Variable importance rankings for the top 10 variables based on the RF a) GW classification model, b) SW classification model, c) GW concentration model, d) SW concentration model, e) % GW systems in violation model, and f) % SW systems in violation model. The (+) or (−) symbols on the bars mean there was a positive or negative relationship between the predictor and response variables, respectively. And the (− +) symbol indicates there was first a negative then a positive relationship, while a (+ −) symbol indicates there was first a positive then a negative relationship. Cat = catchment; Ws = watershed.