Notice of Regulation: Alderney Water Treatment Works



Sembcorp Bournemouth Water : Alderney WTW

Alderney WTW: Alderney supply system : BWH 1326

Improvement Programme Database Reference number – SBW3237


  1. has received a report from Sembcorp Bournemouth Water (the “Company”) dated 23rd June 2011 (the “Report”) which states that there is or has been a significant risk of supplying water from Alderney WTW that would constitute a potential danger to human health.
  2. Gives Notice that the Company is required, in order to mitigate the risk, in accordance with Regulation 28(4):

For risks associated with:

  • Cryptosporidium
  • E.coli
  • Coliforms

(a) to maintain the existing operational measures set out in the Report as specified below:

  1. Undertake continuous (daily filter change) Cryptosporidium analysis of the treated water on-site at a point which does not invalidate the interpretation of changing risks with a 24 hour turnaround.
    Date: until 31st December 2014
  2. Undertake continuous (daily filter change) Cryptosporidium analysis from both raw water sources, River Stour and River Avon, with a 24 hour turnaround.
    Date: until 31st December 2014
  3. Large volume sampling for bacterial parameters on the outlets of contact tanks 4 and 6 and the final treated water storage reservoirs 7 and 8.
    Date: until 31st December 2014

(b) to make operational such measures as are specified below, by the date specified below:

Short term measures

  1. Make operational and maintain the following short-term measures:
    Date: by 24th June 2013
    • Check for and remove large weed growth on a daily basis and carry out appropriate monitoring to establish diurnal variations in ammonia, nitrite and dissolved oxygen levels and chlorine demand of each filter.
      Date: until 31 December 2014.
    • Based on the data gathered, including online turbidity monitoring at the outlet of each filter, prepare and implement a strategy for weed control which limits the impact on performance of each filter throughout its operational cycle.
      Date: from 01 January 2015
    • Ensure filters are visually inspected daily to identify surface irregularities.
      Date: Ongoing
    • Monitor each filter for microbiological parameters weekly.
      Date: Ongoing
    • Monitor the turbidity of the water from each individual filter with online monitors linked to telemetry and alarmed at a maximum of 0.5NTU.
      Date: Ongoing
    • Additional alarms should be set to be triggered by any increase in turbidity in the final water of greater than 50% of the normal average, instigating an investigation by the Company

Medium term measures

  1. Review the following medium-term measures
    Date: by 31st August 2013
    • The condition and lifespan of all concrete process structures on the works and any necessary remedial work necessary, through investigation carried out by appointed experts
      Date: COMPLETE
    • The disinfection strategy for the works to take account of the installation of UV disinfection and other amendments as required
      Date: COMPLETE
  2. Make operational and maintain the following medium-term measures:
    Date: by 31st August 2013
    • Operate each slow sand filter on the site in accordance with Badenoch recommendations
    • Evaluate transition speeds across each slow sand filter to determine if the rate of flow passing through the bed is of a typical expected rate i.e. 0.1 – 0.3 m/hr, and where this is not within the typical range then to show by verification that this is not affecting the efficacy of Cryptosporidium removal
    • Evaluate the depth of each filter and ensure this is within an acceptable tolerance of 0.6 – 1.25m
    • Ensure water depth of filters is between optimal limits of between 1m and 1.5m unless the company can show by validation that an alternative depth range is applicable
    • Carry out an evaluation of the penetration of Cryptosporidium oocysts through the filters by core sampling to determine that they do not penetrate further than 0.6m
      Date: COMPLETE
    • Evaluate the criteria for ripening following skimming and document as best practice for the company.
      Date: COMPLETE
  3. Make operational and maintain the following medium term measures:
    Date: by 31st March 2014
    • All remedial work identified in (b)2
      Date: COMPLETE
    • The installation of a validated and sized UV disinfection appropriate for the verified risks to effectively treat Cryptosporidium specific to the predicted challenges presented at Alderney water treatment works
      Date: COMPLETE

Long term measures

  1. Review the following long-term measures:
    • Final disinfection arrangements
      Date: COMPLETE
    • The sequence of underdrain inspection based on risk assessment
      Date: COMPLETE
    • The effectiveness of an algae control system in Longham Lakes
      Date: by 30th September 2014
    • Determine the need for works to prevent short circuiting in Longham Lakes by modelling
      Date: by 31st December 2014
  2. Implement the following long-term measures:
    • Improve final disinfection arrangements by converting tank 5 into a contact tank (filter located above to be decommissioned) and the decommissioning of tanks 4 and 6
      Date: by 31st March 2015.
    • The installation of turbidity meters on the outlets of all slow sand filters
      Date: by 31st March 2014 – COMPLETE
    • Inspect and remediate all slow sand filter underdrains following a strategy informed by the evaluation of all data and information available on the condition, performance and regeneration needs of each filter
      Date: by 31st December 2018
      • 2014 – filters 9, 13,
      • 2015 – filters 4, 15, 8
      • 2016 – filters 2, 10, 11
      • 2017 – filters 3, 14, 12
      • 2018 – filter 1
    • The strategy should include an inspection methodology that requires the removal of all media. The programme of activity above is the current prioritisation based on risk mitigation assessments and operational needs, and will be reviewed regularly.

(c) to audit whether the measures have been effective by such means as specified below:

  1. Prepare a strategy for auditing the effectiveness of the above measures, to include the following,
    Date: by 31st July 2014
    • Continuous monitoring by an accredited method for Cryptosporidium oocysts at the following points:
      • The River Avon and River Stour
      • Inlet to and outlet from Longham lakes
      • Post primary filters (pre slow sand filters)
      • Final treated water (pre UV)
    • Online turbidity monitoring on the outlets of all filters
    • Continuous particle count on the combined outlet flow from the filter
    • UV intensity, and flow through the plant to be continually monitored and recorded via telemetry
    • UV dose continuously monitored, recorded via telemetry, alarmed and linked to ESD
  2. Implement the audit strategy outlined in (c)1
    Date: until the revocation of this Notice

(d) not to supply water for regulation 4(1) purposes from Alderney WTW unless the conditions specified below are satisfied:

  1. Based on the risk assessment submitted by the Company that states Longham Lakes are a key process in mitigation of Cryptosporidium, they should not be bypassed until the Company has developed a statistically validated and verified abstraction strategy that prevents a decrease in efficiency of any treatment process for all variations in raw water quality at Alderney WTW under all supply conditions.

(e) to provide the following information in such time and manner as specified below to enable monitoring of progress:

  1. Provide annual progress reports to confirm progress with the short and medium term measures
    Date: by 31 January each year, beginning 31st January 2015 and at the following milestones:
    • Submit a revised disinfection strategy to the Inspectorate
      Date: by 31st July 2014
    • Submit a strategy for inspecting and remediating the slow sand filters
      Date: by 31st July 2014
    • Submit a report on the effectiveness of an algae control system and the results of modelling Longham Lakes
      Date: by 31st December 2014
    • Submit an abstraction strategy for Alderney WTW
      Date: by 31st December 2014
    • Review the risk assessment for Alderney WTW as required by Regulation 27(4) and subsequently submit a revised Regulation 28 report (in accordance with Regulation 28(1)) from time to time to include upon commissioning of the UV plant.
      Date: by 31st March 2019
  2. Submit a satisfactory completion report
    Date: by 31st January 2020

Please be aware that breach by the Company of this Notice may result in an enforcement notice, breach of which may itself attract a penalty. Further, breach of condition 2(d) shall constitute a criminal offence liable to a fine on conviction.

This Notice may be amended or revoked by notice from the Secretary of State at any time.

Signed by authority of the Secretary of State,
Milo Purcell
Deputy Chief Inspector
11 July 2014
DWI ref SBW3237
Version 2

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