Notice of Regulation: Hall Water Treatment Works



Anglian Water Services Ltd: Hall Water Treatment Works, Treatment Risks

DWI Reference: ANH-2019-00001

Hall Water Treatment Works (THAW0)
Associated water supply zones:

ZKN78 – Billinghay Pwsz – 33911 [2020]
ZLN34 – Saxilby Pwsz – 30446 [2020]
ZLN57 – Branston Pwsz – 20894 [2020]
ZLN69 – Lincoln South Pwsz – 67064 [2020]
ZLN72 – Lincoln Westgate Pwsz – 28487 [2020]


  1. has received a report from Anglian Water Services Limited (“the Company”) dated 1 October 2018 (“the Report”) which states that there is or has been a significant risk of supplying water from Hall Water Treatment Works (WTW) 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:
    • Disinfection and chlorine demand;
    • Disinfection by-products;
    • Substances and products in contact with drinking water; and
    • Inadequate treatment.


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

  1. Optimise the treatment processes at Hall WTW to ensure continued compliance with regulatory standards and disinfection by-products are kept as low as possible without compromising the effectiveness of the disinfection.
    Date: Ongoing for the duration of the Notice
  2. Carry out enhanced monitoring (sampling) of disinfection by-products at appropriate locations. This includes monitoring once a week for:
    Date: Ongoing for the duration of the Notice
    • Trihalomethanes (THMs), haloacetic acids (HAAs) and chlorate throughout the treatment processes (where practicable), at the point the water leaves the treatment works (final water monitoring point), at the point of blending with Newton WTW (or a representative site) and within the associated water supply zones;
    • Bromide throughout the treatment processes; and
    • Bromate at the point the water leaves the treatment works.
  3. Continue to undertake continuous online monitoring for THMs in the final water.
    Date: Ongoing for the duration of the Notice
  4. Investigate any results that are above 50µg/l for THMs. Report any regulatory exceedances of the parametric concentration for THMs to the Inspectorate as an event, following the provisions of the Water Industry (Suppliers’ Information) Direction 2019, and take all necessary steps to protect human health.
    Date: Ongoing for the duration of the Notice
  5. Calculate chlorine demand at the final water monitoring point at Hall WTW and respond to results as appropriate to ensure human health is protected.
    Date: Ongoing for the duration of the Notice
  6. Continue to undertake online monitoring for hydrogen peroxide immediately following the polishing granular activated carbon treatment process stage.
    Date: Ongoing for the duration of the Notice
  7. Continue to gain further understanding of the organic loading and disinfection by product formation potential at Hall WTW.
    Date: Ongoing for the duration of the Notice
  8. Carry out sampling for total organic carbon at each inter-stage (raw water intake, following each treatment process and at the final water monitoring point) at a frequency of once a week.
    Date: Ongoing for the duration of the Notice
  9. Carry out enhanced monitoring at appropriate pre- and post- treatment processes for:
    Date: Ongoing for the duration of the Notice
    1. key water quality hazards identified through Company’s risk assessment of the catchment, as appropriate and subject to continuous review; and
    2. Targeted full suite of analysis with scans, as appropriate.

(b) to review, revise or make operational the following measures, by the date specified in each case:

  1. Calculate the contact time and surface to volume ratio for the active PAX mixers, taking a worst case scenario when site is out of supply but water remains in the tank, to determine compliance with regulation 31 (4)(b) under all circumstances, considering the unit as a whole and the number of units per cell.
    Date: Complete (31 July 2019)
  2. Review governance of Regulation 31 within the company.
    Date: Complete (31 August 2019)
  3. Carry out a full review of catchment risk assessment. This must include all hazards and hazardous events, and be informed by catchment studies, pollution incident records, land use, industrial processes and discharges, infrastructure, rainfall, and any other potential source of contamination within the catchment which could affect the abstraction. Assess the risks at the abstraction.
    Date: Complete (31 October 2019)
  4. Investigate and assess the efficacy of existing catchment mitigations.
    Date: Complete (31 October 2019)
  5. Carry out a process review to identify the performance capabilities of the existing processes to treat all aspects of the raw water quality under all conditions.
    Date: Complete (31 October 2019)
  6. Carry out a gap analysis against existing catchment mitigations and treatment processes.
    Date: Complete (31 October 2019)
  7. Install appropriate sampling facilities throughout Hall treatment stages to allow for inter-stage analysis.
    Date: Complete
  8. Review the removal efficacy of the current process stages and further optimise the treatment processes based on the results.
    Date: Complete (31 December 2019)
  9. Develop appropriate inter-stage process controls to allow ongoing control and management of the treatment processes.
    Date: Complete (31 December 2019)
  10. Review relevant research on disinfection by-products from advanced oxidation processes, and implications for process operation. Summarise technical reports, optimisation and research work undertaken at Hall WTW into a single peer-reviewed report. Review the recommendations from the report and use the learning to inform further work.
    Date: Complete (31 December 2019)
  11. Complete a technical review of all monitoring results (operational, compliance and the enhanced and interstage monitoring completed under this Notice) obtained to date over the lifetime of this Notice, to evaluate the following:
    Date: 31 March 2021
    • the realised capabilities of each stage of the treatment process;
    • The consequential impact of each treatment process upon each other and any consequential implications on water quality;
    • The reason for the high chlorine demand in the final treatment water tank;
    • The impact of the high chlorine demand upon water quality, particularly THM and HAA formation;
    • The appropriateness of interstage responses and trigger levels; and
    • Compliance with regulation 26(2)(a) to operate and maintain the disinfection process to keep disinfection by-products as low as possible without compromising the effectiveness of the disinfection.
  12. Following the completion of measure (b)10. above; the Company shall identify any additional risk mitigation or enhancement of current mitigation required to address any risks identified.
    Date: 30 September 2021
  13. Complete the construction, installation and commissioning of the chosen solution or enhancement of current mitigation, identified in (b)12 above.
    Date: 30 September 2022

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

  1. Define an audit strategy to monitor the effectiveness of the measures specified in section (a) and (b).
    Date: Complete
  2. Implement, and keep under continuous review, the audit strategy defined in measure (c)1.
    Date: Following completion of measure (c)1.onwards

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

Not applicable.

(e) to provide the following information in the time and manner specified below to enable monitoring of progress towards the mitigation of the risks:

  1. Provide a bi-annual progress report against the measures of this Notice. These reports are to include the following information:
    Date: Bi-annually for the duration of the Notice (on 31 January (as the annual progress report) and 31 July)
    • Results from the enhanced monitoring for disinfection byproducts, including trend analysis;
    • Monitoring of hydrogen peroxide post GAC;
    • Investigational monitoring data, including hazard analysis, interstage monitoring, raw and final data and trend analysis;
    • Evaluation of chlorine residuals seen at the ends of the network within the associated water supply zones from compliance and operational monitoring;
    • Compliance with all regulatory requirements; and
    • Any other relevant information regarding the treatment process and the risks identified in this Notice.
  2. Compliance with regulation 31, with regard to contact time of the PAX system, hydrogen peroxide, and the review of governance of Regulation 31 within the company.
    Date: Completed (30 September 2019)
  3. Catchment risk assessment, treatment process review and gap analysis report.
    Date: Completed (30 November 2019)
  4. Summary of research into understanding of organic loading and disinfection byproducts. Report on optimisation and strategy for treatment and minimisation of disinfection by-products at Hall WTW.
    Date: Completed (31 January 2020)
  5. Submit a report summarising the outcome of the technical review completed under measure (b)11.
    Date: 30 April 2021
  6. Submit a report outlining any measures identified under measure (b)12.
    Date: 31 October 2021
  7. Acknowledge completion of measure (b)13.
    Date: 31 October 2022
  8. Submit a satisfactory completion report accompanied by a revised regulation 28(1) risk assessment report with Board level Director sign-off.
    Date: 30 November 2023

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
20 August 2020
Reference: ANH-2019-00001
Version 3

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