As your Contaminated Land Consultant, we have done our best to test for any plausible pollutant/contaminant linkages. Despite carrying out a Detailed Quantitative Risk Assessment (DQRA), unfortunately we have found that a few exist. So, what happens next?

REMEDIATION

Within the design of the development, a system must be put into place to sever the contaminant pathways that have been proven to exist.

This could be via:

• Removal or treatment of the source
• Intercepting or breaking the pathway
• Modifying the behaviour of receptor.

These are three types of Remediation

Some approaches to remediation only apply in certain circumstances.

For example:

• It is not usually possible to remove a controlled water receptor – although it may be possible to modify its behaviour or limit its uses
• It may be possible to control an individual’s exposure to contaminants by administrative means – such as imposing legal or contractual access restrictions (e.g. Restricted covenants against paving/patios or areas of hardstanding being turned into grass/soft landscape).

Some of the most common remediation approaches sever the pathway for contaminants to impact receptors, especially in the human health scenario. Simple things like:

• Topsoil Capping Systems
• BRE Cover Systems
• Extension of an area of hardstanding.

Introducing BRE Cover Systems

 BRE cover systems offer a modern approach to land remediation. These systems create a protective layer over contaminated soil, serving both to isolate the harmful substances and to foster ecological recovery. By covering contaminated areas with clean materials, BRE systems can establish a new habitat that encourages natural processes, like soil regeneration and plant growth.

Engineered Cover Systems 

Engineered cover systems create layered barriers to isolate contaminants and prevent their migration. A typical setup includes:

• Break Layer/Anti-capillary Barrier: Physical barrier of gap graded coarse grained material (100 – 150mm thick) to prevent further digging and upward migration of contaminants from below. Risk Assessment can omit this layer
• Sub-base/Subsoil Layer: 450 – 700mm thick depending on depth of capping system required. This is subject to the type of receptor we have (communal gardens or private)
• Growth Medium: Supports vegetation, which contributes to soil stability and health. Typically, 150mm of Topsoil.

By utilising locally sourced materials, these systems minimize waste and align with sustainable practices, often lowering costs significantly. But the proprietary material management plans need to be adhered to.

It is possible to remove or treat contaminants using a variety of physical, chemical or biological methods.

Remediation techniques can be applied in situ or ex situ. The meaning of these terms are:

• Ex situ – removed from the ground before above-ground treatment, encapsulation or disposal on or off site
• In situ – treated without prior excavation of solid material or water abstraction from the ground.

Examples of remediation techniques which can affect the source are: 

1. Bioremediation – This method uses biological agents, such as bacteria or plants, to degrade contaminants in soil and water. Bioremediation is often cost-effective making it appealing for developers who desire an eco-friendly solution. 

2. Soil Vapor Extraction – For volatile organic compounds (VOCs) in the soil, soil vapor extraction is a practical technique. This method extracts vapors using a vacuum system, which can reduce contamination concentration by up to 99%.

3. In-Situ Treatment – This approach involves treating contaminants directly on-site without excavation, often applying chemical oxidants or facilitating natural remediation processes through bioaugmentation. Studies have shown that in-situ methods can be as effective as traditional excavation but at a fraction of the cost.

What we try to avoid

 Excavation and Disposal – For severely contaminated sites, removing soil may be necessary. Excavated materials are then sent to disposal or treatment facilities. Although effective, this an expensive option that demands meticulous planning.

 Bioengineering Techniques – Incorporating vegetation to stabilise contaminated soils exemplifies the importance of bioengineering techniques. Using specific plants capable of absorbing and degrading harmful contaminants—an approach known as phytoremediation—can enhance natural soil processes. For example, sunflowers and willow trees have been successfully used to absorb lead and other heavy metals from the soil. These techniques not only help clean the soil but also increase biodiversity. By creating habitats, the local ecosystem can become more resilient, supporting a wide range of species and promoting ecological balance.

The trouble with bioengineering is, it’s a long-term project!

A Sustainable Approach is Best

Sustainable remediation can provide the opportunity to manage unacceptable risks to human health and the environment. If you use a sustainable approach it can help to ensure the:

• Benefit of doing the remediation is greater than its impact
• Impacts of climate change and extreme weather events are taken into account when selecting the final options.

Consider the relative ability of each option to achieve the remedial objectives in a safe and timely manner whilst optimising the environmental, social and economic value of the work.

The Ground & Water Difference

If your development requires a remediation strategy Ground & Water will work with you to select approaches that are appropriate, effective and sustainable, and avoid where possible any techniques that are high cost in terms of your time and money.