**11. Observations of water levels in test wells in Southeastern Missouri**

The study area is extensively irrigated, with many counties having center pivot, furrow and flood irrigation covering 60–70% of the landscape. Ten wells operated and continuously monitored by the United States Geological Survey (USGS) are located across the survey area [19], which sample groundwater associated in the unconfined surficial (alluvial) aquifers. The depth to the mean water table ranges from 1 to 8 m.

For example, in the community of Delta, Missouri, the USGS water level monitoring well continuously documented well water levels centered around 5–7 m below the land surface (**Figure 2**). During very dry summers, the water levels subsided to approximately 8 m and then the water levels rebounded during the winter/spring season to approximately 4.6 m from the surface. In each year and for each of the test wells, the wetter winter/spring season permitted aquifer recharge because of rainfall infiltration and baseflow.

**Figure 2.** Water depth levels for the Delta Missouri USGS monitoring well from 2000 to 2018 [19].
