Sewage Treatment Works Risk Assessment

Long Reach

Case Study

Thames_Water_logo-400x400We were commissioned by Thames Water to undertake a contaminated land assessment at their Long Reach Sewage Treatment works, in support of a planning application for an extension of the current activated sludge treatment plant.


Our investigation of the site, and subsequent conclusions, allowed Thames Water to move forward with works that were needed to bring the plant in line with compliance requirements imposed by the Environment Agency. Costs were reduced overall through cooperation with Thames Water’s geotechnical engineers, allowing the integration of geotechnical boreholes into environmental monitoring networks.

Thames Water commissioned us to undertake a contaminated land assessment at their Long Reach Sewage Treatment works in Kent, where extension of the activated sludge plant was needed to meet new compliance requirements imposed by the Environment Agency.


The majority of the works were expected to come under ‘permitted development’. However, planning permission was required for the construction of a blower house, a substation and a limed sludge storage building.


The objectives of the contaminated land assessment were to satisfy likely planning conditions for the development, namely to demonstrate that the development is on land which is suitable for use (i.e. as a minimum standard, that it would not constitute contaminated land under Part 2A of the Environmental Protection Act 1990) and that the development would not have an unacceptable impact on the environment, namely controlled waters.


The site is underlain by River Terrace deposits (a minor aquifer) and Chalk (a major aquifer) and is in close proximity to the River Thames.


We conducted a desk study and developed a preliminary conceptual model of potential pollutant linkages at the site. Site investigations were then designed to assess potential pollutant linkages, and to provide targeted information at the locations of the proposed buildings. Cooperation with Thames Water’s geotechnical engineers meant that geotechnical boreholes had been incorporated into environmental monitoring networks, thereby reducing overall costs. We supervised drilling works and taking soil, groundwater and gas samples. The conceptual model was updated based on the site investigation data, and recommendations were made on the need for further risk assessment.