A data-driven approach for simplifying the estimation of time for contaminant plumes to reach their maximum extent.

Globally there exist a very large number of contaminated or possibly contaminated sites where a basic preliminary assessment has not been completed. This is largely, among others, due to limited simple methods/models available for estimating key site quantities such as the maximum plume length, further denoted as L and the corresponding time T=T, at which the plume reaches its maximum extent L=L. An approach to easily obtain an estimate of T in particular is presented in this work. Limited availability of high-quality field data, particularly of T, necessitates the use of synthetic data, which constrains the overall model development works. Taking BIOSCREEN-AT (transient 3D model) as a base model, this work proposes second-order polynomial models, with only two parameters, for estimating L and T. This reformulation of the well established solution significantly reduces data requirement and workload for initial site assessment purposes. A global sensitivity analysis (Morris, 1991), using a large number of random synthetic data, identifies the first-order decay rate constants in the plume λ and at the source γ as dominantly most influential for T. For L, the first-order decay rate constant λ and groundwater velocity v are the two important parameters. The sensitivity analysis also identifies that these parameters non-linearly impact T or L. With this information, the proposed polynomial models (each for L and T) were trained to obtain model coefficients, using a large amount of synthetic data. For verification, the developed models were tested using four datasets comprising over 100 sample sets against the results obtained from BIOSCREEN-AT and the developed BIOSCREEN-AT-based steady-state model. Additionally, the developed models were evaluated against two well documented field sites. The proposed models largely simplify estimation, particularly, of T, for which only very limited field or literature information is available.