A groundwater dating tool is offered that can model baseflow stream loading of nitrogen.

Metolachlor readily degrades to MESA in soil without changing its S and R enantiomeric ratios.

The high solubility and persistence of MESA makes it good for tracing its groundwater transport.

Chiral analyses of MESA in a buffer stream gave a time lag for the switch from rac to S-metolachlor.

By modeling the decay in rac-MESA a groundwater flushing time of 3.8 years was estimated