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Missoula Valley Water Quality District
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Missoula Valley Water Quality District

Department: Water Quality District
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Water Quality District

Flood Precautions for Protecting Water Quality

This year’s high snow fall amounts have left significant snowpack in the higher elevations of western Montana.  Cool spring temperatures lead to further accumulation of snow and delay snow melt.  As warmer weather approaches the potential for flooding becomes greater.  The Missoula City-County Health Department wants to help residents prepare for flooding. 

Hazardous Materials – Now is a good time to move any hazardous substances out of potential reach of floodwaters.  If a garage or shed is located in an area which may be inundated, move hazardous materials to a safer building.  Don’t just put them on a higher shelf.  Hazardous materials include such things as pesticides, fertilizers, fuels and paint.

Drinking Water - If you believe your well could be flooded, take precautions now.  Store a supply of water.  If flooding becomes imminent, shut off power to the well and contact a well driller/contractor to install a temporary waterproof well cap.  If there is not enough time to do that, seal the top of the well with heavy plastic and electrical tape or some other type of waterproof tape (not duct tape).  This will prevent debris from entering the well casing through the vent. Remove the waterproofing after flood danger has subsided to allow proper vent function

If flood waters come within 100 feet of your well, we recommend testing your water for bacterial contamination, and if flood waters are within 50 feet of the well, you should definitely test your water.  For wells that are actually flooded, disinfection will be necessary followed by testing.  Bacteriological testing can be done at the Missoula City-County Health Department. Call 258-4755 for water testing questions.

Septic Systems - If your home is served by a septic system, do not dispose of large amounts of water through household drains as this can overwhelm the system. We recommend not using, or minimizing use of your septic system if the drainfield is flooded, as it cannot effectively treat wastewater when saturated. Be aware that flood waters can cause wastewater to back up into your house; if flooding is imminent, you might want to contact a septic system service provider to discuss options to prevent this from happening.


Sandbags – Sandbags are a simple way to temporarily protect buildings and wells from floodwaters.  Sandbags may not protect your home from rising groundwater, and they do not provide a watertight seal from rising surface water, but are adequate for some situations.  Check with Mutual Materials or Time Rental for purchase. Do not purchase large bags as they are too heavy to move and stack.  Filling sand bags on site is generally the easiest way to go.

If you choose to purchase sandbags to protect private property please be aware of a few things:

You need to get permission to place sandbags along riparian (streamside) areas from the Missoula Conservation District at (406) 829-3395 and the Army Corps of Engineers at (406) 441-1375.

If you place sandbags on your property make sure they are placed to protect your structure(s) but not on the tops of stream banks or rivers which could push those waters to flow faster and deeper, harming your downstream neighbors.

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