Using Advective Transport Phenomena to Account for Uncertainty of Conductivity in Monitoring Design

Engineering practice in monitoring design aims at the optimum number of observation wells needed to assess the growth of a contaminated volume groundwater, the plume. Available methodologies rely on a combination of a numerical groundwater transport model, GIS-techniques and an optimization technique and require a relative huge amount of data and computer resources. The method of advective transport phenomena enables to calculate the longitudinal and vertical growth of a contaminant plume along the flow path by simple analytic expressions using only three stochastic parameters, the log conductivity variance and the horizontal and vertical characteristic lengths, that together describe the heterogeneity of the aquifer. In previous work, the calculated plume growth has been verified in 12 large experiments all over the world. The method is used to investigate the relationship between uncertainty in the conductivity variation and the plume growth by calculation of the spreading of water particles in a vertical section along the traveled path. In a very heterogeneous aquifer, virtually all water particles spread forward about equally generating a limited forward growth compared to the traveled distance that is not sensitive to uncertainty in the conductivity. In a nearly homogenous aquifer, only a part of the water particles is spread forward, which is repeated at different depths along the traveled path causing significant uncertainty in the position and length of the plume growth. Therefore, an observation network should be designed more densely in a homogeneous aquifer than in a heterogeneous one. A calculation tool is provided.