In October 2014, we tendered for work on the Thanet sewers programme for the construction of 5 observation boreholes. The boreholes allow the sampling and analysis of groundwater, in particular nitrate levels, in different parts of the aquifer. Information taken from the boreholes would also improve general understanding of the hydro-geology of the chalk aquifer across the Thanet area. Specifically, the boreholes would be continuously monitored to record groundwater levels and electrical conductivity.
In the original tender document it outlined that rotary drilling techniques would most likely be used and that air-lifting would be required to clear the boreholes of debris on completion of drilling. In our submission, we outlined that the cable-tool percussion drilling method is a cleaner it does not wash sediment into the fissures meaning that the borehole itself will not require airlifting. It was also outlined in our proposal that the proposed boreholes were in Environment Agency groundwater source protection zones 2 and 3, therefore it was imperative that the risk of contamination was minimal. Cable-tool percussion requires no water for the drilling process once the water table has been reached and is the method preferred by the Environment Agency when drilling the chalk aquifer.
We were subcontracted for this job by Clancy Docwra and drilling commenced in December 2014. During the construction of the 5 boreholes, our workmen stayed in the area. The whole process took around 8 weeks and was completed in February 2015.