Categories of PDL

In order to effectively respond to site opportunities for open space on PDL it is important to recognise that there is a wide variety of site types. 

Categorisation is the first step in the process of deciding potential end uses. Contamination levels are a key guiding point for categorisation of previously developed land (PDL) as this acts as a constraint to potential end uses due to the costs involved.  However it is important to note that not all contaminated land will be legally determined as such.

The Homes and Communities Agency (at the time, 2008, known as English Partnerships) categorised contaminated sites by cost of remediation into four categories, A, B, C and D (these categories are described in detail below).

Where appropriate, we have used this categorisation as it provides distinct groupings of sites, which will generally be recognisable to the practitioner. We have expanded the description of the site types for certain categories to make these distinctions clearer by providing additional examples, covering a wide variety of sites. We have also added a further category, described here as “Residential and light commercial sites such as offices, shops and restaurants,” for the least contaminated sites. These are not covered by the Best Practice Note due to the very low remediation costs involved. However they retain their relevance to this website due to their importance in the urban renewal setting.

It must be noted that presenting these indicative categories is for information purposes only and for use within the approach laid out in this guide. No formal environmental risk assessment is implied or possible from the following information. It is well documented that due to spatial and temporal differences in contamination from sites with similar end uses, contamination levels and risks present following similar land uses can vary greatly. The user of the Guide must take into account the likely differences between sites and overlaps in site categorisation.

A comprehensive environmental risk assessment in line with best practice will be required for any site as to ensure risks to the environmental receptors identified (including human health) are controlled.

This section of the guide explains these five site categories, giving examples. The general assumptions we have made are also explained to assist with recognition.

Residential and light commercial sites such as offices, shops and restaurants

These sites are characterised by low levels of contamination and therefore site remediation costs tend to be low making it relatively quick and easy to remediate. There is unlikely to be a need for wide scale mass soil or groundwater remediation, however the potential remains for isolated hotspots of elevated contaminants due to former uses.

The sites will often be relatively small scale spaces in the vicinity of residential areas with good transport links. Due to location and low remediation costs land values are likely to be high.  In terms of cost saving however, there will likely be a certain amount of reusable inert building material. There is also the potential for production of low volumes of waste which may be suitable for on-site treatment and re-use. Similarly, waste streams from other sites may be suitable for use on site.  However where waste soil is being re-used, the quality and quantity of the material must be given proper consideration as poor quality soil can prevent greening where chemical properties cannot support plant growth or because compaction or removal mean that the physical qualities necessary to support plant life have been damaged.

Industrial sites, mining and mineral spoil heaps, factories and ‘works’

Contamination levels will be dependent on factory type and/or mined material for example. The material on site will likely be a waste which is difficult to re-use. There is the potential for bulk soil and groundwater contamination and contamination hotspots which may impact on receptors.

Site remediation costs tend to be low and land values will also be relatively low. This type of site is likely to have extensive infrastructure which would need to be removed, buried or re-used. Moderate volumes of waste materials (including hazardous waste) may be created, requiring treatment and disposal.

Commercial garages, mining and mineral extraction sites, railways, textiles, timber treatment, former MOD sites and sewage works

Contamination levels will be dependent on the exact use of the site, for example, factory type, but the material on site will likely be a waste which is difficult to re-use. There is the potential for bulk soil and groundwater contamination and contamination hotspots which may impact on receptors. This is also a notable potential for significant risks to be posed to controlled waters by the high levels of contamination. This will require regulatory consultation and large scale remediation is highly likely.

Railways, sewage works and timber treatment plants may have higher extensive ground contamination. Site remediation costs are average but land values usually relatively low. This type of site is likely to have extensive infrastructure which would need to be removed, buried or re-used. Moderate volumes of waste materials (including hazardous waste) may also be created and would require treatment and disposal.

Paints and solvents sites, metals workings, scrap yards, shipyards and inert waste landfill sites

Contamination levels will vary with the type of previous land use but the material on site will likely be a waste which is difficult to re-use, with extensive ground contamination; bulk site soil or groundwater contamination and contamination hotspots are likely. This is also a notable potential for significant risks to be posed to controlled waters by the high levels of contamination. This will require regulatory consultation (Environment Agency along with Local Authority) and the risk that large scale remediation will be required remains. The impacts of remediation works on site neighbours could be significant with a site of this size and contamination levels so careful consideration of works is required.

Due to the high contamination levels, site development is not always viable. However depending on the site location, development values in some cases can and do make re-development an option. The exposure of receptors at the site would be far less with the creation of an open space compared to other more intrusive developments, so remediation requirements would not have to be as stringent.

Site remediation costs are high but land values will be relatively low. This type of site is likely to have extensive infrastructure which would need to be removed, buried or re-used. Moderate volumes of waste materials (including hazardous waste) may also be created and may require treatment and disposal. Inert landfill sites would likely require some form of capping to create usable public space.

Gas, iron and steel works, chemical works, refineries, ship breaking and building and hazardous landfill sites

This type of site will usually be large scale with a relatively low land value.  Site remediation costs are, however, very high due to high levels of contamination. Bulk site soil or groundwater contamination and contamination hotspots are likely. Potential hazardous materials can include asbestos and heavy metals. There are likely to be large steel structures on this type of site and extensive areas of hard standing, both of which could be costly to remove. There is also a notable potential for significant risks to be posed to controlled waters by the high levels of contamination. This will require regulatory consultation and the that risk large scale remediation will be required remains. The impacts of remediation works on site neighbours could be significant with a site of this size and contamination levels so careful consideration of works is required. Moderate volumes of waste materials (including hazardous waste) may also be created and would require treatment and disposal.