The U.S. Geological Survey recent data showed that 27 sampled wells have a detectable concentration of nitrates in the southern part of Pahrump Valley.
In 2014-2015, the USGS conducted a second phase study focused on the southern part of Pahrump Valley where officials sampled an additional 27 new wells and resampled four wells from a pilot study that was done in 2012.
The results showed that two out of 31 wells had nitrate concentrations above the the U.S. Environmental Protection Agency drinking water standard which is 10 milligrams per liter.
Two additional wells had nitrate concentration close to the USEPA drinking-water standard.
Since 2012, USGS sampled a total of 47 wells for nitrate. Three out of 47 wells had nitrate concentration above 10 milligrams per liter and two additional wells had nitrate concentrations close to the USEPA drinking water standard, which is greater than 9 but less than 10 milligrams per liter.
“So if add those two together, … I get again a value of about 10 percent of wells with nitrate, which I consider to be high. In other words, above or close to the standards,” said Mike Moran, a specialist with USGS who presented findings at the Nye County Water District Governing Board meeting on Monday.
The USGS has been doing studies in Pahrump since 2012 because of the concerns about groundwater quality. In 2012 the agency did a pilot study of domestic wells and a few monitoring wells.
Officials conducted duplicate samples of the four wells that were part of the pilot study in 2012. The concentrations of the resample were very close to the concentration of the original sample conducted two years ago.
Moran said the finding indicates that the nitrate is in relatively stable concentration in the groundwater.
Samples collected during a second phase of the study were analyzed for a broad sweep of contaminants that include major ions, nitrate, nitrogen isotopes, coliform bacteria and wastewater compounds.
“So the idea was not to just see what the distribution of nitrate was but understand the source of nitrate in the wells where we were finding it,” he said.
Officials however are yet to identify the source of the nitrate, a chemical compound that contains nitrogen and water. Nitrogen originates from decomposing organic materials such as manure, human waste and plants.
According to the slide show presented by USGS officials, nitrogen isotopes indicate that septic system waste and manure waste are the main sources for most of the nitrates in Pahrump Valley. Another source is natural soil nitrogen, which is found in all soils everywhere, officials said.
Additionally, the study found that 42 percent of wells had a detection of one or more of the wastewater compounds.
After a doing a basic analysis on correlation between nitrates and septic system, Moreo said USGS wants to conduct further research.
“We’d like to further examine the relationship between nitrate and septic systems,” Moran said. “We’ve done only very basic analysis to this point, the reason why is we simply don’t have the funding to go any farther at this point.”
Contact reporter Daria Sokolova at firstname.lastname@example.org. On Twitter: @dariasokolova77