Stochastic determination of the Wierden (Netherlands) capture zones

A spatial stochastic approach was adopted to estimate the capture zones of a wellfield in eastern Netherlands near the town of Wierden. The main sourc es of uncertainty were found to be the hydraulic conductivity of the produc tion aquifer and the spatial distribution and thickness of an impeding clay layer situated above the production aquifer, Both were modeled as random s pace functions and a Monte Carlo analysis was performed to assess the proba bility distributions of the capture zones for t = 25 years and t --> infini ty. The distributions were compared with two deterministic capture zones to show how the stochastic approach preserves the discontinuous character of the impeding clay layer while the deterministic approach smooths out the di scontinuities. Furthermore, it is shown how the stochastic approach reveals the uncertainty about the location of the capture zones while the determin istic approach obscures it.