Due diligence and gas contaminant linkage assessment

• High-resolution gas sweep survey
• In-depth walkover
• GGS DataPack Plus Report

This light industrial business park required a high-resolution gas sweep survey and detailed walkover to identify potential gas contaminant linkages whilst providing an evaluation of the installed gas protection system.

The site was understood to be located on formally infilled ground. As part of the development design, gas protection measures were incorporated into the construction of the units. Details of the installed protection measures were not clearly documented; however, gas protection included a form of passive venting and alarm system.

Following 20 years of occupation, there were no records of inspection or maintenance of the installed gas protection measures and alarm system. The site was transferred to new ownership/management and concerns were raised as to the effectiveness of the installed gas protection measures, and to whether it was still relevant considering potential changes to the underlying gas regime overtime.

A period of detailed monitoring and assessment was undertaken to investigate the current ground gas regime and effectiveness of the protection measures. Subsequently, it was established that the passive venting measures and alarm system were likely to no longer to be effective, and that they were also no longer required. As such, these measures could be decommissioned, as opposed to being overhauled or upgraded at significant cost and disruption.

Following the decommission of the above ground gas protection system, the client requested that GGS attend site to undertake a high-resolution gas sweep survey and detailed walkover to identify any potential residual contaminant linkage. One key concern was that removal of the system may have disturbed potential ground gas migratory pathways below.

Experienced GGS specialists mobilised to site to undertake the detailed site walkover and survey. GGS methodically surveyed the site using handheld instruments to record methane and carbon dioxide concentrations to parts per million by volume level (ppmv). Particular attention was given to discrete features which may provide a preferential pathway for ground gases, such as service entry points and defects in the slab, or areas where ground gases my accumulate, such a small cupboard space. Alongside measured gas concentrations, GGS recorded all observations pertinent to ground gas on a proforma record sheet.

Following completion of the site visit, GGS provided the client with a DataPack Plus report containing the formalised gas sweep survey records, summary of results and observations, methodologies, calibration certificates, site photographs and a short technical commentary with recommendations.

The detailed GGS high resolution gas sweep survey and concise GGS DataPack Plus Report, provided the client with assurance that there were no unacceptable gas contaminant linkage and that all ongoing liabilities pertaining to ground gas were suitably managed.