DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK INSTRUCTION USE AND DISPOSAL OF CHLORINE SOLUTIONS
Document Title:
Work Instruction –
Use and Disposal of Chlorine Solutions
Document Reference:
DOM-WN-WIN-00000102
Version:
C
Date:
October 2013
Approved By:
Public Health Team
Title:
Public Health Manager
DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT ORK INSTRUCTION USE AND DISPOSAL OF CHLORINE SOLUTIONS
Ref:
DOM-WN-WIN-00000102
Version:
C
Date:
October 2013
Record of Changes and Amendments
Amendment No.
Document Section/ Reference Number
Document / Section Title
Version Number
Amendment Date
1
3.13 (a)
Disinfection of Sample Taps
B
May 2013
Reference to DOMS procedure ‘Sampling from a Hydrant’
2
3.2
Disposal of chlorinated water
B
May 2013
Changes to when to dechlorinate
3
3.3
Dechorination
B
May 2013
Changed text on preferred method
4
All
All
C
October 2013
Archived Document / Section
Archived Document / Section Replaced By
Text Affected
Re-formatting throughout for consistency
Sheet
i
DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK INSTRUCTION USE AND DISPOSAL OF CHLORINE SOLUTIONS
Ref: DOM-WN-WIN-00000102 Version: C Date: October 2013
FOREWORD Background DOMS stands for ‘Distribution Operation & Maintenance Strategy’ and is being used by Scottish Water to: • Safeguard the quality of water to customers. • Ensure that Scottish Water apply due diligence to their Scottish Water distribution network. The DOMS procedures and work instructions affect all functional staff who work on the network, which includes internal employees and employees of external organisations (i.e. planners, operators, delivery teams, Framework Contractors, or any other contractors). Through the application of the DOMS principles in day-to-day network activities, Scottish Water and their approved contractors will operate and maintain their water distribution networks through operational ‘best practice’. This will allow Scottish Water to meet the following objectives: • • • • • •
to maintain water quality. to maintain continuity of supply. to maintain water supply hygiene. to undertake water quality incident management. to maintain a cost-effective water supply. to ensure a course of action for timely network intervention (Capex and/or Opex) to maintain statutory obligations and customer satisfaction.
Responsibility The responsibility for adoption and implementation of all DOMS procedures and work instructions rest with Scottish Water General Managers and senior managers of external organisations. It is the responsibility of all Scottish Water employees and those of external organisations to comply with DOMS procedures and work instructions. 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 (DOMWN-GOV-00000001)’ for change request procedure. Copyright Copyright of this document is owned by Scottish Water. The document may not be copied or reproduced in any way. Page i
DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK INSTRUCTION USE AND DISPOSAL OF CHLORINE SOLUTIONS
Ref: DOM-WN-WIN-00000102 Version: C Date: October 2013
CONTENTS
FOREWORD…………………………………………………………………………………………………. i CONTENTS ……………………………………………………………………………………...................
ii
1 PREAMBLE ………….………………………………………………………………………………….. 1 1.1 1.2 1.3 1.4
Procedure Objectives ……………………………………………..………………………….…. Related Parent Documents………………………………………………….………………….. Related External Controlled Documents…………………………………………................... Related Internal Controlled Documents…………………………………………...................
1 1 1 1
2 PROCEDURE FLOW CHART………………………………………………………………………….. 1 3 DESCRIPTION…….……………………………………………………………………………………… 1 3.1 Preparation and Use of Sodium Hypochlorite Solutions........................................................ 3.1.1 Hypochlorite..…….………………………………………………………………………….. 3.1.2 Instachlor PR Tablets (Rapid Release)…….…………………………………………….. 3.1.3 HTH Chlorine Tablets (Slow Release)…………………………….……………………… 3.2 Disposal of Chlorinated Water…………………………………………………………………….. 3.3 Dechlorination………………………………………………….…………………………………….
2 2 3 6 8 9
Page ii
DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK INSTRUCTION USE AND DISPOSAL OF CHLORINE SOLUTIONS
1.
PREAMBLE
1.1
Procedure Objectives
Ref: DOM-WN-WIN-00000102 Version: C Date: October 2013
Chlorine solutions are regularly used on the Networks as a means of disinfecting equipment, clothing, water mains and fittings and for secondary chlorination at Service Reservoirs. These solutions can cause injury if not used correctly and can cause damage to the environment if not disposed of or neutralised adequately. This instruction outlines the steps to be followed to ensure the safe use and disposal of Chlorine solutions. 1.2
Related Parent Documents None
1.3
Related External Controlled Documents • •
1.4
2.
H&S Guidance COSHH Related Internal Controlled Documents
•
Water Hygiene Code of Practice - APPENDIX II: - GUIDELINES FOR USE AND DISPOSAL OF CHLORINE SOLUTIONS
•
DOM-WN-TBT-00000010 Preparation and Use of a Chlorine Disinfectant Solution PROCEDURE FLOW CHART No procedural flow chart is needed for this procedure.
3.
DESCRIPTION
Hypochlorite (Sodium & Calcium) solutions are commonly used as an effective method of disinfecting equipment, clothing, water mains and fittings and carrying out secondary chlorination at service reservoirs. Appropriate health and safety procedures & PPE must be used when handling / using hypochlorite solutions & tablets. You must refer to the relevant H & S guidance notes, risk assessments and COSHH data sheets when preparing, using or disposing of these materials / solutions. Even in low concentrations chlorinated / chloraminated water can kill fish life / cause environmental damage if discharged to watercourses. It is therefore essential to plan, in advance, how best to dispose of chlorinated / chloraminated water to the environment. Failure to carry out this task correctly could lead to Scottish Water being prosecuted.
Page 1 of 9
DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK INSTRUCTION USE AND DISPOSAL OF CHLORINE SOLUTIONS
Ref: DOM-WN-WIN-00000102 Version: C Date: October 2013
3.1
Preparation and Use of Sodium / Calcium Hypochlorite Solutions
3.1.1
Hypochlorite
Sodium hypochlorite solution is a caustic solution containing between 10% to 15% available chlorine when new. BE SAFE - always use appropriate protective equipment when handling sodium hypochlorite. For details of the appropriate protective clothing please refer to Health & Safety document - DOMS Tool Box Talk No 8. It is particularly suited for disinfection of the following:
Equipment and clothing (it will bleach clothing)
New & existing water mains and associated fittings
Service reservoirs and other containment vessels
For the disinfection of equipment, boots, waterproof clothing, gloves and the exposed surfaces of pipe work, pumps & valves, a diluted solution of 1 part sodium hypochlorite solution to 90 parts water should be used. This will provide a 1,000 mg/l solution; this can be further diluted 1:3 (hypochlorite: water) to give a 250 mg/l chlorine concentration. For the disinfection of water mains the volume of sodium hypochlorite solution to provide residuals of 20 mg/l and 50 mg/l are shown on Table 1 below: Table 1. Pipe Diameter (mm)
Litres of sodium hypochlorite solution required per 1000 metres of pipeline 20mg/l
50mg/l
75
1.0
3.0
100
2.0
5.0
150
4.5
11.0
200
8.0
20.0
225
10.0
25.0
250
12.0
31.0
300
18.0
44.0
450
40.0
99.0
600
70.0
177.0
Approximate amounts in mls (Note: 1000mls = 1 litre) of 10% sodium hypochlorite solution required to make specific volumes of solution (litres) of particular strengths (mg/l) are shown in Table 2 below. Sodium hypochlorite solution, in common with other liquid chlorine solutions, degrades during storage and therefore the calculations are based on a nominal strength of 10%. Page 2 of 9
DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK INSTRUCTION USE AND DISPOSAL OF CHLORINE SOLUTIONS
Ref: DOM-WN-WIN-00000102 Version: C Date: October 2013
Table 2. Solution strength CI2 mg/l or ppm
Solution Volume (litres) 10
100
500
1,000
5,000
0.5
2.5
5
25
1
5
10
50
0.5
5
25
50
250
10
1
10
50
100
500
20
2
20
100
200
1,000
50
5
50
250
500
2,500
100
1,000
5,000
10,000
50,000
0.5
Not Practicable
1 5
1,000
For the disinfection of treated water storage tanks following cleaning, the volume of sodium hypochlorite solution to be added to water in the floor of the tank, for applying to the internal surfaces, at a concentration of 20 mg/l, should be 1 litre per 5 cubic metres (5000l) of water. For disinfection of treated water storage tanks when being refilled, the volume of sodium hypochlorite solution to be added may be dependent upon the chlorine residual of the inlet water. The volume of water to be added to 2 litres of sodium hypochlorite solution, to attain a free chlorine residual of 1.0 mg/l, should be 200 cubic metres (200,000l) of water, unless the free chlorine residual of the inlet water exceeds 0.3 mg/l in which case advice can be obtained from the Process Scientists or Public Health Teams. Please refer to DOM-WNPRC-00000304 – Cleaning of Treated Water Storage Points. 3.1.2
Instachlor PR Tablets (Rapid Release)
Instachlor PR Tablets are a range of rapid dissolving chlorine release tablets which provide a simple and affective means of preparing chlorine solutions of known strength for disinfection purposes. They are best used for making up small quantities of solution e.g. for disinfection of equipment, clothing and for disinfecting communication pipes. When using tablets to disinfect within Scottish Water, always consider the different sizes of tablets and the strength of disinfection solution that will be provided, from the size of tablet being used. Also, always refer to the manufacturer’s instructions / guidance notes in addition to this document and any other relevant SW tool box talks or DOMS documents. NOTE: Palintest Ltd have recently revised their range and grades of INSTACHLOR Rapid Release Chlorine Tablets with a new range which means there are new strengths of tablets, new product codes and descriptions. Below are descriptions of both old and new product ranges and the associated strengths of tablets available. Please ensure you are using the correct tablet and quantities for the job being done. Page 3 of 9
DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK INSTRUCTION USE AND DISPOSAL OF CHLORINE SOLUTIONS
Ref: DOM-WN-WIN-00000102 Version: C Date: October 2013
***Due to an error in the old Palintest range data sheet information the INSTACHLOR PR-250 tablet contained 150 mg/l free available chlorine (weight of [NaDCC] sodium dichloroisocyanurate is 250 mg/l). The new Palintest range equivalent has changed to the INSTACHLOR PR-150 which now reflects the available chlorine and not the weight. All other tablets strengths in the old range are unchanged. These changes are reflected in the following descriptions. OLD INSTACLHOR RANGE (Use until existing stocks are depleted).
INSTACHLOR PR-250 150 mg/l Chlorine
INSTACHLOR PR-1000
INSTACHLOR PR-5000
1000 mg/l Chlorine
5000 mg/l Chlorine
Examples a) INSTACHLOR PR-250 = 150 mg/l Free Available Chlorine: 2 x INSTACHLOR PR-250 DISSOLVED IN 1 LITRE OF WATER GIVES 300 mg/l solution (this should be used to prepare the nominal 250 mg/l solution for disinfecting tools / fittings etc. b) INSTACHLOR PR-1000 = 1000 mg/l Free Available Chlorine: 1 x INSTACHLOR PR-1000 DISSOLVED IN 1 LITRE OF WATER GIVES 1000mg/l solution. c) INSTACHLOR PR-5000 = 5000 mg/l Free Available Chlorine: 1 x INSTACHLOR PR-5000 DISSOLVED IN 1 LITRE OF WATER GIVES 5000mg/l solution.
Page 4 of 9
DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK INSTRUCTION USE AND DISPOSAL OF CHLORINE SOLUTIONS
Ref: DOM-WN-WIN-00000102 Version: C Date: October 2013
NEW INSTACHLOR PR RANGE Nominal Tablet Weight
Tablet Diameter
Code
Description
NaDCC
Chlorine Content
WT 406
Instachlor – PR 5
8.5 mg
5.1 mg
0.06g
5 mm
WT 415
Instachlor – PR 40
67 mg
40.2 mg
0.35g
10 mm
WT 424
Instachlor – PR 150
250 mg
150 mg
1.08g
16 mm
WT 442+
Instachlor – PR 1000
1.7g
1g (1000mg)
3.25g
18 mm
WT 446*
Instachlor – PR 1000
1.7g
1g (1000mg)
3.25g
18 mm
WT 448
Instachlor – PR 3000
5g
3g (3000mg)
9.7g
25 mm
+ = 100 Pack, * = 300 Pack Examples a) INSTACHLOR PR-150 = 150 mg/l Free Available Chlorine: 2 x INSTACHLOR PR-150 DISSOLVED IN 1 LITRE OF WATER GIVES 300 mg/l solution (this should be used to prepare the nominal 250 mg/l solution for disinfecting tools / fittings etc. b) INSTACHLOR PR-3000 = 3000 mg/l Free Available Chlorine: 1 x INSTACHLOR PR-3000 DISSOLVED IN 300 mls OF WATER GIVES nominal 10,000 mg/l (1%) solution (this should be used to prepare the solution for disinfecting taps prior to taking a microbiological sample. All solutions made from tablets must be used on the day of preparation. Disposal of small amounts of excess hypochlorite solution must be to sewer and flushed with copious amounts of clean water. These solutions must not be allowed to enter watercourses or surface water drains.
Skin and Eye protection must be worn when handling tablets or solutions, chlorine solutions are corrosive. Refer to your COSHH information. Table 3 below gives details of Instachlor tablets (old & new range) required to achieve a given solution in 10 litres of clean water:
Page 5 of 9
DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK INSTRUCTION USE AND DISPOSAL OF CHLORINE SOLUTIONS
Ref: DOM-WN-WIN-00000102 Version: C Date: October 2013
Table 3. Tablets required in 10 litres of water for a solution strength of 20mg/l
50mg/l
1000mg/l
Instachlor PR-250
2 (nominal 30 mg/l)
4 (nominal 60 mg/l)
70 (nominal 1050 mg/l)
Instachlor PR-150
2 (nominal 30 mg/l)
4 (nominal 60 mg/l)
70 (nominal 1050 mg/l)
Instachlor PR-1000
-
0.5
10
Table 4 below provides the length of service pipe that can be disinfected using 1 x Instachlor PR-50 tablet (old range - tablet diameter 7mm) to achieve a minimum of 50 mg/l residual free chlorine. The new Instachlor range equivalent tablet is the PR-40 tablet (tablet diameter 10mm) which contains 40.2 mg available chlorine. Therefore to achieve a minimum nominal 50 mg/l chlorine solution 2 x Instachlor PR-40 tablets should be used (actual 80.4 mg). Table 4.
3.1.3
Service Pipe Diameter (mm)
Length of pipe per tablet (metres)
12
8
19
3
25
2
HTH (Steadichlor) Chlorine Tablets (Slow Release)
Chlorine tablets containing Calcium Hypochlorite are available in 7 gram and 20 gram sizes. These tablets are best used for: • • •
Short lengths of new mains Installation of branches, tie-ins, etc. Repairs to burst mains
Page 6 of 9
DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK INSTRUCTION USE AND DISPOSAL OF CHLORINE SOLUTIONS
Ref: DOM-WN-WIN-00000102 Version: C Date: October 2013
Length of pipe that can be disinfected for each tablet to achieve solution strength of :Pipe Diameter (mm)
20mg/l
50mg/l
free chlorine residual
free chlorine residual
20 gram
7 gram
20 gram
7 gram
75
110
38
43
15
100
64
22
26
9
150
29
10
12
4
200
15
5
6
2
225
12
4
5
1.7
250
9
3
4
1.4
300
6
2
3
1.0
450
3
1
1
0.4
600
2
0.6
0.7
0.25
The tablets require to be fixed inside the pipe work using Bostik Adhesive No 1, or other approved adhesive. This is best achieved by applying the adhesive to one face only of the tablet then sticking it to the top inside face of the pipe at approximately 150mm behind the socket. The fixing area for the tablet must be clean and dry and it is essential that the adhesive is allowed to dry for 2 minutes before the tablet is stuck onto the pipe face. Tablets can be stuck to each pipe prior to laying but the main should not be filled within 30 minutes to allow the adhesive to set. Note - When tablets are used it is not possible to swab the main using firm grade swabs only soft grade swabs may be used. Disinfection of Sample Taps Prior to taking a microbiological sample the tap must be cleaned with a tissue moistened with 1% chlorine solution (10,000 mg/l). • Prepare the 1% Chlorine Solution (10,000 mg/l) by dissolving 1 x Instachlor PR-5000 (old Palintest Range) tablet in 500 mls of tap water or 1 x Instachlor PR-3000 (new Palintest Range) in 300 ml of tap water. • Note: this is an extremely concentrated chlorine solution - hand and eye protection must be worn. Also take care when using this solution in Customers’ properties or damage to property may occur. • Ensure that all traces of the 1% Chlorine Solution (10,000 mg/l) are washed away after sterilising a tap. • Alternatively this is equivalent to a 10% solution of liquid hypochlorite solution (10 - 15%) e.g. 10 mls liquid hypochlorite made up to 100 mls with tap water. • Alternatively Presept tablets (2.5g); use 2 x tablets in 250 mls tap water.
Page 7 of 9
DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK INSTRUCTION USE AND DISPOSAL OF CHLORINE SOLUTIONS
(a)
Ref: DOM-WN-WIN-00000102 Version: C Date: October 2013
Standpipes
To ensure that samples are not contaminated by outside agents, 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 sampling from a standpipe has to be done, the following precautions should be used:(i) The standpipe should be disinfected with a 50 mg/l chlorine solution. This should be carried out prior to arrival on site and the standpipe should be transported wrapped in a new plastic bag or similar to ensure that it is ‘clean’ before use. (ii) All possible contamination should be removed from the outside of the hydrant before connection of the standpipe, including water in the hydrant “pot” before connecting the standpipe. Consideration should be given to environmental conditions i.e. heavy rain, oil in the hydrant chamber.
(iii) A DOMS procedure exists for sampling from a Hydrant - DOM-WN-PRC00000332 Sampling from a Hydrant. (b)
Customers taps
Remove any attachment from the tap, clean the inner and outer surfaces of the tap spout with a clean tissue moistened with 1% chlorine solution (10,000 mg/l – see above) or a disinfectant wipe. Taps should be in good condition, if there is any doubt, do not use it as a sampling point. Mixer taps with a plastic insert can give rise to erroneous bacteriological failures; ensure this type of tap is thoroughly cleaned prior to flushing & sampling. 3.2
Disposal of Chlorinated Water
Chlorinated and chloraminated water, even at low levels, can be harmful to fish life and the aquatic environment generally. If the discharge waters are expected to contain sludges or chemical residues then measures must be taken to neutralise or remove them from site. The method adopted for disposal will depend on the total amount of chlorine to be disposed and the particular circumstances of the site in question. Each instance should be assessed for the best disposal route and should be considered on economic and environmental grounds. SEPA’s approval should be sought and local arrangements are often in force. This will depend on whether this is a planned or emergency situation and on the volume and concentration of the water to be disposed.
Page 8 of 9
DISTRIBUTION, OPERATION and MAINTENANCE STRATEGY ASSET MANAGEMENT WORK INSTRUCTION USE AND DISPOSAL OF CHLORINE SOLUTIONS
Ref: DOM-WN-WIN-00000102 Version: C Date: October 2013
1. 2. a) b) c)
Overland (or to Dry Ditches) – Dechlorination is necessary. Foul Sewers - This method is often the most convenient where it is possible subject to:Ensuring that there is no possibility of back syphonage during or after the discharge Ensuring that the sewer is either a foul or combined sewer Ensuring that any large amounts of chlorine discharged will not be detrimental to the effective operation of small rural wastewater treatment plants and septic tanks. 3. Surface Water Sewers - Dechlorination is necessary. 4. Direct Discharge to Watercourses - Where chlorinated water is discharged direct to a watercourse or to a surface water sewer which leads to a watercourse then dechlorination will always be required. 5. Disposal to Soak-away - Dechlorination is necessary. Note: Where there is doubt in any circumstances, dechlorination must be carried out. 3.3 Dechlorination Dechlorination can be achieved by the use of injection equipment (preferred method) or by passing the discharge water through chlorine dissipation apparatus that utilises a thiosulphate or sulphite in solution or tablet form. The appropriate quantities of reagent to completely neutralise any chlorine present will depend upon the residual to be neutralised and advice should be sought from the Process Science Team during normal hours or the Public Health Team out of hours. Generally the amount of sodium thiosulphate required to dechlorinate is detailed in the table below. Amount of sodium thiosulphate solution or weight of solid thiosulphate crystals
Concentration of chlorine residual inactivated
1ml of 1.8% w/v solution
5mg/l (ppm) per litre of water
18 grams of crystals
5mg/l (ppm) per 1000 litres (m3) of water
Therefore to dechlorinate a 50mg/l (ppm) solution: 180 grams of sodium thiosulphate must be used per 10,000 litres of water discharged. Note: Sodium thiosulphate on contact with water releases energy in the form of heat. The solid crystals can fuse into a solid block. If this occurs, the surface area of the crystals in contact with the discharging solution will be reduced and the dechlorination process may not be effective. The best way to avoid this is to use some kind of diffuser (a porous sack) into which the crystals are added throughout the discharge process. This should then be placed in the discharge stream. The preferred and recommended procedure is to use a purpose designed chlorination / dechlorination unit / trailer in accordance with manufacturer’s guidelines.
Page 9 of 9
