Bannock County Groundwater

Nitrate Concerns

High levels of nitrates (above the legal limit) cause blue baby syndrome (an oxygen depletion problem seen in babies and the elderly). It may also cause gastrointestinal problems and cancers.  Pocatello has municipal wells that are frequently over half the legal limit. If these wells reach the legal limit, remediation is very costly (over $500K per well per year – or $31 per customer per well per year).

Septic Tanks and Nitrate Contamination

Septic Tank System

Even if a septic tank is properly functioning, it still discharges nitrates. (It only removes 25% of the nitrates.) The rest of the nitrates enter local ground water. If the ground water flow is high enough, this is not a problem. Problems occur when there are too many septic tanks for the ground water flow and the aquifer can’t dilute the nitrates. This can especially be a problem for private well owners which often have wells near septic tanks. Private well owners are required to monitor their own wells.

Septic Tank Locations

Septic Tank Locations

Johnny Creek, South 5th Avenue, Mink Creek, and Gibson Jack are all area that use septic systems and are generally not served by City sewer. The combination of all of these individual septic tanks discharging high levels of nitrates into our ground water impact the quality of our drinking water.Within Pocatello there are currently three (3) nitrate priority areas. 25% of the wells sampled in these areas had nitrate levels over 5 mg/L (the legal limit is 10 mg/L). 

Nitrate Priority Areas

Nitrate Priority Areas

Priority Areas

If you own a well and live in one of the nitrate priority areas, it is particularly important to test your well water on a regular basis. If your well is not in a nitrate priority area, this does not rule out the potential for nitrate contamination, so testing your well water is still recommended.See an interactive nitrate priority map at

Nitrate Trends

Example of Nitrate Trends

Here’s an example of nitrate contamination in a City of Pocatello well near Ross Park from 1999 – 2008. It shows nitrate levels in parts per million (ppm). You can see how the levels of nitrates were quite low until 2000 at which point it began to fluctuate a lot. The levels of nitrate have always remained below the legal limit of 10 ppm. However, anytime levels go above 5 ppm (as has happened with this well) we should be concerned as removing nitrates is very expensive. If the levels ever go consistently above 10 ppm the City will have to treat that water or take the well off-line. Nitrate Trends for 13 City WellsThis is a messy summary diagram of all the City wells from 1989 – 2009. On this diagram is a line at 3 ppm. Scientists have determined that nitrate concentrations in water that exceed 3 parts per million (ppm) are due to human activities (animal waste, human waste, and agriculture). Therefore, nitrate levels in our drinking water between 3 ppm and 10 ppm (the safe drinking water level) are the result of things that humans are doing to the land (confined animal areas, septic system installations, and over application of fertilizers). On this diagram you can see that 11 of the 17 City wells have nitrate levels above 3 mg/L (ppm). Additionally, many private wells (especially in the S. 5th Ave and Mink Creek areas) have even higher levels of nitrates.

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