To answer question 1. The wells in the shallow aquifer are overlain
with a surficial aquifer consisting primarily of clays, silts [the
Palouse Loess is a wind-blown silt from the Scablands of Washington]
with interveining lens of sands and gravels. Since the inception of
agriculture on the Palouse no contamination has been detected in the
Wanapum basalt aquifer. This is a function of the surficial aquifers
hydraulic characteristics, the ability of the clays, silts, etc. to
move water.
To answer question 2. Reread my original, albiet lengthy reply to
Tim Lohman.
Steve Gill