I’m new in a public works department and reviewing an RFP for a water system project and it’s clear it wasn’t prepared by someone with surveying background with statements like “accuracy of vertical and horizontal control will be to 0.01’ “.
I thought I’d toss this topic out to see how it would typically be addressed in your orbit. From the perspective of a utility surveyor, accuracy on the order of 0.01’ is rather unrealistic and likely unnecessary.
Just because I'm paranoid, doesn't mean they aren't out to get me.
I have seen that before...specs written by an engineer with no understanding of accuracy and significant figures. What they most likely mean is they want coordinates and elevations listed to 0.01 feet. However, it could be that they need more accurate elevations, depending on how flat it is.
@john-hamilton My initial take. What would be the best way to reference some national standard that would avoid this confusion?
Just because I'm paranoid, doesn't mean they aren't out to get me.
@williwaw I think I'd just walk down the hall to the guy who prepared the RFP and have a chat.
@bstrand Of course, that’s the easy part. The question remains what standard of accuracy are they really after and how to communicate that unambiguously to a contractor. Saying that you want 0.01’ accuracy is not the same as reporting accuracy to 0.01’. I’m wondering how others are accustomed to seeing this requirement stated in an RFP or contract.
Just because I'm paranoid, doesn't mean they aren't out to get me.
"water system project" covers a wide array of project types. Could be a storage reservoir, treatment plant, pump station, county wide distribution water lines, ect. Each will have very different accuracy needs. 0.01' elevation accuracy might be valid for a building housing a water storage or treatment facility. For the distribution system; not appropriate.
@bstrand Of course, that’s the easy part. The question remains what standard of accuracy are they really after and how to communicate that unambiguously to a contractor. Saying that you want 0.01’ accuracy is not the same as reporting accuracy to 0.01’. I’m wondering how others are accustomed to seeing this requirement stated in an RFP or contract.
Oh, I misunderstood the question; I thought you were asking for a precision standard instead of examples of RFPs.
As field engineer on a very large project withe every type of underground utility imaginable our project specifications were 0.1 feet horizontal and 0.01 feet vertical. So the accuracy was project specific. I don't know of a standard.
After layout and construction an "as-built" of the project was randomly checked by memebers of a Subsurface Utility Engineering team.
I would only verify what was measured in place before backfill on pipe runs. Although that was not part of the specification, I would never testify or show a record of the slope or location of a utility run between points of inflexion only.
Historic boundaries and conservation efforts.
https://nsps.us.com/page/ModelStandards
These NSPS standards of practice have been around for quite some time.
@mark-mayer Thanks. I’m aware of them but have had little first hand experience in using them in my present capacity so maybe better to vet something as appropriate rather than assume. Are these standards used in your experience with public works projects or something different ? I’m coming from the view that I sometimes don’t know what I don’t know.
Just because I'm paranoid, doesn't mean they aren't out to get me.
I've never seen those standards referenced anywhere else. But they do seem reasonable to me.
In past years I managed at least $150 million in Municipal projects ranging from roadway rehab to water towers. Never once in my bid specs did I include 0.01' H & V tolerances because it's impractical to believe anything is going to be built to those tolerances.
@chris-bouffard Exactly my sentiments. I submitted my suggestions on establishing primary control for the project to NSPS standards, +/-0.03 @ 95% for horizontal and +/-0.01' @ 95% for vertical, with vertical requiring closed level loop verification. I threw in a bit about 'protected, stable and intervisible'. My rational being that everything laid out off of that control should be with >0.1' in the real world. Mostly this is engineers who don't really understand what they are asking for. Tried explaining this to the project engineer and he had that blank, deer in the head lights look. "That's just what we've always done'.
Just because I'm paranoid, doesn't mean they aren't out to get me.
I rarely see benchmark accuracy specified in NC. When it is, it's not consistent.
Although I absolutely hate it, it's usually best just to agree with the absurd requirement and then ignore it. You could give the contractor a plus or minus 0.1' elevation on a manhole and they'll build a waterline without issue. They'll use a tape to measure the vertical separation between sewer and water and any other crossing utilities. Similar with sewer, the contractor is going to get elevations from direct location of inverts and either use a pipe laser or a laser level to make sure they have the correct slope. I'm sure union jobs in cities are different, but not for practical reasons. For instance, why does there need to be three feet of separation between water and sewer unless using ductile iron? It sounds like a good idea, but is there a study to back it up? Similar to the varying separations between potable wells and septic systems, the offsets are based on feelings not rigorous testing.
Surveyors and engineers should spend a bit of time inspecting the construction of water and sewer lines so as to witness first hand what the contractors are doing, or not doing, with our control. Another thing to consider before spending a day running levels through BMs is the as-built requirements. If it's just a record as-built, meaning the engineer will sign off on some cartoonish sketch or markup from the contractor, why on Earth would you waste time running levels through your control when the engineer and owner don't care enough to verify the accuracy of what was actually built?
@murphy Dang it Murphy. There you go making perfect sense in an anything but perfect world. I get in enough trouble as it is for saying what I actually think.
Just because I'm paranoid, doesn't mean they aren't out to get me.
I agree with you except the part about separation requirements being based on feelings only. Of course it is not practical to individually investigate the permiability qualities of every individual scoop of backfill. There has to be an accepted limit within a margin of error. Nevertheless, I think that you would be surprised how much actual laboratory analysis goes into these parameters. Loads of stuff on Youtube about that.
I guess we're lucky. We work with 10 + municipalities and none of them even know what accuracy standards or have any reference to them in the contracts. We use our best judgment based on the needs of the project and haven't had any issues that weren't created by our own occasional errors.
@wa-id-surveyor The company I work for now does quite a bit of construction staking and from what I hear they encounter a fair amount of slop on projects where the design topo was droned or mobile scanned. I don't think specs would be out of line for newer tech like that.
@bstrand Agree 100% but none of our municipalities (with 1 exception) even understand accuracy standards. If they had them they wouldn't know what they meant or have any method to enforce them. We do all our own staking so your situation is never one we're in on purpose. At least once a year we get roped into a situation you described and we only do it to assist a client in a 'situation'.
If they had them they wouldn't know what they meant or have any method to enforce them.
You make a very good point.
Just because I'm paranoid, doesn't mean they aren't out to get me.