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Applying the Monte Carlo Method to wastewater emissions to rivers


Currently the EPA is reviewing many IPPC licenses as a result of changes in ambient quality standards associated with SI 272 – European Communities Environmental Objectives (Surface Waters) Regulations 2009.

EPA guidance in relation to the assessment of emissions is to apply a simple mass balance technique, usually involving 95 %ile flows in the river and maximum emissions based on emission limit values as specified in the IPPC licence. This is a very conservative approach but if it shows that the emission is not having a negative impact then all is well.

However in many cases this conservative approach will throw up problems and another approach is required to adequately model the emission.

One such approach is the Monte Carlo simulation, used by regulators such as SEPA (Scottish EPA). As the environmental quality standards are expressed as %iles then its appropriate to take into account variations in river and effluent flow, and river and effluent concentrations over time. The Monte Carlo simulation models this variation and allows for a more accurate assessment of impact.

For further information please contact Gerard Kelly at 058-51155.