Just to bring the 0.01' requirement to light:
The level sensors that most firms use are accurate to about 0.1%, so over 10' of depth that's 0.01', however this really has nothing to do with the requirement.
The reason for the tolerance is the actual ground water table. The water table doesn't tend to vary a great deal (depending on the size of the site), so it's quite important that the elevation is measured accurately.
I hope this sheds some light on this.
If I would have to take a guess, I've probably surveyed in the neighborhood of 3000 MW's in my career, and did the tech work on countless others.
Surveying a MW to 0.01' elevation makes even more sense as they are surveyed on regular intervals. It's quite impressive to see what frost does to these things.
- Neil
Unless its a tiny area, the .01' is not reasonable. You really are going to do a leveling campain, complete with invar rods, first or second order digital leveling, and all the time and effort this implies. Not to mention something stable at these lame drill holes to measure from? I've seen these silly specs on sites that are tens of square miles in area.
A small gas station site; with enough care and some time it can be done, but most projects I've worked on it's a joke to say you've located the wells to .01'. I looked at one that covered a number of miles along a stream up and down bluffs, the cost for really getting the .01' would have been insane for the benefit. No rational person would pay it.
> Unless its a tiny area, the .01' is not reasonable.
I agree that 0.01' datum accuracy isn't reasonable, but I also understand the advantage of recording elevations to the nearest 0.01' on a small site due to the shallow slope of a typical water table. If the client specifies 0.01' accuracy, I rewrite the scope to state "recorded to the nearest 0.01 foot" to ensure that I don't put myself in the position of fraudulently certifying the results.
Exactly, the data is given to the nearest 0.01' but the accuracy isn't really .01'. I've always chatted with them about it, and what it takes to really meet the .01 accuracy standard and they always have understood that it's not necessary, usually depends on how old they are;-)
> Exactly, the data is given to the nearest 0.01' but the accuracy isn't really .01'.
If you agreed to supply data with a standard deviation of 0.01' (or 0.01' at the 95% level) and used a digital level, and proper procedures, in most cases that specification could be met.
I agree that if tying wells that are miles apart it would be overkill.
For something that didn't require horizontal, levels. For placing them on a map, shot from two locations on an adjusted trig loop and evaluated for precision and accuracy. Most of the time that we did this though, the site was quite open and allowed for that kind of surveying.
It can be done, doubtful anyone is doing it, but maybe. Expensive if it's is a large area, not bad if the site is small.