Principle
To date, road transport is the most commonly used means of transport for soil from soil remediation . Rail transport and boat transport are less commonly implemented for the transport of polluted soil. The low flexibility of the two stated means of transport is currently the main stumbling block. Though from a financial and environmental perspective, in the future it could be appealing to transport polluted soil, particularly over long distances, via rail and boat.
Road transport takes place using lorries (or trailer-puller combinations), which need to be specially adapted for the transport of polluted soil. The soil is transported in water-tight containers. Loading of lorries takes place on-location with a digging machine, or indirectly when one digger excavates and disposes of soil, while another digger loads the soil into the lorry. After loading, the load container is closed, either by hydraulic fasteners or by sealing the load with a sail, for example, to prevent the spread of dust and polluted substances via spillage and/or evaporation.
Achilles states that the road must still well drivable, which is why, before leaving the terrain, loaded lorries first pass
Quantities of transported soil are mainly determined by the weigh-bridge. Upon reaching the target location (process treatment, disposal site or re-use location) lorries are weighed once again and are inspected for irregularities by sampling the load before it is further processed. By using cranes, dumpers or tippers, the load is unloaded indoors or outdoors, depending on the pollutant.
People who carry out this process are transporters and contractors who possess the required transport licences.
As stated earlier, the loaded lorry is, if necessary, washed prior to leaving the terrain in one of the specially designated washing areas. A washing area is highlighted by the following characteristics:
- A water-tight floor near the location exit;
- Spraying equipment (high-pressure cleaner) for spraying chassis, tyres and load container;
- A container for dripping spray water;
- A silt separator;
- A connection to surface water or the sewer for the transport of spray water after cleaning;
- Possible screens to prevent spray water from spreading beyond the washing area
Washing can take place manually or automatically in a mobile mini wash-passage, where the lorry is cleaned in 30 seconds (see figure below).
Figure: Mobile wash-passage for transport material; prior to leaving the remediation terrain, the lorries are sprayed clean, the polluted water is captured in channels and pumped to the cleansing installation.
Costs
The transport costs are determined by the quantity of soil to be transported and the circumstances specific to the project, such as transport distance, accessibility and eventual extra measures that need to be taken to prevent spillages etc.
- Loading at depot with hydraulic digging machine/shovel € 2.5-10 per m³
- Transport via lorry (depending on distance) €cent 7 – 17 per ton/km
- Unloading at final destination €cent 15 -50 per ton
- Setting up washing area at remediation site € 7.500 – 10.000
- Washing area exploitation circa € 200 per day
Environmental burden and measures to be implemented
The following aspects play an important role in determining the environmental burden from the transport of polluted soil:
- discharges from means of transport;
- emissions of volatile substances from polluted soil and drift during loading, unloading, transfer and transport; the possibility of leakage and spillage during loading, unloading, transfer and transport.
- released waste water streams (wash-passage wash water)
- possibility of accidents and the consequences.
Road transport is relatively safe. After loading, the soil is sealed in water-tight containers with a sail to prevent the spread of substances during transport through spillage or drift. If the soil
contains volatile polluting substances, there is a chance of evaporation which could lead to odour problems and a reduction in the environmental yield. The unloading of the soil at the soil remediation centre takes place in an enclosed hall with air suction and pre-treatment of gaseous effluents.
Polluted soil may stick to tyres and the load container during loading and driving over loose soil at the remediation location; this can then lead to the soil being spread across the site. The lorry must be cleaned, prior to leaving the site, at a specially designated washing area.
Lorries are a source of noise and discharge combustion gases. Noise production is determined by the motor capacity, motor type, motor workload and the attenuation. The noise burden is determined by the route distance and the transport route, as well as the location of the remediation site. In general, noise-reducing measures are taken when motorways pass through residential zones. By selecting the most favourable route, noise problems can be kept to a minimum.
The emission of combustion gases in road transport is quite high, as is the required amount of fuel (diesel). For the transport of 1 tonne, approximately 65 g of diesel fuel is needed per km. Per driven kilometre, on average 2.7 g CO, 6.1 g NOx, 0.28 g dust, 0.13 g SO2 and 1.2 g VOS are released.