Introduction. Training Requirements. Hydrants & Standpipes. DOM-WN-PRC SAMPLING FROM A HYDRANT Version D April 2016

Transcription

1 Introduction It is sometimes necessary to take samples e.g. for investigational or operational purposes, from locations such as new, renovated or repaired mains. In these circumstances, the sample may have to be taken directly from the distribution network main by means of a standpipe, attached to a hydrant point or meter box. To ensure samples are not contaminated, all taps used for sampling should be fully disinfected. It is well documented that hydrants with a standpipe attached can give erroneous failures. With this in mind, sampling from a hydrant (bacteriological or chemical) should only be done as a last resort. If it is possible, a sample should be taken from Customers cold kitchen tap, although it is recognised this isn t always possible. Samples for regulatory drinking water compliance purposes must never be taken directly from hydrants. Training Requirements All employees & contractors who access the SW Live Network must be trained in DOMS Modules 1 12 and must have in their possession their (current) DOMS & National Water Hygiene cards while on site. All employees & contractors who take samples must be trained in Module 13 Sampling. Hydrants & Standpipes If sampling from a hydrant / standpipe has to be done, the following precautions must be taken: Standpipe should be disinfected with a 250 mg/l chlorine solution (see Scottish Water Hygiene Code of Practice) prior to arrival on site and then stored and transported wrapped in a new plastic bag or similar, to ensure it is clean / disinfected before use. All potential contamination should be removed from the outside of the hydrant chamber, before connecting standpipe and any debris present in the area surrounding or in proximity to the connection (the hydrant bowl) should be cleared away and disposed of appropriately. This includes water in the hydrant pot or bowl before connecting the standpipe. Consideration should be given to environmental conditions e.g. heavy rain, oil in the hydrant chamber etc. Sampling staff should be aware of potential risks and dangers associated with the nature and type of debris that may accumulate in hydrant boxes (for example the presence of sharp or dangerous objects). Remove hydrant box lid and any debris, bail out accumulated water to well below bottom of the screw threads, using an appropriate container e.g. a clean plastic beaker. If all the water cannot be removed, the amount remaining should be to an acceptable level, e.g. several centimetres below the bottom of the screw threads on the hydrant connection, such that it cannot cause contamination of the water being sampled. Unscrew hydrant cover (if present) and open the hydrant valve carefully to flush out any accumulated debris from the hydrant bowl or pot. Run off about 4 5 litres of water. If the water doesn t drain away, it should be removed and the amount remaining should be to an acceptable level that does not cause contamination to the water being sampled, e.g. several centimetres below the bottom of the screw threads on the hydrant connection. Page 1 of 8

2 Unwrap disinfected standpipe and connect it to the hydrant. Direct standpipe away from the hydrant box towards a suitable drainage location. Open standpipe tap slowly, as rapid opening may cause turbulence in the main and stir up sediment. Flush water through the standpipe until the water runs clear e.g. for a minimum of 5 minutes. Turn off the standpipe tap. The residual chlorine concentration (Free & Total) of the water should then be measured. Any required chemical samples or particle / biology samples using a hydrant bag / net samples (for microbiological / microscopy examination) should be taken at this point from the standpipe. Samples for organic analysis (GCMS including diesel contamination) may be affected when taken from a hydrant and should be avoided. After all chemical and biology / particle samples have been taken, the following procedure can be carried out to take the microbiological sample. Page 2 of 8

3 Non Microbiological Sampling 1) Disinfect standpipe using 250mg/l Chlorine solution prior to arrival on site 2) Standpipe should be stored and transported wrapped in a new plastic bag or similar, to ensure that it is clean before use in the hydrant chamber etc. 3) Consideration should be given to environmental conditions e.g. heavy rain, oil in the hydrant chamber etc. 4) Remove any contamination present from outside the hydrant 5) Remove the hydrant box lid any debris & water from the area of the connection - if unable to remove all water ensure level is several centimetres below the bottom of the screw threads 6) Unwrap the standpipe & connect to the hydrant, directing it to a suitable discharge location. 7) Open the standpipe tap slowly. Flush the standpipe until the water runs clear e.g. minimum of 5 minutes. 8) Check & record Free & Total Chlorine Residuals. 9) Any required chemical samples or particle / biology samples using a hydrant bag / net samples (for microbiological / microscopy examination) should be taken at this point 10) Samples for organic analysis (GCMS including diesel contamination) may be affected when taken from a hydrant and should be avoided. See following page for Microbiological samples Page 3 of 8

4 Microbiological Sampling Standpipes used for microbiological sampling should not be used for other purposes. The hydrant valve should be closed and the standpipe removed (put back in the clean plastic bag used for transportation to avoid contamination). Bail out any excess water in the hydrant bowl using the clean plastic beaker. Pour 10% sodium hypochlorite solution (approximately 100 ml) into the hydrant bowl and over the screw threads. Take care when handling sodium hypochlorite and always wear the appropriate personal protective equipment. Chlorine based materials & solutions: Sodium hypochlorite solution and other chlorine based solutions e.g. dichloroisocyanurate (tablets) are generally used for disinfection. These solutions are highly corrosive and should be handled with care. If these solutions come in contact with skin, the area should be washed immediately with copious amounts of cold or tepid water. Follow all required safety precautions when handling such solutions and always use the required PPE. The standpipe should then be carefully placed back into position to avoid contamination and the hydrant valve opened gently, until a flow of chlorinated water just begins to discharge from the tap. Close the standpipe immediately. The hydrant valve should then be closed and the standpipe left to stand to ensure adequate disinfection time e.g. a minimum of 5 minutes up to a maximum of 10 minutes. The hydrant should then be re-opened and water in the standpipe flushed through the standpipe tap for approximately 1 minute. The chlorine residuals (Free & Total) should be measured to ensure that the disinfectant has been flushed out and to ensure that the chlorine content is in the range normally found in the local distribution zone. Turn off the tap, flame it / disinfect it (see below) and take the microbiological sample in accordance with Scottish Water Sampling Procedures. Tap Disinfection Taps can be disinfected in a number of ways. Where practicable, all external fittings should be removed from the tap. Any accumulated deposits should be removed (in an appropriate manner) from the tap e.g. grease and slime can be removed using a new proprietary isopropyl alcohol wipe. The tap should then be turned on and water run to waste at a uniform flow rate, in order to remove any debris, sediment and/or biofilm contained within the tap and any standing water in the pipe work. Depending on individual circumstances this flushing process may take several minutes or longer. The residual chlorine concentrations should then be measured (Free & Total). When the tap and associated pipe work are free of debris, sediment and/or biofilm and when the chlorine measurements have been taken, the tap should be turned off to allow the tap to be disinfected. Page 4 of 8

5 For disinfecting a tap prior to taking a microbiological sample use a disinfectant solution comprising 1 % available chlorine (equivalent to 10,000 mg/l as chlorine). Suitably labelled wash bottles may be used to store this solution, but these solutions must be prepared on the day of use from either commercially available stock solution e.g. a 1 in 10 dilution (using clean water) of neat % Sodium Hypochlorite solution. If using chlorine tablets to prepare the solution use 1 x INSTACHLOR PR-3000 dissolved in 300 mls of water gives a nominal 10,000 mg/l (1%) solution. This should be used for disinfecting taps prior to taking a microbiological sample only. Disinfect the tap using the above prepared solution. The nozzle of the wash bottle should be inserted as far as possible into the spout of the tap and disinfectant solution injected into the tap until the solution runs out of the tap. Disinfectant solution should also be sprayed onto the exterior part of the tap, particularly around the spout. Care should be taken to ensure that the disinfectant solution does not spray out from the tap onto areas where it might result in damage to fixtures and fittings or cause personal injury. Once the tap has been sprayed with disinfectant solution, it should be left for two to three minutes in order to allow the disinfection process to take place. Once the disinfection time has elapsed, the tap should be turned on gently. Care should be taken with the exterior part of the tap as this may still contain traces of disinfectant. The water should then be allowed to run to waste at a uniform flow rate to ensure that all the disinfectant solution is removed from the inside of the tap. Failure to flush the tap adequately will lead to elevated levels of residual chlorine concentrations. This in turn will lead to a sample being collected that is not representative and contains excess disinfectant solution. In certain circumstances, and recognising that modern plastic anti-splash devices can harbour bacteria and fungi, it may be beneficial to repeat the disinfection process, i.e. disinfect the tap twice. It has been shown that, in some cases, disinfecting the tap, allowing water to run to waste for 2-3 minutes and disinfecting the tap again, can enhance the decontamination process. Flaming Except for metal taps fitted with non-removable plastic anti-splash devices, disinfecting metal taps may be carried out by flaming them. Do not flame Customers taps!. To disinfect a metal tap by flaming, a small proprietary propane or butane burner can be used. The burner should produce a tight, controllable flame. When the burner is being used, care should be taken, and the flame directed away from flammable or heat-sensitive items. Never flame a tap with a plastic insert. With the tap turned off, start flaming it at the nozzle, gently moving the flame backwards and forwards over the spout of the tap, until steam and boiling water issues from the nozzle. See picture below. Care should be taken to ensure that steam and hot water, which may spurt out of the nozzle during flaming, does not cause damage to fixtures and fittings or cause personal injury or injury to others. If the design of the tap is such that water drains out of the tap when it is turned off, the full length of the spout should be heated such that, when the tap is turned back on, the first issue of water boils momentarily. Figure 1 Flaming a tap Page 5 of 8

6 After flaming the tap and prior to collecting the sample, the tap should be turned on and allowed to run to waste, at a uniform flow rate, until pipe work is cleared of standing water for 2 3 minutes. After flushing take the sample in accordance with Scottish Water Sampling Procedures. Always clearly mark the samples on the MCL1158 Sampling Pro-forma Sheets as taken from a hydrant, as failing results may have less significance. Turn off the water; remove the standpipe and replace hydrant cap and the box lid. Only ever use Scottish Water approved standpipes. END OF PROCEDURE Page 6 of 8

7 Document Control This document is a CONTROLLED DOCUMENT when viewed on Wavelength. The document becomes UNCONTROLLED if printed or downloaded from Wavelength or any other source. Refer to the Wavelength site for the latest version of this document. Change Request A change to this document can be requested by completing a Change Request Form - refer to document DISTRIBUTION OPERATION and MAINTENANCE STRATEGY GOVERNANCE (DOM-WN-GOV ) for change request procedure. Legal Notice Copyright of this document is owned by Scottish Water. The document may not be copied or reproduced in any way. This document and the intellectual property rights in it belong to Scottish Water and except where you are specifically licensed to use this document, you have no right to re-use it. Disclosure of this document under freedom of information does not change the position on (i) ownership and (ii) re-use. Page 7 of 8

8 Record of Changes and Amendments Document Section/ Reference Number Document / Section Title Version Number Date Section 3 Responsibilities B Oct 2013 Archived Document / Section Text Affected New section inserted covering DOMS Training Archived Document / Section Replaced By Foreword Foreword C Aug 2014 New legal notice inserted Section 4.4 HYDRANTS & STANDPIPES D Jul 2015 Disinfection solution requirement for standpipes and new template duplicated info removed. FOREWORD, Contents, Preamble, Training All Edited text D April 2016 Rearranged text / edited Page 8 of 8