Berit Thorson is a reporter for the East Oregonian. Contact her at 541-966-0807 or [email protected].

Part of the solution to the high concentration of nitrates in the Lower Umatilla Basin will be determining what the groundwater management area actually looks like under the surface.

However, Oregon State University and the Oregon Water Resources Department have different hypotheses about the Lower Umatilla Basin Groundwater Management Area's aquifer, which also overlaps geographically with four critical groundwater areas. A management area refers to quality of the water while a critical area refers to water quantity, and the Lower Umatilla Basin is low in both measures.

Since 1995, there has been a single conceptual model of the aquifer as a complex, interconnected bathtub or pool with higher and lower flow speeds in different areas. However, a new report from OSU presents a different hypothesis based on data collected during the past 29 years.

OSU's compartmentalization idea

Salini Sasidharan, an assistant professor in OSU's Department of Biological and Ecological Engineering, studies hydrogeology, or how water moves through the ground. She is a sustainable groundwater management engineer and also serves on the research subcommittee within the state's LUBGWMA advisory committee.

Alongside researchers Suraj Jena and Todd Jarvis, Sasidharan conducted a study using past evidence to glean new information, an approach called forensic hydrogeology, with data from the LUBGWMA from the past few decades. The team used publicly available online data, such as well depth details or driller's logs in addition to state-released data.

Through analysis, the researchers hypothesized there could be up to seven distinct compartments within the larger aquifer. These smaller parts still may be connected but have some sort of barrier to flow between them, such as tightly packed sand or clay soils that allow limited water to pass through.

"The one big contribution from our study that we have proposed," Sasidharan said, "is a conceptual model that may indicate that the basin has multiple hydraulically connected or disconnected regions of interest we call compartments."

This conceptual model still needs field work. Sasidharan said the next step is getting more funding to collect new data with this model in mind.

Additionally, she said, bringing in the nitrate component will eventually be needed, as the new conceptual model has nothing to do with tracking the flow of nitrates through the aquifer.

"Without understanding the hydrogeology, we cannot really look into the actual nitrate data and try to understand," she said. "For sure, we cannot really say that compartmentalization is the reason, but that's one of the hypotheses that we need to go and collect more data and understand better."

OWRD's approach

Meanwhile, the Oregon Water Resources Department is working on its own aquifer hydrogeology model, with a goal to have it fully peer reviewed in about a year. As of now, after initial analysis, the department expects its understanding -- based on the 1995 model -- to be supported through the updated data and modeling.

Chris Kowitz, north central region manager with OWRD, said the two models aren't "radically different" but are distinct, as the agency doesn't identify distinct compartments within the aquifer.

Instead of thinking of the low-flow and high-flow areas as distinct, OWRD conceptualizes them as connected but with different substrates -- such as sand, clay, gravel, sandstone or fractured rock -- obstructing the flow. Clay and sand, which are dense when packed, will create a slower flow than larger rocks or sediment.

In terms of the science, Kowitz said, having two alternate hypotheses and determining which -- if either -- seems most aligned with the aquifer is useful.

"As we move these two hypotheses forward, one of them will be more validated by the data than the other over time," he said, "and so we'll eventually have one that is kind of the consensus model."

The state will stay the course

OSU in early October offered its hypotheses in a report to the Oregon Department of Agriculture, which funded the research. OWRD's initial report is expected by the end of April 2025.

Justin Green is the executive director of Water for Eastern Oregon, also known as H2OEO, a nonprofit working toward better drinking and groundwater quality in the LUBGWMA, Understanding the hydrogeology of the basin, he explained, is vital for implementing best practices.

"Without understanding the hydrogeology, there won't be that clear picture of what's working and what isn't," he said. "It's going to be really important for us to understand the hydrology so we can establish a baseline of where we are today, implement projects and then measure progress."

For now, though, the state won't be changing its understanding of the aquifer's hydrogeology. While OSU's role as an academic and scientific institution is to question conventional wisdom and pursue areas of interest, Kowtiz said, OWRD's as a state agency is to regulate in addition to doing the science.

"The state agencies just have a little bit of a different role, especially the regulatory agencies," he said, "which is, we can think about things, but we need to come back to what we know."

As much as everyone involved -- residents in the LUBGWMA, farmers working the land, local and state authorities -- want to start implementing solutions, this is a problem that cannot be fixed with a single, simple solution, especially while there are questions about the hydrogeology.

Meanwhile, interventions can start on other parts of the LUBGWMA. To organize the overarching goals and timelines of the project, the state produced and published its Nitrate Reduction Plan in September. The plan brings together the work of all the state agencies and their efforts in the short-, medium- and long-term with regard to the groundwater management area.