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GIS for contaminated land risk assessment

By [email protected] - 13th July 2006 - 20:27

Steve Smith, Colin Harding, Stuart Gillies and Lander Jimenez-Ocio explain how Stockton Borough Council is discharging its Section 57 land contamination responsibilities using a GIS-based Land Quality Management database
Part IIA of the Environmental Protection Act 1990 was introduced in Section 57 of the Environment Act 1995. This legislation placed a duty on local authorities to take on a leading role in the management of historical land contamination within their area.Government policy is to limit the use of Greenfield sites and to secure a minimum of 60% of new housing on Brownfield sites.Land determined to be Contaminated Land will need to be remediated. Contamination will also be an issue when land is redeveloped. The Planning process will be a major vehicle for obtaining progressive clean up of land contamination. This case study demonstrates how Stockton Borough Council (SBC) has commenced managing its new land contamination responsibilities using a GIS based Land Quality Management database.The new regulatory regime for âContaminated Landâ as defined under Part IIA of the Environmental Protection Act 1990 (to be referred to as the Act), introduced a statutory obligation on all LA to prepare, adopt and publish a written strategy for the identification and remediation of such land by June 2001. The Act also requires each Authority to inspect their area to determine whether any contaminated land is present.The approach required by the regulations is:⢠Prepare a Strategy⢠Carry out a strategic review to identify potentially contaminated areas⢠Inspect individual sites to assess risks⢠Determine whether sites are contaminated land⢠Remediate Contaminated LandTo comply with the requirements of the Act and the Strategy Document, the Council had to undertake a strategic review of all land within its area. This required the collection of a large volume of data. Once gathered, the data had to be assessed to see whether any potential contamination could affect the defined receptors.SBC considered various options and realised that the large volume of data required could be difficult to manage or to use in an efficient manner. GIS was seen as the solution to these issues. Having considered its position, the Council looked into either developing a system in house, or to appoint consultants.Three approaches were considered: 1. Design a software package and input data âIn Houseâ.2. Purchase a basic software package and input data manually themselves.3. Purchasing an existing software package and use external resources.Having carried out preliminary research it was found that several bespoke systems are available from consultants or software providers. As the Council wanted to achieve best value, it undertook an assessment of comparative costs and programmes for preparing a system âIn Houseâ or purchasing a bespoke system. Both time and cost comparisons highlighted the advantages of the bespoke systems. After demonstrations from several suppliers SBC decided to proceed with a GIS based consultancy package provided by the Babtie Group.Babtie Group had developed a methodology for carrying out a strategic inspection to achieve steps 1-5 of the SBC assessment methodology.This methodology uses over one hundred digital datasets to identify areas with historical land uses which may cause contamination, potential pathways and existing receptors. The system adopts established Source-Pathway-Receptor risk assessment principles and applies these using the spatial analytical capabilities of GIS. A model is used to automatically assess the potential for these spatial relationships for the whole LA area at one time. and the system takes recognition of both potentially contaminated sub-areas of land and statutorily recognised human and environmental receptors, while also taking cognisance of environmental pathways i.e. geology. The process adopted automates the assessment methodology by integrating standard GIS proximity analysis techniques into prioritisation and risk assessment algorithmsIn essence, the model outputs a risk-ranked list of potentially contaminated sub-areas to provide SBC with a rationale for focusing resources on detailed inspection of higher-risk sub-areas.Automating the risk assessment process using GIS realised a valuable time saving by reducing to minutes a manual process that may otherwise take months to complete. The system also provided SBC with an auditable system which has become a significant resource for Land management and public information.Scores or âweightingsâ are assigned to potential sources according to their assessed âseverity', pathways according to their likely âefficiencyâ in enabling contaminants to migrate and receptors according to their âsensitivityâ. These scores are then used in the risk assessment algorithm to derive an overall score for each potentially contaminated sub-area. The scores themselves are not an absolute measure of the risk presented by a sub-area, and are intended merely to provide a measure of the relative risk to statutory receptors in comparison to other sub-areas. The primary objective is to provide an internally consistent risk-ranked list of potentially contaminated sub-areas of land. This enables the detailed inspections in a rational, ordered and efficient manner, where sub-areas with the highest likelihood of causing problems can be targeted first.Given the large number and variety of geo-datasets needed to fulfill the requirements of the risk assessment, robust data management is a fundamental part of the process. To achieve this, a comprehensive set of tools was created for ArcView GIS to facilitate data and metadata management. The system is known as Section 57 CoreTools (S57CT) and comprises:⢠ArcView GIS Tools⢠Land Quality Management Database (LQMD)⢠MetadatabaseThe tools include the prioritisation and risk assessment modules for Part IIA work, data selection and management, reporting and mapping and a variety of setup wizards. It also links transparently to the LQMD. Unlike the majority of software solutions available on the market, S57CT provides a comprehensive solution to the LA legislative responsibilities. After risk ranking the whole LA area in a strategic and rational manner, SBC had developed a database to record all relevant information relating to each sub-area.This database is known as the Land Quality Management Database (LQMD) and it is currently populated with information about those sub-areas which have the highest comparative potential to pollute. The LQMD is particularly powerful as it links directly with the GIS and it is therefore essentially an extremely efficient extension to the data storage facilities of the GIS.The LQMD developed for SBC stores a wide and diverse range of information relating to each sub-area. An integral part is also a suite of spreadsheets, based on DoE Industry Profiles, which provide a checklist for each of the contaminants that may be present for a particular industrial use to be investigated.The LQMD developed for SBC allows the following information to be stored for each sub-area:⢠Authorisations⢠Communications⢠Development/post development⢠Ground conditions⢠Other Sourced information⢠Ownership⢠Photographic evidence⢠Planning applications⢠Pollution incidents⢠Priority category assessments⢠Public utilities⢠Site reconnaissance records⢠Remediation details⢠Register Information⢠Risk Assessment reports⢠Site History⢠Site descriptions⢠Site investigation reports⢠Agencies formsA fundamental prerequisite of the legislation is that the data used in the strategic assessment are publicly available and therefore transparent and impartial and auditable. Thus, detailed metadata such as, source, nature, accuracy, extent, intended use, copyright issues, is recorded for all datasets used by the model. The metadatabase is linked with the GIS, such that the user is able to query the metadatabase from the GIS. Stockton-On-Tees Borough Council collected a large amount of data on potential pollution sources, potential pathways and potential receptors and faced the daunting task of analysing this information.The project allowed the strategic review of some 2000 potentially contaminated sites to be carried out using proven methodology within an agreed time scale of 7 months in accordance with Stockton-On-Tees Borough Council's contaminated land strategy.The process described in this paper has produced a prioritised list of sites for further detailed inspection. The preliminary inspection process is underway and all high-risk sites were inspected with data stored in the LQMD.Pictured: LQMD showing sub areas unique reference numbers, links to CLR6 and reporting capabilities-----------------------------------------------Steve Smith, Principal Environmental Health Officer, Stockton-on-Tees Borough Council, [email protected] Harding, Divisional Director, Babtie Group, [email protected] D Gillies, GIS Manager, Babtie Group, [email protected] Jiménez-Ocio, Project Engineer, Babtie Group,

Author: Multiple (source: Babtie Group)

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