4. Groundwater

Oregon Water Resources Dept. has prepared a general as well as detailed **groundwater characterization** (January 2019) for the upper Grande Ronde basin that is on the Union County website (opens in new tab):

https://union-county.org/wp-content/uploads/2021/03/Characterization-of-Groundwater-in-the-Upper-Grande-Ronde-Basin.pdf. Key findings include:

Groundwater supplies are controlled by recharge, available storage, and discharge within the basin and groundwater interflow between the two major aquifer systems, as well as the underlying geologic structure of the basin
Groundwater pumping, especially from the alluvial system, captures some natural groundwater discharge, and has the potential to reduce flows in hydraulically connected streams/rivers
Water levels are declining in both aquifer systems, though most notably in the volcanic aquifer system
New allocations of groundwater from the alluvial aquifer may occur if an approved approach to mitigation is established
The lack of spatially distributed water level data, as well as data over time, prevents a more complete understanding of characteristics of the aquifers

see also Oregon Dept. of Water Resources **groundwater mapping tool** linked below. Wells with hydrographs (charts of water levels over time) are shown as blue dots on this map, and by clicking on them you can access hydrographs, well logs, and more.

https://apps.wrd.state.or.us/apps/gw/gw_info/gw_map/Default.aspx?gw_site_id=9671