How significantly risky a business is managing contaminated land
In this edited paper by Adam Czarnecki and Sarah Dack of GeoDelft Environmental, the application of risk assessment in the management of contaminated land is reviewed within the context of requirements of recently introduced regulations applying in England and Scotland.
Environmental control within the new legislation is in essence not radically different from previously existing water (Water Resources Act (1991), planning legislation and guidance PPG23 Planning and Pollution Control (1994), law or protection from common law. Similarly, the fundamental concepts of risk assessment and the pollution linkages concept which are enshrined within the new legislation have been undertaken by some pro-active practitioners in the UK for several years. In the UK for example GeoDelft Environmental (www.geodelft.co.uk) has been undertaking Quantitative Risk Assessments (QRA) 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. Prior to the new legislation the investigation, management and reclamation of contaminated sites was undertaken within the planning process. A more pro-active process has now been implemented with local authorities now responsible for the identification and if necessary reclamation of contaminated sites.
What is a Risk Assessment?
An excellent overview, Guidelines for Environmental Risk Assessment and Management of the underlying principles of risk assessment, risk management and risk communication was published by the DETR on 31 August 2000.
So what is a risk assessment? It is (and should be) a formalised, transparent and reproducible framework by which we can identify whether or not contaminated land presents an unacceptable level or risk to human health, controlled waters, property or ecological targets.
Where unacceptable risks are identified (by use of Quantified Risk Assessments) 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 the evaluation of contaminated land has been based upon generic non-site specific standards such as ICRCL 59/83, Dutch Intervention Values or the GLC "Kelly" guidelines. These are still reported as being used as land evaluation and reclamation standards today, with R & D Technical Report P260 identifying (from a market survey) that 88% of people still use ICRCL trigger values in their work and even more worryingly that 55% of respondents routinely use the former GLC "Kelly" standards.
Reluctance over risk assessment
Reluctance to the use of risk assessments in the UK probably stems from a lack of formal training (now available at some UK universities) and recognising that the undertaking of risk assessments requires a multi-disciplinary specialist approach by use of a team of hydrogeologists, geologists, geotechnical engineers, ecologists, biologists and toxicologists.
At the time of writing we are still awaiting extensive technical guidance on the use of risk assessments from the DETR. The impending CLEA model which eventually will be routinely used as a tool for evaluating risks to human health is at present under development. For controlled waters (the relevant regulatory authority being the Environment Agency) guidance has been published with 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, commencing with the impact for 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 with a resultant publication of Technical Report P260 Land Contamination Risk Assessment Tools and is also currently engaged in conducting a sensitivity analysis on a beta version of the CLEA2000 model and producing technical guidance in 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 a collation of information relating to the general environmental setting, i.e. geology, hydrogeology, mining activity, local abstractors (unlicensed and licensed), location of controlled waters (springs, rivers, streams, canals, estuaries, ponds), pollution incidents and proximity to active/closed landfill sites etc.
The Tier I investigation may also include a preliminary site investigation in order 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 the collected information together with information gained 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 (EQS) if a nearby surface water receptor is identified. However other standards could be considered such as bathing water standards or standards to protect irrigation or livestock.
Soil and groundwater element/compound concentrations should be compared with
most relevant (and defendable!) screening levels. If there are no exceedances, the site or individual areas of the site can be assumed to not pose an unacceptable risk. If there are exceedances then a following stage of investigatory work is warranted.
Tier II Investigation
A Tier II Investigation usually involves investigatory work based on amended likely pollutant linkages identified within Tier I.
GeoDelft uses a number of models to carry our Tier II Investigations. These include RBCA (based upon the ASTM standard E-1739) produced by Groundwater Services Inc which 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 than the original model. This model has been routinely used on over 300 sites in the past two years. For controlled waters the "P20 method" is also routinely used.
Risc-Human v.3.0 developed by the Dutch Institute for Public Health and the Environment and based upon the CSOIL model 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 zones, 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 in order 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 a potential for an unacceptable level of risk to exist and risk-based site-specific target levels SSTL's are calculated for the site. The site can either be remediated on the basis of the SSTL's or an additional investigation instigated in order to facilitate a Tier III risk assessment. The extra cost of data collection within the Tier III investigation is most likely to be offset by the reduced conservatism and uncertainty in the resulting remediation targets.
Tier III Investigation
A Tier III investigation and risk assessment involves a further reduction in the level of uncertainty of the risk estimates by obtaining more site-specific data for each exposure pathway that has been determined to exceed acceptance criteria at the 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 for the assessment may include three dimensional source characterisation, unsaturated zone porosity, review of building design, hydraulic conductivity and organic carbon data etc.
Other models may well be used in order to take into consideration of surface water dilution at a receiving water body, modelling of biodegradation processes (with use of Biochlor or Bioscreen) or a re-assessment of the degradation half-lives and exposure duration's used in the Tier II investigation.
The Royal Institution of Chartered Surveyors predicted in 1997 that the new Contaminated Land Regulations (2000) would be the single most important piece of legislation to impact on the property industry.
The 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 should will become more sophisticated, environmental insurance policies will become more common and inevitably legal opinion on the designated status of sites will become increasingly necessary.
A report by the Urban Task Force entitled Towards an Urban Renaissance (DETR, 1999) proposes that all polluted sites should be restored by the year 2030.
Our 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 that have been developed have not identified all the potential
sources or pollutant linkages and therefore still pose a risk to human health
and the environment?
Only time will tell.
Risk Assessment Workshops
In order to assist local authorities in the undertaking of their new duties GeoDelft Environmental has developed a Risk Assessment Workshop (first to be run on 15-16 October 2001) that aims to give relevant staff practical experience in the development/verification of qualitative/quantitative risk assessments for potentially contaminated sites.
Demonstrations will be given on the development of appropriate risk models from information gained by desk studies, intrusive/non-intrusive surveys and chemical testing by using different propriety software packages and best-practice guidelines.
Case studies will be presented in the form of a series of different geological/hydrogeological settings; existing site uses together with proposed end use scenarios. Delegates will be assisted in their development of a Conceptual Site Model, and an initial Tier 1 Risk Assessment together with a prioritisation model for screening of multiple sites.
A more sophisticated Tier 2 model would be developed by the delegates from information gained from a series of different types of site investigations, chemical testing and after choosing and deciding upon appropriate toxicological and exposure parameters. Output from the different models would be examined for the different pathways, receptors and contaminants of concern.
Risk Assessment Bureau Service
GeoDelft Environmental has been in consultation with several local authorities over the past six months in the development of a dedicated Risk Bureau Service.
Delegates to each workshop will be given a unique opportunity to participate in a service that will initially provide a dedicated telephone help-line and web-based information knowledge base.