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@mespilus
Email received from HS2/SCS this morning:
'Good morning,
You may be aware of an incident reported by members of the public on Saturday morning, who found foam appearing from the ground in an area of the Ruislip Rugby Club playing fields. SCS teams attended site to investigate and to make the area secure, and the foam was cleared on Saturday.
The foam appeared out of a borehole that was created earlier in the project to investigate the ground conditions in the area. The boreholes are usually sealed afterwards and we are looking into whether this one was correctly treated. We are also checking other boreholes along the route of the tunnel boring machines (TBMs) to ensure they are all sealed as required, including two additional ones on the playing fields.
The foam is created by a “conditioning fluid” that is used to treat the ground in front of the TBM to help make the excavated material more manageable. The fluid is biodegradable and not harmful to plant or animal life and was approved for use by the Environment Agency. There is no danger to the groundwater aquifer.
There may be a small amount of foam that continues to appear over the next 12-18 hours, as it is forced out as the grout we have used sets and hardens in the borehole. The borehole itself has now been fully sealed from below as the TBM passed and the concrete tunnel ring was put in place underneath the bottom of the borehole.
Although the substance is not harmful, we and Hillingdon would like to ensure that it is not walked through by users of the playing field and so we have securely fenced of the area and will undertake security checks in the short term. We will put up posters to inform the community about what has happened and what will happen next. There will also be a FAQ sheet prepared and shared via the HS2 website and our distribution lists. We will of course send yourselves a copy to share with your neighbours as you wish.
Thank you and have a nice day.'