Drinking Water Audit Report

Transcription

1 Drinking Water Audit Report Local Authority: Wicklow County Council Date of Audit: 9 August 2012 Plant(s) visited: Arklow Water Treatment Plant Date of issue of Audit Report: 13 August 2012 File Reference: DW2008/431 Auditors: Mr Darragh Page Audit Criteria: The European Communities (Drinking Water) (No 2) Regulations, 2007 The EPA Handbook on the Implementation of the Regulations for Water Services Authorities for Public Water Supplies (ISBN: ) The recommendations specified in the EPA Report on The Provision and Quality of Drinking Water in Ireland The recommendations in any previous audit reports MAIN FINDINGS i The low chlorine residuals in the distribution network were likely to have been caused by the sudden deterioration in raw water quality, in particular the elevated levels of ammonia and turbidity Wicklow County Council had monitoring equipment in place to detect such problems but did not have alarms set at appropriate levels nor where there documented procedures in place to manage such occurrences ii The operation of the chlorination system in the Arklow PWS needs to be reviewed and in particular some risks, such as the open storage of chlorinated water and the low residuals in the distribution network on an ongoing basis, need to be addressed as they present an unacceptable risk to the security of the supply 1 INTRODUCTION Under the European Communities (Drinking Water) (No 2) Regulations 2007 the Environmental Protection Agency is the supervisory authority in relation to the local authorities and their role in the provision of public water supplies This audit was carried out in response to the notification by Wicklow County Council dated 3 August 2012 of the detection of low chlorine residuals in the distribution network of the Arklow Public Water Supply The Arklow water treatment plant is sourced from a mixture of the Goldmine River (max abstraction 4,000 m 3 /d) and a borehole at Woodenbridge (max abstraction 1,400 m 3 /d) The sources are mixed and gravity fed to an impoundment reservoir adjacent to the plant The water can be directly fed to the plant, bypassing the reservoir, if the quality in the reservoir is inadequate This bypass was in operation on the day of the audit Treatment at the plant consists of dissolved air flotation, rapid gravity filtration, chlorination and fluoridation The supply serves approx 13,000 persons Wicklow County Council has recently received approval for the construction of a new treatment plant at Arklow which will incorporate new groundwater sources The type of treatment has not been decided as it will be constructed as a Design Build Operate contract but work is scheduled to start in October 2012 and will take 2 years 1

2 Photographs taken by Darragh Page during the audit are attached to this report and are referred to in the text where relevant The opening meeting commenced at 930 am at the Arklow Water Treatment Plant The scope and purpose of the audit were outlined at the opening meeting The audit process consisted of interviews with staff, review of records and observations made during an inspection of the treatment plant The audits observations and recommendations are listed in Section 2 and 4 of this report The following were in attendance during the audit Representing Local Authority: (* indicates that person was also present for the closing meeting) Mr Tom Griffin Senior Chemist* Mr Michael McNamara Town Clerk* Mr Sean McBride Caretaker* Mr James Kavanagh - Caretaker Representing the Environmental Protection Agency: Mr Darragh Page Inspector* 2 AUDIT OBSERVATIONS The audit process is a random sample on a particular day of a facility's operation Where an observation or recommendation against a particular issue has not been reported, this should not be construed to mean that this issue is fully addressed 1 Source Protection a The supply originates from a mixture of the Goldmine River and a borehole in Woodenbridge The sources are mixed near Woodenbridge and fed by gravity to the water treatment plant The sources of the supply were not inspected on the day of the audit The WSA reported that the sources are in agricultural catchments and can be subject to changes in quality following heavy rain and that this was the case at the time the incident first occurred b The impoundment reservoir is surrounded by agricultural land but there is a buffer zone of trees between the agricultural land and the reservoir 2 Dissolved Air Flotation a The water is treated using dissolved air flotation The raw water is dosed with aluminium sulphate (normally at 50 ppm), soda ash (normally 33 ppm) and poly b Prior to the incident the alum was being dosed at 8 ppm as the WSA reported that the raw water was clear and of a good quality Following the heavy rain on Wednesday 1 August the dose was increased to 50 ppm, however this did not prevent the final turbidity rising above 5 NTU c Dosing is adjusted manually based on the results of jar tests and the history of the performance of the plant 3 Chlorination and Disinfection a The filtered water is fed into a clear water tank were it is chlorinated using a recirculating loop linked to the chlorine monitor The WSA stated that the recirculating pump takes a sample from the inlet and bases the chlorine dose on the concentration present by dosing chlorine into the clear water tank at the location indicated on Figure 1 However, the inlet and the outlet are on the same side of the tank (which is opposite the dosing point) and it was unclear if this was the actual 2

3 arrangement in place as such a system would be unlikely to lead proper mixing of the chlorine and to a stable chlorine residual in the final water b Chlorinated water from the clear water tank overflows into the four old slow sand filters adjacent when production exceeds output These are uncovered (Photo 1) and there was evidence of algal and macrophyte growth on the filters There was no schmutzdecke on the filters and the WSA reported that they do not have to scrape the filters and thus they are not functioning as slow sand filter but rather roughing filters The level of water in these tanks rises and falls depending on demand in the supply The water is rechlorinated before supply c A manual free chlorine residual sample was taken from the same point as chlorine monitor no1 (used for the recirculation line) and chlorine monitor no2 (the outlet) and levels of 073 and 056 mg/l respectively were detected The first corresponded closely to the monitor no1 but the WSA stated that monitor no2 was not working properly and was reporting a value of 006 mg/l at the time of the audit d The WSA reported that during the incident the chlorine pump was at maximum capacity but this still did not result in adequate chlorine residuals in the network and manual chlorination was undertaken on Friday 3 August This had the desired effect of raising the chlorine residuals Figure 1 Clear Water Tank 4 Monitoring and Sampling a Raw water turbidity, ph and ammonia monitors have been installed since the previous audit The results of the ammonia monitor indicates that a spike of ammonia appeared in the raw water on the evening of Wednesday 1 August and morning of Thursday 2 August (up to 1 mg/l) and again at approx midday on Friday 3 August (up to 3 mg/l) At this time the WSA switched from using the reservoir to direct feed from the sources However, the source intake became blocked and was not in operation intermittently between Wednesday 1 August and Sunday 5 August 2012 b The SCADA indicated that the alarm setting on the ammonia monitor is at 300 mg/l Thus the WSA were not alerted to the elevated levels of ammonia which impacted on the chlorine demand c The results from the ammonia monitor from March to August 2012 were examined and appear to indicate a trend of increasing ammonia levels from May onwards (approx 05 mg/l) d Results of chlorine monitoring in the network from May 2010 to July 2012 were examined These indicated that low chlorine residuals (below 01 mg/l) were present at several locations at the extremities of the network even after flushing (Ballymoney, South Quay, Ballynattin, Potters Bridge and Coolgreaney Road) 3

4 5 Exceedances of the Parametric Values a No exceedances of the parametric values were reported to the EPA prior to the audit, however, notification of the detection of a single E coli in one sample in Abbeylands was made to the EPA immediately following the audit E coli was detected in a sample taken on 8 August 2012 and the results were available to Wicklow County Council in the afternoon of 9 August 2012 following the audit Low chlorine residuals were present in the sample which was at the end of the distribution network Three other sample locations were all clear 6 Treated Water Storage a Treated water from the Arklow WTP is stored in two reservoirs at Lamberton (with storage of approx 1,100 m 3 /d and 3,300 m 3 /d) It is then pumped to a tower prior to distribution to Arklow b The WSA reported that both reservoirs had been cleaned out in 2011 and 2012 and that no significant issues were found Security at the reservoirs was good and all access points and vents were locked or secure 3 AUDITORS COMMENTS The Arklow Water Treatment Plant was placed under considerable stress on 1 and 2 August 2012 due to heavy rains in the catchment which caused a deterioration in raw water quality The plant is equipped to detect such deteriorations in raw water but the absence of alarms on key monitors (ammonia, turbidity) and the absence of documented procedures for dealing with such challenges is likely to have contributed to the extent of the incident In particular the short duration ammonia exceedance which will have placed the chlorination system under considerable strain could have been managed more effectively had an appropriate alarm been in place Had this been linked to a predetermined response (eg a shut down of the intake) it could have prevented the incident A review of the management of raw water needs to be undertaken and the limitation of the plant clearly defined with appropriate responses put in place for when such conditions arise in the future While unlikely to have directly contributed to the incident other aspects of the management of the disinfection system, such as the open storage of chlorinated water and the inadequate residuals at the extremities of the network, put the supply at risk of contamination and need to be addressed to improve the security of the supply 4 RECOMMENDATIONS Source Protection 1 The Water Services Authority should characterise the variability in raw water quality to mitigate any risks to the abstracted water Trends in raw water quality should be analysed and used to determine the optimum treatment conditions for the water at the plant Data should be used to identify whether rapid variations in raw water quality give rise to problems with the treatment process and appropriate procedures should be put in place to mitigate such risks 2 The Water Services Authority should review the alarm settings on the ammonia and turbidity monitors on the raw water and set the alarm at an appropriate level such that it will allow a response before the quality of the raw water becomes an unacceptable risk to the treatment plant A documented procedure should be developed to set out the actions that should be taken to deal with any incidents of the activation of the alarm 4

5 Disinfection 3 The Water Services Authority should review the chlorine dosing arrangements as reported on the day of the audit and confirm to the EPA whether the arrangements were as described on the day of the audit 4 The Water Services Authority should ensure that chlorinated water is not stored uncovered and in this regard should review the storage arrangements in the old slow sand filters 5 The Water Services Authority should clean out the old slow sand filters and remove any potential source of organic material prior to covering them 6 The Water Services Authority should ensure that a free chlorine residual of at least 01 mg/l is present in all parts of the distribution network The WSA should submit a report to the EPA outlining what actions are proposed to ensure that at least 01 mg/l free chlorine residual is present in the areas highlighted in the observations section of this report 7 The Water Services Authority should ensure the chlorine monitor on the outlet of the clear water tank is repaired FOLLOW-UP ACTIONS REQUIRED BY THE LOCAL AUTHORITY During the audit the Water Services Authority representatives were advised of the audit findings and that action must be taken as a priority by the Water Services Authority to address the issues raised This report has been reviewed and approved by Mr Darragh Page, Drinking Water Team Leader The Water Services Authority should submit a report to the Agency within one month of the date of this audit report detailing how it has dealt with the issues of concern identified during this audit The report should include details on the action taken and planned to address the various recommendations, including timeframe for commencement and completion of any planned work The EPA also advises that the findings and recommendations from this audit report should, where relevant, be addressed at all other treatment plants operated and managed by Wicklow County Council Please quote the File Reference Number in any future correspondence in relation to this Report Report prepared by: Date: Inspector 5

6 Photo 1 Storage of Chlorinated Water in Uncovered Old Slow Sand Filters 6