MONITORING MONTANA: GROUND-WATER ASSESSMENT'S STATEWIDE WATER-LEVEL MONITORING NETWORK
Dedicated or unused wells compose about 30 percent of the network and the remainder are low-use stock and domestic wells. There are 95 water-level recorders located on dedicated or unused wells. MBMG operates the network but has cooperative agreements with the U.S. Geological Survey (USGS), The Lewis and Clark County Water Quality Protection District, the Missoula Valley Water Quality District and the Geology Department at Montana State University. In addition to water-levels, about 70 water samples for inorganic chemistry are collected annually.
Montanas geology adds complexity to the network. Intermontaine basins in western Montana are treated as individual hydrogeologic units and network wells are grouped within the basins. Within each valley, ground-water flow maps were used to help locate monitoring wells in up-gradient, mid-gradient, and down-gradient parts of each aquifer. In the eastern two thirds of the state, network wells are along major alluvial valleys and distributed across regional aquifers such as the Tertiary Fort Union Formation, the Fox Hills-Hell Creek Aquifer, and the Madison Limestone. Other factors affecting the locations of network wells are the overall distribution of production wells and the need for the water-level data.
Water-level data are posted on Montanas Ground-Water Information Center (GWIC) web site, usually within a few days of collection. Viewers can examine on-line hydrographs, and can download water-levels, associated well-completion data, and water-quality results to spreadsheets for in-depth analysis.