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Missoula City-County Health Department
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Environmental Health


Groundwater Monitoring - Individual On-Site Septic Systems

If your site shows evidence that subsurface groundwater may come to within 10 feet of the ground surface at any time of the year, groundwater monitoring may be required. Groundwater monitoring creates a special problem for persons wanting to develop their property because it can only be done at certain times of the year, usually early to late spring or later summer when irrigation influences the groundwater level.

To apply for groundwater monitoring you must complete an application before high groundwater peaks in your area. We usually do not accept groundwater applications after May 1 of each year so you should be prepared to apply before then. Applications are available at the bottom of this page in PDF format or in our office.

The rule that governs groundwater testing is below:

(3) Groundwater. Groundwater depth at any time of less than 6 feet from the natural ground surface shall preclude the use of conventional subsurface wastewater treatment and disposal systems. There shall be minimum separation of at least 4 feet between the bottom of the drainfield and the maximum high groundwater elevation. If the groundwater is within 10 feet or less of the ground surface, or if there is any reason to believe that the groundwater will be within 10 feet of the natural ground surface during any time of the year, groundwater test holes to a depth of 9 feet shall be provided in the area of the drainfield to determine the high groundwater during its peak occur­rence. The department may require the applicant to provide one (1) year of groundwater monitoring conducted by the department to delineate the highest groundwater level. The department may refuse to accept seasonal high groundwater data when total precipitation for the previous year (defined as May 1 of the previous year through April 30 of the current year), or April 1 snowpack water equivalent, measured at the nearest officially recognized monitoring station, is more than 20% below the historical average. The department may consider soil morphology data, and data from nearby groundwater monitoring sites with similar soil, geology and proximity to streams or irrigation ditches, if available, to determine maximum groundwater elevation during periods of drought.

Apply for Groundwater Monitoring.

Visit us at the Missoula City-County Health Department on the second floor at 301 W. Alder in Missoula for an application form or download this PDF Groundwater Application. Complete the form and stop by the Health Department to pay your fees and set a time.

Groundwater fees:

Ground Water Monitoring: Base Fee (includes 2 holes per drainfield site)...... 270.00

Distance Charge (distance to site, one-way from Health Department, 1-time charge)...........................................................................................................3.70/mile

Each additional site............................................................................................ 50.00


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