Thanks for all the feedback. Five years ago I surveyed the top of casing (TOC) elevations of 5 monitoring wells (MWs) we installed. Typically we would just use an arbitrary datum as a benchmark (or backshot), but for this project (for various reasons) it was critical to reference elevations from a known datum. I must have moved the tripod 6 to 8 times trying not to shoot long shots and having to turn corners. We recently installed 5 additional MWs, so I used established TOC elevations to calculate TOC elev for new wells, and I checked to see if some of the old data match. There was a difference of 0.15' on a couple of the old MWs.
I find the auto level a bear to work with especially when the receiver is at a joint in the rod, or laser line is way high.
We use an electronic interface meter down the well to measure water levels and oil thickness (if present). It has 0.01 tick marks, so the regulators assume that everything is accurate to 0.01'.
Me thinks thats not an auto level youre using if you have a receiver on the rod.
I find the auto level a bear to work with especially when the receiver is at a joint in the rod, or laser line is way high.
That sounds like you are using a construction laser, not a survey grade level. A construction laser has a precision of maybe 1/16" in 100 feet (50mm/1000m). A survey grade digital level will have an accuracy spec of around 1mm per 1000 meters.
Thanks for all the feedback. Five years ago I surveyed the top of casing (TOC) elevations of 5 monitoring wells (MWs) we installed. Typically we would just use an arbitrary datum as a benchmark (or backshot), but for this project (for various reasons) it was critical to reference elevations from a known datum. I must have moved the tripod 6 to 8 times...
These guys will tell you better, but it sounds like they're wanting the known datum to do something like producing groundwater contours/flow paths. So it would be an important aspect as the work progresses. To do that you'll want to use a survey grade leveling device - total station or auto level I suppose - and close the level by traversing back to your known point. This will "close" the survey and tell you if you have any blunders and more probably a closure error that can be adjusted using appropriate calcs. That adjusted leveling data will be a basis for all future work from which new known benchmarks can be set (and checked).
If you really get to 0.01 ft accuracy, over a north-south extent of several miles, then you will need to do the geoid correction, which a lot of people aren't familiar with because they can ignore in their ordinary work.
And for water work, you really should be using Dynamic Height, so the geoid correction is different than the Orthometric Correction more commonly presented.
We had almost this same discussion in 2012 and 2013 where somebody was trying to hold 2 cm accuracy on aquifer monitoring wells over quite a few miles of South Dakota, and generally surveyors thought it was not practical.
The geoid model is so much better today and digital levels are good, but it would be a major campaign effort and expensive to even make a decent effort over significant distances.
Me thinks thats not an auto level youre using if you have a receiver on the rod.
ah, interesting. We have a Lasermark LMH self-leveling Rotary Laser. The manual shows lots of pics of construction sites.
Wrong tool for the job sir.
Leveling Accuracy:
LMH-C
LMH, LMH-GR
±3/32-in at 100-ft (±3mm at 30m)
±1/16-in at 100-ft (±1.5mm at 30m)
Leveling Type: Electronic Self-Leveling ±5° (±3° LMH-C)
I would at least invest in an auto level, moving from those to a digital level was a big improvement for us, but if you're only doing small sites then an auto level such as a Wild NA1 is probably inexpensive and worth every penny. Use it with a really good level rod and your accuracy will skyrocket. To get really tight you need to move to a digital level/expensive rod, probably not needed for your application.
That sounds like you are using a construction laser, not a survey grade level. A construction laser has a precision of maybe 1/16" in 100 feet (50mm/1000m). A survey grade digital level will have an accuracy spec of around 1mm per 1000 meters.
Although...I had one grizzled old grade hop that would pull out his own lovingly cared for laser level that was calibrated only by him and never by those "idiots at the survey supply".
Had a site about 1000'x1000' and he would transfer accurate grades all over...but he was a unicorn.
First time I met him, he had half the site laid out. I showed up to do some staking, and he said, "You had those two stakes up on that hill, so I pulled off them and laid everything out." And...it was all within a few tenths horizontal and a tenth vertical, which for rough grading is spot on.
Those grade hops do not exist any more.
Wild NA1
No one ever regretted buying one of those.
The manual shows lots of pics of construction sites.
???
I would want any prospective service provider to indicate how they will validate their results? Providing plans using a priori error and accuracy values is not enough.
