Mapping capabilities include amalgamating historical land use maps such as this, circa 1940.

A mixture of busy town centers, urban residential areas, and picturesque villages, Stockton-on-Tees Borough Council (SoTBC) lies in northeastern England. It began as an Anglo-Saxon settlement close to the River Tees. In later times this area became the site of a Norman castle belonging to the Prince Bishops of Durham, and by the 17th century Stockton was established as the main port on the River Tees and had developed an important Baltic trade. It remained a largely agricultural district until the opening of the Stockton and Darlington Railway (the world's first public railway) in 1825, which brought about significant increases in the trade and population of Stockton. This began with the transport of lead from the dales and coal from local mines but later developed to the heavy industries that have left a considerable mark on the country today. These included mineral extraction, brick and tile manufacture, iron and steel manufacturing, shipbuilding, and engineering and chemical works.

The Aftermath

As a result of this long and extensive industrial heritage, there is a considerable legacy of industrial and derelict land within the area. Today, the SoTBC covers 20,400 hectares with a population of approximately 180,000. Projects such as the �350 million Teesdale development have transformed large parts of the council area.

The United Kingdom government policy of limited greenfield site development requires that 60 percent of new urban development be carried out on brownfield (previously developed) sites. Consequently Section 57 of Part IIA of the Environmental Protection Act 1990 (known simply as Section 57) was enacted by the government. This act placed a duty on all British local authorities to take a leading role in managing historical land contamination within their area.

The legislation required strategy preparation, a strategic review of the entire SoTBC area to identify potentially contaminated areas, inspection of individual sites to assess risks, determination of contaminated land sites, and remediation of contaminated land. SoTBC adopted a progressive analysis-driven methodology to identify contaminated land.

Having considered a variety of options, and taking into account the requirements for a "traceable, rational, ordered, and efficient" process by which it could be demonstrated that all land was assessed in a consistent and repeatable manner, SoTBC decided that GIS was the ideal tool for the process. SoTBC assessed various options that were compatible with its corporate ArcView. Babtie Group was commissioned to work in partnership with SoTBC to implement a version of its contaminated land extension (known as Section 57 CoreTools). This methodology used more than 100 digital data sets split into three main groups:

• Areas with historical land uses that may have caused contamination. This would include heavy industries such as shipbuilding and petrochemicals, extractive industries, and any areas of landfill.
• Any potential pathways that may allow contaminants to travel between a contaminated site and a receptor. These typically include surface water, geological strata, and drift geology.
• Existing receptors, which would include anything that would be adversely affected by contaminants. This would not only include humans but also areas of environmental sensitivity.

The Section 57 CoreTools extension adopts established source–pathway–receptor risk assessment principles and applies them using the spatial analytical capabilities of GIS. The incorporated model is used to automatically assess these spatial relationships for the whole SoTBC area at one time.

The process automates the assessment methodology by customizing ArcView to provide a user-friendly application to implement the prioritization and risk assessment algorithms. In essence, the model outputs a risk ranked list of potentially contaminated areas to provide SoTBC with a rationale for focusing resources on detailed inspection of higher risk areas. Scores, or weightings, are assigned to potential sources according to their assessed "severity," pathways according to their likely "efficiency" in enabling contaminants to migrate, and receptors according to their "sensitivity."

These scores are then used in the risk assessment algorithm to derive an overall score for each potentially contaminated area. The scores themselves are not an absolute measure of the risk presented by an area and are intended merely to provide a measure of the relative risk to statutory receptors in comparison to other similar areas. The primary objective is to provide an internally consistent risk ranked list of potentially contaminated areas of land. This enables detailed inspections in a rational, ordered, and efficient manner, where areas with the highest likelihood of causing problems can be targeted first.

Steve Smith, environmental health officer of SoTBC, comments, "Given the complexity of the task, the need for transparency, and the number and variety of geodata sets involved in this project, it was clear that the use of GIS was essential, helping us meet these requirements in a highly effective manner."

Considering the large number and variety of geodata sets needed to fulfill the requirements of the risk assessment, robust data management was a fundamental part of the process. In recognizing this, the Section 57 CoreTools extension comprises

• ArcView tools (data management, modeling, mapping)
• Land quality management database (LQMD)
• Metadatabase

Land Quality Management Database

After risk ranking the whole SoTBC area in a strategic and rational manner, the LQMD was implemented to record all relevant information relating to each potentially contaminated piece of land. The LQMD is populated with information about those areas that have the highest comparative potential to pollute. Since it is directly linked with ArcView shapefiles, the LQMD is an efficient extension to the data storage facilities of the GIS data sets. The reliable integration of ArcView and ODBC compliant databases provides users with a user-friendly map-based interface to their data, rather than their having to access it using less intuitive identifiers.

The LQMD stores a wide and diverse range of information relating to each area. A suite of spreadsheets, based on British Industry Profiles, provides a checklist for each contaminant that might be present for a particular industrial use and should be investigated. The LQMD allows nearly two dozen different types of information to be stored for each area—from agency forms to site investigation reports.

For more information, contact Steve Smith, environmental health officer, Stockton-on-Tees Borough (e-mail: steve.smith@stockton.gov.uk), or Stuart D. Gillies, GIS manager, Babtie Group (e-mail: stuart.gillies@Babtie.com).