Please complete the following questions applying some of the topics we learned in Module 3. You have watched the videos, so now you can use your notes from lecture to solve for the question. For example, if the question asks about storativity, then you can go back to your storativity equations in your notes and answer the lab questions. The text book will also come in handy.

Below is a little bit of background on local aquifers that will help with our final project too! If you would like some more information, please check out a paper that a couple of our past students helped with about the West Plains, Pritchard_et_al-2020-Hydrogeology_Journal (1).pdf, or more specifically for the Spokane Valley Rathdrum Prairie aquifer (SVRP) SVRP Aquifer Report USGS 2007 sir20075041.pdf.

Here is a short intro to our regions main aquifers 1) the SVRP and 2) the Columbia River Basalt (CRB)

The Spokane Valley Rathdrum Prairie Aquifer

The SVRP is a paleochannel of the Spokane River that was filled by sand and gravel during the waning stages of the Missoula floods, Ice Age Floods, Pleistocene megafloods, or glacial outburst floods. During earlier Pleistocene glacial periods there were probably hundreds of floods, but the most preserved int he landscape is from the recent Frasier glaciation and one of the largest of the recent floods was about 16,000 years ago (Baker et al., 2016 GSA field guide). The sand and gravel allow for high water storage and transmissivity, but it is also unconfined and even exposed in some gravel quarries. Here is a map of the aquifer thickness based on geophysical data.

This map is probably a little different than what you have seen in the SVRP atlas, this is because the geophysics show more expansive basalt in the valley, as shown in their cross-section

Based on well data (wells can be miles apart), a more optimistic volume calculation of the aquifer is presented in this generalized cross section by the USGS as,

AWAY from the Spokane Valley, many people in the Columbia Basin receive water from basalt.

The Columbia River Basalt (CRB)

About 16 million years ago voluminous (44,000 mi²) basalt poured across eastern Washington. Below is an extent map and a stratigraphic column modified from a Stephen Reidel summary from 2015). It wasn't until 2017 that folks started doing age-determination on the ash layers between basalt flows using high precision Ar-Ar dating that we knew the basalt flows are older than presented below.

The basalt in the Columbia Basin is up to a mile thick, with a vast majority being part of the Grande Ronde Basalt.