Dealing with contaminated land consists of four key phases for geotechnical firms. These are: desktop study, intrusive site investigation, remediation and finally, validation and verification. Whilst no one phase is more important than any other, it’s of course vital that the remediation phase is carried out with the most care (given how harmful some of these contaminants are).
The team here at Peterborough-based Borehole Solutions Ltd, which offer site investigation and contaminant remediation service, wanted to look at the various methods in which remediation can be carried out.
Bioremediation is an interesting discipline in its own right. It involves using living organisms (microbes and bacteria) in the breakdown and removal of contaminants. Typical examples of bioremediation include the reduction of sulphates to sulphides (using anaerobic bioremediation) and aerobic bioventing in the degradation of hydrocarbon contaminants.
The substrata required to treat the contaminants can be injected through typical welling means or by something more complex like biowalls. There are some limitations of this site investigation method that include it’s relatively slow-acting and the specificity of biological processes requiring a highly complex and individual strategy for each particular situation. Of all remediation methods, however, it is one of the most (if not the most) sustainable.
Phytoremediation is the process of using plants and fauna to clean contaminated soils. It’s one of the most cost-effective remediation methods available to geotechnical consultants. It has been used extensively at the sites of abandoned metal workings, where the soil has been contaminated with heavy metals like lead or cadmium.
Phytoremediation is a testament to the restorative power of nature. Where plants with names like pigweed and alpine pennycress can mitigate the risks posed by contaminants at toxic waste sites! Contaminants can be extracted (phyto-extraction) using plants. Their leaching progress slowed and reduced (phyto-stabilisation) and microbial breakdown activity enhanced (phyto-stimulation).
In Situ Chemical Oxidation (Chem-Ox)
In certain circumstances, chemical means are used rather than biological in the breakdown of contaminants to acceptable environmental levels. There are four chemical agents which are primarily used for ISCO (In-Situ Chemical Oxidation). These are as follows:
- Permanganate. Is predominantly used to help clean up less permeable contaminants and materials.
- Fenton’s Reagent. Used in the destruction of materials such as PCE, this inexpensive agent is commonly utilised in remediation.
- Ozone. Unusual in the fact that it’s a gas, ozone must be injected to the bottom of the contaminated area (from which it then rises up). Ozone is effective in tackling a variety of contaminants, including pesticides, diesel and chlorinated solvents.
- Persulfate. This relatively new reagent is drawing particular interest within the scientific community. This is thanks to its relative stability when compared with reagents such as ozone, for instance.
Chem-ox remediation is not without its drawbacks and limitations, however. The reagents used can react aggressively with the compounds you’re trying to remove, and must therefore be handled with extreme care.
This is a waste minimising technique to treat those soils contaminated with organic, inorganic and radioactive materials. The site investigation technique is carried out in one of two ways. Either the soil particles which have the majority of the contaminants on them are separated from the rest of the soil.
Or, alternatively, the contaminants are removed from the soil. The remaining soil is then either used on the site as inert backfill, as fill or disposed of. Soil washing can either be conducted as a physical process to separate the contaminated soil, or by chemical processes. However this can be more expensive.
Soil mixing is a ground improvement technique that strengthens the characteristics of weak soils by mechanically mixing them with a binder. The action of mixing materials such as cement, fly ash, lime or bentonite with soil causes the properties of the soil to become more like soft rock.
This process can cover contamination as well as improve the geotechnical properties of the ground. Borehole solutions has vast experience in this technique and has close relationships with specialist contractors.
Building research establishment is a research-based consultancy, testing and training organisation in the construction industry. The BRE 365 soakaway design is one of the most widely used BRE publications, providing guidance for designers to support planning and development applications. Digest 365 describes the processes for the design and construction of soakaways and explains how to calculate rainfall design values and soil infiltration rates. It is a very effective way of carrying out geotechnical investigations for soakways.
“Dig And Dump”
The “what it says on the tin” of remediation techniques, dig and dump is exactly that. It involves digging up contaminated soil and transporting it to landfill sites. Although traditionally frowned upon, this remediation method is becoming more widely accepted thanks to the generating of so-called ‘soil hospitals’ on landfill sites. Generally speaking, this is one of more inexpensive remediation strategies.
Contact Borehole Solutions Ltd
Whatever remediation you need carrying out, it’s important that you use a trusted contractor. So, if you’d like to find out more about our site investigation and geo-consultancy services, then get in touch! Contact Borehole Solutions Ltd today on 01733 200501. Or take a look at our Instagram to check out some of our previous work.