A map of the Great Basin indicating where high levels of arsenic are present in domestic wells. DRI Graphic
Arsenic in the drinking water has long been an issue for Carson Valley residents.
Occurring naturally, changes in federal standards in 2006 from 50 parts per billion to 10 parts per billion have altered how utilities have served customers across the Valley.
A recent study published Feb. 16 in “Environmental Science and Technology,” shows that groundwater levels in parts of the Valley exceed 5 parts per billion, which researchers claim could pose unhealthy levels.
“What we are finding is that in our region, we have a high probability for elevated arsenic compared to most other regions in the country,” said study lead author Daniel Saftner, a hydrogeologist at DRI. "And we are seeing that geothermal and tectonic processes that are characteristic of the Great Basin contribute to the high concentrations of naturally occurring arsenic in the region’s groundwater.”
All Carson Valley’s utilities rely on groundwater, and some have had to make changes in where and how that water is delivered.
A pipeline from Minden to Johnson Lane and Indian Hills on its way to Carson City was constructed in 2011 instead of attempting expensive water treatment.
The study focused on private wells and says more than 49,000 may be exposed to unhealthy levels of arsenic in their drinking water.
Researchers said they used data from groundwater wells across the western Great Basin to build a model to predict the probability of elevated arsenic in groundwater, and the location and number of private well users at risk.
Carson Valley has one of the highest populations of well users at risk, in addition to the Carson Desert around Fallon and the Truckee Meadows.
The region’s mountains are also primary sources of arsenic, according to researchers.
“As the arsenic-rich volcanic and meta-sedimentary rocks that form the mountains erode, sediment is transported to the valleys below,” said study co-author Steve Bacon, a DRI geologist.
Water percolating through the valley floor then carries arsenic into the groundwater. Deeper, older groundwater and geothermal waters tend to have a higher arsenic concentration and can migrate upward along faults and mix with shallow groundwater.
“We really wanted to better understand the unique geologic factors that contribute to high arsenic in this study,” Saftner said. “It’s important for us to think about the role of the environment as it pertains to human health – where we live can influence what our long-term health looks like.”
To train and test the predictive model, the research team used data collected through the Healthy Nevada Project, including water samples from 163 domestic wells primarily located near Reno, Carson City, and Fallon. These data were supplemented with 749 groundwater samples compiled from the U.S. Geological Survey National Water Information System.
The model uses tectonic, geothermal, geologic, and hydrologic variables to predict the probability of elevated arsenic levels across the region.
Although the U.S. EPA has set an arsenic concentration guideline of 10 parts per billion for public drinking water, previous research has shown a range of health effects from long-term exposure to levels above 5 parts per billion. Using this concentration as the benchmark, the model and map show that much of the region’s groundwater – particularly in western and central Nevada – is predicted to have more than a 50 percent probability of elevated arsenic levels.
“Community members can use our arsenic hazard map to see what the risk is at their location, which might motivate them to test their well water,” said study co-author DRI Associate Research Professor Monica Arienzo. “Then, if they have high levels of arsenic or other contaminants, they can take steps to reduce their exposure, such as installing a water treatment system.”
The research team plans to use their model to take a closer look at the health impacts of prolonged arsenic exposure.
“Through the Healthy Nevada Project, genetic data and health records are paired with environmental data to help determine whether there are associations between the levels of arsenic in a community’s groundwater and specific health outcomes,” said principal investigator and DRI research professor Joe Grzymski.
