[Shop-talk] plumping question and sandrock sewers

[pethier at comcast.net]

From: Nick Brearley <nick at landform.co.uk>
> pethier at comcast.net wrote:
> >
> > I have mentioned that Saint Paul is a river-bluff town.  Our city datum for 
> > elevations is USGS sea level minus 694.10 feet.  This is based on some 
> > point at some steamboat landing circa 1850.  
> Hi Phil,
> 
> Interesting stuff, labour must have been cheap in those days. 

Yes, it was.  If we were starting fresh today, with expensive labor and advanced machinery, those sewers would probably be conventional.

> A lot of 
> Cornish tin miners emigrated to the US in the 1800s. Saint Paul would 
> have been a natural home for them. 

I don't know that there were a lot of workers with actual mining experience.  Just whomever was hungry, strong, and fearless.

Actually, many of the Cornish miners went to the U.P. of Michigan and to northern Minnesota.  Their influence is felt here.  You can buy pasties in all the grocery stores up there.  You can find them in the Twin Cities if you look.  We get pasties twice a year from a church in Maplewood.  They make them up in the church basement.

>One small point, could that datum be 
> plus 694.10 feet?

It's all in how you look at it.  We say "minus" because the USGS number on a plan is larger than the City Datum number.

USGS sea level reading - 694.10  =  Saint Paul City Datum

If the invert of a manhole is 810 feet above sea level, it will be shown on our maps as 115.90.

Conversely, the sanitary manhole at Laurel and Griggs is marked 221.0.  The invert of that manhole is 915.1 feet above sea level (roughly 221 feet above the Mississippi River).

If a surveyor shoots a job and marks the elevations in sea-level (he must be from out of town), you must subtract 694.10 from each reading to determine relationships to sewer maps.  The normal procedure if you are a private surveyor is to phone our Survey Division for benchmarks.  The tech here will give you the city-datum elevations for the top nuts of at least two fire hydrants near your job.  You go to the site and shoot the hydrants.  It they all agree with each other according to the benchmarks, you can shoot the site in confidence.  If they do not agree, call our Survey Division because one of the hydrants has been hit by a car and replaced by Water Services and not yet re-shot by Survey.  

Sometimes a surveyor will not call for benchmarks and just pick a random place on the site and call it "100.00".   I hate that.  When you design a house, you should know the elevation of available sewer.  It is expensive and annoying to make sludge flow uphill.  The builder ought to spec the job for the surveyor to supply elevations tied to a standard.

--
Phil Ethier  West Side  Saint Paul Minnesota  USA
1962 Triumph TR4 CT2846L, 1992 Saturn SL2, 1993 Suburban,
1994 Miata C package
pethier [at] comcast [dot] net    http://forum.mnautox.com/forums/
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I decry the textmessagization of the American-English language.