Home Water & Environment GWIP
GWIP Overview GWIP Project Summaries GWIP Project Map Reports How To Nominate a GWIP Project

Flathead Valley, Flathead and Lake Counties

Well discharge during an aquifer test of the deep sand and gravel aquifer.

Background

The Flathead Valley deep alluvial aquifer underlies the valley bottom from the north shore of Flathead Lake to near Whitefish and Columbia Falls. This is the most productive aquifer in the valley, supplying high-capacity municipal and irrigation wells in addition to thousands of domestic wells. The deep alluvial aquifer is a thick, unconsolidated, confined aquifer composed of gravel and sand. It is overlain by a confining unit of glacial till and lake sediments. The top of the aquifer lies 100 to over 790 feet below the land surface. Land use in the valley has historically been agricultural with an emphasis on irrigated crops, many of which require high volumes of water. The population in the Kalispell Valley has increased 180% during the past several decades. Between 1960-2014, the number of domestic water wells increased approximately 450% and high-volume irrigation and public water supply wells increased 310% during this same period.

Purpose

The research concerns were to determine: 1) whether withdrawals from the deep alluvial aquifer affect surface-water resources; and 2) if current stresses were creating declining water-level trends.

Project Scope

A network of 96 wells and 12 surface-water sites were monitored from 2010 through 2013 to obtain water levels, water-quality and streamflow information. Eleven wells were installed as part of this project. Aquifer tests conducted at three locations evaluated site-specific characteristics of the deep alluvial aquifer and the confining unit. Results from 95 aquifer tests previously conducted in the valley were compiled and included in the analyses for this project. A 3-dimensional geologic model of the subsurface stratigraphy was developed with an emphasis on the character of the confining unit.

Results

Water can move vertically through the confining unit, but extremely slowly, due to its low hydraulic conductivity. Therefore, throughout much of the valley, withdrawals from the deep aquifer are unlikely to directly affect surface-water sources. Long-term (1996–2017) monitoring of groundwater elevations in the western and southern portions of the focus area generally shows statistically significant decreases; with no statistical decline in the amount of precipitation during this period, pumping from the deep aquifer likely causes these groundwater-level declines. In the northern and eastern areas, there are no statistically significant increasing or decreasing trends; proximity to recharge may explain the relatively stable water levels in these areas.

Project Reports

Presentations

  • Thickness of the Deep Aquifer and Character of the Underlying sediments in the Flathead Valley. Presentation to the Montana American Water Resources Association (AWRA), October 13, 2022, Butte, Montana.

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: 11/17/2022 12:58:23 PM

Program Resources

Program Fact Sheet

GWIP Project Summaries

GWIP Project Map

Contact Information

Program Information

Ginette Abdo, GWIP Manager
(406) 496-4152 | Email

Office locations in Butte and Billings