Natural Attenuation NICOLE

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1 1 Natural Attenuation NICOLE

2 2 Text and figures from this booklet may only be used upon written permission by the authors.

3 3 Preface In Europe we have numerous contaminated sites, some of them well-known to public and regulators others still to be detected. Cleaning up of all these sites costs millions of Euros and in some cases is not feasible at all. With increasing frequency Natural Attenuation is mentioned as being a solution to contaminated sites. However, what exactly is Natural Attenuation is it a do nothing solution or a sound solution of our problems at contaminated sites? And what is biodegradation? What processes are involved and can we use these to clean-up contaminated soil? How do we have to measure these processes? This booklet intends to give answers to some of the questions by giving information on how the soil can purify itself. The preparation of the booklet is a TNO initiative and has been financed by a group of NICOLE participants (Network for Industrially Contaminated Land). This group carried out a project on Monitored Natural Attenuation and prepared a report entitled Monitored Natural Attenuation: review of existing guidelines and protocols. Anja Sinke and Loet van Moll

4 4 WORLDWIDE, THERE ARE MANY SITES WITH... CONTAMINATED SOIL... and/or contaminated groundwater. EXAMPLES INCLUDE SITES STORING AND HANDLING PETROLEUM PRODUCTS... AND CHLORINATED SOLVENTS, SUCH AS DRYCLEANERS. THE CONTAMINATION MAYhave OCCURRED ACCIDENTALLY or... have been a result of historical disposal practises

5 5 Introduction World-wide there may be millions of sites, large and small, where the soil and/or groundwater is polluted with organic and inorganic contaminants. Examples of important contaminants include petroleum products, chlorinated solvents, landfill leachates and phenols. This contamination may have arisen from accidental spills or from waste disposal and may have a history stretching back to the 19th century or even earlier. In some cases inappropriate disposal of chemicals has taken place. The importance of the contamination in each case depends on the risk that it poses to human health and to the wider environment. This is a function of the type of contamination, the use of the land and groundwater and the location of the site. When the risk is significant there are methods to clean up the most hazardous part of the contamination. However, it has also been found that at many locations contamination can be removed by naturally occurring processes, a phenomenon called natural attenuation.

6 6 If soil or groundwater is contaminated... the contamination can often disappear with-out intervention. But where does it really go? some may be adsorbed onto soil particles. or diluted so that it poses no risk. or even vanish by evaporation. destruction of contaminants is usually caused by bacteria. or fungi. this biodegradation can truly clean the soil.

7 7 Natural Attenuation Investigation of contaminated sites has shown that natural attenuation can often, but not always, reduce the concentration of contaminants to acceptable levels without human intervention. The naturally occurring processes include dispersion, dilution, adsorption to soil particles, volatilisation and chemical or biological stabilisation or destruction of contaminants (biodegradation). In most cases, biodegradation is the most important process. Obviously, inorganic compounds such as heavy metals and arsenic can be attenuated by physical and chemical processes but cannot be degraded.

8 8 Biodegradation happens naturally but we need to check things. is it effective? is it fast enough? is it complete... or do undesirable products form? and, how long will it take? when needed, we can stimulate biodegradation with food... or oxygen. although sometimes oxygen is nog helpful.

9 9 The effectiveness of natural attenuation The speed of contaminant degradation depends on the type of contaminant and on the conditions in the soil and the groundwater. In determining whether natural attenuation is a viable option to remediate a contaminated site, there are a number of questions to be answered: does the contaminant degrade? is the degradation fast enough to protect human health and the environment, both now and in the future? when will the site again be suitable for its intended use? How does biodegradation take place? Different micro-organisms (bacteria, fungi) are able to biodegrade different contaminants under different conditions. Many contaminants are used as food by the micro-organisms. However, some can be degraded better when the organisms are using something else as their main foodstuff. Some compounds are best degraded when oxygen is present, some when oxygen is absent, and for some it makes no difference. Despite this apparent complexity, we now understand for most compounds how they degrade under different conditions in soil and groundwater.

10 10 at many sites crude oil or petrol and diesel may be found. petroleum products such as oils float on the groundwater. microorganisms can biodegrade oils... fastest with oxygen but it s not essential. the longer the chain, the longer biodegradation takes. branched chains take longer. aromatic (ring) compounds can also be biodegraded... but complexe polycyclic aromatics take longer.

11 11 Degradation of petroleum hydrocarbons and crude oil There may be contamination of the ground anywhere oil and its products have been stored or handled. Depending on the site history, the contamination may consist of one or more petroleum products (e.g. petrol, diesel, fuel oil) or crude oil itself. All crude oils and petroleum products are made up of a mixture of compounds, which varies from oil to oil. These compounds are biodegraded at different speeds. The smaller and simpler compounds are degraded fastest and the more complex and larger compounds take more time. All hydrocarbons biodegrade best when oxygen is present, although many can also be degraded in absence of oxygen.

12 12 dry cleaning uses chlorinated solvents... as do many industrial cleaning operations. solvents lost may enter into the ground. microorganisms that degrade them often work best... without oxygen... and often need other foods such as natural organic matter... fatty acids or... petrol or diesel!!! in this way, complete biodegradation is possible.

13 13 Degradation of chlorinated solvents Chlorinated solvents are compounds consisting of carbon and chlorine atoms combined in different ways. They are widely used in industry for degreasing (e.g. in the metal working and electronics industries), as chemical feedstocks and for dry cleaning of clothing. Consequently they can be widely found as contaminants in soil and groundwater. The different types of chlorinated solvents are degraded in different ways. Some, especially those with many chlorine atoms, are best degraded in the absence of oxygen and often require another foodsource. This food can be natural organic matter in soil or even other contaminants such as petrol or diesel. Other chlorinated contaminants, especially those with fewer chlorine atoms, can be used directly as food for soil micro-organisms either with or without oxygen. Despite this complexity of biodegradation possibilities, under the right conditions all chlorinated solvents can be biodegraded and have the potential to undergo natural attenuation. When biodegradation of chlorinated solvents proceeds to completion sodium salts, water and CO2 will remain. At some locations, vinylchloride is formed temporarily as an undesirable intermediate. This undesirable substance will degrade further but its presence and concentration behaviour need to be monitored carefully.

14 14 if the contamination is sufficiently degradable... then we can leave it to nature... and we must do the necessary monitoring. for that we can install wells... to investigate and monitor... that natural attenuation is really doing the job. from the monitoring data... we do the vital interpretation work... and confirm that we are acieving our goal!

15 15 Evaluation, monitoring and aftercare When we are faced with contaminants that are biodegradable and that do not pose an unacceptable risk to human health or the environment, then allowing natural attenuation to take its course is a reasonable approach to consider. Ultimately, natural attenuation can address the reduction of risk as effectively as other engineered techniques. When evaluating whether natural attenuation is possible and during the time that it takes for natural attenuation to work, it is essential to sample and test the soil and/or groundwater to prove that the process is operating. This means that natural attenuation is certainly not a do-nothing option. However, when appropriately evaluated and monitored, we can safely allow nature to do the clean-up work on behalf of the human race.

16 16 For more information please contact: NICOLE PO Box GD Apeldoorn The Netherlands Secretariat: