Lecture 25

Lecture 25

Theoretical Time - Drawdown Relationship

Fetter 7.4.6

Confined versus Unconfined

Partial Penetration-

What happens when well screen or open hole does not fully penetrate the aquifer.

All theory presented requires full penetration of well.

Horizontal flow if fully penetrates.

Partial Penetrating-

3-D flow (vertical flow components)

if anisotropic ® K_v and K_h important to know.

Can ignore partial penetration effects if a partially penetrating well is located greater than 1.5b

away from pumped well. (Hantush, 1964)

Then describe drawdown with appropriate equations.

1.5b

If a well penetrates at least 85% of the aquifer, it can be treated as fully

penetrating. (Todd,1980 p.152)

If pumping well is partially penetrating and if a partially penetrating

observation well is located closer than 1.5b, then drawdown in wells is complex.

	(1.) Can have different drawdown in two observation wells equi-distant from pumped well, but screened at different depts.
	(2.) Is possible for more distant well to have greater drawdown than a closer well.
	(3.) Effect of partial penetration similar to time drawdown observed from leakage.
	(4.) May look like recharge boundary.

When designing Aquifer Test, place observation wells more than 1.5b(K_h /K_v )^1/2 if

the pumped well partially penetrates.

If pumped well and observation wells open in either the top or bottom portion of

the aquifer, drawdown in observation well > than fully penetrating.

Find solutions to well function based on the geometry of the aquifer and well design!

In an unconfined aquifer-

		Minimize partial penetration effects if:
			Observation well fully penetrates.
			(2.) r >
			follow late time (Theis Curve)
			(3.) t >
			(4.) If r < Early time (Theis)

ENV 302 - Lectures