Graduation Year

2020

Graduation Month

May

Document Type

Thesis

Degree Name

Bachelor of Science

School or Department

Geosciences

Major

Geosciences

Faculty Mentor

W. Payton Gardner

Faculty Mentor Department

Geosciences

Keywords

groundwater, hydrology, radon, Missoula Valley Aquifer, Clark Fork River

Subject Categories

Geology | Hydrology

Abstract

Radon-222 (222Rn) was measured along 8.7 kilometers of the Clark Fork River, between Harper’s Bridge and Frenchtown, MT. Twelve water samples were taken along the stretch. Samples 1 through 4 and 10 through 12 were collected on a 1 km interval, samples 5 through 9 were taken on a 500 meter interval. Samples were analyzed for dissolved 222Rn using a RAD7 spectral alpha decay detector. Instream 222Rn was modeled to quantify groundwater discharge to the river. Literature on the Missoula Valley aquifer was analyzed, revealing an alluvial aquifer system to the east consisting of interbedded gravel, sand, silt, and clay. To the west, bedrock rises steeply from underneath the river to crop out at the surface. Analysis of the samples reveals that there are measurable quantities of 222 Rn through the entire stretch sampled, starting at 395 mBq/L near Harper’s bridge, with peaks of 950 mBq/L at 2 km and 632 mBq/L at 6.5 km. Lowest concentrations were 395 mBq/L at the start of sampling, 355 mBq/L at 4.3 km, and 336 mBq/L at 8.7 km. Modeling results averaged to 5.5×105 m3/day of groundwater entering the river, with a standard deviation of 1.2×105 m3/day, occurring in areas of high 222Rn activity. This work identifies and quantifies the spatial distribution of groundwater discharge at the west end of the Missoula Valley postulated by previous works.

Honors College Research Project

No

GLI Capstone Project

no

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© Copyright 2020 Daniel William Forsland