Residential development - Part 2A and remediation

GGS provided the following services:

• High resolution ground gas monitoring of sub-floor voids, internal living spaces and boreholes
• Detailed interpretation and risk assessment
• Remediation options appraisal
• Post remediation assessment and residents communication

Background

New homes had been built in 2002 in a former coal mining area. In 2009, the residents of a number of the properties complained to the original developer that they suspected ground-gases were present and affecting their health. Subsequent monitoring identified concentrations of carbon dioxide up to 25,000 ppm within the downstairs living rooms.

A desk study and site records indicated that the properties were constructed with conventional block and beam floors on shallow strip footings. No gas protection measures had been installed. Shallow mine workings had been drilled and grouted.

Investigations

GGS were employed to review available site information, carry out detailed continuous ground-gas monitoring of the sub-floor voids, internal living space and available monitoring wells and carryout a risk assessment with remediation proposals.

High mines gas concentrations, including carbon monoxide were found within the subfloor voids of the affected properties which were attributed to unsealed grout holes which provided a preferential pathway for mines gases to the underside of the affected properties.

Remediation

The affected properties were retrofitted with liquid gas proof membranes, all service entries were sealed. Following remediation further high resolution monitoring was carried out. This demonstrated that the gas hazard had been effectively managed and the risk to residents had been eliminated.