PART 12 Aquifer pumping tests - Dr. M. Zreda - University of Arizona

Aquifer pumping tests 97
When is u sufficiently small to use the Jacob logarithmic approximation?
Look at u = r 2 S/4Tt and note that
(1) u ∝ r 2 ⇒ small r or long t needed
(2) u ∝ S ⇒ confined aquifer better; if unconfined then need long t
(3) u ∝ 1/t ⇒ long time always good
(4) u ∝ 1/T ⇒ large T good; if small T then need long t
In summary, long t is always good.
Distance-drawdown data
At two or more observation wells at the same time:
Let observation wells be: s(r 1 ) = s 1 and s(r 2 ) = s 2 , and r 2 > r 1 (i.e., also s 2 < s 1 ).
Let
s
Q 2.25Tt
---------
4πT r 2 = ln --------------- Jacob approximation
S
∆h = s1– s2 =
∆h
Q
---------
4πT
2.25Tt 2.25Tt
ln---------------
– ln--------------- 2 2
r1S r2S Q
--------- ⎛
r2 --- ⎞
4πT ⎝r⎠ 1
2
= ln
Q r2 ∆h =
--------- ln ---- Thiem equation !
2πT r1 (Note that although this is not steady-state flow, Thiem equation works, by accident).
Hydrogeology, 431/531 - University of Arizona - Fall 2007 Dr. Marek Zreda