The previous steps predict the extent of contamination and the risks associated with it. Before taking actions that are often expensive it is wise to check whether the predictions made using this manual, based on generic rules and models, are true for the specific site and conditions.
Two questions must be asked:
Are the types of pesticides found in the soil or groundwater the same as those predicted?
Are the concentrations of those pesticides the same as those predicted?
Step 9 describes what needs to be done to answer these two questions and what needs to be done if the results are different from those predicted.
Take samples from the soil and groundwater and have them analysed in a chemical laboratory. It is important, however, that the samples are taken in the right manner and in the right places, otherwise the results will be unreliable and therefore useless for checking purposes.
Where to sample
The places where sampling will be most useful are those places where humans are most exposed to the soil or water. These include wells used for drinking-water (by humans or cattle), fields used for agriculture (in particular the growing of vegetables) and the topsoil near houses or schools. Of course, a sampling spot should be within the parameters of contamination predicted by the manual. In selecting these spots, it is essential to take into account the prevailing wind direction and the direction of groundwater flow. Take the samples downwind or downstream (the groundwater flow direction will normally be known by the given country's Ministry of Agriculture, Land Use Planning or Water Supply department). Sample those spots that are nearest to where the obsolete pesticides have been stored.
Sampling is not useful when contamination by other activities may have occurred. Examples of unsuitable spots are roads, areas where other waste has been stored, areas near factories and spots where wastewater is discharged.
How to sample water
The sampling of groundwater is not difficult. Fill a clean bottle, preferably of glass, with water. As a rule, sample one litre.
How to sample soil
Aim. To obtain soil samples by employing a uniform, high-quality method.
Principle. Soil excavated during boring should be sampled in such a manner that the sample obtained is sufficiently representative of the soil layer concerned and that the contaminant concentrations have not suffered evaporation or contamination caused by the packaging or the sampling equipment.
Three main types of soil samples should be distinguished:
Undisturbed soil samples. Split-spoon samplers, thin-wall tube samplers and core barrels can be used to obtain undisturbed soil samples. The sampling tubes are pressed, hammered or rotated into the soil and can be shipped to the laboratory or subsampled in the field. Undisturbed sampling is recommended for the analysis of volatile compounds.
Semi-undisturbed soil samples. Undisturbed drill cuttings can be obtained by using gouges or piston samplers. The exposed surface of the cuttings can be removed with a spatula and the inner cuttings can be placed immediately in a sampling jar.
Disturbed samples. The soil samples obtained by using edelman augers and solid-stem augers will be moderately disturbed during the drilling activities but in most cases can be used for chemical analysis purposes. The exposed surface of the cuttings can be removed with a spatula and the inner cuttings can be collected in a sampling jar. It should be noted that high-quality samples of the shallow soil could be obtained by excavating profile pits, using a spatula to take samples directly from the pit walls.
Survey of sample quantities and data on the filtration and preservation of groundwater samples in the field
|Analysis||Bottle||To be topped up||Filtr||Preservation|
|Volume (litre)||Colour||Agent||Amount||Holding time|
|Aromatic solvents, chlorinated solvents, volatile chlorobenzenes||0.25||Green||Yes||HNO3 pH<2||0.2 ml||7 days|
|Chlorophenols, phenols (GC)||0.5||Green||Yes||24 h|
|Chromium VI||0.5||Green||Yes||24 h|
|Cyanide||0.25||Green||Yes||Yes||NaOH pH=12||0.25 ml||24 h|
|Phenols (volatile)||0.25||Green||Yes||H3PO4 pH<4 CuSO4||3 drops 0.25 g||24 h|
|GC-MS volatile||1||Green||Yes||24 h|
|GC-MS semivolatiles||1||Green||Yes||24 h|
|Mercury||0.25||White||No||Yes||HNO3 pH<1 K3Cr2O7||2 ml 0.05 g||1 month|
|Heavy metals||0.25||White||No||Yes||HNO3pH<2||0.2 ml||1 month|
|Non-volatile chlorobenzenes||1||Green||Yes||HNO3pH<2||0.75 ml||7 days|
|Oil (GC)||0.5||Green||Yes||HNO3 or HCI pH<2||7 days|
|Organophosphorus pesticides, organonitrogen pesticides||1||Green||Yes||24 h|
|PAH (polycyclic aromatic hydrocarbons)||1||Green||Yes||HNO3 pH<2||0.75 ml||24 h|
|PCBs, organochlorine pesticides||1||Green||Yes||7 days|
|Vinyl chloride*||0.02||White||No||ASAP (24 h)|
|Volatile hydrocarbons (C4-G4)||0.5||Green||Yes||HNO3 pH<2||0.4 ml||7 days|
|VOX||0.25||Green||Yes||HNO3 pH<2||0.2 ml||7 days|
|Water-soluble solvents and acrylates (headspace)||0.25||Green||Yes||24 h|
* Prescription used by Tauw Laboratory: inject 15 ml of sample into a 20-ml headspace phial; deliver three phials for each well.
sampling jars with screw lids;
split-spoon samplers, thin-wall tube samplers, core barrels;
Wear gloves during sampling to prevent contaminated soil from coming into contact with your hands.
Always use HDPE or PE foil to store samples and equipment.
Sampling must be done for each different type of soil (based on texture and organic matter content) and for different degrees of contamination (based on sensory observations), and normally 50 cm at most of excavated material may be collected per sampling jar.
When volatile components are to be analysed:
Important: Samples must be taken directly and without delay from the boring system and stored under cool conditions in order to avoid contaminant losses due to volatilization.
The sample jars must be kept closed as much as possible in between filling phases.
Each sampling jar must be filled to its limit. Clean the screw thread and the lid of each jar, and screw the lid on tightly to lower the chance of the contaminants' evaporating.
When non-volatile components are to be analysed:
Samples of 50 cm drilling depth should be taken from the boring system and placed in order on plastic foil.
Soil sampled with a piston sampler must be placed on foil or in a PVC gully in one long strip. To measure the boring, place a tape measure next to the strip of soil.
Note that direct sampling from the boring system generally reduces the representativeness of the sample in comparison with sampling from a foil. In the case of volatile contaminants, however, this effect is negligible compared with the effects of volatilization.
Instructions for filling a jar:
Collect the soil that is the least “smeared” by using a spatula or the lid of the sampling jar. Scrape the soil into the sampling jar using the inside (to avoid contact with the ink) of the sampling jar's lid.
When sampling clay and loam, break off pieces of clay by hand (wearing clean latex gloves!) or cut the soil with a spatula.
To ensure that the mass of soil in the sampling jar is representative of the section from which it was taken, check that the locations of the subsamples were proportionally distributed over that section.
Each sampling jar must be filled to its limit. Clean the screw thread and the lid of each jar, and screw the lid on tightly.
Coding of soil samples. The jars containing the soil samples should be marked with the following data: site name, bore hole number, section depth and date of sampling.
Storage and shipment of soil samples. For the duration of the fieldwork, sampling jars and sampling tubes filled with soil must be stored at a location that is as cool as possible (approximately 2–4°C) and protected from sunlight. The soil samples must be transported to the laboratory as soon as possible after the fieldwork is completed.
Note that cuttings and samples not kept for analysis should be stored and disposed of in agreement with the responsible site manager.
Holding time. The holding time of soil samples is limited due to volatilization and biodegradation. A sample should be extracted in the laboratory within the holding time. The holding times are summarized in Table 9.2.
Reporting. Enter in the bore log the codes marked on the sampling jars and the depths at which the samples were taken. At the completion of the fieldwork, enter in the boring order form the total number of soil samples taken.
How to analyse the samples
All samples need to be analysed for the presence of the pesticides that were predicted in the manual, as well as for the presence of harmful pesticides other than those predicted. Since there are many hundreds of different pesticides, however, checking all of them would be far too expensive. A good solution is to request that the laboratory screen the samples for the five to ten pesticides that show the highest concentrations. Most laboratories are able to carry out this screening with the help of gas chromotography-mass spectrometry (GC-MS) or atomic absorption (AAS) equipment.
Concentrations are lower than predicted
The manual predicts the contamination and risks caused by improper pesticide storage based on a worst-case scenario. This means that the manual predicts a contaminated area as wide as realistically possible and assumes that the pesticide concentrations are as high in this entire area as the highest concentration predicted.
In reality, concentrations will be smaller based on prevailing wind or water distribution patterns. Therefore, during checking, concentrations lower than those predicted will often be found. In this case, ignore the results of the check and proceed as if the predicted values had been found. Or, sample and analyse again to confirm the first analysis. If the results of the second sample are also lower than the predicted values, use the average results of the samples rather than the values predicted with this manual.
Holding time for soil samples
|Chlorinated pesticides and PCB||7 days|
|Chromium VI||48 h|
|Mercury (total)||15 days|
Concentrations are higher than predicted
If the concentrations found through sampling and analysis are higher than those predicted with the manual, it is important to repeat the sampling and analysis, since the results of one sample are considered to be reliable only if confirmed by a second sample. If the second sample also shows higher-than-predicted values, take the average of the two sample results, rather than the values predicted with the manual. If the second sample is lower than the predicted one, either take the predicted value, or sample for a third time.
When deteriorated packaging of obsolete pesticides has caused contamination to occur, measures (sometimes simple, sometimes elaborate and expensive) must be taken to prevent further damage.
First, the cause of the problem (improperly stored pesticides) needs to be addressed. The pesticides, their deteriorated packaging and the severely contaminated soil must be packed in proper containers.
To prevent a recurrence of the problem, the pesticides need to be removed and treated properly, which generally means incinerated in a dedicated waste incinerator. Some types of pesticides may be incinerated also in cement kilns, provided that those kilns are managed properly. This solution, however, is still the subject of debate.
Measures may also be necessary to treat the area that has been contaminated by the pesticides. There are three basic types of measures:
removing the contamination (e.g. excavation of soil, pumping-up of groundwater);
containing the contamination (e.g. covering contaminated soil with buildings, asphalt or another impermeable layer, and preventing contaminated groundwater from flowing downstream);
preventing human contact with the contamination (e.g. covering the contamination with clean soil, fencing-off contaminated areas, closing contaminated wells).
Removing the contamination also means that the material removed needs to be put somewhere else. Contaminated soil is usually disposed of in a controlled landfill, whereas contaminated groundwater is treated (contamination is removed) and then discharged. Landfilling should be avoided as much as possible. Note that in-situ measures (e.g. treating the contamination at the spot without removing it) are generally not possible with obsolete pesticides because of their characteristics (low degradation, low volatility, low leachability). More modern pesticides generally degrade much more easily.
For soil contaminated with organochlorine pesticides such as HCH, on-site biological treatment may be a cost-effective alternative. The treatment includes an initial phase in which the soil is covered with a layer of water to which nutrients are added. This stimulates anaerobic biological degradation. Subsequently, the soil is laid to dry and is ploughed or turned over, in order to stimulate aerobic biological activity. The treatment may take a few years but is relatively cheap.
Generally speaking, removing contamination is more expensive than containing it, which in turn is more expensive than taking protective measures. On the other hand, removing it is a more final solution (all contamination is gone), whereas containment measures must be maintained forever. Protective measures are effective only for as long as they are maintained, which may be difficult to ensure over a longer period.
The choice of measures depends on the seriousness of the contamination (whether contamination poses risks and whether those risks are high; the higher the risks, the longer-lasting the solution must be). It also depends on the vulnerability of the surroundings: a higher level of contamination may be more acceptable in industrial areas than in agricultural or residential areas. It also depends on the budgets available for direct investments and recurring costs. Also important is whether measures are needed for the immediate protection of human beings only or to prevent contamination from spreading and causing damage in the future.
When choosing which measures to take, the following guidelines apply:
If the topsoil is contaminated and poses risks to human beings, removing it is recommended.
If the topsoil is contaminated but does not pose risks, measures, strictly speaking, are not necessary. For psychological reasons (i.e. for the peace of mind of the area's inhabitants), protection measures may be recommended.
Expensive measures (removal, containment) are necessary only when risks are considerable and the control of protective measures is not likely to be strict.
If the subsoil is contaminated, removal is often not necessary since the topsoil will prevent human contact with it; to prevent further contamination towards and via the groundwater, containment measures are recommended (e.g. by sealing off the surface, thus preventing rainwater from transporting contamination from the subsoil to the groundwater).
If the groundwater is contaminated and poses risks to humans, removal of it is recommended. If the obsolete pesticides that caused the contamination are removed, their removal may have to continue for as long as the body of water remains contaminated. Protective measures are also recommended, especially in poorer countries, but need strict control to be effective.
If the groundwater is contaminated but does not pose risks, and the improperly stored pesticides have been repacked or removed, no measures are needed. The site should be monitored (e.g. samples taken from wells once a year) to determine whether contamination is recurring.