Spatial evaluation of the risk of groundwater quality degradation. A comparison between disjunctive kriging and geostatistical simulation |
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Authors: | E Barca G Passarella |
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Institution: | (1) Water Research Institute, IRSA – CNR, National Research Council, via F. De Blasio, 5, 70123 Bari, Italy |
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Abstract: | In some previous papers a probabilistic methodology was introduced to estimate a spatial index of risk of groundwater quality
degradation, defined as the conditional probability of exceeding assigned thresholds of concentration of a generic chemical
sampled in the studied water system. A crucial stage of this methodology was the use of geostatistical techniques to provide
an estimation of the above-mentioned probability in a number of selected points by crossing spatial and temporal information.
In this work, spatial risk values were obtained using alternatively stochastic conditional simulation and disjunctive kriging.
A comparison between the resulting two sets of spatial risks, based on global and local statistical tests, showed that they
do not come from the same statistical population and, consequently, they cannot be viewed as equivalent in a statistical sense.
At a first glance, geostatistical conditional simulation may appear to represent the spatial variability of the phenomenon
more effectively, as the latter tends to be smoothed by DK. However, a close examination of real case study results suggests
that disjunctive kriging is more effective than simulation in estimating the spatial risk of groundwater quality degradation.
In the study case, the potentially ‘harmful event’ considered, threatening a natural ‘vulnerable groundwater system,’ is fertilizer
and manure application. |
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Keywords: | Groundwater Disjunctive kriging Geostatistical simulation Risk assessment |
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