Method

Contamination type

Soil
type

Docu-
menta-
tion e)

Other condi-
tions

Org./ Inorg.

a)

Volatility

b)

Degrada-
bility

c)

Perme-
ability

d)

Soil contamination

Excavation with off-site treatment

+/(-)

All

+

All

++

f)

Excavation with landfilling

+/+

All

All

All

++

g)

Excavation and on-site treatment

+/-

+

(+)h)

(+)h)

+

i)

Soil vapour extraction

+/-

++

-

+

++

Bioventing

+/-

+

++j)

+

+k)

Forced leaching

+/+l)

-

-

++

+

^m)

Immobilisation

+/+

(+)n)

All o)

All

+

Steam stripping

+/-

+

All

+

(+)p)

q)

Groundwater contamination

Remedial pumping, draining

+/+l)

All

All

+

++r)

s)

Bio-slurping

(including suction probes)

+/+t)

All

All

+

+

In-situ remedial methods for groundwater contamination

Air sparging

+/-

+u)

-v)

+

+

x)

Adding oxidising agents (ORC)

+/-

All

+

+

(+)y)

Vertical cut-off barriers

+/+

(+)n)

All

All

+

Reactive permeable barriers

+/+

All

+z)

+

(+)y)

æ)

Natural attenuation

+/-

All

+ø)

All

(+)y)

å)

Method

Costs, excluding VAT

Soil contamination

Excavation

The cost of excavation and transport (within a radius of 150 km excluding transport by water) will amount to approximately DKK 90-200/tonne for a normal excavation, depending of the amount of soil, contamination position, transportation distance, and geographical position. The cost of filling the excavated area back up is approximately DKK 60-100/tonne depending on amount, type, and requirements for compactness. Additional costs include restoration, environmental inspection, documentation, decontamination, and any monitoring. Restoration costs vary greatly, depending on physical conditions and the type and strength of contamination. Experience shows that with oil/petrol contamination; the cost of contamination excavation will amount to DKK 400-1,000/tonne (including excavation, decontamination, and back-filling of new or treated soil) in cases where more than 1,000 tonnes of soil are excavated. For smaller contamination projects involving up to 1,000 tonnes of soil, costs will typically fall between DKK 400-2,500/tonne (normally DKK600-800 /tonne).

Soil treatment

The cost of soil treatment at central treatment plants is approximately DKK 160-600/tonne for biological soil treatment, depending on contamination type and amount (lighter types of contamination are cheaper). The cost of incineration is typically DKK 600/tonne at power plants and up to DKK 1,000/tonne at treatment plants (heavy organic contamination, e.g. tar), whereas thermal treatment for very contaminated soil can cost up to DKK 3,500 – 4,000/tonne (excluding heavy metals).

Landfilling

The cost of disposal at landfill sites varies greatly. However, the cost normally included a waste tax, which currently amounts to DKK 335/tonne (1997). Soil which is contaminated by heavy metals may in some cases (weak contamination – up to contamination level 3) be deposited at special landfills. The cost is approximately DKK 130 – 150/tonne. Prices of DKK 450-800 (including waste tax) per tonne must be expected for disposing of soil contaminated by heavy metals at landfill sites, depending on geographic position and level of contamination (up to contamination level 3). Soil which is heavily contaminated by heavy metals (corresponding to level 4) can be deposited at landfills or sent to KOMMUNEKEMI at a cost of approximately DKK 1,000/tonne.

On-site treatment of excavated soil

The cost of on-site treatment varies according to the method and the composition of the contamination. Prices of DKK 50-150/tonne have been observed for landfarming, whereas prices of up to DKK 1,000/tonne have been observed for mobile thermic on-site plants (heavier contamination).

Soil vapour extraction

This method is relatively cheap. A standard plant comprising 5 borings (63 mm diameter to a depth of 4 m), piping, ventilation with discharge, noise reduction, and electric wiring normally costs less than DKK 150,000. Cost of operation and monitoring (electricity, inspection, and final documentation) must be added to this. For the plant outlined above, these costs will amount to approximately DKK 50,000 a year. If the exhaust air is to be treated, approximately DKK 30,000 must be added to cover set-up (carbon filters for air flows of up to 600 m³/h). Operation costs will also be increased due to carbon-filter replacements. For example, with an airflow of 500 m³/t, the lifespan of a carbon filter with 260 kg of carbon will be approximately 60 days for 50 mg/m³ benzene, 110 days for the same amount of toluene, and 120 days for the same amount of trichloroethylene. This corresponds to annual costs of carbon-filter replacement of approximately DKK 175,000; 95,000; and 90,000, respectively. Attention should be given to the fact that concentrations drop significantly at the beginning, causing similar reductions in the cost of treatment of discharged air.

The plant outlined above would typically cover a contaminated area of 200-500 m²; depending mainly of the type of soil.

Bio-ventilation

In terms of set-up, this method is inexpensive. However, the tasks of monitoring and inspection are comprehensive, leading to high operation costs. The prices are comparable to soil vapour extraction.

Forced leaching

A plant including a pumping well (to a maximum depth of 15 m), distribution well, leach field (20 m), placement of pumping plant with level control, and piping can be set up for less than DKK 100,000. This does not include decontamination and screening of pumped-up water (see Section 9.3.5). Operation costs must also be added to this; these costs mainly involve plant inspection and monitoring.

Immobilisation

Costs should be assessed in each case, depending on what is to be done. Normal surface sealing using asphalt or paving is a relatively cheap solution, as this can often be combined with a building project. Examples of costs of approximately DKK 700/tonne are observed for stabilising.

Steam stripping

This method has not been attractive in Denmark, primarily because of the great costs of this very energy-intensive method (examples from the USA indicate prices of 1,200 to 3,400/tonne). Moreover, this method requires that all objects larger than approximately 0.3 m be removed from the soil and that the terrain does not slope more than 1 %.

Groundwater contamination

Remedial pumping

The cost of construction depends on the technical layout. For example, the cost of a unit with a 10" well well to a depth of 20 m with a 160 mm screen diameter, complete with dry well, pump, raw-water station, electricity, and discharge will be approximately DKK 70,000 – 90,000. Any costs involving treatment units, operation, etc. must be added to this figure.

Drainage

With simple cases, drainage can be established at a cost of approximately DKK 300 per metre.

Suction probes

Suction probe equipment often comprises 20 suction probes to a maximum depth of 6 m and can be established for less than DKK 15,000. It is often advantageous to hire the vacuum facility due to limited time scales. Hiring a facility such as the one outlined above amounts to approximately 4,000 a week.

Bio-slurping

On-site treatment of abstracted groundwater

Discharge

Taxes impose significant expenses on discharge of abstracted groundwater to sewers. This tax varies among local authorities. The diversion tax typically amounts to DKK 10-15 per m³ (1996).

Oil/water separators

A traditional gravimetric oil/water separator can be purchased for DKK 10,000 – 20,000 depending on size, whereas coalescence oil/water separators cost more than three times as much.

Coalescence separators

Coalescence separators can be purchased for DKK 50,000 – 100,000. Cleaning water by passing it through screens is a well-documented method. The choice of material depends on the actual contamination situation.

Filters

The cost of setting up a double carbon-filter plant for a water flow of up to approximately 5 m³/h amounts to DKK 70,000-80,000. This does not include any pre-filter, nor any containers, etc. The operation costs depend on the relevant contamination situation (carbon-filter replacement). For example, at a water volume of 2 m³/hour, the replacement frequency of two 450 kg carbon filters is approximately once a year for water concentrations of 1 mg of benzene/l; once every two years for 1 mg of toluene/l, and once every two years for 1 mg of trichloroethylene/l. This corresponds to annual costs of approximately DKK 70,000; 35,000; and 35,000 respectively, not including inspection and monitoring.

Air stripping

The cost of setting up an air stripping plant is relatively high, approximately DKK 100,000 – 150,000. Careful control and monitoring must be added to this figure. In addition to this, pre-filtering must normally be included in calculations, just as a subsequent treatment of the air is often required.

Photochemical oxidation

Plant investments amount to approximately DKK 80,000 – 150,000 depending on design. Operation costs mainly comprise the oxidation agent (hydrogen peroxide), lamp replacement, electricity, and regular inspection.

In-situ remediation methods for groundwater contamination

Air sparging

The cost of a standard plant, comprising a system of 10 remedial wells to depths of approximately 10 m, including dry well, piping, containers with noise reduction for the operation unit, and muffled air intake, including the cost of air treatment, amounts to approximately DKK 1 – 1.5 million. This does not include the cost of soil vapour extraction from the unsaturated zone. Moreover, relatively high operation and monitoring costs must be expected due to energy consumption and the need for inspection; for the plant outlined above this will typically amount to DKK 200,000 per year. Wells are usually positioned at intervals of approximately 10 m, so the plant outlined in the above would cover a contaminated area of approximately 1,000 m².

Adding oxidising agents (ORC)

The method is cheap and environmentally sound, and is likely to become widespread in Denmark.

Vertical cut-off barriers

It is possible to cut off groundwater contamination by establishing vertical barriers in the groundwater aquifer. This is done by means of various methods, such as sheet piling, deep soil mixing (DSM), slurry walls, and grouting.

Reactive permeable barriers

Reactive permeable walls are barriers which allow the groundwater to pass, but which degrade or remove contamination during passage. This method is at the experimental stage in Denmark, but is used in field work in the USA with degradation of chlorinated compounds by adding iron to the barriers.

Natural attenuation

This ‘method’ shows promise, as the resulting environmental impact is very low. Consequently, it may have a future, especially as regards clean-up of oil/petrol contamination.

Precautions against landfill gas

Preventing gas from spreading by means of interceptive methods can entail relatively high costs. For example, the initial investment to render a site safe by means of interceptive drainage of approximately 100 m to a depth of approximately 4 m will be approximately DKK 500,000, whereas the annual operation and monitoring costs amount to approximately DKK 15,000 – 20,000. With new building, the constructional precautions form a very small part of the total cost when taken into consideration during the initial stages of the project.