Hamilton, Ravalli County

Background

Population growth over the past several decades in the Bitterroot Valley has resulted in a conversion of irrigated land to residential development. This has resulted in a higher density of wells and septic systems, thereby increasing the demand for groundwater resources. As the demand on the aquifer increases, questions have arisen regarding the effects on groundwater availability and quality and surface-water resources.

Purpose

The purpose of this project is to provide a detailed investigation, water budget, and conceptual model that can be used to evaluate future land-use changes due to residential development on groundwater quantity. The influence of residential growth and septic systems on groundwater quality was evaluated.

Project Scope

Data collection efforts included monitoring water levels in 59 wells, and flows at 36 surface water and irrigation canal sites, from 2014-2015. Water-quality samples were collected quarterly from select wells to evaluate nitrate concentrations. Water chemistry analyses, including isotopes to assess groundwater/surface-water interactions, were used to evaluate groundwater recharge sources.

Three aquifer tests provided information on properties for the Bitterroot River and Skalkaho Creek alluvial aquifers and the Tertiary sediment aquifer on the benches. A groundwater budget and long-term water-level trends were evaluated.

Results

Groundwater and surface-water budgets for the Hamilton area indicate the Bitterroot River gains water from the groundwater throughout the year. Irrigation-related recharge (including ditch/canal water lost during conveyance and excess water applied to irrigated fields) accounts for about 35% of the inflows to the groundwater system. Analysis on the long-term groundwater-elevation and nitrate-concentration trends show site-specific trends that are related to local aquifer properties rather than regional changes in the groundwater system.

Project Reports

• Groundwater quantity and quality near Hamilton, Montana (Myse, T., and Hanson, A.E.H., 2023)
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Download report (41.3 MB)


• Aquifer tests completed in the Bitterroot Valley, Hamilton, Montana (Myse, T., and Snyder, D., 2021)
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Download report (2.6 MB)

Presentations

• Hydrogeologic Investigation of the Hamilton, Montana Area: Some Preliminary Results. Presentation to the Montana American Water Resources Association (AWRA), October 13, 2022, Butte, Montana.
• The Geologic History and Hydrogeology of Hamilton, Montana. Dean Snyder, Bitterroot College, Hamilton, Montana, April 28, 2017.
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• Investigating Groundwater and Surface-water Interactions Using Stable Water Isotopes in the Bitterroot Valley, Montana. Todd Myse, Bitterroot College, Hamilton, Montana, April 28, 2017.
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Link to Project Data

Data collected for this project can be accessed through the Ground Water Information Center (GWIC) database:

Download project data from GWIC

Content last updated: 5/5/2022 11:14:10 AM