Ground Gas & Vapour
The Site comprises a light industrial warehouse development located down gradient of a former large metal tube works.
Though the Site itself does not have a history of significant contaminated land uses, the former tube works was known to have released trichloroethene (TCE) into the ground with a resulting plume migrating towards the Site. Limited remedial works are understood to have been undertaken to mitigate risks to surface water receptors.
In order to support the divestment of the Site, Delta-Simons undertook groundwater sampling to assess the potential impact on the Site from the off-site source. This expanded to include soil gas vapour assessment and internal vapour monitoring due to the findings of the groundwater sampling indicating an increase in concentrations associated with off-Site demolition and redevelopment works.
Scope of Works
Delta-Simons' role in the project included:
▲ Review of existing ground investigation data relating to the Site and off-Site sources;
▲ Low flow groundwater sampling;
▲ Installation of soil gas monitoring wells and vapour sampling using evacuated vacuum canisters;
▲ Passive soil and indoor air diffusion tube sampling;
▲ Detailed Quantitative Risk Assessment (DQRA) to assess potential risks to human health;
▲ Support to the wider project team to support the marketing of the asset for divestment.
Outcomes / Client Benefit
The monitoring works provided sufficient clarity to demonstrate that a spike in groundwater concentrations recorded on-Site was associated with short term ground disturbance during the clearance and preparatory earthworks associated with the redevelopment of the off-site former tube works. The vapour and air monitoring DQRA confirmed that the worst-case groundwater concentrations did not represent a risk to human health through vapour inhalation. Longer term monitoring confirmed that groundwater concentrations reduced following completion of the off-Site works to steady baseline levels.
Through a period of regular groundwater monitoring and periodic vapour sampling, the team were able to demonstrate that the off-Site source of contamination did not present a significant risk to human health in the context of the current commercial development or a long term impact on the value of the asset, thereby facilitating the divestment of the Site without significant reduction in value. Following the completion of the asset transfer, Delta-Simons were retained to continue the monitoring programme by the new owners to provide an extended period of monitoring.