Contaminated Land Phase 1 Desk Study

Approach and Delivery

Following the completion of a Phase 1 Contaminated Land Desk Study, 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 Arthian highlighted the presence of possible unrecorded historical mine workings beneath the site.

Project Outcomes

To address these challenges comprehensively, Arthian 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, we 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.