A risk assessment evaluates the potential hazard to human and ecological receptors that may result from release of a contaminant. The risk assessment is a key analysis in making future risk management decisions. The final risk management strategy may be based on the risks associated with each risk management alternative. Project components include:

• Groundwater modelling: Using the hydrogeologic setting information and contamination data gathered under site characterization, Schlumberger Water Services can employ a number of hydrogeologic models to assess the risks and pathways to human and ecological receptors or to identify impacts on natural resources.
• Schlumberger Water Services will select an appropriate model based on the configuration of the groundwater regime in relationship to the plume or source term. Simple sites can be modeled using saturated flow models which are in common use. Hydrogeologic flow in vadose zone conditions will require a different type of model as will flow in non-continuous media such as braided fluvial deposits and fractured bedrock.
• Our technical experts will perform the modeling to evaluate where the subsurface hydrology interfaces with groundwater usage. This determination will be made based on the surface hydrology and well information.

Project Examples:

Title:	Environmental risk assessment of carcass and C&D disposal sites
Location:	England and Wales
Client:	Department for Environment, Food and Rural Affairs
Description:	Following the outbreak of Foot and Mouth Disease in 2001, Schlumberger Water Services undertook retrospective risk assessments of all carcass and ash burial sites in England and Wales, and all cleansing and disinfection (C&D) disposal sites in Wales. A tiered risk assessment methodology was developed and applied to the sites, examining the ongoing risk of contamination of groundwater and surface water. The results were presented in a comprehensive database, and included recommendations for monitoring and remedial action.

Title:	Cryptosporidium risk assessment
Location:	Southern England
Client:	Southern Water Services
Description:	A multi-criteria decision analysis methodology was developed for assessing the risk to public water supply groundwater sources of contamination by Cryptosporidium (a protozoan parasite, the oocysts of which are resistant to most disinfection regimes). The methodology was applied to all Southern Water's groundwater sources, to prioritise action, and to form part of the official submission to the Drinking Water Inspectorate. The methodology has been published (QJEGH, Vol.34, pp187-194, May 2001).