Explanation ENV6

13.27

 The decomposition of material within landfill sites can cause the generation of landfill gas. This gas can migrate in any direction through permeable ground, structures such as drains or even dissolved in water.  Gas can subsequently enter or affect adjacent land or buildings and pose an unacceptable risk to human health, property or ecosystems.  Without control, the accumulation of gas may lead to explosions and fire risk, or to odours and the risk of asphyxiation or toxic effects.  The latter may also affect ecosystems.

13.28

In the event of failure of active gas control measures an unacceptable risk would be presented to property. Gas monitors used to back up such systems may also fail. In the event of such failures there would be a very high risk of a serious incident. It is therefore the Council’s policy not to permit residential development where site conditions are such as to require active gas control measures. This approach is in line with guidance (see footnotes ¹⁸ and ¹⁹)

Procedures

13.29

Article 10 of the Town and Country Planning (General Development Procedure) Order 1995 requires the Council to consult with the Waste Regulation Authority (now the Environment Agency) before granting planning permission for development within 250 metres of land which:

a)  Is or has, at any time in the 30 years prior to the submission of the application, been used for the deposit of refuse or waste; or

b)  Is or has been notified to the Council by the Waste Regulation Authority for the purposes of this provision.

13.30

The Environment Agency maintains a publicly available register of former landfill sites, and notifies Knowsley Council of sites within the Borough. The statutory distance where consultation is required (250 metres) is a minimum, and the Council may consult the Environment Agency about suspect sites outside the consultation zone. The Council will consult closely with the Environment Agency at all stages of an application, as advised in Department of the Environment Circular 17/89.

13.31

It is the developer’s responsibility to supply the following information if required:

i)  A site investigation report containing information on the nature and extent of landfill gas and any other harmful mobile substances;

i)  A site specific risk assessment for gas;

iii)  A schedule of any remedial measures that are necessary to prevent migrating gas or other harmful substances causing a hazard either during the course of development or during the subsequent use of the site;

iv)  Where remedial measures are put in place a verification report; and

v)  Where appropriate, evidence that adequate provision has been made for the continued monitoring of gas on site.

13.32

Planning conditions or legal agreements will be used to ensure that appropriate measures are incorporated into proposals to control the migration of gas or other mobile substances and to monitor and if necessary remediate any potential problems following development.

¹⁸ Building Regulations 2000, Approved Document C “Site Preparation and Resistance to Moisture

¹⁹ BR212 “Construction of New Building on Gas Contaminated Land” Building Research Establishment

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