Ground source heat pump boreholes in a protection zone

A vertical borehole ground source heat pump in a groundwater Source Protection Zone is usually deliverable, and the constraint that decides it is not planning. The Environment Agency's groundwater protection position is what governs, and its concern is the borehole as a pathway: a 120 metre hole through a confining layer can connect a contaminated shallow aquifer to a clean deep one, and no amount of carbon saving outweighs that.

So the sequence is the reverse of what most design programmes assume. Establish the groundwater position before the array layout, not after.

What the groundwater concern actually is

Source Protection Zones are mapped around public water supply abstractions and are defined by groundwater travel time. The inner zone covers a 50-day travel time to the source, the outer zone 400 days, and the third zone the whole catchment feeding the abstraction. The zones exist because contamination entering within them reaches a drinking water supply before natural attenuation can deal with it.

Four mechanisms worry the regulator:

• creating a vertical pathway between aquifers or between made ground and an aquifer, so contamination migrates downwards
• the heat transfer fluid itself escaping into groundwater through a pipe failure or a poorly sealed annulus
• drilling fluids, cuttings and surface runoff at the wellhead entering the ground during construction
• thermal change in the aquifer, which matters more for open loop schemes and large arrays than for a single domestic borehole

The first is the one that causes objections. A grouting failure is not detectable from the surface and cannot be corrected once the borehole is complete.

Closed and open loop systems compared

For most buildings the choice is made for you. Open loop needs a productive aquifer and a route for the returned water, and in a Source Protection Zone it draws far more scrutiny. Closed loop is the default, and the design discussion is about grouting and fluid selection rather than about hydrogeology.

Permitting and notification requirements

Three separate obligations, none of them planning.

First, notification of the boring. Section 199 of the Water Resources Act 1991 requires notice to the Environment Agency of an intention to construct a boring deeper than 15 metres, which captures essentially every vertical ground source scheme. Give the notice, keep the acknowledgement, and treat it as the point at which the Agency's view becomes known.

Second, environmental permitting. A closed loop system that contains its fluid does not normally need a permit, but where a heat transfer fluid could enter groundwater, a groundwater activity permit under the Environmental Permitting (England and Wales) Regulations 2016 may be required. An open loop scheme needs an abstraction licence where the abstraction exceeds the licensing threshold, plus a permit for the water returned to ground or discharged to surface water.

Third, borehole records. Records are deposited with the British Geological Survey, and the existing record set is the first place to look when assessing what the ground actually does below your site.

Ask the Environment Agency's local groundwater team for a pre-application view in writing. On a scheme of any size that conversation takes weeks and saves months.

Depth, grouting and aquifer separation

This is where the design either satisfies the regulator or does not.

The expectation is that the annulus between the pipe loop and the borehole wall is grouted along the full length with a low-permeability, thermally enhanced grout, placed from the base upwards through a tremie so no voids remain. Partial grouting, or grouting only the upper section, creates the pathway the whole regime exists to prevent.

Where the ground includes more than one aquifer separated by a confining layer, the design has to maintain that separation. That usually means casing and sealing through the upper aquifer before drilling on, and it means a drilling method statement that says what happens if artesian flow or a loss of circulation is encountered. Where the shallow ground is made ground or known to be contaminated, the sensible answer is often to case and seal through it entirely, and to have a Contaminated Land Assessment that establishes what is there first. Phase 1 and Phase 2 land contamination work must be carried out by suitably qualified and experienced people, so this is not a stage to compress.

Fluid selection matters to the regulator. Propylene glycol is generally preferred over ethylene glycol on toxicity grounds, concentrations should be no higher than the design needs, and the fluid and its concentration should be stated in the submission rather than left to the installer.

Include a decommissioning plan. A borehole abandoned without proper sealing at the end of the system's life is the pathway again, decades later.

Where the Environment Agency objects

The pattern is consistent:

1. Boreholes proposed within the inner protection zone, particularly close to the abstraction point itself.
2. Designs that penetrate a confining layer without demonstrating how separation is maintained.
3. Drilling through made ground of unknown quality into an aquifer, with no contamination assessment.
4. Partial or unspecified grouting, or a specification left to the drilling contractor.
5. Open loop schemes where the thermal plume could reach a public supply, or where the discharge quality and location are unresolved.
6. Sites over or adjacent to landfill, where the objection is usually absolute.

An objection is not always final. Many are resolved by a revised borehole layout, a shallower scheme with more boreholes, a switch from open to closed loop, or relocating the array outside the most sensitive part of the zone. What rarely works is arguing the carbon benefit, because the Agency is not weighing planning considerations.

Protection zone boundaries are redrawn as monitoring improves, so check the current mapping rather than a report from a previous project on the same street. Constraints do change, and understanding which planning constraints lapse, expire or are revoked is a useful habit, though a Source Protection Zone is more likely to be extended than removed.

Planning permission and permitted development

Ground source heat pump installations are widely covered by permitted development rights in Part 14 of Schedule 2 to the General Permitted Development Order, for both domestic and non-domestic premises, subject to the conditions in the relevant class. The ground array itself is generally the least contentious element, because once installed there is nothing to see.

What can still need permission: the plant enclosure or external housing, particularly where it is visible or in a conservation area; works to a listed building where pipework enters the fabric, which needs listed building consent for anything affecting character; and engineering operations on a larger scheme where the permitted development limits are exceeded.

A lawful development certificate under section 192 of the Town and Country Planning Act 1990 is the only formal way to confirm that proposed works would be lawful, and on a commercial scheme in a sensitive location it is worth the fee. Note that permitted development status does not displace the groundwater regime. A scheme can be lawful in planning terms and still be unlawful to construct without satisfying the Environment Agency.

Evidence for the application

Where planning permission is needed, or where the local authority asks for supporting information on a permitted development scheme, the material that answers the questions is:

• a desk study identifying the protection zone, groundwater vulnerability, aquifer designation and any historical contaminative use, using the Environment Agency's published mapping and British Geological Survey records
• a conceptual ground model showing the aquifer sequence and the confining layers the boreholes will pass through
• borehole layout, depth and spacing, with the grouting specification and placement method stated
• heat transfer fluid type and concentration
• a drilling method statement covering contingency for loss of circulation, artesian flow and contaminated arisings
• a decommissioning plan
• the section 199 notification and any written response from the Environment Agency

Where ground conditions are uncertain, a Geotechnical Assessment covering the same ground investigation serves both the foundation design and the borehole design, and councils usually expect a suitably qualified author for it. The heat pump's contribution should then appear in the Energy Statement with the seasonal performance assumption stated, and where water resources are a local constraint the scheme may also touch the ground covered by a Water Supply Assessment.

This is general guidance rather than legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.