Water Supply Reticulation

Transcription

1 To: Infrastructure Committee Report Prepared By: Dan Harris Date: 20 July 2017 Significant Decision: No Water Supply Reticulation Recommendation Executive Summary Background TO IMPROVE THE SAFETY TO CONSUMERS, THE INFRASTRUCTURE COMMITTEE APPROVES THE USE OF CHLORINE ON ALL SUPPLIES CURRENTLY WITHOUT RESIDUAL DISINFECTANT(option 2). Chlorine/ is the best method of disinfecting the water supply pipelines, referred to as the reticulation. Treating water at its source deals with any contaminants prior to entering the reticulation yet it does not deal with any contaminants that enter the reticulation. Typically, they can enter through poorly performing infrastructure, damage or above ground storage assets. HDC currently has five (5) sources of water without any method of reticulation management. Three (3) of these are secure sources, from deep aquifers, that regular laboratory testing has shown these to be free of harmful bacteria. The other two (2) have their source water treated by Ultra Violet (UV) light. Of the 21 sources, Racecourse, Leithfield Beach (feeding the Beach and Ashley scheme), Hanmer Springs, Hawarden/Waikari and Culverden do not receive any permanent chlorine treatment. Aside from the five (5) sources referred to above, chlorine has been introduced to some of the secure supplies and UV treated supplies in recent times to manage the risk to the reticulation because events have transpired giving cause for concern to its integrity. In late 2016 and early 2017 Amberley Beach received a low level positive test for Ecoli. The secure sources providing water to this community were tested and found to be void of any Ecoli, suggesting it was entering via the reticulation. For this reason, chlorine was introduced and has been operating since December It is likely the contaminant was entering via a reservoir. This scheme has received similar transgressions prior to Amuri Plains scheme is treated via an uncertified UV unit. The reticulation to this scheme was put at risk during the earthquake as it was designated the source of water usage for the contractors and was also being compromised by the work being undertaken for the Amuri Irrigation project. To ensure the community were not put at risk chlorine was added to this supply. Hanmer Springs has a robust automated treatment process in place to disinfect the high levels of contamination from the Rogerson storage ponds. It doesn t have a permanent method of managing contaminants in the reticulation. There is a known risk in this network (rectangular reservoir) that is a potential threat that permanent chlorination would mitigate. Hawarden/Waikari has an uncertified UV treatment at source, similar to

2 Hanmer Springs, yet doesn t have a method of managing contaminants in the reticulation. This scheme is a combination of both rural and urban supplies and has suffered from reticulation transgressions in the recent past. Reticulation transgressions Key Reticulation threats Since FY2012 across all water supplies there have been 3981 reticulation tests carried out with 88 transgressions. 17% of those transgressions were on non-chemically treated supplies, meaning contaminants are prevalent and could compromise public health. The following is a list of the causes of contamination ingress. 1. Reservoirs seals compromised 2. Break tanks not sealed correctly 3. Air relief valves damaged or incorrectly installed 4. Backflow from customer tanks or systems 5. Joint failures or line breakages 6. Repairs Note that the risk at Items 3 to 6 increase markedly at a point where the pressure can be low through: 1. Local high velocity 2. Location e.g on top of a hill 3. System starting and stopping The picture below depicts a damaged collar caused by ground movement and the subsequent repair. Working in this type of environment can introduce contaminants during the repair process. NB: process changes have meant repairs will be carried out under improved sterile conditions limiting the opportunity for contamination. The table below depicts the rate of repairs across all schemes in Incident Rate Joint Failure 42% Mechanical damage 11% Fitting Failure 3% Blockage 4% Pipe Split 40% Total 228 faults were recorded relating to reticulation damage. Cost of chlorination Chlorine dosing pumps are already established in all unchlorinated locations

3 Options Option 1 in case of Ecoli presence. The cost to run chlorine dosing for these supplies can be absorbed into existing budgets for the 2017/18 FY. Do nothing. Advantages No additional cost incurred Disadvantages Risk to consumers health from contaminants entering reticulation continues to exist. Option 2 Chlorinate all supplies Advantages Risk to consumers health by receiving contaminated water will be reduced Disadvantages Additional costs incurred Some members of public have a poor perception of chemicals being added to water. Option 3 Continue to chlorinate supplies that have recently had chlorine added (refer Appendix 1) Advantages Risk to consumers health by receiving contaminated water will be reduced Disadvantages Additional costs incurred Some members of public have a poor perception of chemicals being added to water that could reflect on HDC as being seen as disregarding consumer views Appendices Appendix 1 Current state of treatment by water source Appendix 2 Recommendation from CDHB regarding chlorination of supplies

4 Report Prepared by: Dan Harris Manager Infrastructure Services - Delivery Report Reviewed by: Officer in Attendance: Hamish Dobbie Chief Executive Officer The report author will be in attendance to speak to this report.

5 Appendix 1 Current State of Treatment by Water Source The following table shows each water source and the type of treatment occurring at the time of writing the report Scheme / Source Treatment Type Amberley /Racecourse None Temporary chlorination on the portion of water going to Amberley /Leithfield Amberley. No chlorination to Leithfield beach and rural Ashley Scheme (Leithfield up to Balcairn and their local surrounding areas) Amberley /State Highway 1 Temporary chlorination to minimise recent ecoli transgression Amberley /Kowhai Temporary chlorination to minimise recent ecoli transgression Ashley UV and Waipara Cheviot Hurunui No 1 Parnassus Lower Waitohi Peaks Waiau Rural Water Kaiwara Blythe Waiau Township Ultra-filtration and chlorine Hanmer Springs Filtration and UV and auto chlorine dosed during high turbidity Balmoral Chlorine Upper Waitohi Chlorine Amuri Plains UV and Temporary chlorine Culverden None Hawarden/Waikari UV Highlighted entries shows where Chlorine is required to manage reticulation risks.

6 Appendix 2 CDHB recommendation, provided by Kirsty Mcleod Drinking Water Assessor (DWA) CDHB strongly support the permanent chlorination of Hurunui s secure groundwater supplies. Public health is best protected when drinking water is supplied under a multiple barrier approach. This approach is internationally accepted as the most effective way of consistently providing safe water. The multiple barrier approach ensures that risk is mitigated from catchment to point of supply. Secure groundwater supplies provide good protection of drinking water quality at the source but in the absence of treatment with a disinfectant that provides a residual (e.g. chlorine), water is then at risk of becoming contaminated in the reticulation (i.e. the final barrier, prevention of contamination in the distribution system is essentially missing/ineffective). Drinking water reticulation systems are often mistakenly viewed as sealed systems and therefore protected. This is not the case. Reticulation systems are exposed to a wide range of contaminants from a variety of potential routes. Reservoirs access (by birds, vermin, roof-water runoff), pipework repair and renewal work, tanker access to water mains, leaking/old pipework, backflow from high to low pressure areas are all common examples of how reticulation systems can be contaminated. Many of Hurunui DC s supplies have aging pipework, frequent repair work, long lengths of reticulation pipework and multiple reservoirs. These all add up to significant opportunities for contaminant entry into the system. Significant examples of reticulation contamination in a secure groundwater supply that CDHB have been involved with in the last 12 months are Governors Bay, where CCC had to issue a boil water notice following reservoir contamination (this supply is sourced from one of the Christchurch secure bores) and Amberley/Amberley Beach where once again, reservoir contamination led to E.coli being repeatedly detected in the reticulation and therefore a boil water notice had to be issued.