City NAVD88 Requirement & RedLines

And they are not going to accept the fact that their maps may be wrong?

Looks like they need to engage a surveyor to update their maps.

Interesting.

Since we have RTK, I'd do a quick check against another BM (that would expose a 0.6' bust in the BMs), and perhaps remeasure the "downs".

Then what? Will the city back off if you provide notes that support your elevations?

Maybe this is a result of that error in the mile high BM at the State Capital. 😉

Do the rim elevations check?

> perhaps remeasure the "downs".

I'd do that before I got too much further on this. But if they check you should stick to your guns.

The only other possibility I see is to hold one of their invert elevations as a project benchmark and adjust everything to match.

> mile high BM at the State Capital.

(Beavis voice) Hey, Hey. You used "BM" and "state capitol" together in a sentence.

Inverts do change. Cities are often upgrading lines from old clay pipe to new plastic. The question is how old are the maps, and how old are the lines.

Don't the sewer construction plans show a Benchmark on the front page/title sheet? See example from our agency's sewer plans:

> City requires that the PGB be tied to a City BM with NAVD88
>
> No problem - The city has a list of City bench marks with published NAVD88 elevations and the nearest is only 3 blocks away. Description & cap markings match that of the record.
>
> Great - simple level loop;
> closes 0.03' and 6 TP's
>

Did you run through a second BM, or close on a 2nd? Maybe the one you started and ended your loop on is bad?

Related to this, are the inverts based on "plan" versus "reality" is another question.

"Elevation equation"

🙁 :coffee:

Sounds like you are basing your elevations on a single benchmark. I would never trust a single benchmark without some kind of verification-such as tying to another by leveling, using GPS to tie to another, etc. If you did include another BM, then never mind.

There are MANY survey marks in Pittsburgh that were knocked out when they put in "wheelchair cuts" in the sidewalks at the intersections. Then the contractor carefully put them back "right where they were before". Other than seeing new concrete around the monument box, you couldn't tell that it wasn't in the same place. Also, I have seen BM's on bridges that got put back AFTER the bridge was replaced, no restamping. Then of course there is subsidence, frost heave, etc.

Ties into another City BM and checked within expected tolerances (0.05')
That bench was 6 blocks by 4 blocks away, had total of 12 TP's - there and back.

Well, it's either the city has bad elevations on the BM's or the maps have a bust.

Talking with some tech at the city yesterday, he could not tell me if the maps he As-Built drawings / maps OR IF THEY WERE DESIGN MAPS -- He didn't know

I asked to see the field work or notes that determined the invert elevations, he said it was not their policy to supply such information. ????

Either way- They insist that the survey and PBG match the city invert elevation AND that the survey be tied into a City BM and note that the datum is NAVD88

I'm going to state what the equation is to match
Just like in the days of olde

- WHAT A FRICK'N PITA -

> Ties into another City BM and checked within expected tolerances (0.05')

Did you spot check a rim elevation, using levelling, and a dip? In other words, have you proved, by independent means, that there is no error in your data? It happens.

> Either way- They insist that the survey and PBG match the city invert elevation AND that the survey be tied into a City BM and note that the datum is NAVD88

You are dealing with a tech, who is an idiot. Take it to the next level. Hopefully this idiot techs boss is not also an idiot.

> I'm going to state what the equation is to match.

I very much doubt that will get you anywhere. It will only further complicate the situation.