Submerged Orifice

[Timber]

Imagine you are assigned with the task of determing additional pumping cost associated with ground water infiltration into an existing pump station wet well.

The existing wet well is designed to collect a small neibhorhood of sanitary sewer. The well is constructed of concrete, it is cylindrical in shape, with an 8' diameter. The top of the well has an elevation of 1120' NGVD matching the surface grade. The bottom of the well is set at 1110' NGVD. Suppose the surrounding normal water table is consistently measured at an elevation of 7' below the wet well rim. If an eroded 1" circular hole is located 12' deep on the side of the wet well, how much additional volumeteric fluid flow will be collected and pumped out of the wet well on a daily basis. Assuming the water table elevation will remain constant regardelss of ifluence from the infiltration. One can also assume the existing lift station was designed to serve 400 single family homes with an average daily flow of 0.14 MGD. For arguements sake, the current pumping cost is $10 per day per every 100,000 gallons pumped. How significant would the increase be. Is it worth addressing? Is this possible?

Give it a try.

 

[EdinNO]

Can we phone a friend? 50/50?

What topic is this? Civil Water Resources?

Ed

 

[Timber]

Yes -

Q = C * A * (2 * G * H) ^0.5

Just thought I'd drop in leave a post. Water Resources

 

[Art]

the wet well is 1120 - 1110 = 10 deep

the hole is at 12', not in the wet well...no infiltration

if on the bottom of the wet well, say 10':

a 1" hole with 3' of head would flow ~ 0.5 (0.5/12^2) Pi x (2 x 32.2 x (Pe-Pw))^1/2 x 7.48 x 60 gpm ~ 9.8 x (Pe - Pw)^1/2 in feet of head if the well is empty, ie, 3 ft of head then 17 gpm or 0.024 MGD or a 17% increase in cost...

0.14 MGD ~14$/day

0.14 + 0.024 MGD ~ $16.4/day

at 2 feet of pump cover: 1 ft of delta head

9.8 GPM or 0.14 MGD

a cost increase of 10% or $1.40/day....

now if we assume we keep 3' of sewage on the pumps to keep them from burning up the net increase will be 0 once again

I would be more worried about DEP fines for polluting the water table if the wet well level rises above 3 ft due to improper pump sizing

 

[Fudgey]

Submerged orifice, hmmmm. Sounds a lot like farting in the bathtub to me!