Project Aims
Following the completion of a Phase 1 Contaminated Land Desk Study and a comprehensive contaminated land risk assessment, it was determined that the site, previously used as a mill, could pose significant contamination risks to the proposed residential development.
Additionally, the site was located in a Coal Authority Development High Risk Area, indicating potential risks from mining subsidence. A preliminary Coal Mining Risk Assessment conducted by IKM highlighted the presence of possible unrecorded historical mine workings beneath the site.
Strategy Employed
To address these challenges comprehensively, IKM Consulting undertook a detailed Phase 2 ground investigation with both geoenvironmental and geotechnical objectives. This included:
- Rotary Cored Boreholes: These identified the suspected historical mine workings, which posed a long-term stability risk. We recommended a programme of grouting to consolidate the workings, ensuring long-term stability to the satisfaction of the Coal Authority.
- Continuous Percussive Boreholes: Soil and groundwater samples were collected to gather site-specific data. Additionally, continuous gas monitors were installed in both shallow wells and the mine workings to assess potential risks from mine gases.
Following the analysis of soil, groundwater, and mine gas data, our contaminated land specialists found elevated concentrations of heavy metals in the soil, presenting a potential risk to human health. Given the significant thickness of made ground, we recommended a capping strategy with clean cover to remove potential pathways to end users. Fortunately, no significant risks were identified regarding the water environment.
A detailed mine gas risk assessment was conducted in line with the 2021 CL guidance, adopting a lines of evidence approach. This assessment ruled out significant risks, thus standard gas protection measures were not necessary. However, as a precaution due to the site’s high-risk nature, we recommended enhanced concrete and preferential sealing of service entries.
