Ask A Scientist Chemistry Archive

Question:
After the EPA comment that surface water is frequently more contaminated 
with pesticides than well water I am wanting to know the mechanism by which
the same water can become clean when withdrawn from a well but not when taken 
from a river.   These mechanisms come to my mind: Absorption, ion exchange
on to soil particals, physical straining, bacterial predator.
What have I missed?  Through what depth of soil is necessary?  Over what 
legnth of time is necessary?  Is there a sutitable resource for High School 
to give more information on this topic?
 hebard r olsen

Answer:
I can think of two active processes: alkaline and acid hyrolysis. The
simple passage of time can be an important variable depending on the
half life of the pesticide.  Try the chemistry section for more!
 michael b lomonaco