Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to a newer version or another browser.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

A significantly risky business

Adam Czarnecki and Sarah Dack, GeoDelft Environmental, on the Contaminated Land Regulations (2000).

After more than a decade of formulation and consultation, the Contaminated Land Regulations (2000) were introduced in England on 1 April 2000 and in Scotland on 14 July. The new legislation requires land owners, local authorities, property developers, contractors, professional advisers, the Environment Agency and allied service sectors (such as lenders and insurers) to identify and remediate contaminated/special sites in accordance with prescribed risk assessment procedures.

Environmental control within the new regulations is not radically different from previous water planning legislation (the Water Resources Act (1991)), guidance law (PPG23 Planning and Pollution Control (1994) or protection from common law.

Some UK practitioners have been using its fundamental concepts of risk assessment and pollution linkages for several years.

GeoDelft Environmental, for example, has been undertaking Quantitative Risk Assessment as a means of identifying and assessing potentially contaminated sites for the past eight years.

UK policy dictates that land development is undertaken in accordance with the 'Framework for Contaminated Land' (DoE, 1994) and states that existing contamination which poses a threat to human health or the environment is controlled and treated within the suitable for use approach. Before the new legislation, the investigation, management and reclamation of contaminated sites was undertaken within the planning process. A more proactive process has now been implemented, making local authorities responsible for the identification and if necessary reclamation of contaminated sites.

What is a risk assessment?

An excellent overview of the underlying principles, Guidelines for environmental risk assessment and management, was published by the DETR in August 2000.

So what is a risk assessment? It is (and should be) a formalised, transparent and reproducible framework by which engineers can identify whether or not contaminated land presents an unacceptable level or risk to human health, controlled waters, property or ecological targets. Figure 1 gives a flowchart for the risk assessment and management process.

Where unacceptable risks are identified (by use of QRA) the modelling can derive site-specific clean-up target values that will reduce the risks to an acceptable level.

This is an important point as previous guidance on evaluation of contaminated land was based on generic non-site specific standards such as ICRCL 59/83, Dutch Intervention Values or the GLC 'Kelly'guidelines.These are still being used as land evaluation and reclamation standards today. R&D Technical Report P260 found that 88% of people still use ICRCL (International Committee for the Reclamation of Derelict Land) trigger values in their work and, even more worryingly, that 55% of respondents routinely use the former GLC 'Kelly' standards.

Reluctance to use risk assessments in the UK probably stems from a lack of formal training recognition that its undertaking requires a multidisciplinary specialist approach using a team of hydrogeologists, geologists, geotechnical engineers, ecologists, biologists and toxicologists.

We are still awaiting extensive technical guidance on the use of risk assessments from the DETR. The impending Contaminated Land Exposure Assessment model, which eventually will be routinely used as a tool for evaluating risks to human health, is under development. For controlled waters, the Environment Agency has published Methodology for the derivation of remedial targets for soil and groundwater to protect water resources, R&D P20.This provides guidance on different levels (tiers) of risk assessment when evaluating potential risk to controlled waters, from the impact of soil contaminants on pore water, to risk to sensitive receptors such as water courses and abstraction boreholes.

GeoDelft has also been involved in the development of the new standards for the Environment Agency, resulting in publication of Technical Report P260 Land contamination risk assessment tools and is also engaged in conducting a sensitivity analysis on a beta version of the CLEA2000 model and producing technical guidance on its use.

Risk assessment procedures Tier I investigation Any cost-effective investigation of a potentially contaminated site should start with a preliminary phase where information is gained on existing and former on-site and neighbouring land uses(s).This is normally a historical desk study and a walk-over survey (often essential and neglected), together with collation of information relating to the general environmental setting geology, hydrogeology, mining activity, local abstractors (unlicensed and licensed), location of controlled waters (springs, rivers, streams, canals, estuaries and ponds), pollution incidents and proximity to active/closed landfill sites.

The tier I investigation may also include a preliminary site investigation to develop a conceptual site model (CSM) for the likely areas of contaminated material (sources), potential pathways (or linkages) and potential receptors (humans, controlled waters, building or ecology).

A tier I investigation normally integrates all the information described above into the CSM. Elevated concentrations of certain elements/compounds are compared with screening concentration values which are non-site specific.For controlled waters the P20 methodology either calculates pore water concentrations from soil concentrations and derives a tier I remedial target concentration by multiplying the partitioning against a suitable water quality standard, or directly compares leaching test concentrations against a suitable water quality standard.

Suitable screening levels could be drinking water standards for groundwater or Environmental Quality Standards if a nearby surface water receptor is identified.However, others which could be considered include bathing water standards or standards to protect irrigation or livestock.

Soil and groundwater element/compound concentrations should be compared with the most relevant (and defendable! ) screening levels. If values do not exceed these levels, the site or individual areas of the site can be assumed to not pose an unacceptable risk. If they do exceed the levels then another stage of investigation is warranted.

Tier II investigation This usually involves an investigation based on amended likely pollutant linkages identified within tier I.

GeoDelft uses a number of models to carry out tier II investigations.These include risk based corrective action (RBCA), based on the ASTM standard E-739, produced by Groundwater Services.This models both human health exposure pathways and groundwater migration pathways. The model incorporates a large chemical and toxicological database that is continuing to be revised and expanded.GeoDelft has modified RBCA to become more UK-focused. This model has been routinely used on more than 300 sites in the past two years. For controlled waters the 'P20 method' is also routinely used.

Risc-Human v3.0, developed by the Dutch Institute for Public Health and the Environment, is based upon the CSOIL model and can at present only be used for human health exposures.

Information required for a tier II human health risk assessment include site-specific geological information, physical and chemical properties of the unsaturated and saturated zones and site-specific human health exposure parameters such as ingestion rates or breathing rates. The estimated quantity of contaminant inhaled, adsorbed or ingested is compared against acceptable daily intake values.

For controlled waters, the assessment again requires site-specific soil and groundwater parameters for inclusion in simple groundwater fate and transport algorithms based on the Domenico equation.These algorithms model the movement of contaminants in the saturated and unsaturated zones to identified receptors such as aquifers, abstraction wells or surface water bodies. Concentrations predicted at the various receptors are compared against target values such as drinking water standards or environmental quality standards.

Groundwater modelling may include conservative biodegradation half-lives to account for biodegradation, degradation and attenuation processes occurring in the aquifer.

If the contaminant is above the acceptable intake value for any identified receptor it is assumed that there is potential for an unacceptable level of risk to exist and risk-based site-specific target levels (SSTLs) are calculated for the site.The site can either be remediated on the basis of the SSTLs or an additional investigation instigated to facilitate a tier III risk assessment.The extra cost of data collection in the tier III investigation is most likely to be offset by the reduced conservatism and uncertainty in the resulting remediation targets.

Tier III investigation This involves a further reduction in the level of uncertainty of the risk estimates by obtaining more site-specific data for each exposure pathway that exceeds acceptance criteria at tier II stage.

A tier III risk assessment involves more sophisticated fate and contaminant transport modelling and the use of probabilistic risk assessment techniques.

Additional site-specific information required may include three-dimensional source characterisation (Figure 2), unsaturated zone porosity, review of building design, hydraulic conductivity and organic carbon data.

Other models may well be used to consider surface water dilution at a receiving water body, modelling of biodegradation processes (with use of Biochlor or Bioscreen) or a reassessment of the degradation half-lives and exposure durations used in the tier II investigation.The process of risk assessments is summarised in Table 1.

Summary In 1997 the Royal Institution of Chartered Surveyors predicted that the Contaminated Land Regulations (2000) would be the single most important piece of legislation to impact on the property industry.

Development of brownfield or contaminated land has now achieved a degree of maturity, with sophisticated scientific methods required to quantify risk for human health, controlled waters, buildings and in some cases ecological receptors.

Practitioners and regulators will need to respond to this new regime; staff training in risk assessment techniques will be necessary, site investigations will become more sophisticated, environmental insurance policies more common and inevitably legal opinion on the designated status of sites increasingly necessary.

A report by the Urban Task Force, Towards an Urban Renaissance (DETR, 1999), proposes that all polluted sites should be restored by 2030.

The question is, how many sites have been unnecessarily reclaimed because no site-specific risk assessment was ever performed? Even more worryingly, how many contaminated sites have been developed where not all the potential sources or pollutant linkages have been identified and therefore still pose a risk to human health and the environment? Only time will tell.

References Czarnecki A (1996).ABC of ICRCL.Ground Engineering July/August issue, p10.

Czarnecki A & Robertson W (2001).Regulating Pollution Control, Chemical Engineer April, p40-42.

Dack S & Loxham M (2000). The risk assessment of PCB contaminated soil and water-calculated and perceived risk. VTT Symposium, Helsinki, Finland, September 2000.

DETR (1995).Part IIA, Contaminated Land, Section 57, Section 78 to 78YC, Environment Act 1995.

Environment Agency (2000).Land contamination risk assessment tools: an evaluation of some of the commonly used methods.R&D Technical Report P260.

Environment Agency (2000). Integrated methodology for the derivation of remedial targets for soil and groundwater to protect water resources. R&D Technical Report P20.

DETR (1999).Towards an urban renaissance.Report by the Urban Task Force.

Loxham M & Dack S (2000). Clean-up criteria for contaminated land management - How to achieve a cost effective balance.VTT Symposium, Helsinki, Finland, September 2000.

Have your say

You must sign in to make a comment

Please remember that the submission of any material is governed by our Terms and Conditions and by submitting material you confirm your agreement to these Terms and Conditions. Please note comments made online may also be published in the print edition of New Civil Engineer. Links may be included in your comments but HTML is not permitted.