Despite clean water being vital to life, it is often taken for granted. For many of us, we trust that the water coming from our faucets is clean, and don’t think much about where it comes from or where it goes after we use it. So once you flush the toilet or drain the sink, where does that dirty water go? And how do we know the water we are putting back into our streams and rivers isn’t polluting the next person that needs it downstream? 

Thankfully, almost all towns and cities in the U.S. have municipal wastewater treatment plants (WWTPs) that treat and clean our sewage before it can be released to nearby rivers and streams. Idaho has 112 WWTPs that do just this by making sure pollutants like nitrogen and phosphorus (which can both lead to the growth of toxic algae, making our water bodies unsafe), E. Coli, total suspended solids (TSS), and other harmful pollutants are sufficiently removed from our sewage. 

Recognizing that every Idahoans deserves access to clean water, ICL reviews data from every single WWTP report in Idaho every year, helping ensure that the water you drink is safe and clean. Each year, we release our Wastewater Treatment Plant Report (coming early this summer) that outlines which WWTP are keeping you safe, and which are polluting at levels over legal limits. However, when ICL staff was recently reviewing publicly available data on WWTPs, we noticed one such facility in Idaho is dealing with a very unexpected, yet potentially deadly pollutant: cyanide. Yup, you read that right—cyanide.

As the Centers for Disease Control and Prevention (CDC) reports, “cyanide is a rapidly acting, potentially deadly chemical that interferes with the body’s ability to use oxygen”—not something you want in your water! 

According to the Environmental Protection Agency’s ECHO Database, which shows the enforcement and compliance history of WWTPs across the country, the City of Blackfoot’s WWTP discharged a staggering 6,956 pounds of cyanide to the Snake River in 2023! Only 20 facilities in the U.S. (WWTP or otherwise) discharged more cyanide last year.

An aerial view of the Blackfoot WWTP. Image Credit: City of Blackfoot

This isn’t the first time cyanide has been a problem for this particular plant. Since 2013, when the Blackfoot WWTP first started monitoring for cyanide, the same EPA ECHO Database shows that the facility has discharged erratic amounts of cyanide. The chart below shows the annual amount of cyanide estimated to have been discharged from the facility each year.

For most people, cyanide probably brings up images of spy movies and poison pills, so you might be wondering—what is it doing in the Blackfoot WWTP’s discharge? Cyanide is not normally present in human waste nor is it a byproduct of its treatment, but it is used in some industrial applications. The Blackfoot WWTP does receive and treat some industrial waste water from local facilities. However, none of those facilities would be expected to use or produce cyanide and tests of incoming wastewater to the WWTP show no significant amounts of cyanide present. 

ICL relayed our concerns to the Idaho Department of Environmental Quality (DEQ), which is responsible for administering wastewater treatment permits to facilities like the Blackfoot WWTP. Since the Blackfoot WWTP must monitor for cyanide, but does not have a permitted limit for how much cyanide they can discharge, DEQ was not immediately aware of the issue. 

Thankfully, DEQ was responsive to our concerns and has been in discussion with Blackfoot WWTP staff about the issue. They have relayed that the WWTP is unsure exactly where the cyanide is coming from, but has reason to believe it is infiltrating to the facility from stormwater runoff, possibly from nearby soil or groundwater that was contaminated by previous industrial activity at the site. The Blackfoot WWTP is in the process of developing a water and soil sampling plan to further understand where exactly the cyanide is coming from and ultimately address the issue. 

Since the Blackfoot WWTP discharges to the adjacent Snake River, there is the potential that the released cyanide is having a negative impact on water quality and poisoning animals and plants. However, the way in which cyanide reacts with water, air, and other elements and compounds in both mediums is particularly complex. As such, it is possible that the discharged cyanide is being sufficiently diluted by the Snake River or is being rendered inert in some other way. Yet, it is also possible the Snake River is experiencing significant ecological damage to wildlife and vegetation. To better understand this uncertainty, ICL is asking DEQ to conduct preliminary assessments of the Snake River downstream of the WWTP discharge. 

ICL will continue to track this issue and update the public on new developments. 

If you care about the health of the Snake River and Idaho’s water, you can also help by supporting our work by becoming an ICL member! This “watchdog” work wouldn’t be possible without the financial support of our members. ICL has expert staff who focus on protecting the waters of Idaho from degradation and pollution by keeping a watchful eye on polluters. Because after all, we all need—and deserve—clean water.

If you have any specific questions or comments on water pollution or WWTP you can contact ICL’s Conservation Associate Will Tiedemann.

For the love of clean water, join ICL today!