This line chart shows groundwater monitoring data from two EPA wells at Bog of the Ring, plotting water levels over time with an optional linear regression trendline. The visualization uses a linked-brush interaction, where selecting a date range in the smaller brush chart filters the main chart's time axis. Built with D3 v5, it employs `brushX` for brushing, `scaleTime` and `scaleLinear` for axes, and `nest` to group data by well. Data is loaded from CSV files using D3's `csv` function, and the regression calculation uses `leastSquares` from the custom `Regression` module.