Contaminated Land Remediation & Validation

Contaminated Land Remediation Strategies

 

G&J designs remedial strategies for a broad range of sites that have their unique land contamination issues and challenges, to ensure the most cost-effective and sustainable solution. We aim to maximise the re-use of soils on the site of origin (with or without treatment) and avoid off-site disposal and all the associated costs and environmental implications. The need for remediation is usually established through a Phase II Site Investigation and subsequent contaminated land risk assessment, and is most commonly required on Brownfield sites with a known history of industrial use. However, some Greenfield or low-risk sites can still require remedial measures as a result of undocumented activities such as illegal waste disposal.

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It is essential to deal adequately with contamination to protect human health and the environment in accordance with current regulatory framework, most commonly in the form of planning conditions.  Failing to do so can leave potential liabilities and contravene environmental regulations.

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Remediation may simply require a development design to consider soil quality and ensure affected soils are used only in low-sensitivity areas (such as beneath hardstanding) or allow for the incorporation of a barrier layer in certain areas. Where more significant soil contamination is present, remedial solutions may be required that reduce the concentration or mobility of contaminants to prevent significant harm. Common remedial techniques include:

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• In-situ and ex-situ bioremediation

• Physical or chemical stabilisation

• Pumping and treatment of groundwater

• Free product recovery

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Bioremediation is a common technique for soils contaminated with organic substances such as hydrocarbons, and utilises the microorganisms that are naturally present in soil to reduce concentrations through biodegradation for future use. In situ refers to treatment undertaken on soils (or water) that remains in the ground, while ex-situ refers to treatment of excavated soils. In some cases, bioremediation may simply involve the introduction of air through mechanical means (turning soils in stockpiles known as ‘windrows’ using an excavator) to stimulate natural biodegradation, or otherwise the process may be enhanced by the direct introduction of oxygen, organic matter or other nutrients. It is also crucial to address hazardous substances, such as chemicals and heavy metals, which are often present in contaminated sites.

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Stabilisation reduces the risks posed by contaminants in soil by either introducing a chemical agent that converts them to a less harmful form or reduces their leachability, or by mixing with an additive such as cement, which locks the contamination within a solidified mass and renders it immobile.

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Pump and treat involves the removal of groundwater from extraction wells (or sometimes from an excavation) and passing it through a treatment plant (which may include carbon filters, oil separators, air strippers etc) located at the surface, before being either discharged to a surface watercourse/sewer, or returned to ground. A similar mechanism can be used to recover Light Non-Aqueous Phase Liquids (LNAPLs), essentially free-phase hydrocarbons that float on the groundwater and present an ongoing source of contamination if not removed. Free-phase hydrocarbons removed in this way are taken off-site for recovery or disposal.

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In some cases, more specialised remedial solutions may be required, such as soil-vapour extraction, chemical oxidation, soil washing and thermal desorption, and we can work alongside dedicated remediation technology providers for the successful implementation to deliver the most appropriate solution.

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From the placement of a simple cover of clean soil to manage low levels of contamination, to the long-term remediation of a heavily contaminated industrial site, we have the expertise to design remediation works that are appropriate to the type and scale of the problem.

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Contaminated Land Remediation - Validation and Verification

 

It essential that the success of remedial works are demonstrated through a suitable programme of validation and verification.  This may involve trials to demonstrate that a particular remedial technique can meet the remediation objectives (prior to site-wide implementation), and the collection of data to show that contaminant concentrations have been reduced to acceptable levels after remediation.  Where mitigation measures such as barriers or vapour protection measures have been installed, it is necessary to prove that such measures have been installed as per the specification, and perform to the necessary standards.

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We ensure all remedial works are completed to the required standard, provide independent verification and agree regulatory sign-off through close consultation with Local Authorities, the Environment Agency and warranty providers such as the NHBC.

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Definition of Contaminated Land

 

Land is considered to be contaminated if there is 'significant risk of significant harm' to human health or the environment by virtue of substances that are in, on or under the land.  The definitions of 'significant risk' and 'significant harm' are contained within the legislation and associated guidance, most notably Part IIA of the Environmental Protection Act 1990 and the associated statutory guidance.  ​Remediation and verification works seek to ensure that land does not meet the statutory definition of contaminated land, and therefore does not continue to present a significant risk to human health or the environment.  Polluters and / or landowners can be found liable for remediation costs for any land that can be defined as contaminated land, and for any costs associated with damage caused by land contamination.​​

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​Why Remediate Contaminated Land?

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​If land has clearly been demonstrated to be causing significant harm, or that it presents a significant risk of significant harm, Part IIA of the Environmental Protection Act places the responsibility for remediation on the polluter or the landowner, and this is enforced by the Environment Agency or Local Authority.  However, the majority of contaminated is remediated through the planning process.  The burden of proof (that land does not represent a significant risk) through the planning process is generally higher than for land to be determined as contaminated through Part IIA, so benchmarks for risk assessments and remediation works tend to be more stringent.  Remediation works have to be completed to the satisfaction of the Local Authority and the Environment Agency to allow planning conditions to be discharged. 

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Otherwise, remediation works can be undertaken voluntarily to reduce potential environmental liabilities and to ensure the there are no unacceptable risks to human health of the environment.  Investigation and remediation works may be undertaken as part of environmental due diligence, for corporate social responsibility reasons or to satisfy insurers or other stakeholders.

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Suitability for Use​

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One of the key concepts for land remediation is the 'suitability for use' principle, which means that for land to be considered to meet the definition of contaminated land, the sensitivity of the site use should be considered, as well as the level of contamination present.  For example, if land is to be used for a residential development, the remediation standards will be higher than if the land is used for a commercial development.  The presence of contamination can therefore have implications for the type of development on a site, based on an assessment of the costs, risks and benefits of different land use categories.

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