Publication Summary

This report characterizes the groundwater contribution to the Wenatchee River and its major tributaries including Icicle, Mission, Peshastin, Chumstick, Nason, and Brender creeks. Groundwater data from 54 mini-piezometers installed at selected sites were compared to surface water data to evaluate the dynamics of the groundwater and surface water system. Gaining and losing river reaches were identified using hydraulic gradient measurements and water temperature profiles. Additionally, historic groundwater quality data were evaluated to support the temperature and dissolved oxygen Total Maximum Daily Load (TMDL) assessments.

Errata of September 2007: Tables 4-9 were modified, and a paragraph was added under Data Quality Objectives, Blanks. These modifications do not affect the statistical analysis of the overall dataset, change the conclusions, or significantly alter the results of the study.

The Wenatchee River flows off the east side of the Cascade Mountain range in north-central Washington and eventually drains into the Columbia River near the city of Wenatchee.

The purpose of this study is to characterize the groundwater contribution to the Wenatchee River and its major tributaries including Icicle, Mission, Peshastin, Chumstick, Nason, and Brender creeks. Groundwater data from 54 mini-piezometers installed at selected sites were compared to surface water data to evaluate the dynamics of the groundwater and surface water system. Gaining and losing river reaches were identified using hydraulic gradient measurements and water temperature profiles. Additionally, historic groundwater quality data were evaluated; these data were from the state Department of Ecology, the state Department of Health, and the U.S. Geological Survey.

Overall, the groundwater quality is excellent in the Upper Wenatchee subbasin, deteriorates slightly in the Icicle Creek and Leavenworth areas, and continues to deteriorate downstream. Elevated nutrient concentrations are highest in the Peshastin and Cashmere areas. The nitrate standard of 10 mg N/l was exceeded seven times in the Lower Wenatchee subbasin, with a maximum detected value of 12.2 mg N/l. The elevated nutrient concentrations in groundwater may be contributing to low dissolved oxygen values in the river.

Link to EIM data for User Study ID WENRTMDL