In 2005, the Cornerstone Estates subdivision was proposed (0.4 acres per dwelling) in the Scratchgravel Hills area. Because of ongoing development, in particular the proposal for the Cornerstone Estates subdivision, people living near and within the Scratchgravel Hills became concerned about the long-term capacity of area aquifers to supply water and the potential for septic effluent to contaminate these aquifers. The Montana Department of Natural Resources and Conservation responded to citizen concerns by establishing the Green Meadow Temporary Controlled Groundwater Area in April 2008.
The Scratchgravel Hills GWIP investigation evaluates the sustainability of current and future groundwater supply and the potential for septic effluent to impact groundwater quality.
A network of 67 wells, 7 springs, and 18 surface-water sites established to obtain groundwater level, flow, stage, and water-quality information were monitored from February 2010 to June 2011. Synoptic water-quality sampling events were conducted in April, August, and October 2010. Selected wells were sampled in April 2011 to test for common endocrine-disrupting chemicals. Groundwater monitoring wells were drilled in 10 areas. Six aquifer tests provided additional information on aquifer properties and flow boundaries. A water budget was developed and numerical groundwater models were constructed, calibrated, and used to test residential development scenarios.
Unconsolidated materials can produce significant volumes of water, but fractured bedrock units do not always have the ability to supply sufficient water. Some wells pumping at rates that exceed the local aquifer’s capacity caused water levels to decline over time; however, these wells are isolated and area-wide groundwater depletion is not occurring. Groundwater modeling indicates that if bedrock aquifers were used to supply water to high-density subdivisions, noticeable groundwater-level declines would likely occur.
For this study, groundwater samples were collected from 25 wells. Drinking water standards were exceeded for nitrate (3 sites), arsenic (1 site), and uranium (1 site). Septic effluent appears to be the cause of increased nitrate concentrations. Elevated arsenic and uranium concentrations are associated with alteration zones near the Bald Butte Fault and are adjacent to igneous intrusions.
Download Report (19 MB)
Download Report (12.8 MB)
Download Scenario 1 (243.6 MB)
Download Scenario 2 (243.9 MB)
Download Scenario 3 (261.6 MB)
Download Scenario 4 (263.2)
Download Steady State modeling files (5.2 MB)
Download transient modeling files (17.6 MB)
Download Model Maps zip file (161.2 MB)
Download Report (14.8 MB)
Data collected for this project can be accessed through the Ground Water Information Center (GWIC) database:
Download project data from GWIC
Content last updated: 2/11/2022 1:18:26 PM
Program Resources
Contact Information
Program Information
Ginette Abdo, GWIP Manager
(406) 496-4152 | Email