Using the right References

[tucents]

Vets, Candidates, Hopefulls & Spectators,

I just came across an interesting situation while doing practice problems in the Lindeburg book. I was asked to find a diameter on a primary clarifier. I used a surface loading value given in Metcalf & Eddy's Wastewater Engineering text, 2003, a reference book highly suggested for the exam. It suggested using a value of 1500 gal/day-ft. Using this yeilded option A (43 ft). Going to the solution, Lindeburg (arbitrarily?) suggests we use 1000 gal/day-ft. of course this yeilded option B (56 ft).

I wouldnt want an instance where my solving procedure is dead-on, but I get the question wrong because of conflicting reference values.

Since I'll be taking multiple texts with me to the exam, which reference would you trust? Lindeburg or OTHER?

Please advise.

P.S. its about a 23% difference in answer values.

 

[RIP - VTEnviro]

I used a surface loading value given in Metcalf & Eddy's Wastewater Engineering text, 2003, a reference book highly suggested for the exam. It suggested using a value of 1500 gal/day-ft. Using this yeilded option A (43 ft). Going to the solution, Lindeburg (arbitrarily?) suggests we use 1000 gal/day-ft. of course this yeilded option B (56 ft).
I wouldnt want an instance where my solving procedure is dead-on, but I get the question wrong because of conflicting reference values.

There won't be guess work on the exam. Different references and state codes use a range of values that are all legit.

Values will either be given or you'll need to pick off a standard table that doesn't change from state to state. For example, the loading rate my vary by state or municipality, but the density of water at 10 C is the same everywhere.

I had a sewer I&I practice problem were the rate per day/in diameter/mi of pipe was not given. I assumed the value used in the state wastewater manual, which was less than the one PPI picked out of left field (they didn't cite a reference). Right procedure, wrong answer.

 

[dastuff]

One interesting sidenote. For concrete design you can solve a problem using either Appendix C or chapter 9. I always have used App C just because that's how I was taught but the test used chapter 9.

They didn't even mention it, so when i was designing with App C all my numbers were a little off then I switched to Chap. 9 and was hitting them pretty much dead on. That led to a mid-test heart attack.

But i would trust a trusted (or a code-specified) reference over Lindeberg even if the values won't match with the Lindeberg test.

Also, VT is right. They should try to eliminate any confusion for you in the test (it's not meant to be a riddle).

 

[Dleg]

Yeah, what they said. You will not need to decide which value to use on the test - constants should be specified in the problem statement.

But this isn't to minimize the importance of knowing where to find the "right" numbers in real life. In your example, Metcalf & Eddy would be much preferable to Lindberg as a reference for designing an actual treatment plant. Or, the Ten States Standards.

 

[tucents]

Thanks a bunch gents! Just got the Metcalf & Eddy book last night.