Water Resources Research Act Program

Details for Project ID 2011MT241B

Using 222Rn and Isotopic Tracers to Trace Groundwater-Lake Interactions

Institute: Montana
Year Established: 2011 Start Date: 2011-03-01 End Date: 2013-02-28
Total Federal Funds: $10,622 Total Non-Federal Funds: $34,865

Principal Investigators: Glenn Shaw

Abstract: Traditional well-hydraulic techniques for characterizing groundwater and lake interactions in geologically complex montane catchments can be extremely difficult due to regional and local heterogeneities, including faults, folds, and fractures. In this study, a promising tracer, 222Rn, will be combined with stable isotopes of the water molecule and major chemistry to investigate groundwater and lake interactions in Georgetown Lake, Granite County, Montana. Major chemistry and stable isotopes may be used to determine groundwater inputs and/or evaporation on a whole-lake scale, but 222Rn will be used to investigate groundwater seepage at discrete locations to the lake. Sampling will primarily take place during winter months when the lake is frozen and degassing of 222Rn will be negligible. In order to calibrate the 222Rn mass balance, seepage meters will be installed during summer months in locations where high fluxes of 222Rn are identified. These techniques have never before been combined to investigate groundwater and lake interactions in catchments such as Georgetown Lake. In addition, recent work suggests that nutrient levels are currently elevated in the lake. One possible source of nutrients is leaking septic systems in the relatively developed areas around the lake. In order to determine if groundwater discharging to Georgetown Lake is contaminated by septic effluent, nutrients will be collected in conjunction with other groundwater and lake water samples.