Thank you for registering for the AIPG MN Section's Tuesday, January 9th, 2024, technical talk. 

CORRECTION: The AIPG MN January Meeting is on January 9th, 2024, NOT January 2nd, 2024.

Groundwater Age in Southeastern Minnesota

Presented by Jared Trost, Hydrologist, USGS Upper Midwest Water Science Center

Presentation Overview

A measurable chemical ‘signal’ in a groundwater sample from a spring or well from contaminant release or land use change can be delayed years to decades because water moves slowly from the land surface through the groundwater system. Groundwater age refers to the time elapsed since water entered an aquifer system at the water table. A groundwater sample contains a mixture of ages that is described by a groundwater age distribution. Environmental tracer concentrations in groundwater samples are commonly used as a basis for estimating groundwater age distributions in wells, springs, or other groundwater discharge. Common environmental tracers include tritium, helium, chlorofluorocarbons (CFCs), and sulfur hexafluoride (SF6). Environmental tracers were used along with lumped parameter models to estimate groundwater age distributions in 18 samples from wells, piezometers, and springs in southeastern Minnesota. Samples were from the Stewartville Formation, Prairie du Chien Group, Jordan Sandstone, St. Lawrence Formation and Tunnel City Group. The use of multiple environmental tracers enabled more precise quantification of groundwater age compared to the general classifications (e.g. modern, mixed, premodern) interpretable from a single measurement of tritium. Mean groundwater ages ranged from about 30 to 80 years. The “modern” fraction (water that entered groundwater after 1953) of samples varied from 37 to 100 percent. Results suggest that groundwater quality changes from improved practices on land surface may take decades to be observed at the sampling locations in these studies. Groundwater age distributions can help guide reasonable timeframe expectations for when water quality improvements may occur following the implementation of new land management strategies. 

Coauthors: Colin Livdahl (USGS) and Kirsten Faulkner (USGS) 

Collaborators: John Nieber (University of Minnesota), Joe Magner (University of Minnesota), Kevin Keuhner (Minnesota Department of Agriculture), Anthony Runkel (Minnesota Geological Survey), Kim Kaiser (Minnesota Department of Agriculture), and Nikol Ross (Minnesota Department of Agriculture)

Funding: Minnesota Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources, Minnesota Department of Agriculture, and the USGS Water Cooperative Matching Fund.

Biography

Jared Trost is a hydrologist with the USGS Upper Midwest Water Science Center.  He holds a B.A. in biology and chemistry from Augsburg College (2000) in Minneapolis, MN, and an M.S. in Water Resource Science from the University of Minnesota (2010) with a focus on soil hydrology.  He is a scientist with over 20 years of experience leading, managing, and communicating about environmental research topics ranging from plant ecology to groundwater quality.  He has extensive experience at facilitating collaborative research and communication among scientists to enable their scientific success.