In an era of tightening regulation and growing concerns about climate change, Churngold Construction’s Duncan Houlden explains the key considerations for managing groundwater on construction sites
What you will learn in this CPD
- Water risks on construction sites and regulatory rules
- The differences between environmental permits and exemptions
- The three treatment stages commonly used for contaminated groundwater
Whether delivering complex groundworks on constrained brownfield sites or preparing greenfield developments where water poses a risk, effective management of groundwater and surface water run-off is fundamental to safe, compliant and efficient project delivery.
Uncontrolled water can halt construction activity, undermine excavations, damage newly installed infrastructure and, crucially, lead to the release of silt-laden or contaminated water into the wider environment.
For contractors and developers, the regulatory, financial and reputational consequences can be significant. Environmental legislation requires strict control of discharges to watercourses and groundwater, while clients increasingly expect robust environmental risk management as part of responsible construction practices.
By deploying engineered treatment solutions, including separators, settlement tanks, attenuation systems and activated carbon filtration, contractors can maintain programme certainty while ensuring strict environmental compliance.
A key consideration for any groundwater treatment strategy is understanding whether an activity requires an environmental permit or whether it can operate under an exemption.
Key legislation and guidance
Construction professionals involved in groundwater management should be familiar with the following legislation and guidance documents:
In simple terms, exemptions generally apply to lower-risk activities that fall within predefined operational rules set by the regulator.
Permits, however, are required for higher-risk activities, more complex treatment systems, or situations where activities fall outside exemption criteria. Environmental permits are always formally registered, as are most exemptions.
For construction projects, temporary discharge activities often require:
- Environmental permits from the Environment Agency or Natural Resources Wales;
- Trade effluent or discharge consents from the relevant water utility provider;
- Supporting risk assessments, monitoring plans and sampling protocols.
Understanding the distinction between permits and exemptions at project planning stage is essential, as incorrect assumptions can result in enforcement action, project delays and costly redesign of temporary treatment systems.
Construction sites create multiple pathways for water contamination. Excavations frequently expose groundwater containing suspended solids or legacy pollutants, while site activities such as earthworks, vehicle movements and stockpiling can increase turbidity in surface run-off.
Environmental conditions can further complicate matters. Heavy rainfall, perched groundwater layers and seasonal water table fluctuations often lead to sudden increases in water volumes requiring treatment.
If groundwater is not properly controlled, several risks emerge:
- Regulatory non-compliance. Discharging untreated water may breach environmental legislation such as the Water Resources Act or Environmental Permitting Regulations.
- Programme disruption. Water ingress can flood excavations, destabilise working platforms and halt operations until conditions are stabilised.
- Environmental damage. Sediment or contaminant release can impact downstream ecosystems, potentially triggering regulatory enforcement.
- Structural risk. Excess groundwater may undermine earthworks, compromise foundations and require expensive engineering redesign.
Integrated treatment systems
Modern groundwater management rarely relies on a single treatment intervention. Instead, effective systems typically combine several technologies to address different contaminants and flow conditions.
Three core treatment stages are commonly used across construction sites.
1. Sediment control through separation and settlement
Suspended solids are one of the most common water-quality challenges encountered on construction projects. High turbidity not only breaches discharge permit limits but can also damage natural watercourses by smothering aquatic habitats.
Lamella plate separators – often referred to as ‘Siltbuster-style’ systems – are designed to accelerate the settlement process. By passing water across multiple inclined plates, the system increases the effective surface area for sediment to settle, significantly improving efficiency compared with conventional settlement tanks.
These systems are particularly useful because they can:
- Manage high flow rates during peak run-off periods;
- Operate effectively during poor weather conditions;
- Remove fine suspended particles to levels compliant with environmental discharge standards.
Where soils are particularly clay-rich or slow to settle, flocculants may be introduced to enhance sediment separation.
2. Attenuation and controlled discharge
While sediment removal addresses water quality, flow management is equally important. Construction sites often experience rapid fluctuations in water volume, particularly during dewatering operations or heavy rainfall events.
Attenuation tanks are used to regulate these flows by temporarily storing water before it enters the treatment process or is discharged from site. By acting as a buffer, they ensure downstream systems operate at a consistent rate and prevent uncontrolled releases.
Attenuation systems are especially valuable when:
- Managing peak flows during excavation dewatering;
- Holding water temporarily during storms;
- Protecting treatment systems from overload.
Case study: Groundwater management on a tunnelling project in Stroud
On a tunnelling project in Stroud, deep sewer excavation works encountered unforeseen hydrocarbon-impacted groundwater, placing the programme under significant pressure and threatening prolonged delays.
Churngold mobilised personnel to sample and characterise the groundwater contamination, enabling a full environmental risk assessment and agreement of a temporary discharge strategy with the relevant authorities.
A mobile treatment system was deployed consisting of:
- Two lamella separation units;
- Oil/water separation systems;
- Four granular activated carbon (GAC) filtration vessels operating on rotation;
- Transfer tanks and pumps to maintain continuous treatment flow.
Unlike traditional attenuation systems, water was pumped directly from the sewer excavation through the treatment train and into the existing sewer network under a short-term discharge authorisation.
The treatment operation ran for approximately 14 months, processing an average of 45m³ of groundwater per day. The staged system successfully removed suspended solids and hydrocarbon contaminants, enabling treated water to consistently meet Severn Trent discharge requirements and allowing tunnelling operations to continue safely and compliantly.
3. Activated carbon filtration for contaminated water
Where groundwater contains dissolved contaminants such as hydrocarbons, volatile organic compounds or organic pollutants, additional treatment stages may be required.
Activated carbon filtration is widely used to ‘polish’ treated water before discharge. The highly porous structure of activated carbon allows it to adsorb dissolved contaminants effectively.
Carbon filters are particularly effective at removing:
- Petrochemical residues;
- Polycyclic aromatic hydrocarbons (PAHs);
- Organic compounds and odours;
- Certain dissolved pollutants.
These units are typically installed as the final stage in a treatment train and can be scaled depending on the flow rate and contamination levels present.
Their modular design also allows them to be deployed quickly on projects where groundwater contamination emerges unexpectedly.
Beyond engineering solutions, groundwater management requires careful regulatory oversight. Construction teams must work closely with environmental consultants, regulators and water authorities to ensure compliance throughout the project lifecycle.
Depending on the project location and discharge route, consultation may be required with:
- Environment Agency;
- Natural Resources Wales;
- Local water utility providers regarding trade effluent agreements and sewer discharge consents;
- Environmental consultants and contaminated land specialists.
Key compliance considerations include:
- Monitoring and sampling water quality at agreed intervals;
- Ensuring discharge meets permit conditions or agreed thresholds;
- Maintaining treatment systems to ensure consistent performance;
- Managing contaminated residues in accordance with duty-of-care obligations.
Accurate record keeping is essential. Site teams should maintain documentation such as sampling records, treatment system configurations, waste transfer notes and photographic logs. These records provide a clear audit trail and demonstrate environmental compliance during inspections or regulatory reviews.
Case Study: Groundwater treatment on a former plastics factory in Somerset
At a former plastics factory in Somerset, Churngold delivered a phased remediation programme to prepare the site for residential redevelopment. The site was impacted by hydrocarbons and a localised cyanide hotspot, requiring both soil remediation and groundwater treatment.
The onsite treatment facility consisted of:
- Sediment settlement tanks;
- Oil/water separation units;
- Granular activated carbon (GAC) treatment vessels.
Hydrocarbon-impacted soils were excavated and treated onsite within biopiles. Materials were blended with nutrients and regularly aerated through windrow turning to stimulate biological degradation before successful reuse onsite.
Groundwater treatment was undertaken using a staged pump-and-treat process. During phases 1 and 2, only minor hydrocarbon sheens were encountered, allowing groundwater to pass directly through the treatment system. However, during phase 3, significant free product contamination required tankering offsite before groundwater could enter the treatment process.
Treatment included:
- Free-product skimming;
- Pump-and-treat groundwater recovery;
- Oil/water separation;
- Activated carbon filtration;
- Oxygen-release compounds (ORCs) to support long-term aerobic biodegradation.
Treated water was discharged to the sewer network under consent, with regular sampling undertaken prior to discharge to confirm compliance with agreed environmental thresholds.
This integrated remediation and groundwater-treatment strategy enabled the site to be safely prepared for redevelopment while maintaining environmental compliance throughout the programme.
Adapting to changing climate conditions
As climate patterns shift and brownfield redevelopment accelerates across the UK, groundwater management challenges are expected to increase.
Construction professionals should anticipate:
- Greater regulatory scrutiny of temporary discharge systems;
- Increased reliance on multi-stage treatment solutions;
- Adoption of digital monitoring and telemetry to track water quality in real time;
- Growing focus on energy-efficient and low-carbon treatment technologies.
Meeting these challenges will require continued investment in both technology and professional expertise.
Effective groundwater management is no longer simply an environmental requirement; it is a critical component of risk management and sustainable construction delivery.
By integrating robust treatment systems, proactive monitoring and specialist knowledge into project planning, construction teams can protect the environment, maintain regulatory compliance and safeguard project programmes.
