Groundwater Abstraction: Boreholes and Wells
Everything you need to know about abstracting groundwater from boreholes and wells in England and Wales, from site investigation to pump testing and long-term management.
Introduction to Groundwater Abstraction
Groundwater — water stored in the pore spaces and fractures of rocks below the ground surface — provides approximately 30% of public water supply in England and Wales. It is also widely used for agriculture, industry, and private water supply.
Principal Aquifers in England and Wales
| Aquifer | Rock Type | Location | Typical Yield |
|---|---|---|---|
| Chalk | Limestone | SE England, E Anglia, Yorkshire Wolds | 1–50 l/s |
| Triassic Sandstone | Sandstone | Midlands, NW England | 5–100 l/s |
| Jurassic Limestone | Limestone | Cotswolds, Lincoln Edge | 1–20 l/s |
| Lower Greensand | Sandstone | Surrey, Kent, Bedfordshire | 1–10 l/s |
| Carboniferous Limestone | Limestone | Wales, Pennines | Variable |
Site Investigation
Before drilling a borehole, a thorough site investigation is essential:
Desk Study
- Review British Geological Survey (BGS) maps and borehole records.
- Check EA/NRW groundwater level and quality data.
- Review existing abstraction licences in the area.
- Assess potential contamination sources.
Geophysical Survey
Electrical resistivity or seismic surveys can help identify:
- Aquifer boundaries and depth.
- Fault zones and fractures (important in hard rock aquifers).
- Contamination plumes.
Borehole Construction
Drilling Methods
- Cable tool (percussion) drilling: Slow but effective in all formations; produces minimal disturbance.
- Rotary drilling: Faster; uses drilling fluid (mud or air) to remove cuttings.
- Air flush rotary: Preferred for hard rock aquifers; uses compressed air.
Casing and Lining
- Steel casing: Used in the upper, unstable section of the borehole.
- Slotted/perforated casing (screen): Installed opposite the water-bearing zone to allow water entry while excluding fine material.
- Gravel pack: Placed around the screen to improve yield and reduce sand pumping.
- Grouting: Cement grout placed between the casing and borehole wall to prevent surface water ingress and contamination.
Pump Testing
Pump testing is required to:
- Establish the yield of the borehole.
- Determine aquifer properties (transmissivity, storage coefficient).
- Assess impacts on neighbouring boreholes and surface water.
Step Test
A step test involves pumping at progressively increasing rates to determine the relationship between pumping rate and drawdown. This identifies the sustainable yield.
Constant Rate Test
A constant rate test (typically 24–72 hours) at the proposed abstraction rate, with monitoring of water levels in the pumped borehole and any observation boreholes, provides data for aquifer characterisation.
Recovery Test
Monitoring water level recovery after pumping ceases provides additional aquifer data.
Groundwater Quality
Groundwater quality varies with aquifer type and land use:
- Chalk: Generally good quality; may have elevated nitrate in agricultural areas.
- Triassic Sandstone: Generally good quality; may have elevated iron and manganese.
- Hard rock: Variable; may have elevated radon, arsenic, or fluoride.
All groundwater intended for drinking must be tested and treated to meet the Water Supply (Water Quality) Regulations 2016.
Environmental Considerations
Groundwater abstraction can:
- Lower water tables, affecting groundwater-dependent ecosystems (e.g., chalk streams, wetlands, springs).
- Reduce baseflow to rivers, affecting river flows particularly in dry weather.
- Cause land subsidence in some geological settings.
- Induce saline intrusion in coastal aquifers.
The EA uses groundwater flow models to assess these impacts when determining licence applications.