Publication Summary

During 2006-07, the Washington State Department of Ecology undertook a variety of Total Maximum Daily Load (TMDL)-based field studies to assess stream temperatures and water quality conditions along the Palouse River, the South Fork Palouse River, and Paradise Creek, in Whitman and Adam Counties. This study, which was part of that overall effort, was conducted to gain a better understanding of groundwater′s influence on area stream temperatures and water quality conditions.

The Palouse River, the South Fork Palouse River, and Paradise Creek were included on Washington State′s 2004 303(d) list of impaired waters for violations of surface-water temperature, pH, dissolved oxygen, or fecal coliform standards.

In summer 2006, the Washington State Department of Ecology initiated several TMDL-based field studies to assess current stream temperatures and water quality conditions along these rivers and streams. This study, which was part of that effort, was undertaken to characterize the thermal and water quality influences that groundwater imparts to these rivers along gaining reaches.

Multiple field techniques were employed to derive both point-based and reach-based estimates of the water volume and nutrient mass load that groundwater contributes to area rivers. These techniques included stream seepage evaluations, installation and monitoring of instream piezometers, collection and evaluation of groundwater quality samples, and monitoring of streambed thermal profiles.

The reach-based gains and losses observed during seepage runs were generally supported by the point-based vertical hydraulic gradients and streambed thermal profiles measured at instream piezometer sites.

Measurable concentrations of dissolved orthophosphate (0.018 to 0.171 mg/L) and dissolved total phosphorus (0.073 to 0.875 mg/L) were found at all sampled piezometer sites. Measurable concentrations of dissolved nitrate+nitrite-N and ammonia were found at roughly half of the sampled piezometers at concentrations ranging from 0.013 to 10.1 mg/L and 0.03 to 0.549 mg/, respectively.

The average estimated unit-area-mass loading to the river from discharging groundwater varied by parameter and location. The loading ranged from 0.03 to 107 mg/d/m2 of streambed for dissolved total phosphorus, and 0.01 to 3,119 mg/d/m2 for dissolved nitrate+nitrite-N. These load values are considered upper bound estimates since they do not account for biological or chemical reactions that may potentially reduce nutrient concentrations in discharging groundwater as it passes through the final few feet of the streambed.

Link to EIM data for User Study ID JICA0000

Link to EIM data for User Study ID JICA0001