Groundwater Protection

Montanans rely heavily on groundwater as the primary source of drinking water for many rural domestic water supplies as well as public water systems. Groundwater is also important for irrigation, livestock, and indirectly for thermoelectric power. Montana’s programs for the protection and remediation of groundwater are driven by the need to keep groundwater safe from contamination and to protect and support the current and future uses of groundwater

Although DEQ has primary responsibility for groundwater protection, a number of programs across the state aid in the protection of groundwater. Several agencies, the Department of Environmental Quality, Department of Natural Resources and Conservation, and the Department of Agriculture implement the majority of federal and state programs relating to groundwater.

How DEQ Protects Groundwater

  • Source Water Assessment and Protection
  • Groundwater Pollution Control System
  • Groundwater Monitoring
  • Education for Private Well Owners

Montana depends on Groundwater for much of its drinking water supply from either public sources or private wells. It is important to understand how groundwater is protected and made safe for drinking.

Groundwater Quality Standards

Drinking water standards and guidelines place a ceiling on contaminant levels in the drinking water supplied by public water systems, regardless of whether the source is Groundwater or surface water.

There is no regulation for ensuring that private wells meet safe drinking water standards. However, private well owners can have their wells tested and use federal drinking water standards as a guide for assessing water quality.

Visit the Water Quality Standards Page for information on water quality standards.

When Groundwater Provides Your Drinking Water from a Public System

Water systems that have groundwater sources may be susceptible to fecal contamination. In many cases, fecal contamination can contain disease causing pathogens. The Groundwater Rule (GWR) applies to public water systems that use groundwater as a source of drinking water and that may be susceptible to fecal contamination. The rule also applies to any system that delivers surface and groundwater to consumers where the groundwater is added to the distribution system without treatment. The purpose of the Groundwater Rule is to reduce disease incidence associated with harmful microorganisms in drinking water.

Requirements of the Groundwater Rule

  1. Periodic sanitary surveys of groundwater systems require the evaluation of eight critical elements and the identification of significant deficiencies (e.g., a well located near a leaking septic system).
  2. Source water monitoring to test for the presence of E. coli, enterococci, or coliphage in the sample. There are two monitoring provisions: Triggered monitoring for systems that do not already provide treatment that achieves at least 99.99 percent (4-log) inactivation or removal of viruses and that have a total coliform-positive routine sample under Total Coliform Rule sampling in the distribution system. Assessment monitoring-As a complement to triggered monitoring, Montana has the option to require systems, at any time, to conduct source water assessment monitoring to help identify high risk systems.
  3. Assessment monitoring as a complement to triggered monitoring. Montana has the option to require systems, at any time, to conduct source water assessment monitoring to help identify high risk systems.
  4. Corrective actions required for any system with a significant deficiency or source water fecal contamination. The system must implement one or more of the following correction action options:
    • Correct all significant deficiencies;
    • Eliminate the source of contamination;
    • Provide an alternate source of water;
    • Provide treatment which reliably achieves 99.99 percent (4-log) inactivation or removal of viruses.
  5. Compliance monitoring to ensure that treatment technology installed to treat drinking water reliably achieves at least 99.99 percent (4-log) inactivation or removal of viruses.

Groundwater From a Private Well Used for Drinking:

Private well owners are responsible for the quality of their water, and no regulatory oversight exists to ensure water quality. However, there are numerous resources for private well owners to assist them in maintaining high quality drinking water.

For More Information:

Protecting Groundwater Quality in Montana

Montana Groundwater Rules

Montana Groundwater Quality Standards (DEQ-7)

Montana Water Quality Report

EPA Groundwater Rule Summary

EPA Groundwater Rule Quick Reference Guide

All groundwater sources in Montana are to be assessed as either Groundwater (GW) or Groundwater Under the Direct Influence of Surface Water (GWUDISW). See Circular PWS-5, for the complete GWUDISW rule.

'Under the direct influence of surface water' means the groundwater source is located close enough to nearby surface water, such as a river or lake, to receive direct surface water recharge. Since a portion of the groundwater source's recharge is from surface water, the groundwater source is considered at risk of contamination from pathogens such as Giardia lamblia, cryptosporidium, and viruses, which are not normally found in true Groundwaters.

Sources most likely to be under the direct influence of surface water are:

  • Infiltration gallery systems and horizontal wells;
  • Spring systems;
  • Wells located near surface waters.

A source of subsurface water (well, spring, horizontal well, or infiltration gallery) is presumed to be groundwater at the start of the process. It is only if evidence appears that there may be the direct influence of surface water in the source that the designation of the source could change to GWUDISW.

The first step in determining if a source is under direct influence of surface water is for DEQ staff to complete a preliminary assessment form. Based on the results of the preliminary assessment, the source will either be characterized as groundwater or be required to undergo further assessment.

If the source is classified as groundwater under direct influence of surface water (GWUDISW), it must meet the same treatment technologies as surface water and the system must install filtration and disinfection in accordance with the surface water treatment rule.