Bramley water quality: sample results

The following information has been prepared as accompanying guidance to sample data provided by Thames Water in relation to the ongoing investigation in Bramley, GU5.

Some key points to be noted:

• Samples are collected by trained Water Quality Technicians who are independently assessed by the United Kingdom Accreditation Service (UKAS). Samples are analysed at our company laboratories in Reading.
• Similarly, many of our analytical methods are UKAS accredited and subject to rigorous quality assurance and control. Note, in some cases, non-accredited methods are used where this may benefit the investigation e.g for example, where an analytical ‘scan’ may be carried out more broadly to identify the presence of non-target compounds.
• In addition to laboratory analysis, some tests can be carried out on-site, such as an assessment of the taste, odour or appearance of the water or measurement of the chlorine levels.
• The term ‘LOD’ refers to ‘Limit of Detection’. This simply means the measured result is less than the lowest limit that the analytical method can quantify.
• There is a lag between the date samples are taken and when the results are received, this is due to the time taken to carry out the analysis. We are fast-tracking all analysis currently however there is a still a minimum time requirement for the analysis.
• The table summarises all samples taken since August 2023 except for three individual properties known to have experienced more acute levels of contamination, and which had therefore already been subject to ‘Do Not Drink’ restriction of use advice before the 30 May.
• There are 3 colours from the table with the sample results: 

• Black text on white background: values below UK standards for drinking water.
• White text on back background: values above UK standards for drinking water.
• Blue: Provisional results waiting for final approval from quality control checks. The results can vary slightly but this is unlikely.

Summary of key parameters of note

Upon identification of hydrocarbons in the drinking water samples, we utilise independent toxicology laboratory data, and work alongside our colleagues in the UK Health Security Agency (UKHSA). The results from the table are focusing on Dissolved Hydrocarbons (DHCs), Benzene, Toluene and Ethylbenzene. All these compounds are specific derivatives from fuel. 

1. DHCs  - Dissolved Hydrocarbons 

Dissolved hydrocarbons (DHCs) include 10 named compounds – essentially, the methodology uses mass spectrophotometry, a complex analytical process that is used to detect and quantify the presence of volatile organic compounds such as those that are found in fuel (e.g. hydrocarbons). It is calibrated and targeted to 10 compounds and the method is independently accredited.

The results are expressed in ‘µg/l’ (micrograms per litre or 1 part per billion) and where compounds have been identified via this method, they have been considered to indicate the presence of fuel-derived contamination. The significance of the results reported are assessed according to their likely impact on public health risk or aesthetic impact to water quality. 

There is no prescribed regulatory limit for many of the compounds identified and so when they are detected, their significance is assessed in two ways:

1. Are they considered to represent a risk to public health? To answer this, we may consult with independent experts such as UKHSA, as well as our other independent sources of toxicological information. The World Health Organization (WHO) produces international norms on water quality and human health in the form of guidelines that are used as the basis for regulation and standard setting world-wide. These are based on lifetime exposure and considering vulnerable groups.
2. Have they or are they likely to cause an objectionable taste or odour to the drinking water?
   Below 10 ug/L (10 micrograms per litre, also referred to as parts per billion), the levels of compounds are at such low levels that no risk to health would be apparent, nor any likely taste or odour to the drinking water.

2. Benzene

Benzene has a regulatory limit of 1 µg/l.

Prior to results reported on 30 May 2024 (from samples collected on 28 May 2024), all benzene results had remained below this regulatory limit – except for three individual properties known to have experienced more acute levels of contamination, and which had therefore already been subject to ‘Do Not Drink’ restriction of use advice.

The more widespread issuing of ‘Do Not Drink’ notices on 30 May 2024 was taken in response to sample results reported earlier that day which indicated benzene concentrations had increased above 1 µg/l and therefore above the regulatory limit. Thames Water had increased levels of local sampling since October 2023 and this was the first time the results had been elevated in the wider village.

3. Toluene

Toluene doesn’t have a regulatory limit. WHO drinking water guidelines are 700ug/L.

4. Ethylbenzene

Similar to Toluene, Ethylbenzene doesn’t have a regulatory limit. WHO drinking water guidelines are 300ug/L.
Prior to results reported on 30 May 2024 (from samples collected on 28 May 2024), all Ethlybenzene results had remained below this level – (with the exception of the three previously mentioned individual properties that experienced more acute levels of contamination, and which had therefore already been subject to ‘Do Not Drink’ restriction of use advice).