London Borough Council, South London 1

London Borough Council, South London - London

Mayer was commissioned to investigate selected residential gardens in an area of South London on behalf of the local council. The investigation was designed to assist the council in deciding whether the gardens could be determined as contaminated land under Part 2A of the Environmental Protection Act 1990.

Historically, the area had housed a number of potentially contaminative industries including a motor garage, coach-building facility, stables and general engineering works.

We used information from a previous investigation undertaken by a different consultancy to determine which gardens required further examination. The investigation  involved taking near-surface samples in areas identified as containing elevated levels of arsenic, lead and benzo(a)pyrene.

Mayer attended those gardens identified as containing potentially significant levels of contaminants, and took several additional near-surface samples by hand. We worked closely with the local authority at every stage, in order to ensure work was completed as quickly and efficiently as possible, with minimal disruption to residents.

The Mayer solution

A phased approach to the risk assessment was undertaken to determine the significance of the contaminants detected.

Initially, a qualitative risk assessment was undertaken comparing the values detected to published soil guideline values (SGVs). Where these were not available, in-house derived assessment criteria values were used instead.

A number of properties displayed levels of arsenic and benzo(a)pyrene above the relevant SGVs and ACVs. Statistical analysis was undertaken on the data from these properties.

The statistical analysis established that arsenic and benzo(a)pyrene remained an issue in a small number of properties. A detailed quantitative risk assessment (DQRA) was undertaken for the benzo(a)pyrene levels identified, using the Contaminated Land Exposure Assessment (CLEA) model based on site-specific information.

Physiologically Based Extraction Technique (PBET) analysis was undertaken on samples with elevated arsenic concentrations to determine the bio-accessible fraction of the arsenic present. The bio-accessible fraction data was then used within the CLEA model to generate a site-specific criteria value for arsenic.

The DQRAs undertaken eliminated a number of properties, as they did not contain significant levels of contaminants.

Additional sampling was undertaken around the small number of properties where contaminant ‘hotspots’ were considered to be present.

The data from this sampling, together with all previous data and information, was presented to the Health Protection Agency (HPA) by the council, for additional advice on potential levels of contaminants that may cause significant risk to residents.

The properties were subsequently determined as not containing levels of contaminants that would pose a significant risk to residents. The council was therefore not required to determine the site under Part 2A of the Environmental Protection Act 1990.

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