SALEM — The Oregon Department of Environmental Quality released a Groundwater Nitrate Trend Analysis for the Lower Umatilla Basin Groundwater Management Area in Morrow and Umatilla counties.

The DEQ published the report Wednesday, Jan. 22, as an update to another the department released in 2012. The analysis says the overall trend of nitrate concentrations in the groundwater is increasing and much of the area’s drinking water exceeds federal nitrate standards. These results were expected, according to Antony Sparrow, DEQ public affairs specialist, because there are continued sources of nitrogen in the area.

“ Groundwater recharge and nitrate loading relative to contamination takes a very long time,” Sparrow said. “What we’re seeing now may not be indicative of the amount that’s going into the ground.”

The analysis marks the first completed step of the DEQ’s work identified in section 5.1.2 of the state’s Nitrate Reduction Plan, released in September 2024. The trend analysis at the time was expected to be complete in 2024, putting the DEQ just a few weeks behind its anticipated schedule.

About the analysis

The report itself is based on data collected throughout 32 years at 33 wells in Morrow and Umatilla counties within the LUBGWMA. Most of the wells — 30 — are domestic, two are irrigation and one is an industrial well. Since 2010, the wells have been sampled four times per year.

The data shows about 40% of wells recently have exceeded the federal nitrate concentration drinking water standard of 10 milligrams per liter. Additionally, there’s no predictive pattern to the higher concentration wells, although they tend to be in the western part of the network. The concentrations are impacted by well depth and construction, nitrate sources, soil types, precipitation and air temperature, soil and water chemistry, as well as how the water physically moves through the aquifer.

“The groundwater nitrate concentration observed at any particular well at any particular time is a composite of what was already there and what was recently added, both of which are affected by natural factors and human activities,” Sparrow said. “Without more data, it is difficult to determine the amount of influence each of these factors has on groundwater nitrate concentrations.”

The wells’ geography, depth and proximity don’t seem to determine nitrate concentrations. However, the data does indicate a connection between nitrate concentrations and surface activities. Some data points showed steep trends or abrupt changes in nitrate, which could have something to do with changing conditions on the surface.

“ There is a stronger link between changing land use practices and changing groundwater quality at the wells in our well network,” Sparrow said, “ but we don’t have the land use information right now to show a direct correlation.”

The analysis also found about half the monitoring wells show seasonality, meaning there’s a pattern to when they have higher and lower concentrations. Typically, nitrate levels were higher in those wells in the spring than in the fall. Fluctuations for two-thirds of the wells were less than 10 mg/L.

Next steps

One of the DEQ’s next steps will be enhancing its well monitoring network to cover the whole management area, Sparrow said. The DEQ doesn’t know how many wells would make up a network representative of the whole LUBGWMA, or where they should be located, Sparrow said, but the updated trend analysis recommends a geostatistical analysis to help determine a strategic expansion.

Another priority is evaluating data from sites with DEQ permits for wastewater application and septic systems. The January 2025 analysis says expanding the network, possibly by supplementing the data with information from permitted sites, would “improve understanding of regional groundwater quality and could lead to a better understanding of influences from surface activities.” 

The final list of permitted facilities included in the next trend analysis will be determined by factors such as the amount, quality, timing, and geographic distribution of their groundwater nitrate data, according to Sparrow.

Facilities being considered include current industrial wastewater land application facilities such as the Port of Morrow or Lamb-Weston; former application facilities such as Shearer’s Foods and Hermiston Foods; domestic application facilities such as the cities of Boardman and Irrigon; landfills such as the Umatilla Chemical Depot Landfill or the Finley Buttes Landfill; and confined animal feeding operations such as Threemile Canyon Farms or Meenderinck Dairy.

Sparrow said, “The more we start to develop a network capable of monitoring the entire LUBGWMA, the more data we collect, the better understanding that we will have of impacts on the surface, that we’ll have (of impacts) on the aquifer.”