BMT Cordah were commissioned by the Singapore Office of the American Bureau of Shipping (ABS), to undertake a Quantitative Environmental Risk Assessment to determine the risk posed by a newly-installed buried aviation fuel pipeline within a military facility. The site was positioned adjacent to a large reservoir in Singapore and any uncontrolled release from the pipeline network into this surface water receptor, would have represented a ‘national incident’.
The study was completed using a logical, staged approach which included the following activities:
Stage 1 – Initial site visit, meetings and collection of data.
Stage 2 – Construction of a Site Conceptual Model (CSM) to identify potential release points (sources), ways in which contamination could migrate away from such areas (pathways) and the exact position of the reservoir (receptors).
Stage 3 – Design of a site investigation to determine the type of lithology and permeability within strata below ground, so that the rate of contaminant transport could be determined.
Stage 4 – Quantitative Risk Assessment for (1) Groundwater migration along local hydrogeologic gradients; and (2) Drainage Risk Assessment associated with rapid transport through the surface drainage network which discharges rainwater into the reservoir.
Stage 5 – Report writing and in-country presentation.
During the study, the Emergency Response Plan (ERP) for fuel releases was reviewed along with the position and operation of surface water drainage emergency shut-off valves. Following communication with the client, environmental issues associated with the temporary storage of fire water following a emergency incident, was incorporated into the wider study.
The Groundwater QRA was undertaken using specialist modelling software (ConSim) which considers contaminant mobilisation and transport within geological strata. The model uses a probabilistic methodology to permit data uncertainty to be integrated within the analysis, so that the results of the assessment are both rational and consistent. ConSim modelling software is commonly used as a decision making tool, in order to identify the range and nature of mitigation measures that should be employed to provide adequate protection of environmental receptors. Geochemical characteristics of the aviation fuel were incorporated into the model, so that adsorption potential to clay particles and organic matter could be included, along with degradation and water solubility characteristics.
The Conclusions of the study were presented in the form of a priority-based, tabulated set of additional mitigation measures required.
Risks associated with operation of the surface water drainage network were assessed using a combination of Excel-based calculations and a generic risk assessment methodology.