What is in the groundwater?

Naturally Occurring Elements

The groundwater contains small amounts of naturally occurring iron, manganese and arsenic. Iron and manganese are not considered a risk to human health and federal regulations do not require treatment to remove them from drinking water. Many people take vitamin and mineral supplements containing iron and manganese, and when ingested in small concentrations, both can provide a health benefit. However, at the concentrations found in the Mint Farm aquifer, state regulations do require treatment because iron and manganese cause objectionable aesthetic issues like taste, odor, color and a tendency to stain. The City plans to treat for iron and manganese removal in order to produce high quality drinking water and prevent those types of problems.


The groundwater also contains trace amounts of naturally occurring arsenic. For many years, the drinking water standard for arsenic was 50 parts per billion (ppb). In 2004, regulations tightened the drinking water standard for arsenic from 50 to 10 ppb to lessen people's long-term exposure.

The groundwater at the Mint Farm contains approximately 6 ppb of arsenic, roughly one-half the allowable limit. At that concentration, drinking water regulations only require that we notify our customers that arsenic exists above the specified reporting level. Our current water source, the Cowlitz River, also contains arsenic but at lower levels. Although not required, the City plans to treat for further arsenic removal and reduce the arsenic concentration to approximately 2 to 3 ppb.

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?