Site Survey

What is a site survey?

A site survey, often referred to in construction as a site investigation or ground investigation, is the comprehensive process of appraising the physical, geological, and environmental characteristics of a parcel of land before development begins.¹

A site survey is fundamentally different from a topographical survey. While a topographical survey focuses on mapping the surface of the land — recording physical features, terrain relief, and boundaries — a site investigation focuses primarily on what lies beneath the surface.¹ Topographical surveys provide the geometric baseline for design; site investigations provide the physical and chemical properties of the earth required for safe foundation and drainage design.

The UK 2026 site investigation is governed by two principal British Standards:¹

• BS 5930 — Code of practice for ground investigations. Defines how to describe soils and rocks, and how to conduct geotechnical site investigations and in-situ testing.
• BS 10175 — Investigation of potentially contaminated sites. Defines how to investigate, sample, and assess land that may be affected by historical contamination.

The hierarchy of disciplines

The terms site survey, site investigation, ground investigation, geotechnical engineering, and contaminated land assessment are frequently used interchangeably but represent a nested hierarchy:¹

• Site Investigation — the overarching term for the entire process of gathering information about a site, including both above-ground and below-ground conditions.
• Ground Investigation — the specific intrusive physical exploration of the subsurface (e.g. drilling boreholes and digging trial pits).
• Geotechnical Engineering — the engineering discipline that analyses the physical mechanics of the soil and rock to design safe foundations, retaining walls, and earthworks.
• Contaminated Land Assessments — the environmental discipline focusing on the chemical composition of the soil and groundwater to detect hazardous materials, ensuring the site is safe for its intended end-use.

What's included in a 2026 site investigation

A comprehensive site investigation follows a phased approach:¹

Phase 1 — Desk Study (the "paper survey")

The initial stage involves reviewing all available data before venturing into the field:¹

• Existing topographic maps, historical aerial photographs, and geological, geomorphological, and pedological (soil) maps.
• Historical land use records — to flag potential contamination sources (former gas works, landfills, industrial sites).
• Remote sensing and aerial photography — to detect signs of slope instability, solution features (chalk dissolution), derelict land, or contaminated land.
• Local authority planning records — for any prior ground investigations or contamination reports.

Walkover Survey

A detailed field reconnaissance where the engineer physically visits the site to verify the desk-study findings, locate existing features (wells, sumps, old foundations), and plan the logistics for intrusive machinery.¹

Phase 2 — Intrusive Investigation

Physical exploration of the subsurface, including:¹

• Window sampling — small, tracked rigs that fit through standard garden gates for shallow investigations.
• Cable percussion boreholes — for deeper sampling and Standard Penetration Tests (SPT).
• Rotary core drilling — for rock investigation and deep foundations.
• Trial pits — hand-dug or machine-excavated for shallow foundation assessment.

Laboratory Analysis

Recovered samples are sent to accredited laboratories for:¹

• Geotechnical testing — plasticity, moisture content, shear strength, particle size distribution, consolidation.
• Environmental testing — screening for heavy metals, asbestos, hydrocarbons, pH, organic matter.

2026 cost bands

UK 2026 site investigation costs vary dramatically based on the site's history, accessibility, and the proposed structure's load:¹²³

When is a contaminated land survey legally required?

If your site has a history of industrial use, or if you are changing the land use to a more sensitive category (such as building homes on former agricultural land or industrial land), the Local Planning Authority will almost always attach a condition to your planning permission requiring at least a Phase 1 Desk Study to assess contamination risks.¹

Can the site investigation find old mine workings or sinkholes?

Yes. The Phase 1 desk study identifies historical mining records or susceptible geological formations (like chalk). If risks are flagged, the Phase 2 intrusive investigation will use deep drilling or geophysical surveys to locate subterranean voids.¹

Will the ground investigation destroy my existing driveway or garden?

Intrusive testing involves heavy machinery, so some disruption is unavoidable. However, engineers can use small, tracked "window sampling" rigs that fit through standard garden gates to minimise damage, and hard surfaces can be temporarily reinstated afterward.¹

If the site is contaminated, does that mean I can't build on it?

No. It simply means the contamination must be managed or "remediated." This might involve removing the topsoil, installing gas-resistant membranes in the foundations, or capping the ground with clean, imported soil to ensure end-user safety.¹

How long does a full site investigation take?

A Phase 1 Desk Study typically takes 1 to 2 weeks. If Phase 2 intrusive works are required, the site work may take a few days, but geotechnical and chemical laboratory testing often takes an additional 2 to 4 weeks before the final interpretive engineering report is ready.¹

How to commission a site survey in 2026

1. Send the brief. Site address, proposed development (residential extension, new build, commercial), planning application status, and any known site history (former industrial use, mining area, etc.).
2. Receive a fixed-fee quote. Most 2026 quotes are returned within 48 hours. The quote will be split into Phase 1 (desk study) and Phase 2 (intrusive) if both are needed.
3. Surveyor credentials. RICS or CICES membership (for the survey aspect), with contaminated land assessment by a Qualified Person under the Environmental Permitting Regulations.⁴
4. Phase 1 desk study. The engineer reviews historical records, geological maps, and planning history to produce a Phase 1 report.
5. Phase 2 intrusive works. Boreholes, trial pits, in-situ testing, and sampling.
6. Laboratory analysis. Accredited lab testing (typically 2–4 weeks for full results).
7. Interpretive report. The engineer issues a Phase 2 report with foundation recommendations, contamination status, and any remediation requirements.
8. Aftercare. If planning conditions require further verification (e.g. gas monitoring, groundwater sampling), the engineer can provide ongoing monitoring.

Frequently asked questions

References