Mike Coldrick looks at one local authority's experience in developing a comprehensive geographical information system to produce a strategy to deal with contaminated land.

Local authorities have until 1 July 2001, to produce a strategy on how they are going to deal with contaminated land. The majority will use geographic information systems (GIS) to aid them in this mammoth identification task, but few are sufficiently familiar with the software to take advantage of all it offers. The new regime for the identification and remediation of contaminated land, provided for in Part IIA of the Environmental Protection Act 1990, came into force on 1 April 2000. This was closely followed by a Government announcement that the equivalent of five new towns the size of Southampton are to be built over the next 16 years, much of it on industrial or brownfield land.

The task of identifying contaminated land and approving sites as safe for development usually falls to environmental health departments. Identification of contaminated land involves the study of historical land use and other environmental data, which often stretches back to the mid-to-late 19th century. The data is taken from pre and post-war maps, to a scale of 25 inch and six inch. Typically, the information used for identification will have come from many different sources. It has been estimated that the majority of the 470 authorities required to produce a strategy will meet the July deadline, however many authorities may not be in a position to adequately use the mapping, data sets and GIS systems to deliver it. The task is a huge, logistical one and most departments will not have had to cope with such large volumes of data. The biggest hurdle they face will be in the verification of potentially contaminated sites.

The problem is not the technology. What local authorities need to be able to understand is the constraints of the data and the potential that GIS systems have to dramatically reduce the workload and provide better quality reporting. The main difficulties for local authorities stem from the data itself. In particular the sheer volume of information which has to be processed and filtered, which comes from a wide range of sources. Much of the data may be incomplete, incorrectly formatted, duplicated, or providing different attributes to a given site. This is not the fault of the agencies supplying the information, more that they are working with different data capture processes. An example would be a map showing a piece of land as an old refuse tip which has been used to dump inert material. Another map may show that the site was used to dispose of non-inert household waste. Both sources might be right, but at different times. But, both uses need to be compared, verified and recorded. There is a direct relationship between the variation in the data and the variation in the maps. Maps of different scale will show different information. Maps from different epochs will also show different information. It is, therefore, important to match each source of data with all available maps to verify the site accurately. Bearing in mind that there are 19 courses of appeal, every effort must be made to ensure that the verification process is as thorough as possible.

The system used by Huntingdonshire DC's environmental health services was originally procured for work with home energy efficiency and house conditions. Specific tools have been developed to simplify the use of the system and a number of new features have been added. For example, ordnance survey maps and aerial photographs can be downloaded, sites can be searched using actual addresses or grid references and there is access to comprehensive information including the location of historical buildings dating from 1880 to 1950. Other enhancements have included input and output interfaces for mathematical modelling of air pollution dispersion from transport and industry, and colour coding of energy efficiency ratings for individual properties. The package of tools enables the authority to use the data effectively and assess which sites need to be investigated as a priority. It allows council staff to load the information correctly and ensure the data is properly formatted, easily retrievable and can be compared against all the other data. The ability to filter, compare and check the data quickly, can help to reduce the number of site visits needed, leaving staff time to visit those that are further along the verification process.

According to Adrian Beeching, scientific officer at Huntingdonshire: "Before we had the relevant software, we had to visit the county records office, dredge through old maps and make educated guesses as to what the site had been used for before. This is not acceptable now that there is a requirement for more accurate information to be delivered quicker and on a much larger scale. "Historical maps of the area were scanned in, which was not a straightforward job as the 850 original maps were drawn with different projections. They needed to be stretched, re-shaped and manipulated to fit so that we could overlay historical information on top of current maps and build up a complete picture of a site. Used in conjunction with other environmental data sets from various suppliers, we were then able to get a much clearer picture of the environmental setting of any individual site, and make direct comparisons with what the site is currently being used for."

Now that the council has all this information and the bespoke tools specially developed for its system, it is able to assign a risk ranking to sites depending on historical use and a sensitivity rating for those that might be affected by contamination. If, for example, an area had previously been used as a landfill site it will receive a high risk rating for use as a site for domestic housing. A level of accuracy and detail that was not available before.

Mike Coldrick is head of Cadack BIS, which specialises in systems integration. For more information contact Mike Coldrick on Tel: 0208 543 3411 or visit the Website: www.cadac.co.uk
Readers may be interested in the WHO Environmental Health Pamphlets on contaminated land, as well as town planning and housing issues, available from the publications department for £7.60 each. Tel: 020 7827 5882