Contaminated Site Issues in Permaculture
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There may be some instances when permaculturists will need to consider potential site contamination issues when purchasing a property or before commencing a project.
Some examples might include:
The development of community gardens in urban areas, particularly in or near areas with a history of industrial land use;
When purchasing an urban or semi-urban property, or wanting to develop a garden or orchard close to (particularly down gradient of) a high risk site such as a service station;
When purchasing or developing permaculture works on a rural property which has a history of sheep or cattle grazing (in particular where there is infrastructure in place for dipping (ie old dipping race)
When utilising an ex-orchard, where persistent organic chemicals such as DDT or aldrin may have been used on plants and consequently accumulated in the soil.
The purpose of this article is to provide some background information regarding the technical and legislative issues involved when considering the use of a potentially contaminated site for food production, and to outline what options might be available for remediation (clean up) to enable safe use.
The Need to Consider Site Contamination Issues
As mentioned above, for the rural permaculturist, site contamination issues may need to be considered where it is suspected the site has been used as a commercial orchard or for sheep/ cattle grazing. I must confess to having limited experience on such sites- although I have assessed a couple of both (and have not identified any concerning substances in the soil). In an urban setting, the classic one to look out for is the humble service station- the majority of servos have underground tanks which leak, or have leaked, petroleum products into the soil or groundwater. The potential risk here is buying or developing a site down gradient of a contaminated groundwater plume, where vapours can migrate up through the soil, or where deep rooted plants in shallow aquifers could take up contaminants.
If you are considering the purchase of a site which has been subject to a contaminating land use, the legislative process should protect you in so far as the contamination status of the site must be divulged by the vendor prior to sale. However, even when a consultants report gives the all-clear to a site, be aware that there are inherent inadequacies in the process of assessing any site- any assessment allows for a certain statistical probability that contamination may still exist in the soil or groundwater that has not been identified. It is the classic case of the science being woefully inadequate to give a true picture of the reality on ground, and this is usually compounded by time and budget constraints leading to inadequate data collection. There are national guidelines in place for assessing contaminated sites (the NEPM papers on site contamination) which have been adopted in one form or another by state regulators (in NSW the NSW EPA), but these are not always adhered to by consultants. Generally if an assessment has been reviewed by an EPA accredited auditor, the review process should pick up any inadequacies against the standard. However, even if a site has been assessed by these standards, this is no guarantee that all areas of contamination have been identified. It is good to be aware of this when considering a purchase.
Some common contaminants of potential concern
Some common contaminants associated with particular land use histories are listed below.:
Metals (commonly copper, arsenic, manganese, lead, zinc, mercury)- metal contamination can be associated with a wide range of land uses. All of these metals are present in the soil to some degree but when concentrations get excessively high relative to 'background' levels, they become toxic to humans and other beings in the ecosystem. Arsenic contamination is commonly identified at cattle/ sheep dip sites and is also used at timber treatment plants. Lead is a very common contaminant (and is toxic at relatively low levels) and is found at a wide range of former industrial sites.
Hydrocarbons- Total Petroleum Hydrocarbons (TPH) are generally associated with hydrocarbon fuels such as as petrol, diesel and oil. The light end TPH fractions (C6-C9) are generally associated with unleaded petrol, the C10-C14 fractions with diesel fuel and C14+ with oils. Increased chain length = increased viscosity of the contaminant and reduced volatility (ability to form a vapor). So while light end contaminants such as petrol are considered very volatile and can migrate up through the soil from a contaminated aquifer into building spaces etc (increasing the risk of exposure), diesel contamination will not do this to any great degree. Light end (volatile) contaminants are, however, more amenable to remediation as the short chain bonds are more easily broken.
OrganoChlorine (OC) and OrganoPhosphate (OP) Pesticides. OCPs include the well known nasties such as aldrin, dieldrin, heptachlor and DDT. These compounds are very persistent (ie resistent to environmental breakdown ) and very toxic to a wide range of lifeforms. OCPs and OCPs are the groups of contaminants to look out for at former agricultural sites where herbicide sprays may have been used;
Polycyclic Aromatic Hydrocarbons (PAHs)- generally associated with heavy oil products or ash. The most toxic ones are benzo(a)pyrene and naphthalene. Unlike the light end hydrocarbons they are not volatile so exposure occurs only through skin contact or accidental ingestion. Commonly identified at a range of former industrial sites. Napthalene is a minor component of diesel fuel and oils;
Other 'organic' contaminants- organic here has a very different meaning to the permaculture definition and refers simply to Carbon based compounds- some of which are very nasty indeed. A particularly nasty group are known as the chlorinated hydrocarbons- common one is tetrachloroethylene (TCE) which is associated with a wide range of industrial processes but is also used at traditional dry cleaners, and is sometimes stored in waste tanks beneath the site. When released to the environment, TCE breaks down to other toxic compounds such as vinyl chloride and PCE. These are all extremely volatile and extremely toxic. Best to avoid sites with a history of these contaminants in the soil or groundwater- probably not suitable for food production at all!
It is worth noting that when chlorinated hydrocarbons are released into an aquifer, they act as DNAPLs (dense non aqeous phase liquids) and will sink to the bottom of the water table. In contrast, most fuels act as LNAPLs (light non aqeous phase liquids) and will float on top of the water table. This means that fuels and oils in an aquifer are more amenable to remediation by pumping or skimming.
The Problem is the Solution
Looking at all this from a permaculture perspective, a history of site contamination, or close proximity to a known contaminated site can reduce property value significantly, and the informed permie could potentially pick up a bargain property if they're prepared to do some remediation work. There are a host of interesting remediation techniques out there, particularly phytoremediation (using plants) and mycoremediation (using fungi) both of which work on the premise that certain trees and fungi can feed on particular contaminants, particularly heavy metals and hydrocarbons. The creation of contaminated soil biopiles to attenuate hydrocarbon contamination is a bit like making a compost heap- the idea being to provide structure, aeration, organic matter, water and nutrients to facilitate the growth of bacteria which feed on the contaminants. The use of bioremediation is a strategy which is very much in line with permaculture principles. However, as most bioremediation methods are relatively slow, they do not generally get utilised when there is a developer looking to sub divide and sell land as soon as possible. By purchasing a contaminated site pre-remediation we have the freedom to employ the most sustainable land rehabilitation technique which will restore the health of the soil, rather than the quickest and easiest 'fix', which in most cases is a combination of 'dig and dump' (digging out contaminated soil and disposing of it at landfill) or ongoing monitoring (a euphemism for doing nothing).
If anyone has questions about the potential purchase of a contaminated site for a permaculture project, I am happy if you shoot me an email and Ill provide whatever advice I can.
Cheers,
Barney
