This visualization shows groundwater monitoring data from EPA wells at the Bog of the Ring, displaying water level measurements as time-series line charts with a brushable overview panel and a bar chart of effective rainfall. Users can brush a date range in the lower chart to filter the main display, which updates the trendline computed via least squares regression and shows the equation. Built with D3 v5, the example uses scaleLinear, scaleTime, brushX, and axis functions for the SVG rendering. The trendline and regression statistics are calculated using a custom leastSquares function.