How do I know the groundwater won’t become contaminated?


An extensive sampling program collected numerous soil and water samples from multiple locations and performed more than 14,500 analytical tests to identify any potential contaminants in the groundwater. In addition to contaminants that are regulated by the State for drinking water, we also tested for non-regulated contaminants, emerging contaminants (pharmaceuticals and personal care products) that may be of concern in the future, and compounds specific to local industry. In all of these tests, naturally occurring iron, manganese and arsenic were the only contaminants detected at levels which warrant treatment.

Sentry Wells

In addition, a network of monitoring wells (or sentry wells) has been constructed around the perimeter of the Mint Farm and proposed well field. These monitoring wells will become a critical part of a Well Head Protection Program and will be regularly monitored for changes in water quality. They are intended to safeguard the well field by providing early detection of potential contaminant migration, allowing the City several years advance notice to install additional treatment equipment or implement an alternative solution.

Difficulty to Contaminate

Water Seepage Resistant Soil

While drilling the first 17 shallow and deep monitoring wells, soil samples were collected to confirm that a confining layer exists which is very resistant to water seepage, and that confining layer protects the deep aquifer from potential contamination at the surface.


In addition, the deep aquifer is under pressure, which prevents potential shallow contamination from migrating into the deep aquifer. We constructed a full size production well and tested the well by pumping it at 5.5 million gallons per day continuously for 36 days and the pressure in the aquifer dropped only the equivalent of 3-feet (less that 2 pounds per square inch), confirming that the aquifer will remain under pressure after our plant begins operation. We collected water samples before, during, and after test pumping, specifically looking for indications of migration of potential contaminants, and actually found that the water quality improved slightly during pump testing.

Show All Answers

1. Why does my tap water appear to be discolored?
2. Why didn't we rebuild the Fisher's Lane water treatment plant?
3. Why didn't we stay with the Cowlitz River?
4. How long will the groundwater supply last?
5. Will the groundwater stain my laundry and household fixtures?
6. Why not move the water supply intake to a better location on the Cowlitz River or Columbia River?
7. What is in the groundwater?
8. Until how long is the groundwater supply expected to last?
9. How do I know the groundwater won’t become contaminated?
10. Where does the groundwater come from?
11. Has there been a change in the pH levels after switching to the new water source?
12. What if the water smells funny?
13. Should I consider getting a water softener?
14. What can I do about hard water?
15. How does hard water impact my life?
16. What is the City doing to reduce hardness?
17. What is the hardness of the City's new groundwater source?
18. Where do hard water minerals come from?
19. Is hard water safe?
20. What is water hardness?