Released HS2 data for 2023 shows pollution being mobilised in the chalk aquifer in Protection zones 1 and 2 for the Ickenham and Blackford (PWS)s, this is a Drinking Water Protected Area. Objectives in this protected area must be complied with. These are to maintain good chemical quality at the Blackford water source and achieve good chemical quality at the Ickenham source by 2027. Neither appear to be happening.

Under Freedom of Information HS2 has release the water quality data from monitoring of their Colne Valley works for May 2022 to April 2023. Pollution events and exceedances are listed in Table 1 below.

One main concern is that the Blackford PWS at Moorhall Road pumping station, will not avoid deterioration in status. The Blackford source is licensed for 20 Million litres a day and had good chemical quality before it was closed in May 2021 due to the close proximity of HS2 works. HS2 say the planned closure is a precautionary measure so that pollution does not make its way to our taps. During the time Blackford pumping station is closed, replacement water is being bought and piped into the area. There is a legal duty to reopen the Blackford source and for it to produce the same quantity and quality of public drinking water as before HS2. This means the groundwater in the aquifer should be of the same quality as before, clear and not needing additional treatment. This will not be possible if pollution from HS2 works and other contamination, is mobilised in the aquifer and migrates into the Blackford SPZ. It is not possible to flush out the chalk aquifer before reopening the Blackford pumping station, pollutants may be lodged in the rock matrix which could move at any time.

Worrying examples of pollution: In March 2023 there was a worrying Turbidity spike of 1067 (NTUs) Nephelometric Turbidity Units, recorded at a borehole ML026-RO426 in Load Test Pile Site 2 Harvil Road. Align Ltd states that this may be due to mobilisation of polymers from the test piles. Polymers are a risk to drinking water as residual monomer acrylamide can be left. Acrylamide is a banned substance in groundwater as it causes cancer. We do not know whether HS2 has done any testing for acrylamide since the high turbidity readings were taken. There is no indication of the direction of travel of the polymers, or whether they are moving towards the Blackford source.

Chromium 6 is another cancer causing substance which HS2 has repeated found at their sites and is derived from cement use. Align Ltd have made various arrangements to transport waste water contaminated with chromium 6, to their Water Treatment Plant at the south portal site, to remove the chromium. Align Ltd repeatedly state that the chromium 6 being found at their sites has not entered the aquifer. On 21st March 2023 chromium 6 was measures in borehole ML026-CR032 in the chalk aquifer at 5.3 ug/l. This is a priority hazardous substance which must be prevented from entering groundwater and in particular must be prevented from entering groundwater in the Blackford SPZ.

HS2 are blaming other chemical imbalances on the Council landfill site, up hill on the eastern edge of the Colne Valley, south of Harefield. Pollution includes; TPH aromatics, Ammoniacal nitrogen, sodium, potassium, electrical conductivity, calcium. HS2 works should not be mobilising the landfill leachate or causing the pollutants to travel into the Blackford SPZ1 but this appears to be happening.

March monthly data report states. ‘TPH were previously detected on 4th January, but different carbon bands were identified (C7-C10 aromatic). Discussion with S2 contractor SCS have mentioned presence of TPH in groundwater owing to historic landfill contamination within/close to their area.’

Hazardous pollutants have been found in the Newyears Green Bourne (NYGB) which runs through the disused Contaminated Land, under Harvil Road and down to the Hillingdon Outdoor Activity Centre (HOAC) Lake which forms part of the Blackford inner source protection zone.

ML026-CRO32 is west of Harvil Road, south of Dews Lane and north of Newyears Green Bourne.

ML026-RO426 is a test borehole west of Harvil Road, south of Newyears Green Bourne, in the Load Test Pile Site 2.

Table 1: extracts from Align Ltd. C1 Monthly Water Monitoring Reports (download here)