Publication Summary

The Spokane River/Aquifer Interaction Study was intended to provide baseline data of the physical and chemical influences of the Spokane River on the upper Spokane Valley aquifer. Of particular interest is the influence of dissolved metals (cadmium, lead, zinc) that have exceeded water quality criteria in the river. The study encompassed the spring high-flow period through the fall low-flow period (May - November) of 1999.

The Spokane River/Aquifer Interaction Study was intended to provide baseline data of the physical and chemical influences of the Spokane River on the upper Spokane Valley aquifer. Of particular interest is the influence of dissolved metals (cadmium, lead, zinc) that have exceeded water quality criteria in the river. The study encompassed the spring high-flow period through the fall low-flow period (May - November) of 1999.

The Washington State Department of Ecology, in cooperation with Spokane County, sampled 12 monitoring wells monthly between the Washington/Idaho state line (RM 96) and Sullivan Road (RM 87). Six of the wells were part of two three-well transects that were 100-200 feet from the river at Sullivan Road and Barker Road. The remaining six wells were located throughout the Spokane Valley portion of the aquifer within ¼ mile to 1¼ mile of the river. Groundwater samples were collected for major cations, major anions, nitrate-nitrite, and select dissolved metals. Surface water data from four stations between Post Falls, Idaho (RM 100) and Sullivan Road were provided by the U.S. Geological Survey.

The primary findings of this study support previous work in which the Spokane River has been identified as losing water to the aquifer in the area of the Barker Road. Water level elevations show the groundwater table sloping away from the river at Barker Road, indicating the river is recharging groundwater at this location. Water quality data collected from the Barker well set also correlate with data collected from the Spokane River. Overall, field measurements of temperature and specific conductance, as well as cation/anion concentrations, were much lower in the river and the Barker well set than those measured within the rest of the aquifer.

Dissolved cadmium, lead, and zinc were also most prominent in the Barker well set. Cadmium and zinc concentrations decreased substantially in the Barker well, 200 feet south of the river. These decreases in concentration generally suggest that dissolved metals entering the aquifer from the river are diluted as distance from the river increases. Dissolved cadmium, lead, and zinc concentrations detected in the monitoring wells were below the Maximum Contaminant Levels for drinking water.

To further understand the complex relation between the river and aquifer, a more comprehensive analysis of water levels, river flow data, and water quality should be considered.

Link to EIM data for User Study ID SPOKAQ99