Groundwater Depletion

What is Groundwater?
To understand more about what groundwater is and how it works, check out this YouTube video:

Aquifers in the Helena Area:
There are three main aquifers that we pull from for water in the Helena area:

  • Tertiary Aquifers: limited yields and recharge. Water quality is generally poor, with high levels of dissolved solids
  • Bedrock Aquifers: generally good but variable yields, with primary recharge from snow melt infiltration. Water quality varies, but generally is good with low dissolved solids.
  • The Helena Valley Aquifer: high yields, and shallow depths to ground water, with recharge from streams and irrigation waters. Generally good water quality.

  • To view more details on the Geology and Hydrology of the Helena area, you can click here to view this Story Map.

    Groundwater Monitoring
    The Lewis and Clark County Water Quality Protection District monitors over 130 wells monthly, and has been collecting this data for over a decade. All of the information collected by the District is uploaded to the Montana Bureau of Mines and Geology’s Groundwater Information Center (GWIC). Each well has a corresponding “GWIC ID” that you can use to search for and download data from that well.

    The monthly groundwater level measurements have allowed local scientists to track trends over time, and identify areas that are experiencing signs of depletion.

    To view all monitoring wells and their GWIC ID’s, you can click here to view this Story Map.

    Groundwater Depletion
    Aquifers that receive little to no recharge from surface waters or groundwater are vulnerable to groundwater depletion. When the amount of water being pumped out of the aquifer exceeds that coming in, the water level will continue to drop, causing yield deficiencies for wells that are no longer deep enough to reach the water level (wells are at a higher risk to “go dry”). Below is a map that highlights the areas where there are signs of groundwater depletion. It is important to note that these hydro-geologic systems are complex, and local scientists still do not yet fully understand why we are seeing depletion in some areas.


    Map 1: Groundwater depletion in the Helena area. Each circle represents an individual well. The minimum value of the groundwater level (when the water was at its highest point) was extracted for each year, for each well. The “trend” was determined based on the percentage of years where the highest groundwater level point is lower than the year before. Groundwater level data were extracted from the Montana Bureau of Mines and Geology’s Groundwater Information Center, from as early as 1995 until the most recent data collected in 2018. The number of measurements per well varies.

    In the case below, 100% of the maximum height values per year were lower than the year before. This well would be colored red on the map, and indicative of signs of groundwater depletion.




    So what is the solution?
    In order to balance recharge with withdrawals, strategies to enhance recharge and/or reduce withdrawals can be employed. We typically rely on nature to supply groundwater for aquifer recharge, however there are methods to provide groundwater recharge through artificial means.

    Managed Aquifer Recharge (MAR)
    MAR refers to the intentional recharge of water into an aquifer for later recovery and use. MAR may employ a variety of techniques that include:

  • infiltration ponds
  • injection wells
  • surface water diversions


  • Water from a variety of sources including surface watercourses (streams, ditches, canals), stormwater runoff, and even wastewater or graywater can be used in the recharge process.


    Where methods to enhance recharge are not feasible, or do not provide sufficient volumes to maintain water levels, water conservation measures and methods to reduce withdrawals can be used.

    Groundwater Conservation

  • Reduce groundwater use through:
  • catchment systems (greywater, runoff capture)
  • xeriscaping
  • HOA agreements


  • Other Methods

  • Drill a deeper well ($$, groundwater withdrawal, impacts to neighbors)
  • Establish public water supply/community well ($$, water rights, regulations)
  • Water hauling/cistern ($$, no local water hauling in Helena)

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