The human and financial resource realities present in most developing cities suggest that a risk assessment approach can be a cost-effective and practical way to inform those tasked with formulating policies in an aquifer protection plan. In this project we employed, as practical examples of good practice, the approach from Foster & Hirata (1988), which uses the interaction between hazard from contaminant load and aquifer vulnerability to determine the risk of pollutants reaching the aquifer.
For the purposes of developing groundwater protection and management policies, the main aids to visualisation of the assessments of aquifer vulnerability and contaminant load are maps. They feed into an Action Plan typically through a two-stage process: a technical stage, compiling and interpreting available information to produce practical but technically defensible assessments, and a policy evolution stage, in which draft(s) of policy options developed from consideration of the results of the technical stage are discussed and added to by informed stakeholders.
A number of maps inform the process:
• A groundwater vulnerability map (GVM) describes the intrinsic properties of the subsurface that will either protect, or make susceptible, the groundwater system to contamination from urban activities;
• A potentially hazardous activities map (PHAM) is a first-pass approximation to an inventory and is used in conjunction with waste disposal patterns to infer nature and likely type of contaminant loading which are potentially hazardous to groundwater;
• A 'hot-spot' map comprises the superposition of the first two maps as layers, to show where inappropriate activities are currently taking place, providing a present contamination hazard, or where unplanned expansion could prejudice the resource in future;
• A groundwater resource protection/planning map (GRPM) considers the features of the aquifer vulnerability and the potentially hazardous activities component maps in the context of the city's expansion, regulatory framework and enforcement and water resource realities;
• The GRPM is a map intended for policy-making purposes and needs to be both simple and amenable to use with planning policies that may be enacted through regulatory, financial or other policy instruments.
The use of these maps in the risk assessment procedures is described.
Groundwater Management Action Plan. Stage 3. Strategy Definition. Characterising and prioritising groundwater pollution threats - pollution risk assessments.