Disinfection and Flushing of Water Mains

Purpose of this plumbing method statement is to ensure that disinfection and flushing of water mains and related pipe lines are executed safely and in accordance with the contract requirements and that all quality assurance / control activities are conducted in a systematic manner, works are inspected and conformance is verified and documented for the project.

Prior to the commencement of any activities, the workforce will receive an induction talk on the Project site safety requirements, this induction talk will include both activity specific safety issues, as well as general safety requirements.

Where possible hazards may arise from disinfection and flushing of water mains work related activities, the necessary safety measures will be taken to prevent accident or injury at all times, which may include barriers, warning tape/ Net, signage, watchman, and proper lighting.

Contractor will enforce that Personal Protective Equipment be worn by site personnel at all times during the pipe flushing activities.

Heat Stress Training will be provided.

Provisions of adequate cool drinking water, shade, and salt water tablets will be in  place.

Plant & Equipment will be provided back-up alarms, lights, and all other applicable safety Devices.

List of materials and tools:

Water

Air vents

Blank flange with 4’’ saddle

Chlorine solution

Water Test Kit

Injection Pump

Water meter 4’’

NRV 4’’

Roles and Responsibilities

Site Engineer: To co-ordinate with consultant, supervise the site works and ensure quality and safety procedures are implemented as required.

Foreman: To supervise the site works, Control of manpower / operators and ensure quality and safety.

Pipe Fitters: To perform the pressure test, spot the leakages (if any) and repair /Replace damaged sections / joints of the pipeline.

Labors: To assist the pipe fitters and perform any manual works required.

Prior Activities

Submit program for Flushing and disinfection.

Pipe line pressure test should be passed.

Submit witnessing request and obtain approval to start flushing from Client / Engineer.

Arrange valid Calibration Certificate for Gauges.

Approval of Shop Drawings after any changes if applicable.

Drain point approval.

Shut down work for the main line shall be implemented.

Detailed proposal for flushing / disinfection to be submitted showing the quantity of water required for flushing/disinfection before 1 week to concerned department.

Water Main Flushing Method

Fill the pipeline with water through filling point after obtaining approval. At the same time chlorine solution will be injected through chlorine injection point as shown in the drawings.

The free available chlorine will be checked, it should be more than 20mg/liter.

After 24 hours, check the free available chlorine in the water by comparator kit and it should not be less than 1mg/liter.

If sample fails, add more chlorine and check the free available chlorine after 24 hours.

Step-3 has to be repeated until the concentration remains more than 1mg/liter.

Empty the water containing chlorine solution from the line after a period of 24 hours through discharge point as shown on the drawing.

Flush the line (the quantity of water to be flushed is three times the volume of the line) from filling point as shown on the drawing.

Water velocity will be minimum 1m/s to clean the line.

Water in the existing network at the point of extraction shall register a minimum of 0.4 mg/l of free available chlorine when tested with a site comparator prior to any approval being given to commence flushing.

During water flushing, the free chlorine will be checked at the sampling and discharge points till chlorine content not exceed 0.4 mg/L .

Once flushed, the water in the new pipelines shall be allowed to stand for a further 24 hours.

Lab representative will take the water samples from the line in presence of Consultant’s representative for bacteriological and chemical test.

If the sample fails repeat whole procedure at contractor’s expense until the target values/requirements are met.

Records / References

• Drawing
• Risk Assessments
• Inspection check lists

Inspection Checks:

• pipe has been tested and approved
• sample is collected for water analysis
• check number of passes as agreed with consultant
• chlorine solution injected through chlorine injection point
• check the free available chlorine in the water by comparator kit and it should not be less than 1mg/liter