South East Water Limited – Maidenhead (College Avenue) Treatment Works, Chromium Risk

Notice under regulation 28(4) of the Water Supply (Water Quality) Regulations 2016 (as amended)

Reference: SEW-2018-00016

Version Number: 2

Water undertaker as appointed under section 6 of the Water Industry Act 1991 (as amended): South East Water Limited, with registered number 02679874 (hereinafter called ‘the Company’).

Assets Affected:

Asset Name

Asset Reference

Maidenhead Treatment Works


College Avenue Groundwater catchment


Maidenhead (College Avenue) Supply System


Table 1: List of assets affected and associated reference numbers

Details of this Notice:

  1. The Drinking Water Inspectorate (‘the Inspectorate’) has received a regulation 28(1) report of the Water Supply (Water Quality) Regulations 2016 (as amended) (‘the Regulations’) from the Company dated 01 November 2017, which states that there is or has been a significant risk of supplying water from Maidenhead Treatment Works (also known as College Avenue Treatment Works) (and associated assets as applicable) that could constitute a potential danger to human health or could be unwholesome.
  2. Consequently, this Notice is served on the Company by the Inspectorate on behalf of the Secretary of State, under regulation 28(4) for the assets listed above, for risks associated with chromium.
  3. The Company are required to satisfy the following requirements.

The date given is that until or by which the requirements must be maintained or satisfied, as appropriate.


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

  1. Increased operational monitoring for chromium in the catchment and at Maidenhead Treatment Works.
    Date: until completion of measure (b)4.
  2. Blending of the raw water sources to ensure the treated water chromium concentrations comply with regulation 4(2) of the Regulations.
    Date: until completion of measure (b)4.
  3. Ongoing investigation and liaison with relevant stakeholders to identify chromium risks within the catchment. Ongoing investigation and implementation of catchment management measures to reduce chromium risk.
    Date: Ongoing for the duration of this Notice
  4. Ongoing evaluation of the risk from chromium VI, with defined responses based on the level of risk, taking into account the Inspectorate’s guidance on chromium VI and that from other relevant stakeholders as appropriate.
    Date: Ongoing for the duration of this Notice

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

  1. Chromium water treatment pilot trials to be carried out to identify a suitable treatment option.
    Date: 31 December 2022
  2. Evaluate the chromium risk through completion of a review of the following information:
  • any findings from the ongoing catchment investigations and liaison with relevant stakeholders;
  • any results from catchment initiatives implemented;
  • findings from the ongoing evaluation of the risk of chromium VI; and
  • the results from the enhanced ongoing monitoring programme.
    Date: 30 November 2023
  1. Design a solution to address any risks identified through the completion of the review required under measure (b)2. The design must also consider the findings from the pilot treatment trials completed under measure (b)1.
    Date: 31 March 2024
  2. Install and commission the chosen solution at Maidenhead Treatment Works to mitigate the risk of chromium, as designed under measure (b)3. Commissioning must include the following to account for the changes made:
  • An appropriate maintenance regime for any installed treatment;
  • Full integration of any new treatment processes into the site control and monitoring systems;
  • Updating of the Site-Specific Disinfection Policy and any associated site-specific procedures;
  • Updating of the Site Operating Manual and removal of all out-of-date material from circulation; and
  • Provisions of adequate training for all relevant personnel on the operation, repair and maintenance of the chosen solution and the revised procedures, policies and manual.
    Date: 30 April 2026

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

  1. Review and update the defined audit strategy to monitor the effectiveness of the measures specified in sections (a) and (b). To include as a minimum:
  • Pre-completion of measure (b)4: sampling at a minimum frequency of weekly of the raw and treated water for chromium; and
  • Post-completion of measure (b)4: sampling at a minimum frequency of weekly of the raw, post-chromium treatment and final water for chromium.
    Date: 31 December 2022
  1. 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 Maidenhead Treatment Works, or not to so supply unless the specified conditions below are satisfied:

  1. 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 progress report annually.
    Date: by 31 January each year.
  2. A report summarising the findings from the pilot trials completed under measure (b)1.
    Date: 31 January 2023
  3. A report summarising the findings of the review completed under measure (b)2.
    Date: 31 December 2023
  4. Outline the chosen solution designed under measure (b)3.
    Date: 30 April 2024
  5. Provide evidenced confirmation of the installation and commissioning of the chosen solution, as required under measure (b)4.
    Date: 31 May 2026
  6. Submit the updated audit strategy for auditing the effectiveness of the measures, as specified in measure (c)1.
    Date: 31 January 2023
  7. Submit any revisions of the audit strategy produced under measure (c)2.
    Date: Within 1 month of a revision
  8. Submit a report in the event that any completed measures of this Notice need to be altered in any way, for any reason.
    Date: Ongoing for the duration of this Notice
  9. Submit a satisfactory completion report accompanied by a revised regulation 28(1) report with Board level Director sign-off.
    Date: 31 May 2027

Further Details of this Notice:

  1. Any product or substance used as a result of the requirements in this Notice must comply with regulation 31.
  2. Under regulation 28(6) the Inspectorate, on behalf of the Secretary of State, may by notice served on the Company, revoke or vary this Notice.
  3. Failure by the Company to comply with this Notice may result in enforcement proceedings under section 18 of the Water Industry Act 1991 (as amended).


Nicholas Adjei
Deputy Chief Inspector, on behalf of the Secretary of State for Environment, Food and Rural Affairs
18 November 2022
Reference: SEW-2018-00016 v2

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