Landfill Hydrological Risk Assessment

Case Study

We undertook a site investigation and risk assessment to assess whether the waste in a landfill site posed a risk to Groby Pool in Leicestershire. We established that there was no significant risk posed to groundwater. On the basis of this conclusion, the client submitted an application to the Environment Agency to amend their site permit.

We were commissioned by Waste Recycling Ltd (WRL) to carry out a hydrological risk assessment for a landfill site in Leicestershire. The Environment Agency had imposed conditions within the site permit to maintain groundwater at a lower level compared to natural levels adjacent to the landfill in order to minimise the chances of contamination in the landfill migrating towards Groby Pool. Due to the fact that the landfill is located within low permeability hard rock strata (Diorite), WRL found it difficult to effectively lower groundwater levels. WRL, therefore, required a hydrogeological risk assessment to be undertaken to specifically look at the risk posed to Groby Pool from the wastes present in the landfill and to evaluate whether it was necessary to control groundwater levels.

 

In order to undertake the risk assessment, a site investigation was required to provide the necessary data. A number of boreholes were drilled between the landfill and Groby Pool. These boreholes were cored and geophysical logs run in order to provide information about fissures and fractures within the hard rock strata. The boreholes were completed as groundwater monitoring wells and groundwater level quality data was collected. In addition a surface geophysical survey was undertaken to determine the depth to the Diorite, which is buried beneath a variable depth of Mercia Mudstone at the site.

 

On the basis of the data collected, a detailed conceptual model was developed of possible source – pathway – receptor linkages. A number of potential pathways were identified, through the Mercia Mudstone and fissures present within the Diorite. A detailed quantitative risk assessment was undertaken of these potential linkages using our RAM software. The risk assessment concluded that there was no significant risk to Groby Pool due to the relatively small flux through the Diorite fissures compared to the volume of water in Groby Pool and the fact that Groby Pool was demonstrated to be isolated from the diorite by a thickness of Mercia Mudstone. On this basis, an application was made to the Environment Agency to amend the site permit.