The essential strategy for inland spill clean up techniques should be containment, recovery and temporary storage. Secondary needs will include transportation and possible disposal - or recycling.
It is important to discover the source of the spill which might not be straight forward. A steady slow seepage from a leaking disused oil storage tank may be very difficult to trace.
Since oil spills vary so much due to location, type of oil spilled, weather etc., there are various points to consider.
If the oil is spilled in an area other than directly into a water course the source of the spill should be identified as quickly as possible. The oil pollution may enter a water course through:
- Surface drains
- Seeping into water bearing strata
The speed with which contamination may take place will be determined by the type of oil, how much was originally spilled, was the oil hot when spilled and is the ambient temperature cool by comparison. If so, this will affect speed of flow and spread as well as the degree of penetration of the oil into the ground. This penetration will also depend on other factors, such as whether or not the soil is wet - so reducing the permeability and how quickly the response team can begin to remove the pollution - since if the ground is impervious, this will result in quick and large scale spreading of the oil pollution.
If the oil is volatile - light ends type when evaporation will take place and the speed of evaporation will b dependent upon ambient temperatures and wind conditions.
A low viscosity oil on a porous surface will reduce surface spread, but will greatly increase penetration, but if the land area is water-logged then it will be totally impervious to the ingress of oil.
If, as previously mentioned, the oil is volatile, consideration must be given to risk of explosion. This will depend upon the volatility of the product, volume spilt, ambient temperature, wind conditions and amount of spreading.
Where there may be a risk of explosion conditions should be tested before equipment is used. If found to be considered as an explosion risk, then suitable explosion proof equipment must be used and monitoring of the spill site is essential.
Land Spill- Metalled Highway
If a spill occurs on a road surface, the oil will rapidly spread out and flow to the nearest drain.
- Take precautions to prevent oil from draining away. Block all drain inlets, pipes, cable ducts etc., use adsorbent filters, booms and or earth/sand bunds.
- Concentrate oil again using booms etc., to facilitate easy transfer to temporary storage - or road tankers direct.
- If, due to quantity the oil drains into an interceptor and overflows, the outlet valve should be shut and the oil allowed to back up in the drains. In this case flooding will occur and precautions taken to avoid run off from the site. Use methods indicated in (2) above and instigate removal of oil immediately. If available use specialist equipment which will not pick up the free water. If equipment is not available, adsorbents should be used. If large quantities are involved use pumps - only if conditions allow - see previous notes re explosion risk.
- The pumps may be fitted to tankers, where available vacuum tankers can be used. If the site of the spill gives access to soft ground, storage of large amounts of spilled oil can be made in plastic lined pits. Also 200 litre drums, or special pillow tanks should be used, also refuse skips should be considered.
Oil Spill Contamination of SubSoil
Penetration of oil will occur in porous material and the depth of penetration will be dependent on oil gravity.
The area/volume of contamination will also depend upon how wet, permeable, deep and structure of the subsoil. If there is only a relatively thin/wet layer of subsoil lying on an impermeable layer, then the spreading effect will be greater than that of a relatively dry, deep layer of subsoil.
To dispose of contaminated subsoil effectively, various methods should be considered. They include:
- Excavation and then subsequently taken for incineration or to licensed tips for dumping. Possibilities also for washing depending upon relative on-going pollution on site clearance requirements.
- Treatment in situ by bioremediation enhancement of naturally occurring bacteria is possible together with seeding the contaminated area with specially developed bacteria and the addition of fertiliser - either phosphorous based, or those with nitrogen are favoured, It is important to seek specialist advice on this sort of treatment.
- As a final alternative - the contaminated soil can be spread on to designated unpolluted areas and aerated to increase the bioremediation through natural means.
If excavation methods are employed due to potential contamination of groundwaters care should be taken not to disturb underground services such as power lines, gas or water pipes etc. Also, it is very important that excavation of the polluted subsoil does not penetrate the impermeable layer(s), otherwise this will increase the potential pollution penetration to ground waters.
Oil in GroundWater
If oil reaches groundwater tracking and recovering the oil becomes complicated, various techniques can be used.
The following is an example of the simple but effective ways of dealing with groundwater pollution:
- If the groundwater are less than 3m from the surface, interceptor trenches can be dug across the oil pollution flow path.
- In order to remove the oil successfully, investigation should be made to determine:
- Amount and type of oil that has seeped into the ground
- Depth and area that the oil has spread into the water table
- Type of soil
- Position of water table in relation to the oil penetration.
Other systems may be employed and again expert advice should be sought. One such system would include the creation of a 'cone of depression' and the sinking of boreholes which with flushing encourages water to flow into them bringing oil pollution to dedicated locations for removal by vertical deployment of mops (to reduce free water pick up) or by using pumps and separators - to remove the free water.