Building Regs’ Guide to Dealing with Contaminated Land
The Regs have plenty to say about keeping you safe from the nasties that may be lurking on your plot, as Paul Hymers explains
“the legacy of an industrial past can remain in the soil after the source of pollution has been long forgotten”
Building Regs don’t just cover the technicalities of building, renovating or extending your home. They’re also concerned with keeping us healthy and safe in our own homes, as Part C – Site preparation and resistance to contaminates and moisture – covered in this article, goes to show.
What are Contaminates?
You’d expect to find contaminates – or contaminated soil – on brownfield plots where, perhaps, an industrial building, petrol station or coal yards stood. However, its presence is not always so obvious, and a site history check may reveal a lighter industrial past or agricultural use resulting in contamination.
Even when nature has recovered the land, the legacy of its past can remain in the soil after the source of pollution has been forgotten. Plots in towns or villages that once saw timber yards or a garage can remain contaminated for decades later and soil reports can read like an inventory for chemical warfare. Mercury, arsenic, lead, phosphates — every kind of poison known to man seems traceable.
An old timber yard site, for example, may be rich
in copper-chrome-arsenic (CCA) from timber preservative spilled over years of wood treatment; a garage plot may be rinsed with hydrocarbons from spilt fuel; and even seemingly green land used for agriculture can be polluted by insecticides from years of crop-spraying.
Dealing with Contamination
The process for revealing if contamination is even likely starts with a desktop study. This is an in-depth historical check of the plot, and the first of potentially four stages to work through and one that is often made a condition of planning permission.
Even where it isn’t a planning condition, requirement C1 of the Building Regulations requires precautions to protect health and safety from contamination in the ground.
The good news is that even when the chemical analysis of the soil on site reveals a multitude of contaminants, often the levels are extremely low and below the action level set for each contaminant at which they can be a risk to our health.
Some chemicals and metals present may not be directly harmful but they could be damaging to eco systems or the groundwater and so they do affect us indirectly.
The controls therefore allow for a surprisingly wide range of circumstances, from residents growing their own food to aquifer areas where groundwater is collected for our water supplies and even (and this bit absolutely astounds me) soil digestion. Yes, humans eating the soil. Apparently it is quite common among children under two, meaning small traces of some contaminants are still a threat.
“Some chemicals and metals could be damaging to eco systems or the groundwater”
Where found in a presence exceeding the set action level for each contaminant (which is set out in the Regs), they may well have to be dealt with, but only when there is a defined receptor path through which they can cause us harm. A receptor path is the link between contamination and human harm, such as via a watercourse, underground aquifer or growing vegetables in the garden.
Assessing your Plot
Contaminated land assessments are undertaken by environmental or geo-technical consultants in four stages: Desktop study (including conceptual site model) Site investigation report (including site walkover survey and soil analysis)
Remediation strategy Validation and certification.
Desktop studies are the foundation stone of any assessment, since they look at the site history, geology and location and provide the baseline about whether the site is likely to be contaminated or not. The CSM (conceptual site model) in- cluded is a risk assessment that identifies the receptor pathway from the source to the recipient (e.g. small children living in the home or aquifer water zones).
In the case of ‘mobile’ contaminants, some will have definite paths — such as radon gas or methane, where the vapour will head to the surface. Other chemicals can sink to pollute the groundwater and so on.
The Site Investigation Report
if the desktop study recommends it, this report will involve a site walkover survey and soil sampling to identify any chemicals present, or even drilling boreholes to test groundwater for contamination or to monitor rising gas levels.
Soil and water samples are usually sent to a laboratory for analysis but soil screening for volatile organic compounds (VOCs) and petroleum hydrocarbons
(TPH) can also be carried out on site using a photo -ionisation detector.
The report will identify what contaminants are present as well as their concentration levels and whether they are inert or mobile. All chemicals have different action levels that once reached will be considered too high to be ignored if a receptor path is present.
Your garden surrounding the home is the main problem. Soil will be valuable at the surface as a growing me- dium for vegetables and it will be exposed for children to come into contact with. For these reasons alone, contaminated land has to be dealt with effectively.
Remediation
This is usually a specialist contractor’s job, with British Standard documentation setting out how it should be done. The report needs to conclude with any remedial treatment necessary and most importantly, an analysis of the cost. if there are particular hotspots on the plot then there may be options: for example these ‘hotspots’ could be removed by bulk excavation and refilled with topsoil, or they may be covered over by a hard-surface driveway and parking area, or even be diluted or bio-treated.
It is also possible that continual long-term monitoring of the soil is needed, particularly where contamination of groundwater is a risk. given the ‘perceived risk’ generated by such monitoring exercises and the threat of devaluing or blighting your new home, you might want to think long and hard about building on a plot where long-term monitoring is required.
Common solutions to contamination, include: Removing contaminated soil. it’s the commonest solution, but a licence for transporting it to a landfill site will be needed.
Biochemical or fungal treatment to stabilise the contaminants may be an option as a form of natural treatment, but it’s only available for certain chemicals. Metals, like lead and iron, can’t be treated in this way.
Flushing contaminants out with water or other chemicals as a method of washing the soil can also be done with some contaminants, and indeed even vacuum suction treatment can deal with petrol hydrocarbons and other volatile pollutants. if the nasties can’t be economically taken out of the soil, they may be able to be contained within it by an impervious layer that prevents them from surfacing. Clay is a natural containing material that is often used to line landfill sites — in particular thicknesses it prevents any gases from migrating through. Plastic linings have also been used before for the same purpose, but beware: as they have life expectancies beyond comprehension, they themselves serve to contaminate the environment.
Validation and Certification
The re-testing and certifying of the soil after treatment is the final part of the process, since it will prove that protection is effective or the ground has been effectively cleansed.
Your building control officer and mostly likely your home warranty surveyor will require copies of this certification before your new home is deemed safe for occupation.
NEXT MONTH:
Parts J and L explained