[Shop-talk] plumping question and sandrock sewers

[pethier at comcast.net]

From: Nick Brearley <nick at landform.co.uk>
> pethier at comcast.net wrote:
> >> 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
> >
> Right... I see now. Any UK surveyor working in the US is going to need a 
> speedy re-education course, and vice versa.

Maybe not, depending on location.  I'm sure there are newer communities which have all their records in USGS sea-level numbers.

> > 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.
> >
> >   
> As a contractor I find that method of levelling (temporary bench mark) 
> easier to work with. 

Except that you can't look a plan so marked and know the elevation of the city sewer.  Build the footing of your basement lower than the sewer and see how easy things become.