Notice for Regulation: Mosswood Water Treatment Works – Resilience and Power Supply




Mosswood Water Treatment Works (Durham Supply) (T0700335)
Mosswood Water Treatment Works (Sunderland Supply) (T0021824)

DWI Reference: NES-202-/00006


  1. has received a report from Northumbrian, Essex and Suffolk Water (the “company”) dated 11 October 2019 (the “Report”) which states that there is or has been a significant risk of supplying water from Mosswood water Treatment Works that could constitute a potential danger to human health and could be unwholesome.
  2. GIVES NOTICE to the company under regulation 28(4) of the Water Supply (Water Quality) Regulations 2016 (as amended) that it must satisfy the following requirements:

For risks associated with:

  • Power failure/ power cut
  • Insufficient supply or loss of supply
  • Inaccurate instrumentation/ instrumentation failure
  • Regulation 26 (1)(b) Sufficiently prepare water for disinfection
  • Contamination


(a) to maintain the following measures for the period specified:

  1. Up to date Site Operating Manual and Site Specific Disinfection Policy defining normal operating ranges, triggers, response and contingency procedures with controlled update and review programmes.
    Date: Ongoing for duration of Notice
  2. Operation of all processes within defined operating ranges with appropriate triggers, responses and contingency procedures.
    Date: Ongoing for duration of Notice
  3. Ensure the works control and shutdown system is operational and that site monitors are calibrated at the predefined frequencies.
    Date: Ongoing for duration of Notice
  4. Adhere to the company ‘Process Instrument Verification and Calibration’ (PDP.04) document and any subsequent revisions. Uphold procedures within for the frequency of manual sampling and analysis.
    Date: Ongoing for duration of Notice
  5. Ensure that staff who are fully trained, conversant and competent in the use, maintenance and repair of the emergency back-up power supply system and all its associated controls and monitoring are available to supervise normal operation and to react to emergency operation where necessary.
    Date: Ongoing for duration of Notice
  6. Use load banks to load test the Mosswood works generators every 2 years to ensure generator reliability.
    Date: Ongoing for duration of Notice
  7. Water Quality response procedures for investigation of contraventions including process optimisation and reporting.
    Date: Ongoing for duration of Notice
  8. Ensure new risks identified are assessed in accordance with the Company’s Drinking Water Safety Plan (DWSP) methodology and submitted to the Inspectorate under Regulation 28.
    Date: Ongoing for duration of Notice

(b) to review, revise and/or make operational the following measures, by the date specified below:

Staff Resource and Manual Sampling

  1. Review escalation guidelines at Mosswood works and the staffing resource available on site, particularly with regard to manual sampling capacity. Update site manual and procedures to address deficiencies.
    Date: 30 September 2020
  2. Develop and implement a controlled document to record specific samples and analysis results at critical locations throughout the treatment process
    Date: 30 September 2020

Power Supply

  1. Complete a gap analysis of Mosswood treatment works power supply and backup power supply system. This must include at least the following:
    Date: 01 November 2020
    • A hazard review and operability study of the current back-up power system and the assets connected. Taking into account logic, controls, monitoring and protected assets and functions toachieve correct operation and actions in response to failure modes
    • Evaluation of control signals, switch gear, synchronisation equipment, fuel supply and consumption to bring online and maintain emergency back-up power supply.
    • Consideration of critical equipment spares
    • Understanding of what constitutes as the base load for works start up
    • Critical review of works start up sequence considering load profiles, in-rush current evaluation, harmonic interferenceand control logic
    • Evaluate protection and safeguarding of System Control and Data Acquisition (SCADA) equipment in the event of a power interruption and subsequent restart. Include monitor health, instrumentation, pumps and alarms, data saving and shutdown automation
    • Consider storm and triad planning and the triggers for manually switching to back-up power system
    • Review recovery arrangements which achieve and maintain compliance with Regulation 26,ensure site fails safe
    • Review of procedures and contracts for maintenance and testing. Consideration of whether procedures are robust and conducted at appropriate frequencies
  2. Develop an action plan from the gap analysis findings ((b)3.) for power supply resilience improvements
    Date: 01 December 2020
  3. Deliver action plan defined in (b)4.
    Date: 31 March 2025
  4. Review of power supply arrangements at all other Northumbrian, Essex and Suffolk Water treatment works. Include consideration of works shutdown, start up and the frequency of maintenance and testing (including load testing) on back-up power systems.
    Date: 01 June 2021

Run to Waste

  1. To address short and medium term risks of supplying improperly treated water to consumers, review the likely modes of failure at Mosswood treatment works
    Date: 01 October 2020
  2. Identify the use of existing onsite assets to improve risk mitigation following a deterioration of treated water quality.
    Date: 01 October 2020
  3. Following (b)7. and 8. develop and implement appropriate mitigation
    Date: 31 January 2021
  4. Develop plans for a run to waste facility at Mosswood works to discharge improperly treated water
    Date: 31 March 2023
  5. Install and commission a run to waste facility at Mosswood works
    Date: 31 March 2024

(c) to audit whether the measures have been effective by the following means:

  1. Define and keep under continuous review an audit strategy to monitor the effectiveness of the above measures.
    Date: 1 month after Notice served
  2. Implement the audit strategy defined in (c)1.
    Date: For the duration of the Notice.

(d) not to supply water for regulation 4(1) purposes from Mosswood Treatment Works


(e) to provide the following information in the time and manner specified below to enable monitoring of progress towards the mitigation of the risk of supplying water that would constitute a potential danger to human health:

  1. Provide a progress update annually by 31 January and against the following milestones:
    • Provide summary of outcomes following review of escalation guidelines and staffing resources ((b)1.). Provide evidence of completion of (b)2.
      Date: 31 October 2020
    • Confirm completion of gap analysis in (b)3. and submit the associated action plan outlined in (b)4.
      Date: 31 January 2020
    • Provide summary of outcomes following completion of (b)7. and 8.
      Date: 01 November 2020
    • Confirm completion of companywide review and provide report detailing findings from (b)6.
      Date: 01 July 2021
    • Submit outline of plans (including construction design) of run to waste facility ((b)10.)
      Date: 30 April 2023
    • Confirm successful installation and commissioning of Mosswood works run to waste facility ((b) xi.)
      Date: 30 April 2024
  2. Review the risk assessment for Mosswood Treatment Works as required by regulation 27(3) and subsequently submit a revised regulation 28 report accompanied by a signed board level declaration.
    Date: Ongoing until revocation of Notice
  3. Submit a satisfactory completion report.
    Date: 31 May 2026

Failure by the company to comply with this Notice may result in enforcement proceedings under section 18 of the Water Industry Act 1991.

Signed by authority of the Secretary of State
Milo Purcell
Deputy Chief Inspector
25 August 2020
DWI Reference: NES 2020/00006
Version 1

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