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The Cost of Unforeseen Ground Conditions

Our Groundwater Assessment is a relatively small price to pay compared to the risk of not understanding the groundwater conditions at your site. The sooner you get clarity on seasonal groundwater levels, the sooner you and your design team can make even better decisions about drainage design and SuDS feasibility.
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Geotechnical Engineers Committed to Getting Your Site Safely Built

Your assessment will be carried out by an experienced groundwater specialist, supported by a knowledgeable team with a proven track record of securing regulatory approval across the UK. We ensure that groundwater conditions are fully understood, risks are properly assessed, and appropriate mitigation measures are identified.

Our groundwater assessments are informed by site data, desk studies, and, where required, monitoring and testing. Each report provides clear, technically robust conclusions on groundwater levels, flow conditions, and potential risks to and from the development, supporting planning applications and compliance with environmental regulations.

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  • Tick Icon Compliant with Environment Agency and LLFA requirements
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Groundwater Assessment

Our team of geotechnical engineers and consultants can review your site and guide you through the complex process of undertaking a Groundwater Assessment, so you can get your site approved and built.

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Answer a few questions, so together we can come up with a plan that fits your timescales and budget.

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Groundwater Assessment

We work through the complex process of organising the site works and carrying out the Groundwater Assessment.

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Receive Report

Written with an engineer in mind, so they know what action to take for design purposes.

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What is a Groundwater Assessment?

A Groundwater Assessment involves the monitoring and analysis of groundwater conditions at a site. This typically includes the installation of monitoring standpipes within boreholes, followed by a programme of regular groundwater level measurements over a defined period. The data is used to establish the seasonal variation in groundwater levels, the highest anticipated groundwater table, and the potential risk of groundwater flooding. 

Groundwater assessments have become increasingly important in the planning process. Lead Local Flood Authorities (LLFAs) frequently require seasonal groundwater monitoring data as part of the evidence base for approving infiltration-based sustainable drainage systems (SuDS). Where the peak groundwater level is too close to the base of a proposed soakaway or other infiltration feature, the LLFA may not accept infiltration as a viable drainage solution. Understanding groundwater conditions early in the project programme is therefore critical to avoiding delays and redesign costs. 

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Why do you need a Groundwater Assessment?

Groundwater can have a significant influence on how a site is designed, particularly where development interacts with below-ground conditions or the water environment.

If groundwater conditions are not properly understood, projects can face issues such as flooding of excavations, constraints on foundation and drainage design, contamination risks, and objections from the Environment Agency (EA) or Lead Local Flood Authority (LLFA).

A groundwater assessment provides clarity on groundwater levels, seasonal variation, and flow conditions, allowing risks to be identified early and managed appropriately.

Groundwater assessments are typically required in the following situations:

Groundwater Levels & Flood Risk

High groundwater levels can impact excavation stability and increase the risk of flooding during construction. Understanding peak groundwater levels allows appropriate design measures to be incorporated at an early stage.

Drainage & Soakaway Feasibility

Where infiltration drainage or soakaways are proposed, groundwater conditions must be considered alongside soil permeability. High groundwater levels can limit infiltration and affect the viability of SuDS drainage systems.

Basement & Below-Ground Structures

Developments with basements or deep foundations must account for groundwater pressures and potential ingress. Early assessment helps inform waterproofing design and structural detailing.

Ground Gas Interaction

Groundwater movement can influence ground gas behaviour, including migration pathways and concentration levels. Monitoring both parameters together provides a more robust understanding of risk.

Contamination & Controlled Waters

Where contamination is present or suspected, groundwater can act as a pathway for pollutant migration. A groundwater assessment helps evaluate risks to controlled waters and supports compliance with environmental regulations.

By understanding groundwater conditions early, you reduce uncertainty, avoid costly redesign, and ensure your development can be delivered safely, compliantly, and efficiently.

How is a Groundwater Assessment carried out?

Groundwater assessments are typically undertaken following a ground investigation, with monitoring installations designed to capture groundwater conditions over time.

Our approach is tailored to the site and project requirements but will typically include:

  • Installation of groundwater monitoring standpipes
    Monitoring standpipes are installed within boreholes, typically extending to around 5 metres below ground level. Where ground gas monitoring is also required, combined gas and groundwater installations can be specified, allowing both datasets to be collected from the same location.
  • Groundwater level monitoring
    Groundwater levels are monitored over a defined period, typically on a fortnightly or monthly basis. Monitoring programmes are designed to capture seasonal variation, with most Lead Local Flood Authorities (LLFAs) requiring data covering the winter period (October to March), when groundwater levels are generally at their highest. Where relevant, gas monitoring can be undertaken concurrently to assess any relationship between groundwater fluctuation and gas concentrations.
  • Groundwater sampling and testing
    Where contamination is suspected or confirmed, groundwater samples may be collected during monitoring visits to assess dissolved-phase contaminants and track changes in groundwater quality over time.
  • Data analysis and interpretation
    Monitoring data is analysed to establish peak groundwater levels, seasonal trends, and groundwater flow conditions. This includes assessing the relationship between groundwater and proposed drainage formation levels, foundation depths, and any potential contaminant sources.
  • Reporting and recommendations
    Findings are presented in a clear interpretative report, including monitoring data, analysis, and conclusions. The report provides practical recommendations to inform drainage design, foundation detailing, ground gas protection measures, and any mitigation required in relation to groundwater management or controlled waters risk.

How long does groundwater monitoring need to be carried out for?

Most LLFAs require a minimum monitoring period that captures the winter months, typically October to March inclusive. This is because groundwater levels tend to peak around February to March.  

Some LLFAs may accept a shorter monitoring period if supported by a strong technical justification, but it is advisable to programme monitoring well in advance to avoid delays. 

 

 

 

 

 

 

When is a groundwater assessment required?

A groundwater assessment is typically required where development may be affected by groundwater levels or where there is potential risk to controlled waters. This includes sites with basements, infiltration drainage proposals, or where required by the Environment Agency or Lead Local Flood Authority as part of a planning application.

What time of year should groundwater monitoring commence? 

Ideally, monitoring should commence no later than October to ensure the full winter period is captured. If you are planning a spring or summer planning submission, early engagement is essential so that monitoring data is available in time.

Can groundwater monitoring be undertaken at the same time as a site investigation? 

Yes. The monitoring standpipes can be installed in boreholes drilled as part of a geotechnical or geo-environmental site investigation.  

This is the most cost-effective approach, as it avoids a separate mobilisation. 

What happens if the groundwater level is too high for soakaways?

If the monitoring data demonstrates that the peak groundwater level does not provide sufficient clearance below the base of the proposed soakaway, alternative drainage solutions will need to be considered. These may include attenuation and controlled discharge to a watercourse or sewer, permeable paving, or other SuDS components that do not rely on infiltration.  

Our Flood Risk and Drainage team can advise on the most appropriate alternative. 

Does groundwater monitoring also cover ground gas?

Where a ground gas risk has been identified (for example on or near former landfill sites, areas of made ground containing biodegradable material, or sites with natural organic deposits such as peat or alluvium), we can install combined gas and groundwater monitoring standpipes. This allows both groundwater levels and ground gas concentrations to be recorded during the same monitoring visits.  

The correlated dataset is particularly valuable for understanding the “piston effect,” where rising groundwater levels displace soil gases upwards, and ensures that gas protection measures are designed for worst-case conditions. 

Can groundwater monitoring also assess contamination risk?

Yes. Where contaminated land conditions are suspected, we can collect groundwater samples during the monitoring visits for laboratory analysis.  

This provides data on dissolved-phase contamination and allows the assessment of risks to controlled waters in accordance with the Environment Agency’s LCRM guidance.  

Combining groundwater quality monitoring with level monitoring within a single programme is more cost-effective and provides a more robust dataset than undertaking them separately. 

What if my site has a basement, do I need a groundwater assessment?

If your development includes a basement or other below-ground construction, a groundwater assessment is strongly recommended.  

The data informs waterproofing design, assesses the risk of hydrostatic uplift, and enables evaluation of whether the proposed structure could impede natural groundwater flow.  

Some local planning authorities such as London Borough of Richmond upon Thames for example specifically require a groundwater impact assessment where basement or semi-basement construction is proposed, particularly in areas with shallow groundwater tables and where groundwater flow-through risks are present. 

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