This example visualizes EPA groundwater monitoring data for two observation wells at the Bog of the Ring using D3 v5 with SVG rendering. A main line chart displays water levels over time with an ordinal color scale and legend, while a smaller brush chart below allows users to select a date range. The brushed region updates the main chart’s x-axis domain and fits a least-squares regression trendline with its equation shown. Data is loaded from CSV files, parsed with d3.timeParse, and the chart uses d3.brushX, d3.line, d3.nest, and d3.scaleTime.