Date of Award
MS Geological Engineering
Beverly K Hartline
This study addressed potential groundwater surface-water interactions along the lower reach of Lolo Creek in Lolo, Montana as part of a larger ongoing study conducted by the Montana Bureau of Mines and Geology (MBMG) Groundwater Investigation Program (GWIP). The GWIP focus is to address the causes of late summer dewatering along the lower reaches of Lolo Creek. This study’s work attempts to: (1) identify gaining/losing reaches along a 6.5 km stretch and (2) test several methods for investigating groundwater and surface-water interactions. The methods included measuring incremental streamflow, hydraulic gradients, one-dimensional temperature profiles, and collection and evaluation of radon-222. Four sites were chosen along a 6.5 km stretch of Lolo Creek for monitoring streamflow and stage in conjunction with a paired shallow piezometer. The piezometers were instrumented with a transducer and two thermistors at different depths. Stream discharges were measured monthly at each site between June and November 2016 and show a gain of 0.028 to 0.11 m3/s (1 to 4 ft3/s) for the uppermost reach, loss of 0.23 m3/s for the second reach, and loss of 0.14 to 0.28 (5 to 10 ft3/s) for the third reach. Hydraulic gradients are negative at each site with the highest values at the downgradient site and the smallest values at the site that is closest to bedrock. Temperature profiles at the two lowest sites show downward conduction of surface water into groundwater with downward fluxes ranging from 0.33 m/day to 0.53 m/day at the second lowest site and 0.55 m/day to 0.85 m/day at the lowest site. The thermographs from the uppermost site show very little downward conduction of surface water with fluxes ranging from 0.05 to 0.09 m/day. Radon-222 sampling show very low concentrations (~10 pCi/L) at the lowest site with elevated concentrations (40-90 pCi/L) between the uppermost site and the second lowest site. A radon box model developed by Cook et al (2003) was used to estimate gas transfer velocity and an average velocity was determined to be 24 cm/hr. All data are available through MBMG’s Ground Water Information Center at www.mbmggwic.mtech.edu (Appendix I).
Chambers, Michael, "SEVERAL METHODS TO ASSESS GROUNDWATER SURFACE-WATER INTERACTIONS IN LOLO CREEK, MONTANA" (2016). Graduate Theses & Non-Theses. 103.