# ENVIRONMENTAL - Morning



## 3gorgesdam (Sep 29, 2006)

Please post some "interesting" questions on this subject. Thanks.


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## GTScott (Sep 29, 2006)

I have some GW probs, but also need more.

Is changing some numbers around enough to make it ok to post a question published elsewhere? Or, can I just scan them and post them?

-GT


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## JasonT33 (Sep 29, 2006)

Ok

Determing permeability of an artesian aquifer being pumped by a fully penetrating well. The aquifer is composed of medium sand and is 90 ft thick. The steady-state pumping rate is 850 gpm. The drawdown of an observation well 50 ft away is 10 ft and the drawdown in a second observation well 500 ft away is 1 ft.


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## RIP - VTEnviro (Sep 30, 2006)

That one is either the Theis equation or the Thiem equation. Either of which would be in a standard groundwater text.

The one I used was "Applied Hydrogeology" by Fetter. Really good book.


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## GTScott (Oct 2, 2006)

What DO concentration (range) is required in a stream to support a fish population?

Find it in the CERM.

-GT


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## RIP - VTEnviro (Oct 2, 2006)

Typically, you want to keep a DO of 5 mg/L or higher to maintain healthy fish populations.

When you get below that, you start getting undesirable ecosystem changes.


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## 3gorgesdam (Oct 2, 2006)

for a large fish population DO should be around 6 mg/L. Just reviewed this part last night.


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## RIP - VTEnviro (Oct 2, 2006)

I smell a Streeter-Phelps DO sag curve on the way.


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## GTScott (Oct 2, 2006)

4-6 mg/L

Not a tough one, but a good exercise to find that info in the CERM.

-GT


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## 3gorgesdam (Oct 2, 2006)

Population Equivalent:

P1000, eq = (BOD mg/L * Q ft/sec* 8.34 mg-L/MGD-sec )/(1000*10^6)

Please explain where 8.34 comes from? I know it is due to unit conversion. But I can't seem get that. Thanks.


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## 3gorgesdam (Oct 2, 2006)

> 4-6 mg/LNot a tough one, but a good exercise to find that info in the CERM.
> 
> -GT


Thanks, I see your status changed to Junior Engineer now. Did it come with a raise? :thumbsup:


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## 3gorgesdam (Oct 2, 2006)

> I smell a Streeter-Phelps DO sag curve on the way.


Morning or Afternoon? I will remember that example, that is pretty much what I do with Environmental, I don't really understand it even after read it over and over.


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## RIP - VTEnviro (Oct 2, 2006)

The whole S-P curve and related problems conceptually make sense if you think about them. It's just that the equations are so awkward that it's easy to screw up the calcs.


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## 3gorgesdam (Oct 2, 2006)

> The whole S-P curve and related problems conceptually make sense if you think about them. It's just that the equations are so awkward that it's easy to screw up the calcs.


I agree, it is cumbersome. Okay, here is a question about that long equation for Dt and tv. The log 10 base term, the book said if Kd or Kr was given in e-base, change the log 10 to ln in the equation, everthing else stays the same. Did I understand this correct?


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## RIP - VTEnviro (Oct 2, 2006)

What terms do Dt and tv? I learned it with different notation.

And as for base 10 vs. base e, I've only ever used it with base e.


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