Metro Water Services is committed to the protection of public health and delivering clean, safe, reliable drinking water to our customers. We go above and beyond to ensure you can trust your tap. This means making sure our water meets or exceeds all federal and state standards for drinking water and following current research and developments on contaminants of emerging concern.
On April 10, 2024, the Environmental Protection Agency (EPA) issued the first-ever national drinking water standards for six PFAS. The final rule establishes maximum contaminant levels goals (MCLGs) and maximum contaminant levels (MCLs) for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS), and a hazard index level for Perfluorohexanesulfonic acid (PFHxS), Perfluorononanoic acid (PFNA), Perfluorobutanesulfonic acid (PFBS), GenX Chemicals (HFPO-DA).
Analysis shows that Metro Water Services meets the new drinking water standards.
What are maximum contaminant level goals (MCLGs)
The non-enforceable level of a contaminant in drinking water at which there is no known or anticipated adverse effects on the health of persons to occur. MCLGs allow for a margin of safety.
What are maximum contaminant levels (MCLs)
The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to the MCLGs as feasible using the best available treatment technology.
What are PFAS?
Per- and polyfluoroalkyl substances (PFAS) are a large and diverse group of man-made chemicals. These chemicals have unique properties, such as resistance to high and low temperatures, resistance to degradation, and non-stick characteristics.
They are known as "forever chemicals" because they linger in humans and the environment.
Where are PFAS found?
Per- and polyfluoroalkyl substances (PFAS) have a widespread presence in our environment. Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are two compounds that were widely used to make carpets, fabric, food packaging and other products resistant to water, grease, or stains. It can be found in clothing, food packaging, non-stick cookware, shampoos and other items used daily.
It is even found in rainwater! A recent study found that levels of PFOA and PFOS in rainwater often greatly exceed US Environmental Protection Agency (EPA) Lifetime Drinking Water Health Advisory levels, even in remote areas. (Environ. Sci. Technol. 2022, 56, 16, 11172–11179)
Most uses of compounds were voluntarily phased out by U.S. manufacturer in the mid-2000s, although there are some ongoing uses, and due to their properties, these chemicals remain in the environment due to their lack of degradation.
What is Metro Water Services doing about PFAS?
Certain technologies have been found to be effective in removing per- and polyfluoroalkyl substances (PFAS) from drinking water, especially perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). One of these technologies, activated carbon adsorption, has been used in Metro Water Services water treatment process to remove taste and odor compounds, and synthetic organic chemicals. Metro Water Services began using powder activated carbon (PAC) before 1980.
Metro Water Services began voluntarily testing for these compounds in 2015. Tests on drinking water leaving our treatment plants conducted in 2015, 2019, 2021, and again in 2023 found no reportable levels of PFAS.
Our latest testing was done in November 2023 and results of that analysis were non- detect.
Metro Water Services 2023 results
| PFAS Compound | K.R. Harrington Water Treatment Plant Finished Water | Omohundro Water Treatment Plant Finished Water | MCL |
|---|---|---|---|
| PFOA | Non-Detect | Non-Detect | 4.0 ppt |
| PFOS | Non-Detect | Non-Detect | 4.0 ppt |
| PFHxS | Non-Detect | Non-Detect | 10.0 ppt |
| Gen X | Non-Detect | Non-Detect | 10.0 ppt |
| PFNA | Non-Detect | Non-Detect | 10.0 ppt |
| PFBS | Non-Detect | Non-Detect | 10.0 ppt |
Unfortunately, the burden for keeping these compounds away from consumers has been placed on drinking water treatment operations when it should be placed on the manufacturers – PFAS uses should be eliminated and companies should be responsible for research and elimination of the substances.
Removing PFAS from drinking water and biosolids is possible but extremely challenging and expensive.
Future Improvements
In 2018, Metro Water Services initiated a water treatment pilot plant research project to explore emerging technologies to best provide safe and reliable drinking water to our customers. Two different water treatment technologies were selected for piloting - ozone and granular activated carbon (GAC).
Results from the two-year pilot plant project effort determined that GAC Post Filter Adsorbers achieved the Metro Water Services water quality and process enhancements goals. Additionally, GAC Post Filtration Adsorbers have proven effectiveness in addressing a wide range of emerging contaminants including, but not limited to, per- and polyfluoroalkyl substances (PFAS).
While both forms of activated carbon are effective, GAC is most effective as it is more porous and has a larger surface area to which contaminants may adsorb.
Metro Water Services plans to begin using GAC Post Filter Adsorber among other improvements at both water treatment plants, K.R. Harrington and Omohundro, by 2033.
Removing PFAS from drinking water and biosolids is possible but extremely challenging and expensive. The burden for keeping these compounds away from consumers should be shifted away from drinking water treatment operations and placed on manufacturers. PFAS uses should be eliminated and companies should be responsible for research and elimination of the substances.
What about Music City Gold, Nashville’s Biosolids?
There are currently no established standards for per- and polyfluoroalkyl substances (PFAS) in biosolids.
The Environmental Protection Agency is currently performing a risk assessment for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) in biosolids. The assessment is expected to be completed by 2024 and limits and monitoring/reporting requirements will be established if there is sufficient evidence of harm to human health or the environment.
Metro Water Services voluntarily tested a fresh unbagged representative sample of our finished Class A EQ Biosolids earlier this year, using a third-party State certified laboratory. In our analysis, only 5 of the 36 chemicals were at levels that could be accurately quantified - 17 of the 36 chemicals were undetected, and 14 were detected but below the instrument’s ability to accurately quantify (LOQ).
| Class A EQ biosolids | PFOA | PFOS |
|---|---|---|
| Level | Non-Detect | 3.72 PPB |
The lower the level, the lower the risk and public health is our highest priority.
Therefore, Metro Water Services will continue to follow studies and research to help us develop strategies to reduce levels of PFAS in drinking water and biosolids.