The Disinfection of Network Pipes and Fittings

Transcription

1 Page 1 of 8 1 PURPOSE The purpose of this procedure is to set out the minimum requirements for the disinfection of all new or renovated mains, service pipes and fittings prior to them being connected to the Company s distribution network or returned to service. 2 SCOPE All new mains and service pipes laid by Bristol Water, contractors on behalf of Bristol Water or Self Lay Organisations (SLOs) where the mains are to be connected to the Bristol Water network. All mains renovated by Bristol Water or their appointed contractors. All fittings and lengths of main used in the repair of the existing network by Bristol Water or their appointed contractor. 3 RESPONSIBILITIES The Director of Water Quality for this procedure and its administration. The Director of Network for ensuring Network staff and contractors working on the Company s behalf are aware of this procedure. The Development Services Manager for ensuring all Self Lay Organisations are aware of this procedure. The Director of Civil Engineering for ensuring Engineering staff and contractors working on the Company s behalf are aware of this procedure. 4 PROCEDURE 4.0 General Requirements 4.1 Activities detailed in this procedure are restricted operations. All staff and contractors carrying out such work must have a valid EUSR card and should maintain an awareness of the information published in the Water UK document Principles of Water Supply Hygiene and the associated Technical Guidance Notes. 4.2 All activities (storage, transport, etc) associated with a main, service or fitting prior to it being used to convey potable water must be documented in an auditable way. 4.3 All pipes and fittings must be stored, transported, installed and connected in ways which minimise the risk of contamination. 4.4 The minimum requirements for the disinfection of mains, services and fittings are: i. For all new mains including renovated mains using open cut method, any

2 Page 2 of 8 replacement mains greater than 25 m in length used to repair the existing network and any service pipe with a nominal internal diameter greater than 100 mm and a length greater than 25 m see Section 5 ii. For renovated mains using pipe-bursting or slip-lining with coils see Section 6 iii. For renovated mains using spray linings see Section 7 iv. For service pipes with a nominal internal diameter equal to or less than 100 mm and greater than 25m in length see Section 8. v. For any replacement main less than 25 m in length used to repair the existing network, any service pipes less than 25 m in length irrespective of diameter and any fitting see Section Prior to disinfection all new or renovated mains and replacement mains greater than 25 m in length and services with a nominal internal diameter greater than 100 mm and greater than 25 m in length: i. Must be swabbed with the swab being retained and inspected by the relevant responsible person once removed from the main or pipe. The swab must be stored in a sealed plastic bag for a minimum of three days. ii. Must be charged with mains water ensuring the turbidity measured at the end hydrant or downstream end of pipe is below 1.0 NTU. 4.6 Disinfection of the main or service must only take place if the relevant responsible person and the person carrying out the disinfection process are satisfied the main or pipe is in a suitable condition to be chlorinated. 4.7 Irrespective of the chlorination process used the following information must be recorded as a minimum: i. Person carrying out chlorination ii. Date and time of start of period of chlorination iii. Date and time of end of period of chlorination iv. Length and diameter of main or pipe chlorinated v. The measured free & total chlorine residual in mg/l (ppm = parts per million) at the end of the chlorinated section of main prior to the main being left to stand vi. The measured free chlorine residual in mg/l (ppm) at the end of the chlorinated section of main at the end of the required contact period vii. Date, time and location of samples collected. viii. Free and total chlorine residual in mg/l (ppm) for each sample ix. Turbidity of water prior to disinfection An example of a typical form to capture these details can be found in Appendix A. 4.8 All samples must be collected and transported to the laboratory by appropriately trained persons in accordance with guidance described in The Microbiology of Drinking Water (2010) Part 2 Practices and procedures for sampling and detailed in the Company s sampling manual. 4.9 All samples must be analysed by a laboratory accredited to ISO

3 Page 3 of Samples must be analysed for: Total coliforms E. Coli Colony counts at 37 C (48 hours) Colony counts at 22 C (72 hours) Turbidity Appearance Odour 4.11 Unless otherwise stated in the relevant section no new, replacement or renovated main or service can be connected to the Bristol Water network without approval from the Bristol Water Process Science Department as detailed in procedure SC025 Certification of New Mains, Bowser, Tankers and Service Reservoirs All new, renovated or replacement mains; and services with a nominal internal diameter greater than 100 mm and a length greater than 25m must be brought into service within 15 days of a satisfactory sample being taken. If the main or service is not brought into service within this period it must be flushed with mains water and resampled. If contamination is suspected it must be re-chlorinated and sampled. The main must be flushed with mains water following connection All service pipes with a nominal internal diameter equal to or less than 100 mm and a length greater than 25 m must be brought into service within 30 days of completing disinfection. If this does not happen consideration must be given to repeating the disinfection process if deterioration of water quality may have occurred during the period. The service pipe must be flushed with mains water following connection. 5.0 All new mains including all renovated mains using open cut method, all replacement mains with a length greater than 25 m used to repair the existing network and all services with a nominal internal diameter greater than 100 mm and a length greater than 25 m 5.1 All new mains, including renovated mains using open cut method, any replacement mains with a length greater than 25m and any service with a nominal internal diameter greater than 100 mm and a length greater than 25m must be disinfected using one of the following methods: a. Disinfected with water containing sufficient free chlorine to give a measured value of 20 mg/l (ppm) throughout the entire pipe length. The main or pipe must be left standing with this level of chlorine for a minimum of 16 hours to ensure adequate dispersion and contact of the chlorine with the water and the entire internal surface of the main or pipe and fittings. b. Disinfected with water containing sufficient free chlorine to give a measured level of 50 mg/l (ppm) throughout the entire pipe length. The main or pipe must be left standing with this level of chlorine for a minimum of 1 hour to ensure adequate dispersion and

4 Page 4 of 8 contact of the chlorine with the water and the entire internal surface of the main or pipe and fittings. 5.2 At the end of the contact period and prior to flushing the level of free chlorine must be measured at the end hydrant or downstream end of pipe. If this level is more than 5 mg/l (ppm) lower than the measured value at the start of the contact period the disinfection process must be repeated. 5.3 The main or pipe must then be flushed until all the chlorinated water has been removed and the chlorine level measured at the end hydrant or downstream end of pipe is the same as the incoming water supply used to flush the main or pipe. The main or pipe must be left charged with normal mains water for a minimum of 16 hours prior to sampling. 5.4 Samples must be taken from appropriate points including a mains reference point and the downstream end hydrant or end of pipe and from any branches. For long sections of main or pipe a minimum of one sample per 250 m of main or pipe must be collected in addition to the mains reference and downstream end hydrant or end of pipe. When it is not possible to collect samples at points a maximum distance of 250 m apart on the main or pipe, sufficient samples must be taken from the end hydrant at appropriate intervals so that water sampled is representative of that held within the main or pipe at 250 m intervals. For example on a 1 Km of 100 mm main, after the initial end hydrant sample additional samples will be collected from the end hydrant after 1964 litres, 3928 litres and 5892 litres have been discharged from the main. 6.0 All renovated Mains Pipe-bursting or slip-lining with coils 6.1 All renovated mains using pipe-bursting or slip-lining, where a single coil or liner is installed in an existing main, must be disinfected using one of the following methods: a. Disinfected with water containing sufficient free chlorine to give a measured level of 20 mg/l (ppm) throughout the entire pipe length. The main must be left standing with this level of chlorine for a minimum of 16 hours to ensure adequate dispersion and contact of the chlorine with the water and the entire internal surface of the main and fittings. At the end of the contact period and prior to flushing the level of free chlorine must be measured at the end hydrant. If this level is more than 5 mg/l (ppm) lower than the measured value at the start of the contact period the disinfection process must be repeated. The main must then be flushed until all the chlorinated water has been removed and the chlorine level measured at the end hydrant is the same as the incoming water supply used to flush the main. The main must be left charged with normal mains water for a minimum of 16 hours prior to sampling. b. Disinfected with water containing sufficient free chlorine to give a measured level of 50 mg/l (ppm) throughout the entire length of pipe. The main must be left standing with this level of chlorine for a minimum of 1 hour to ensure adequate dispersion and contact of the chlorine with the water and the entire internal surface of the main and

5 Page 5 of 8 fittings. At the end of the contact period and prior to flushing the level of free chlorine must be measured at the end hydrant. If this level is more than 5 mg/l (ppm) lower than the measured value at the start of the contact period the disinfection process must be repeated. The main must then be flushed until all the chlorinated water has been removed and the chlorine level measured at the end hydrant is the same as the incoming water supply used to flush the main. The main must be left charged with normal mains water prior to sampling 6.2 Samples must be taken from appropriate points including a mains reference point and the downstream end hydrant and from any branches. For long sections of main a minimum of one sample per 250 m of main must be collected in addition to the mains reference and downstream end hydrant. When it is not possible to collect samples at points a maximum distance of 250 m apart on the main, sufficient samples must be taken from the end hydrant at appropriate intervals so that water sampled is representative of that held within the main at 250 m intervals. For example on a 1 Km of 100 mm main, after the initial end hydrant sample additional samples will be collected from the end hydrant after 1964 litres, 3928 litres and 5892 litres have been discharged from the main. 6.3 Mains renovated by pipe-bursting or slip-lining and disinfected using the 1 hour contact period can be returned to service before sample results become available, providing only a single unbroken coil of main is used whose length is not greater than 100 m or the diameter is not greater than 180 mm. 7.0 All Renovated Mains spray lined 7.1 Lining of mains with polyurethane (PU) must be carried out in accordance with the Information and Guidance Note (IGN ) and Water Industry Standard (WIS ) using approved material applied in accordance with the manufacturer s instruction. PU linings can only be applied by accredited contractors in accordance with specified conditions of approval. 7.2 All renovated mains using spraying lining must be disinfected using water containing sufficient free chlorine to give a measured level of 50 mg/l (ppm) throughout the entire length of pipe. The main must be left standing with this level of chlorine for a minimum of 1 hour to ensure adequate dispersion and contact of the chlorine with the water and the entire internal surface of the main and fittings. 7.3 At the end of the contact period and prior to flushing the level of free chlorine must be measured at the end hydrant. If this level is more than 5 mg/l (ppm) lower than the measured value at the start of the contact period the disinfection process must be repeated. 7.4 The main must then be flushed in accordance with the manufactures instruction or for a minimum of 1 hour at 0.5 ms-1. The chlorine level measured at the end hydrant must be the same as the incoming water supply used to flush the main. Flushing must continue until the chlorine level measured at the end hydrant is the same as the incoming water supply. The main must be left charged with normal mains water prior to sampling.

6 Page 6 of Samples must be taken from appropriate points including a mains reference point and the downstream end hydrant and from any branches. For long sections of main a minimum of one sample per 250 m of main must be collected in addition to the mains reference and downstream end hydrant. When it is not possible to collect samples at points a maximum distance of 250 m apart on the main, sufficient samples must be taken from the end hydrant at appropriate intervals so that water sampled is representative of that held within the main at 250 m intervals. For example on a 1 Km of 100 mm main, after the initial end hydrant sample additional samples will be collected from the end hydrant after 1964 litres, 3928 litres and 5892 litres have been discharged from the main. 7.6 In additional to the normal analytical suite, samples collected following spray lining must also be analysed for general organics (GCMS) 7.7 Mains renovated by spray lining and disinfected using the 1 hour contact period can be returned to service before sample results become available. 7.8 Mains renovated by spray lining with a dead end or a shut valve must have a continuous flow for the first 24 hours of service after recommissioning to ensure the residence time does not exceed 1 hour. 8.0 All service pipes with a nominal internal diameter equal to or less than 100 mm and greater than 25m in length 8.1 Service pipes must be disinfected using one of the following methods: a. With water containing sufficient free chlorine to give a measured value of 20 mg/l (ppm) throughout the entire pipe length. The pipe must be left standing with this level of chlorine for a minimum of 16 hours to ensure adequate dispersion and contact of the chlorine with the water and the entire internal surface of the pipe and fittings. b. With water containing sufficient free chlorine to give a measured level of 50 mg/l (ppm) throughout the entire length of pipe. The pipe must be left standing with this level of chlorine for a minimum of 1 hour to ensure adequate dispersion and contact of the chlorine with the water and the entire internal surface of the pipe and fittings. 8.2 At the end of the contact period and prior to flushing the level of free chlorine must be measured at the downstream end of pipe. If this level is more than 5 mg/l (ppm) lower than the measured value at the start of the contact period the disinfection process must be repeated. 8.3 The pipe must then be flushed until all the chlorinated water has been removed and the chlorine level measured at the downstream end of pipe is the same as the incoming water supply used to flush the pipe. The pipe must be left charged with normal mains water.

7 Page 7 of All replacement mains less than 25 m in length used to repair the existing network and service pipes less than 25 m in length irrespective of diameter and all fittings. 9.1 All replacement mains less than 25 m in length used to carry out repairs to the existing network must be disinfected using one of the following methods: a. If at any time during the repair process contamination of the isolated section of main is suspected or on-site risk assessment has determined the need for disinfection the main should be disinfected using 50 mg/l (ppm) free chlorine solution for a minimum of 30 minutes. b. For all other repairs with the appropriate volume of freshly made 1000 mg/l (ppm) free chlorine solution. All exposed ends of the pipe or fitting and internal surfaces must be wetted. This may be carried out using a spray application or pushing a swab soaked in 1000 mg/l (ppm) through the pipe. 9.2 Following repair the main must be flushed at an appropriate downstream hydrant until the turbidity is below 4.0 NTU and the measured free chlorine level is within 0.20 mg/l (ppm) of the incoming supply. If there is any doubt an upstream hydrant must be used to check the level of free chlorine entering the main. 9.3 Samples must be collected as described in the company working instruction WIWS003 - Sampling after burst mains. 9.4 All service pipes and fittings including pumps and meters must be disinfected using the appropriate volume of freshly made 1000 mg/l (ppm) free chlorine solution. All exposed ends of pipes or fitting and internal surfaces must be wetted. This can be achieved using a spray application or pushing a swab soaked in 1000 mg/l (ppm) through the pipe. After disinfection service pipes must be flushed through the boundary box using at least one pipe volume of mains water. The pipe should be left charged with normal mains water.

8 Page 8 of 8 Appendix A Example of a form for capturing disinfection job details. SECTION 1 JOB DETAILS Bristol Water Job No.(if known): Organisation carrying out chlorination: Your reference No. Job Location/Site: Pipe length (m) Pipe diameter (mm) Pipe material Nature of pipe to be chlorinated (tick) new main new service renovated main open cut directional drilled pipe burst sliplined other (state) I confirm that the main has been swabbed and after passes of a swab, the water in front of the final swab was clear with no particulate material present and the swabs have been returned for inspection. date signed name SECTION 2 CHLORINATION DETAILS Main flushed date/time - start turbidity - end NTU date/time end Chlorination date/time - start Cl2 concentration start mg/l (ppm) date/time - end Cl2 concentration end mg/l (ppm) contact period hours Cl2 concentration change mg/l (ppm) I confirm the main has been chlorinated, flushed and charged with mains water ready for sampling. date signed name SECTION 3 SAMPLE DETAILS sampler name: date: sample Mains ref WO 1 WO 2 WO 3 WO 4 SECTION 4 time (24 hr clock) Location (including house/plot no.) Free Cl2 mg/l (ppm) Total Cl2 mg/l (ppm) Main returned to service before sample results available? (tick) Yes No