Borehole drilling and deposit guidance

Water borehole drilling best practice 

Whilst BGS, and by extension the NGDC, is named as the legal place of the deposit for data, from our own extensive knowledge and expertise relating to borehole drilling, we can offer the following advice for general practice;  

• Location: It is good practice to site a borehole as far away as possible, and preferably upslope, from any potential sources of pollution, including septic or fuel tanks, soakaways, slurry pits and areas of intensive grazing. A minimum distance of 50m between a water borehole and any potentially polluting activity is recommended.  

• Construction: For boreholes abstracting from the superficial deposits, the top few metres should be cased out (the depth of plain casing depending on the aquifer thickness at the specific site). A borehole abstracting water from a bedrock aquifer should be sealed off through the superficial deposits by installing a length of plain casing to at least 5m below the upper surface of the bedrock. The casing should be grouted effectively in order to minimise the risk of poor-quality surface or shallow groundwater entering the borehole.  

• Water quality: It is recommended that a water sample, taken during the final stages of the pumping test, is sent for full analysis to a reputable laboratory. They, or if a potable private supply is envisaged the Environmental Health Officer of the local council, should be able to advise on the range of analyses to be undertaken. This would normally include; pathogenic indicator bacteria, iron, manganese and nitrate. An adequate and well-maintained disinfection treatment would be considered advisable for any supply intended for potable use.  

Further guidance on physical core 

Present-day methods of boring do not produce cores from the majority of boreholes for water. Nevertheless, specimens obtained should be as good as possible, and their depths below the ground surface recorded as accurately as possible. Care should be given to the description of strata recorded in the journal. 

Cores, when taken, should be laid out in regular order with marks at intervals showing depths of origin, and gaps in which the cores are absent or imperfect should be marked with an indication of the extent of the missing core and such fragmentary specimens as have been obtained at that depth should be retained in place.  

Specimens of the material obtained in well sinking should be laid out in order, and those from each depth should be kept together. If any band encountered contains fossils, all materials from that band should be kept together as those fossils may furnish important evidence of the geological horizon penetrated in the sinking.  

Any portions of cores or materials from well sinking or borings of special interest, or liable to disintegrate if exposed to rain and the action of the air, should receive special attention to ensure their preservation. Precautions should be taken to prevent disturbance by members of the public, or by cattle, sheep or other animals.  

In cases of special interest, it may be desirable for repeated visits to be paid by the officers of the NGDC to a well or borehole under construction and it is requested that, when desired, notification of the progress of work and particularly of any unforeseen developments should be sent to the British Geological Survey to ensure that no valuable information should be lost. For this purpose, it is hoped that the active co-operation of the contractors undertaking the work will be extended to the officers of the NGDC.