Analyzing Groundwater Quality Data and Contamination Plumes with GWSDAT

Abstract

The main functionalities of GWSDAT include trend analyses, data smoothing, spatiotemporal smoothing, and determination of contamination plume characteristics. Groundwater quality observation data for individual monitoring points can be fitted to a linear or log linear regression model, where the significance of a trend can be determined by using the Mann-Kendall approach, which is widely used for trend detection in groundwater and surface water studies (Bouza-Deaño et al. 2008; Wahlin and Grimvall 2010). Groundwater concentration maps are developed by using a spatiotemporal solute concentration smoother derived from a penalized-splines nonparametric regression (Eilers and Marx 1996). The simultaneous statistical smoothing over space and time generally provides a more accurate, more consistent illustration of a contamination plume when compared against contour maps of individual sampling rounds (Cressie and Wikle 2011). In general, the spatiotemporally smoothed plume will be less biased by missing sampling rounds or missing data within sample rounds (Cressie and Wikle 2011). GWSDAT calculates a number of quantitative plume metrics by using the Ricker (2008) method describing the temporal plume behavior based on the contaminant mass of the plumes, average concentration, plume footprint area, and location of the center of mass. All of these are based on a spatial integration of the plume concentrations above a predefined concentration threshold. Further details on the input and output features of GSWDAT can be found in the supporting information (Appendixes S1 and S2). Additional information on each of the methodologies (including descriptions of the R packages used, but excluding the plume metrics, which are added in the latest version of GWSDAT) can be found in Jones et al. (2014). This work was funded by Shell Global Solutions (UK) Ltd. The views expressed are those of the authors and may not reflect the policy or position of Royal Dutch Shell plc. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.