Delineation of Wellhead Protection Areas (WHPAs) is a basic tool for the protection of drinkable groundwater resources. At the present, WHPAs definition is usually carried out according to the backward particle tracking model, a deterministic model based on the concept of the time of travel (TOT); it accounts only of advective mechanism of transport ignoring the hydrodynamic dispersion. The aim of this study is to present a WHPAs method which accounts of dispersion phenomena without requiring too many additional computation, compared with the common backward particle tracking method. For this purpose a backward probabilistic (BP) method, based on the adjoint equation of the classical transport advective-dispersive equation (Neupauer and Wilson, 1999), has been implemented. With only one simulation, for every point of the model domain the probability that a solute particle located in that point will reach the well within the fixed TOT is computed. This result is obtained running a flow model (MODFLOW2000), whose output is opportunely modified, and then a transport model (e.g. MT3D); the transport model variable is not yet a concentration, but a capture probability, that moves backwards along the stream lines and spreads according to contaminant dispersion processes. The backward particle tracking method gives a deterministic perimeter of the WHPA, while the introduction of dispersion phenomena originates a probability map. In this paper the results of the BP model are discussed and compared with the particle tracking results. In particular, the 50% capture probability line and the particle tracking perimeter, which should match, are compared; the size, shape and surface of the areas held by different capture probabilities are calculated at the varying the TOT.

A Backward probabilistic model to calculate well head protection areas / Tosco, TIZIANA ANNA ELISABETTA; Sethi, Rajandrea; DI MOLFETTA, Antonio. - STAMPA. - (2007), pp. 731-737. ((Intervento presentato al convegno International Conference on Water Pollution in natural Porous media at different scales. Assessment of fate, impact and indicators, WAPO2 tenutosi a Barcellona nel 11-13 aprile.

A Backward probabilistic model to calculate well head protection areas

TOSCO, TIZIANA ANNA ELISABETTA;SETHI, RAJANDREA;DI MOLFETTA, Antonio
2007

Abstract

Delineation of Wellhead Protection Areas (WHPAs) is a basic tool for the protection of drinkable groundwater resources. At the present, WHPAs definition is usually carried out according to the backward particle tracking model, a deterministic model based on the concept of the time of travel (TOT); it accounts only of advective mechanism of transport ignoring the hydrodynamic dispersion. The aim of this study is to present a WHPAs method which accounts of dispersion phenomena without requiring too many additional computation, compared with the common backward particle tracking method. For this purpose a backward probabilistic (BP) method, based on the adjoint equation of the classical transport advective-dispersive equation (Neupauer and Wilson, 1999), has been implemented. With only one simulation, for every point of the model domain the probability that a solute particle located in that point will reach the well within the fixed TOT is computed. This result is obtained running a flow model (MODFLOW2000), whose output is opportunely modified, and then a transport model (e.g. MT3D); the transport model variable is not yet a concentration, but a capture probability, that moves backwards along the stream lines and spreads according to contaminant dispersion processes. The backward particle tracking method gives a deterministic perimeter of the WHPA, while the introduction of dispersion phenomena originates a probability map. In this paper the results of the BP model are discussed and compared with the particle tracking results. In particular, the 50% capture probability line and the particle tracking perimeter, which should match, are compared; the size, shape and surface of the areas held by different capture probabilities are calculated at the varying the TOT.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11583/1612146
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