GasSim is a probabilistic model. This means the uncertainty in particular model parameters can be represented in a model simulation to provide a measure of the effect of the uncertainty of the input parameters in the model outputs. GasSim uses a Monte Carlo simulation technique to select values for parameters in the model by random selection from a user-defined range of potential inputs. This process is repeated many times to give a range of output values. Users are guided via a graphical representation of the conceptual model to enter site specific values into the relevant parts of the model.
Latest features of GasSim 2.5 are:
- Monthly timestep. No other landfill gas model gives this degree of resolution;
- Degradation rates can be changed during the filling of cells or post closure to reflect site conditions;
- Cellular filling, full spatial representation of cells and individual gas plant;
- Cells can be surcharged;
- All gas plant have individual emissions simulated and the facility to turndown flares or engines;
- Automated assessment of atmospheric impacts at Tier 1 (screening), and a fully Environment Agency compliant Tier 2 atmospheric dispersion model based on the USEPA's AERMOD;
- Representation of landfills and landraise landforms;
- Flexibility to simulate adjacent landfills and include or exclude impacts from these, to represent e.g. older non-permitted cells providing fuel for utilisation plant.
GasSim 2.5 outputs can be divided into five sections:
- Gas Generation and Emissions - GasSim 2 determines the quantity of gas generated and fugitive emissions on a cell by cell basis. Cells can exhibit different engineering, and the history of capping, sacrificial gas collection and permanent gas collection systems can be represented.
- Atmospheric Dispersion of fugitive and combustion plant emissions; Tier 1 screening; Tier 2 AERMOD dispersion; and export to Tier 3 models. Flares and gas engines of various designs can be represented.
- Lateral Migration - concentration versus distance graphs for individual cells of different engineering designs;
- Pollution Inventory Reporting for gas emissions;
- Global Impact - the global warming potential of greenhouse gas emissions;