Aquifer vulnerability

Default categories

The suggested criteria derive from the input factors of established index methods such as DRASTIC and fall into two categories: the protection above the water table and the conditions that govern contaminant transport. The criteria are suggested inputs, not a pre-configured index; ratings and weights are defined by the user. These default categories can be renamed or removed by the user, and new categories can be added.

The criteria library is maintained continuously. In each project, criteria can be added, removed or renamed.

Vulnerability concepts

The concept represented by the map depends on the selected criteria. The suggested criteria describe intrinsic vulnerability; contaminant properties and pollution sources can be added as further categories.

Index methods

Published index methods differ in the aquifer type they address and in the factors they combine. Their factors can be set up as criteria in a project, with the method’s ratings entered as class scores and its weights as analyst weights.

Method	Aquifer type	Factors	Source
DRASTIC	Porous and fractured	Depth to water, net recharge, aquifer media, soil media, topography, impact of the vadose zone, hydraulic conductivity	Aller et al. (1987)
GOD	All types, data-scarce settings	Groundwater confinement, overlying strata, depth to groundwater	Foster (1987)
SINTACS	Porous and fractured	Seven DRASTIC-type factors, with weight sets for different hydrogeological settings	Civita (1994)
AVI	Porous	Hydraulic resistance of the layers above the aquifer, from their thickness and hydraulic conductivity	Van Stempvoort et al. (1993)
EPIK	Karst	Epikarst, protective cover, infiltration conditions, karst network development	Doerfliger et al. (1999)
PI	Karst and other aquifers	Protective cover, infiltration conditions	Goldscheider et al. (2000)
COP	Karst	Concentration of flow, overlying layers, precipitation	Vías et al. (2006)
IKAV	Karst	Potential vulnerability from rated factors; actual vulnerability from contaminant transport modelling	Moreno-Gómez et al. (2022)

Constraints

Vulnerability maps usually cover the whole study area. Constraints serve to mask areas outside the extent of the assessed aquifer or areas without data; the application suggests none.

From criteria to vulnerability

1. CriteriaStandardised so that high scores consistently mean high vulnerability
2. Category mapsWeights within each category give its vulnerability map
3. Vulnerability mapWeights between the categories combine the category maps
4. Priority areasContiguous areas of very high vulnerability in which no criterion falls below a minimum value

The direction of each criterion usually follows from its role in the contaminant pathway: a shallow water table, permeable soils and high recharge increase vulnerability, while a thick, fine-grained unsaturated zone decreases it. Weights come from the analytic hierarchy process, ranking, rating, the multi-influencing factor method or an anonymous stakeholder survey.

Results

The result classes rank the locations within the study area by their relative vulnerability; they do not predict contaminant concentrations or travel times.

Sensitivity analysis shows which areas keep their class when the weights change. Validation against observed groundwater quality, such as nitrate concentrations in monitoring wells, will follow in a later version.

Typical questions

• Where is the aquifer least protected by the overlying soil and unsaturated zone?
• Which wellfields and springs lie in areas of high vulnerability?
• Where should new monitoring wells be placed?
• How does vulnerability change between seasonal high and low water tables?

Case stories

No case stories for this application yet.

References

• Aller, L., Bennett, T., Lehr, J.H., Petty, R.J., Hackett, G. (1987). DRASTIC: A standardized system for evaluating ground water pollution potential using hydrogeologic settings. EPA/600/2-87/035. US Environmental Protection Agency, Ada, Oklahoma.
• Foster, S.S.D. (1987). Fundamental concepts in aquifer vulnerability, pollution risk and protection strategy. In: van Duijvenbooden, W., van Waegeningh, H.G. (eds.), Vulnerability of Soil and Groundwater to Pollutants. TNO Committee on Hydrological Research, Proceedings and Information 38, 69–86.
• Machiwal, D., Jha, M.K., Singh, V.P., Mohan, C. (2018). Assessment and mapping of groundwater vulnerability to pollution: Current status and challenges. Earth-Science Reviews 185, 901–927. doi:10.1016/j.earscirev.2018.08.009
• Moreno-Gómez, M., Martínez-Salvador, C., Moulahoum, A.-W., Liedl, R., Stefan, C., Pacheco, J. (2019). First steps into an integrated karst aquifer vulnerability approach (IKAV). Intrinsic groundwater vulnerability analysis of the Yucatan karst, Mexico. Water 11(8), 1610. doi:10.3390/w11081610
• Moreno-Gómez, M., Martínez-Salvador, C., Liedl, R., Stefan, C., Pacheco, J. (2022). First application of the Integrated Karst Aquifer Vulnerability (IKAV) method – potential and actual vulnerability in Yucatán, Mexico. Natural Hazards and Earth System Sciences 22, 1591–1608. doi:10.5194/nhess-22-1591-2022
• Vrba, J., Zaporozec, A. (eds.) (1994). Guidebook on Mapping Groundwater Vulnerability. International Contributions to Hydrogeology 16. Heise, Hannover.