Land remediation is becoming a growth sector as government targets for brownfield development have been increased. In this month's cost model, Davis Langdon & Everest looks at new laws on contaminated land and details the cost of clean-up techniques
Introduction July 1999 will see the introduction of new contaminated land provisions, contained in part IIa of the Environmental Protection Act 1990. A primary objective of the measures is to encourage the recycling of brownfield land. More attention is being focused on reusing land as the DETR has increased its target for building new housing on brownfield sites to 60% and because the urban taskforce is looking at the issue.
Under the Environmental Protection Act, action to remediate land is required only where there are unacceptable actual or potential risks to health or the environment.
Sites that have been polluted from previous land use may not need remediating until the land use is changed. In addition, it may be necessary to take action only where there are appropriate, cost-effective remediation processes that take the use of the site into account.
Local authorities are not required to make public any records of sites that have been investigated for contamination. The risks involved in the purchase of potentially contaminated sites is high, particularly considering that a transaction can result in the transfer of liability for historic contamination from the vendor to the purchaser.
<B><FONT size="+2">Statutory framework</FONT></B>The contaminated land provisions of the Environmental Protection Act 1990 are only one element of a series of statutory measures dealing with pollution and land remediation that are to be introduced this year. Others include:
- groundwater regulations, including pollution prevention measures
- an integrated prevention and control regime for pollution
- sections of the Water Resources Act 1991, which deals with works notices for site controls, restoration and clean up.
The contaminated land measures incorporate statutory guidance on the inspection, definition, remediation, apportionment of liabilities and recovery of costs of remediation. The measures are to be applied in accordance with the following criteria:
- the standard of remediation should relate to the present use
- the costs of remediation should be reasonable in relation to the seriousness of the potential harm
- the proposals should be practical in relation to the availability of remediation technology, impact of site constraints and the effectiveness of the proposed clean-up method.
Liability for the costs of remediation rests with either the party that "caused or knowingly permitted" contamination, or with the current owners or occupiers of the land.
Apportionment of liability, where shared, is determined by the local authority. Although owners or occupiers become liable only if the polluter cannot be identified, the liability for contamination is commonly passed on when land is sold.
Clearly, the ability to forecast the extent and cost of remedial measures is essential for both parties, so that they can be accurately reflected in the price of the land.
If neither the polluter nor owner can be found, the clean-up is funded from public resources.
<B><FONT size="+2">Sources of public funding</FONT></B>Although the principle that the polluter pays has been established, public funding is available to deal with the consequences of historic contamination if the responsible parties cannot be found, or to encourage the redevelopment of derelict sites. In the UK, there are three main sources of public funding. These are:
- The DETR. The department provides financial support (£13m in 1997) to local authorities, through the Contaminated Land Supplementary Credit Approval Programme, for the clean-up of derelict sites where no other development proposal is in place
- The Environmental Agency. In 1997, it received £1.3m from the DETR for land remediation works
- Regeneration agencies. English Partnerships spent £34.8m in 1997 on the remediation of 1350 ha of land linked to development proposals. This month, its role is transferred to eight regional development agencies.
<B><FONT size="+2">Potential sources of contamination</FONT></B>The identification of contaminated land in the UK follows a source-pathway-receptor model. In other words, potential sources of contamination on the site need to be concentrated enough to cause significant harm; a receptor (a person or building, for example) has to be present on the site as part of the existing or planned land use, and there must be a connection between the two.
The following hazards are potential contaminants, depending on their concentration and the planned land use:
- Absorption of contaminants by food plants grown in contaminated soil. Cadmium and lead can affect domestic gardens, allotments and agricultural land
- Ingestion and inhalation. Arsenic, cadmium, lead, free cyanide, coal tars, phenols and sulphates are potential hazards in sites developed as domestic gardens, or for recreational and amenity uses. Naturally occurring radon gas is also a hazard in areas such as Cornwall and Derbyshire. The presence of asbestos, even in low concentrations, is a potential hazard to construction workers
- Skin contact. Acids and alkalis, organic substances such as coal tars and phenols, asbestos and radioactive materials are a particular threat to site workers and investigation teams
- Phytotoxicity. Sulphates, copper, nickel, zinc and landfill gas can prevent or inhibit plant growth
- Contamination of water resources. Phenols, cyanide, sulphates and soluble metals pose a threat to water supplies through run-off or leaching
- Fire and explosion. Methane, sulphur and combustible materials such as coal dust, oil, tar, pitch and rubber are hazards
- Chemical attack. This can result in building material degradation. Sulphates, cyanide, chloride, coal tars, phenols and mineral oils can affect below-ground works.
The level of concentration of contaminants necessary to cause "significant harm" varies in accordance with land use, with lower trigger concentrations of pollutants being demanded for sensitive uses such as domestic gardens.
Appropriate concentrations are defined for the UK by the Interdepartmental Committee on the Redevelopment of Contaminated Land in the publication ICRCL 59/83. The guidance, which is not mandatory, sets out threshold and trigger values for different pollutants and land uses.
The threshold concentration is the value below which no contamination is considered to be present, and the trigger concentration is the point above which remediation measures are judged to be necessary. Where concentrations are between the two values, the necessity for remediation will be determined by professional judgement, taking into account planned land use, risks of contamination and clean-up costs.
<B><FONT size="+2">Assessing contamination</FONT></B>Site investigation to establish the presence of contamination and its extent and nature, is essential for both the purchaser and land owner.
A systematic approach to assessing contaminated sites can entail a combination of desk-top study, site investigation and chemical analysis of samples. The issues that need to be addressed include:
- The history of uses on the site and likely sources of contamination, including issues of working practices, on-site disposal methods, use and storage of contaminants, and the presence of imported fill
- The intended use of the site
- The potential hazards that could affect the proposed use
- Confirmation of whether contaminants are present and, if so, whether their concentrations are high enough to be a hazard
- Consideration of whether a different land use could remove or reduce the hazard, either by removing the pathway or the receptor
- Consideration of what remedial treatments are practical, given the proposed end-use of the site.
The desk-top study, typically carried out by specialists, is a preliminary stage used to determine the likelihood of contamination on a site. The output, a preliminary site investigation report, will identify the degree of contamination and will help determine the overall viability of a development. The preliminary report will also detail proposals for further site investigations.
As the next step, analysis of soil and groundwater samples should confirm the presence of contaminants and their concentrations. Interpretation of the results, in conjunction with the appropriate trigger concentrations of contaminants, will indicate whether the site is "clean" or whether it requires remediation.
The assessment of contamination, based on a very limited sample, provides a risk assessment of the extent and location of all contaminants, together with an appraisal of the remediation options available.
<B><FONT size="+2">Land remediation techniques</FONT></B>There are two principal approaches to remediation – dealing with the contamination in situ or off site.
The selection of the approach will be influenced by factors such as:
- Initial and long-term cost
- Timeframe for remediation
- Types of contamination present
- Depth and distribution of contamination
- The existing and planned topography
- Adjacent land uses
- Patterns of surface drainage
- The location of existing on-site services
- Depth of excavation necessary for foundations and below-ground services
- Environmental impact and safety
- Prospects for future changes in land use
- Long-term monitoring and maintenance of insitu treatment.
<B>Off-site techniques Removal</B> This is the most common and cost-effective approach to remediation in the UK, providing a broad spectrum solution by dealing with all contaminants. Removal is suited to sites where sources of contamination can be easily identified.
If used in combination with material-handling techniques such as soil washing, the volume of material disposed at landfill sites can be significantly reduced. The disadvantages of the technique include the fact that the contamination is not destroyed, there are risks of pollution during excavation and transfer; road haulage may also cause a local nuisance.
<B>Insitu techniques</B> A range of insitu techniques is available for dealing with contaminants.
Dilution This involves the reduction of the concentrations of contaminants to below trigger levels by on-site mixing with cleaner material.
<B>Clean cover</B> A layer of clean soil is used to segregate contamination from receptor. This technique is best suited to sites with widely dispersed contamination. Costs will vary according to the need for barrier layers to prevent migration of the contaminant.
<B>On-site encapsulation</B> This involves the physical containment of contaminants using barriers such as slurry trench cut-off walls. The cost of on-site encapsulation varies in relation to the type and extent of barriers required, the costs of which range from £35/m2 to more than £100/m2.
There are also insitu techniques for treating more specific contaminants.
<B>Bio-remediation</B> This is used to remove oily, organic contaminants through natural digestion by micro-organisms. The process is slow, taking from one to three years, and is particularly effective for the long-term improvement of a site, prior to a change of use.
<B>Soil washing</B> This involves the separation of a contaminated soil fraction or oily residue through a washing process. The dewatered contaminant still requires disposal to landfill. In order to be cost effective, 70-90% of soil mass needs to be recovered.
<B>Soil flushing</B> This involves the washing out of oily contaminants from soil insitu using treated ground water.
<B>Vacuum extraction</B> This involves the extraction of liquid and gas contaminants from soil by vacuum.
<B>Thermal treatment</B> This features the incineration of contaminated soils on site. The uncontaminated soil residue can be recycled. By-products of incineration can create air pollution and exhaust air treatment may be necessary.
<B>Stabilisation</B> Cement or lime, is used to physically or chemically bond oily or metal contaminants to prevent leaching or migration. Stabilisation can be used in both insitu and off-site locations.
<B><FONT size="+2">Cost drivers</FONT></B>Cost drivers relate to the selected remediation technique, site conditions and the size and location of a project.
The wide variation of costs shown in table 1 is largely because of differing site conditions. Factors that need to be considered include:
- Waste classification of the material
- Underground obstructions, pockets of contamination and live services
- Ground water flows and the requirement for barriers to prevent the migration of contaminants
- Health and safety requirements and environmental protection measures
- Location, ownership and the land use of adjoining sites
- Distance from landfill tips, capacity of the tip to accept contaminated materials, and transport restrictions.
Other project-related variables include size, access to disposal sites and tipping charges; the interaction of these factors can have a substantial impact on overall unit rates.
Table 2 sets out the costs of remediation using dig-and-dump methods for different sizes of project. Variation in site establishment and disposal cost accounts for 60-70% of the range in cost.
The strict health and safety requirements of remediation can push up the overall costs of site organisation to as much as 50% of overall project cost. A high proportion of these costs are fixed and, as a result, the unit costs of site organisation increase disproportionally on smaller projects.
Haulage costs are largely determined by the distances to a licensed tip. Current average haulage rates, based on a return journey, range from £1.10 to £1.40 a mile. Short journeys to tips, which involve proportionally longer standing times, typically incur higher mileage rates.
A further source of cost variation relates to tipping charges. Table 3 summarises typical tipping charges for 1999, exclusive of landfill tax.
Tipping charges fluctuate in relation to the grades of material a tip can accept at any point in time. This fluctuation is a further source of cost risk.
Over the past two years, prices at licensed tips have varied by as much as 50%. In addition, a special waste regulation charge of £15 per load, equivalent to 80p a tonne, is also payable.
Landfill tax, currently charged at £10 a tonne for active waste, is also payable, although exemptions are available for the disposal of historically contaminated material.
Current exemptions from landfill tax are due to be reviewed in 2000, after which they are likely to be phased out to encourage insitu treatment methods.
<B><FONT size="+2">Procurement and insurance</FONT></B>No form of contract has been developed specifically for the requirements of land remediation. Traditional lump-sum and design-and-build contracts using JCT and ICE forms are common.
Fixed-price lump-sum contracts may not be suitable, as the scope of work can be difficult to establish at tender stage. The best procurement routes are often those in which the risks of variation in the cost and quantity of work are shared by contractor and client. A balance of pricing and risk can be achieved through competitive tendering of general items and preliminaries, with measured work subject to remeasure, priced on previous rates.
Pollution cover has been excluded from standard public liability policies since 1990, so property owners are potentially in danger of claims for pollution damage or liability for remediation. Such insurance will become increasingly necessary, if landowners are to protect themselves, once the contaminated land provisions of the Environmental Protection Act 1990 come into force. In most cases, an Environmental Clean-up Policy provides cover for further remediation costs, of original pollutants after the agreed remediation programme. Cover is available for up to 10 years. Single policies can cover developers, contractors and landowners
<B><FONT size="+2">Cost model</FONT></B>The cost model features the remediation of a 0.5 ha brownfield site, by removal of contaminated waste to a licensed tip.
Costs are current, based on a location in central England, and reflect prices from a competitive tender. Costs of site abnormals, professional fees, landfill tax and VAT are excluded from the detailed breakdown. Costs of insitu treatments to groundwater, soil, or other contaminants are also excluded. The rates in the cost model breakdown can vary widely, mainly as a result of differences in grade of waste, haulage cost and distances to a tip. The potential effect of some of these variations are examined in the table of cost drivers, illustrating the overall cost implication of rate or quantity variations.