The visualization shows groundwater monitoring data from two observation wells at the Bog of the Ring, plotting water levels over time as a line chart with a brushed time-range selector below. A dashed linear regression trendline appears for the selected period, calculated via the least-squares method in the `Regression.js` module. The implementation uses D3 v5 APIs including `d3.brushX`, `d3.scaleTime`, `d3.scaleLinear`, `d3.nest`, and `d3.line`, rendering to SVG with a categorical color scale to distinguish the two wells. Data is loaded from external CSV files.