A study conducted by ISU students and faculty members has confirmed that nitrate contamination of the Lower Portneuf Valley Watershed is caused by septic tanks, not from agriculture or ranching like it has in the past.
Courtney Ohr, an ISU Geographic Information System student, produced the study with assistance from professor of geosciences Sarah Godsey and collaboration with the Department of Biological Sciences, the Idaho Geological Survey, Department of Geosciences and other ISU faculty.
The study evaluated 100 private wells in the surrounding Pocatello and Chubbuck areas.
According to Godsey, approximately one-third of the wells studied contained a clear link with septic contamination, while an additional one-third is likely to be linked with it.
A total of 41 wells were confirmed to be contaminated by septic systems, while another 22 were likely to be linked to septics.
As Ohr outlined in her paper, it is important for the community to understand what is causing the nitrate contamination in the watershed so tax dollars are not spent in an attempt to mitigate the wrong sources of contamination.
Researchers noted this study was restricted to private wells, and before any type of filtration or treatment was done to the water. The municipal water supply is considered safe by all counts of the possible contaminates required by law.
With that in mind, 11 of the wells tested contained levels of nitrates higher than the Environmental Protection Agency’s maximum contamination level of at least five milligrams per liter.
The greatest hurdle for this study was to differentiate the source of contamination from septic or sewer problems, or from cattle and agriculture.
The traditional method of evaluating isotopes of nitrates requires researchers to know specific environmental processes at each site where samples were taken.
Nitrate sources can be broken down into several different isotopes depending on exactly which process takes place, and there is overlap between septic and manure sources.
Ohr decided to evaluate another group of contaminants, Pharmaceuticals and Personal Care Products. These include different types of drugs and synthetic chemicals like caffeine and DEET, the active ingredient in insect repellents.
Because they are synthetic, there are typically very low background levels in the watershed, making them very good tracers and predictors for where the contamination occurred.
Another useful characteristic of PPCPs is that some are broken down in water treatment facilities, while others are not. If there are high levels of certain PPCPs that should have been broken down but are not, it is a good indicator there is a raw sewage contamination. Of the 26 PPCPs tested for, nine were found in the samples taken, with 31 of the wells containing at least one of those nine.
“Wells in which PPCPs were detected also had significantly higher nitrate concentrations,” according to the study.
This study was done as part of the Managing Idaho’s Landscape for Ecosystems Service at ISU. The MILES project is meant to build scientific infrastructure and knowledge of Idaho’s ecosystems and is set to continue through 2020.