AUGMENTING GROUNDWATER RESOURCES WITH SURFACE WATER: AN APPROACH TO SUSTAINABLE WATER RESOURCES IN THE PALOUSE BASIN

The Palouse basin aquifer system consists of two distinct aquifers that extend from the southern panhandle region of Idaho into southeast Washington. The deeper, larger, and more productive aquifer is known as the Grande Ronde aquifer. It is the primary water supply for Pullman, Washington, and Moscow, Idaho, supplying over 90 percent of the water used by these communities. This aquifer supplies approximately 2.4 billion gallons of water per year to the Palouse basin region. The apparent Grande Ronde aquifer recharge rate is negligible, and aquifer mining is occurring.

The aquifer’s piezometric surface is dropping at a rate of 1 to 2 feet per year, and has been for over the past 50 years. We have been investigating means to artificially recharge the aquifer in order to stem water level declines. One means of artificial recharge would involve collecting, treating, and injecting local surface water, mainly from Paradise Creek. To determine if this is feasible, it is necessary to determine the spatial and temporal distribution of water quantity and quality.

The quantity of water is being analyzed through the use of a United States Geological Survey (USGS) stream gaging station is located on Paradise Creek near UI, with a complete data record from October of 1978 to the present. Regression analysis is also being used to extend the records of the tributaries. Also, three new stream gaging sites were recently installed at various locations along Paradise Creek.

The initial surface water quality study was limited to measuring a few parameters: turbidity, total suspended solids (TSS), pH, electroconductivity, temperature, nitrates, and total coliforms. These parameters are periodically measured at the three newer gaging sites. Other data were obtained from Total Maximum Daily Load (TMDL) studies completed in 1997 by the Department of Environmental Quality. In the future we will establish the relationship of quality to quantity to determine the best times to collect surface water for injection into the aquifer.

The results from this preliminary quantity and quality study will be completed prior to the conference, and will be further discussed in the presentation. From this research we hope to identify a feasible and sustainable solution to the problem of declining water levels in the Palouse Basin.