion and state amount.
8.3.10. Visually inspect for signs of stagnation such as water surface dirt, oil films, insects, smell, and low input.
8.3.11. Visually inspect the water surface for; dirt, oil films, insects, and state amount.
8.3.12. Visually inspect for slimy deposits on the internal walls of the tank and state the color of the substance and state amount.
8.3.13. Visually inspect for algae growth indicated by either green or red plant-like growth on the water surface.
8.3.14. Visually inspect the insulation for signs of wear and tear and areas where the insulation has been removed.
8.3.15. Visually inspect that the lid is correctly fitted and that any bolts are securely tightened.
8.3.16. Visually inspect that all insect/rodent screens fitted are clear from debris so that water can flow easily.
8.3.17. Visually inspect that the ball valve opens and closes correctly.
8.3.18. Visually inspect all pipework for signs of corrosion and leaks, and check the condition of insulation fitted.
8.3.19. Visually inspect all valves for correct operation, signs of corrosion, and leaks.
8.3.20. Visually inspect all booster pumps fitted for correct operation.
8.3.21. Indicate the date that the tank was last cleaned and disinfected and indicate whether it was disinfected as routine or due to adverse conditions
8.4. Water Storage Tank & Piping – Disinfection steps
8.4.1. The pH of the water shall be measured and must be between 5.5 and 9.0 before the chlorinating solution is introduced. If pH is found to be below 5.5 the system shall be drained, flushed, and refilled with fresh water.
8.4.2. The tank (s) shall be filled with fresh water and chlorinating agent to give a minimum free chlorine concentration of 50ppm (50mg/l), and when full, allowed to stand for 1 hour.
8.4.3. After 1 hour, measure the free chlorine level, if the free chlorine level is below 30 ppm, repeat the above step.
8.4.4. The tank(s) shall be drained and then thoroughly flushed out with clean mains water until tests indicate that the residual chlorine concentration is no greater than 0.5ppm (0.5mg/l), or that present in the mains water supply.
8.4.5. Where the volume exceeds 2000 liters, the disinfected water must be neutralized, using Sodium thiosulfate before disposal. The neutralized waste MUST NOT be drained through the system.
8.4.6. Fix the ball valve in a close position.
8.4.7. Isolate the Tank from the system, outlets must be sealed from inside the tank
8.4.8. Empty the Tank via drain-point or by using a submersible or barrel-type pump, in the absence of a drain- point or if draining from the drain point is impracticable
8.4.9. Clean the Tank and remove all deposits of scale, corrosion, and sludge deposition using a combination of hand scraping and brushing together with the application of chemicals to dissolve or soften the scale (where necessary). Vacuum out all loose debris and deposits.
8.4.10. When using high-pressure jet washers to clean the internal surfaces of the Tank, suitable PPE must be used, including a positive-pressure respirator. In this circumstance, the escape of aerosols must be restricted or minimized.
8.4.11. Where oil and grease contaminants on the tank surface are implicated, they shall be removed using suitable de-greases. Where necessary (and practicable) the tank can be steam cleaned to remove grease contaminants.
8.4.12. Where “significant” or “highly-significant” levels of biological contamination are reported, the Tank shall be disinfected (using the disinfection method below), before the cleaning process is commenced.
8.4.13. Using a suitable sterile container, collect a water sample and submit it for biological analysis. The analysis shall measure the presence of contamination by general bacteria (Total Viable Colony Count – TVCC). Samples are to be collected no earlier than 48 hours following disinfection.
8.5. Calculating the amount of Disinfectant
8.5.1. The Responsible Company - [Company Name] shall use food-grade Disinfectants, suitable for use in Customer Water Storage Tanks and Piping.
8.5.2. The Responsible Company shall follow the directions and instructions of the manufacturer when determining the amount of Disinfectant needed to properly cover all internal surfaces of the Customer Water Storage Tank, as well as material safety data sheets (“MSDS”).
8.6. Water quality parameters to be tested and limits
Water quality is based on the makeup/supply water quality as mentioned above. Actual values will be analyzed at the site
8.6.1. Accessible for Inspection and Sampling Procedure
8.6.2. Open Tank cover.
8.6.3. Take a water sample from the Tank's bottom.
8.6.4. Transport sample to an Accredited Laboratory
8.6.5. Complete ‘Customer Water Storage Tank Inspection and Sampling Checklist’
8.6.6. Inform the Responsible Person of the test results.
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