Jim Frame, post: 393293, member: 10 wrote: My point wasn't to criticize you or your methods, it was to complain (further) about clients asking for something not economically attainable and then finding surveyors willing to certify to accuracies that they didn't attain.
If you're dealing with engineers at the client end, while they may not have taken a surveying course in college, I'd think that they did take statistics. Isn't there a statistical explanation that should cut through the fog surrounding the specification?
I do like Mark's suggestion of specifying the relative accuracy of levels taken on adjacent manholes at some uncertainty that is at the 0.01 ft. level or better (assuming that is as acheivable as I would think that it is).
Naturally, the other strategy is to provide a Chinese restaurant menu version of services, i.e. quote fees for different uncertainty levels in absolute manhole elevations that shows the dramatic difference that exists in the time required for each.
Mark Mayer, post: 393299, member: 424 wrote: Your former employer should invest in a digital level. Closures under a hundreth are the norm with those things given even moderate care and attention to practice.
I don't think they have any surveyors anymore. I guess we were not that highly valued, which would explain our lack of a digital level. I moved on before things got too bad.
Dan Patterson, post: 393277, member: 1179 wrote: Do you mean for monitoring wells? We have that requirement here and have had it for a long time for all monitoring wells. There is a form that has to be filled out, certified, signed and sealed called a Form 'B'. The one place I worked did a ton of them (it was an environmental consulting firm that had its own civil/survey department). Even on the large sites as you described (landfills, etc) we would run long level loops. If we didn't close our loop within a couple hundredths or so we ran it again. I'd say most or nearly all of those were within 0.01'. It is possible, but it's a pain.
Yes, I did a number of projects for monitoring wells in the 70's, there wasn't a "standard" then, but the report would state a NE to the nearest 1' and .1' for the elevation. Everything was trig leveled and it was over large areas; many sections. Control was all trig levels and the country was often very rough semi-mountains. Of course the wells weren't within .1' vertically, but were reported to that number.
Moving forward; maybe sometime in the 90's I started to see the .01' requirement for monitoring wells for small areas. Sometimes it would be along a stream, one gas station with a cluster, then upstream a mile and another cluster, and so on. Of course there is no way to tie each cluster together and be within .01' without a Yuuuge expense, if it's even really possible. And then I started to see that same thing even for our clients doing the big projects, clearly you aren't going to want to spend the real expense to try and get wells within .01' in distance valleys. I would say it can't be done, but of course no one will ever challenge you.
It's basically nonsense, I can usually argue with them to remove it.
Like Jim says, clients without a clue.
There's more to vertical precision. There is global precision and local precision; and even "levels" of that. Basically, I think they would want the relative elevation of a MH to be relatively precise to the two adjacent MH rims. That is to say, that they can get the "vertical difference" between any two MH's to be fairly accurate. That also means that it is probably more relatively accurate than the full loop precision. Second, there is the benchmark you are using. Do you always check between two or more benchmarks? Are you sure it is accurate to it's original elevation (and do you or the client care". That would be closer to the "global accuracy". Of course you state that your elevations are based on XX benchmark using the published elevation of ####.## . You might want a statement like Mark says throwing in some language that covers your but. "you have a local precision of xxx, based on a published elevation. you are publishing the elevations to the nearest hundredth of a foot for local use...or something like that.
It's sad that we can put the data to any precision by rounding to three or more spaces in our printouts and that is confused for the precision.
Tom Adams, post: 393311, member: 7285 wrote: Basically, I think they would want the relative elevation of a MH to be relatively precise to the two adjacent MH rims.
Since they're intended use of the elevations is to model the entire system, I expect they want to hold as much accuracy as they can afford over the whole shebang. But then hydraulic modeling isn't something about which I have any knowledge.
With regard to bench marks, since this is in a subsiding area my proposal includes densifying within a recent height modernization network, but that part of the proposal isn't what's causing the headaches.
I would talk with the Engineer doing the model. Depending on the circumstances .1' could make as much as 20 percent difference in capacity calculations.
It's always best to find out where you're going before you walk too far...
Jim Frame, post: 393315, member: 10 wrote: Since [their] intended use of the elevations is to model the entire system, I expect they want to hold as much accuracy as they can afford over the whole shebang. But then hydraulic modeling isn't something about which I have any knowledge.
With regard to bench marks, since this is in a subsiding area my proposal includes densifying within a recent height modernization network, but that part of the proposal isn't what's causing the headaches.
In hydraulic modeling, the slope, S, is the important number for a run of pipe between manholes, but the SQRT of S is the term that applies to flow calculations. So capacity is relatively insensitive to small variations in S. For example, for a 300 ft. run of pipe, an error of 0.10 ft. in the elevation difference from end to end translates into an error of 0.00033 in S. The difference between the capacity of a pipe with a slope of 1% (0.01000) and 1.033% (0.01033) is only about 1.6%.
I'd expect that uncertainties in other factors like pipe roughness coefficients on older, pipes with eroded surfaces would completely overrun the errors resulting from random small errors in pipe slopes.
Jim Frame, post: 393315, member: 10 wrote: Since they're intended use of the elevations is to model the entire system, I expect they want to hold as much accuracy as they can afford over the whole shebang. But then hydraulic modeling isn't something about which I have any knowledge.
With regard to bench marks, since this is in a subsiding area my proposal includes densifying within a recent height modernization network, but that part of the proposal isn't what's causing the headaches.
I would think the most important thing to them would be the "relative" elevations of the whole system. But if they don't have a problem with your densifying, then I would be all for increasing the vertical network whenever possible.
Kent McMillan, post: 393320, member: 3 wrote: In hydraulic modeling, the slope, S, is the important number for a run of pipe between manholes, but the SQRT of S is the term that applies to flow calculations. So capacity is relatively insensitive to small variations in S. For example, for a 300 ft. run of pipe, an error of 0.10 ft. in the elevation difference from end to end translates into an error of 0.00033 in S. The difference between the capacity of a pipe with a slope of 1% (0.01000) and 1.033% (0.01033) is only about 1.6%.
I'd expect that uncertainties in other factors like pipe roughness coefficients on older, pipes with eroded surfaces would completely overrun the errors resulting from random small errors in pipe slopes.
Slopes of .2% and less aren't unusual in our valleys. Not smart but not rare...
The 0.01' usually comes from State requirements. The requirement may say report elevations to the nearest 0.01', which is not necessarily meaning to a precision of 0.01'. From that measure down point they are generally using a cloth/nylon tape with a weight to measure down to the water surface. Add that all up and they are lucky to have WSE to within 0.1' or more.
Monitoring wells almost never get all installed at the same time. A gas station starts with 4 observation wells around the installed tanks from start up. Once a problem is discerned, most sites start with 4 monitoring wells and as data is gathered and evaluated and the underground plume moves more are added. My most recent site has 5 new wells on the PQ and 3 adjacent parcels, 2 being across a highway. Total is 23 to date, 7 being stickups in a detention basin like area. This is the third site in a row on which I am also doing a property line survey. Easements or agreements are required for off site wells and this area also has multiple drainage and sewer easements. Drainage swales along the North and South property lines and portions of all lots are in the 100 year floodplain. As of yesterday I have one adjacent and two offsite property monuments, 4 prior and 4 new wells, and 3 buildings located. I have one more building to complete locating, 1 new and two more existing wells, utility markouts and we sit down to figure out how everything ties together and the survey priority sequence. Because of the long time and multiple prior steps, not everything will be in agreement with prior data.
The station owner started me off with a 2002 site plan and coffee. Township office is one block up the highway. My Right to Know request yielded 4 adjacent site plans, $40 well spent. Per the site plans some station features are over the lot lines.
I started at the only mag nail found to date on site as my OPUS control point. Do not yet have information tying it to prior well surveys. I GPSed 4 traverse points and have seven total traverse points. Five are sprayed out from my control point and await back and cross observations before adjustment.
Paul in PA
thebionicman, post: 393323, member: 8136 wrote: Slopes of .2% and less aren't unusual in our valleys. Not smart but not rare...
The same analysis applies, though. The error in capacity of a run of pipe at 0.2% slope and 300 ft. in length that results from a 0.10 ft. error in elevation at either end will be only 7.4%, which is probably going to be less than any error in the roughness coefficients used to compute friction losses.
If the pipe is at 0.5% slope, the error in theoretical capacity resulting from an error of 0.033% is only 3.2%.
Speaking of Monitor Wells...
USACE / NAVFAC / AFCESA / NASA UFGS-33 24 13 (August 2008)
USACE Superseding UFGS-33 24 13 (April 2008)
UNIFIED FACILITIES GUIDE SPECIFICATIONS
References are in agreement with UMRL dated October 2010
DIVISION 33 - UTILITIES
SECTION 33 24 13
GROUNDWATER MONITORING WELLS
SECTION 33 24 13 Page 29 (Click Here)
3.4 SURVEYS
Establish coordinates and elevations for each monitoring well/test hole. Determine horizontal coordinates to the closest 300 mm 1.0 foot and referenced to the State Plane Coordinate System, or Universal Transverse Mercator (UTM). If the State Plane Coordinate System/UTM is not readily available, use an existing local grid system. Obtain a ground elevation to the closest 30 mm 0.1 foot at each well. The highest point on the top of the riser pipe serves as a measurement point; reference this elevation and survey to the nearest 3 mm 0.01 foot using the National Geodetic Vertical Datum of [1929] [1988]. If the datum is not readily available, use the existing local vertical datum. Plot the location, identification, coordinates, and elevations of the well and monuments on maps with a scale large enough to show their location with reference to other structures.
SECTION 33 24 13 Page 33
3.8.2 INSTALLATION DIAGRAMS
k. Elevations/depths/heights of key features of the well, such as top of well casing/riser pipe, top and bottom of protective casing, ground surface, the depth of maximum frost penetration (frost line), bottom of well screen, top and bottom of filter pack, and top and bottom of seal.
m. Well location by coordinates. A plan sheet shall also be included showing the coordinate system used and the location of each well. A plan sheet is not required for each well installation diagram; multiple wells may be shown on the same sheet.
3.8.7 SURVEY MAPS AND NOTES
Prepare and submit a tabulated list of all monitoring wells and monuments, copies of all field books, maps showing the locations, and elevations of all monitoring wells, and all computation sheets, consisting of the designated number of the well or monument, the X and Y coordinates, and all the required elevations.
RCRA GROUND-WATER MONITORING
DRAFT TECHNICAL GUIDANCE
OFFICE OF SOLID WASTE
U.S. ENVIRONMENTAL PROTECTION AGENCY
401 M STREET, S.W.
WASHINGTON, D.C. 20460
NOVEMBER 1992
6.6 Well Surveying
The location of all wells should be surveyed by a licensed professional surveyor (or equivalent) to determine their X-Y coordinates as well as their distances from the units being monitored and their distances from each other. A State Plane Coordinate System, Universal Transverse Mercator System, or Latitude/Longitude should be used, as approved by the Regional Administrator. The survey should also note the coordinates of any temporary benchmarks. A surveyed reference mark should be placed on the top of the well casing, not on the protective casing or the well apron, for use as a measuring point because the well casing is more stable than the protective casing or well apron (both the protective casing and the well apron are more susceptible to frost heave and spalling). The height of the reference survey datum, permanently marked on top of the inner well casing, should be determined within å±0.01 foot in relation to mean sea level, which in turn is established by reference to an established National Geodetic Vertical Datum. The reference marked on top of inner well casings should be resurveyed at least once every 5 years, unless changes in ground-water flow patterns/direction, or damage caused by freeze/thaw or desiccation processes, are noted. In such cases, the Regional Administrator may require that well casings be resurveyed on a more frequent basis.
DDSM:clink::beer:
Kent McMillan, post: 393329, member: 3 wrote: The same analysis applies, though. The error in capacity of a run of pipe at 0.2% slope and 300 ft. in length that results from a 0.10 ft. error in elevation at either end will be only 7.4%, which is probably going to be less than any error in the roughness coefficients used to compute friction losses.
If the pipe is at 0.5% slope, the error in theoretical capacity resulting from an error of 0.033% is only 3.2%.
And if you are less than .2% with potential of .1' on each end you are easily approaching 20 percent.
And note that random small errors in pipe slope in a network will come out in the wash if the pipe is flowing full since friction losses on adjacent runs will tend to have compensating errors, i.e. one slightly higher and the next slightly lower.
thebionicman, post: 393343, member: 8136 wrote: And if you are less than .2% with potential of .1' on each end you are easily approaching 20 percent.
Except that what will happen is that the flow at the entrance to the pipe will just have another 0.10 ft. of depth at the beginning of the run and the flow will still be the same. It wasn't clear from Jim Frame's post whether the pipe network was for storm sewer or wastewaster, but I'm assuming they are wastewater mains that are the subject of interest and are intended to flow as open channels, less than 3/4 full.
Kent McMillan, post: 393361, member: 3 wrote: And note that random small errors in pipe slope in a network will come out in the wash if the pipe is flowing full since friction losses on adjacent runs will tend to have compensating errors, i.e. one slightly higher and the next slightly lower.
Except that what will happen is that the entrance to the pipe will just have another 0.10 ft. of head on it at the beginning of the run and the flow will still be the same. It wasn't clear from Jim Frame's post whether the pipe network was for storm sewer or wastewaster, but I'm assuming they are wastewater mains that are the subject of interest and are intended to flow less than 3/4 full.
Maybe he could just get an elevation @ the very beginning and very end of the system.....;-)
0.01' relative to Mean Seal Level?
The government cannot even do that on it's benchmarks, which it no longer considers important anyway.
Paul in PA
Paul in PA, post: 393364, member: 236 wrote: 0.01' relative to Mean Seal Level?
The government cannot even do that on it's benchmarks, which it no longer considers important anyway.
Paul in PA
"Mean Sea Level" isn't a real known anyway. It's all a matter of terminologies and definitions of words. "Orthometric Height" above a particular Geoid.....can't be that precise. You want "relative local precision" of the manholes in a particular datum. Your accuracy in that datum will not be a precise as your relative local precision.
Dan B. Robison, post: 393335, member: 34 wrote: Speaking of Monitor Wells...
USACE / NAVFAC / AFCESA / NASA UFGS-33 24 13 (August 2008)
USACE Superseding UFGS-33 24 13 (April 2008)
UNIFIED FACILITIES GUIDE SPECIFICATIONS
References are in agreement with UMRL dated October 2010DIVISION 33 - UTILITIES
SECTION 33 24 13
GROUNDWATER MONITORING WELLS
SECTION 33 24 13 Page 29 (Click Here)
3.4 SURVEYSEstablish coordinates and elevations for each monitoring well/test hole. Determine horizontal coordinates to the closest 300 mm 1.0 foot and referenced to the State Plane Coordinate System, or Universal Transverse Mercator (UTM). If the State Plane Coordinate System/UTM is not readily available, use an existing local grid system. Obtain a ground elevation to the closest 30 mm 0.1 foot at each well. The highest point on the top of the riser pipe serves as a measurement point; reference this elevation and survey to the nearest 3 mm 0.01 foot using the National Geodetic Vertical Datum of [1929] [1988]. If the datum is not readily available, use the existing local vertical datum. Plot the location, identification, coordinates, and elevations of the well and monuments on maps with a scale large enough to show their location with reference to other structures.
SECTION 33 24 13 Page 33
3.8.2 INSTALLATION DIAGRAMS
k. Elevations/depths/heights of key features of the well, such as top of well casing/riser pipe, top and bottom of protective casing, ground surface, the depth of maximum frost penetration (frost line), bottom of well screen, top and bottom of filter pack, and top and bottom of seal.
m. Well location by coordinates. A plan sheet shall also be included showing the coordinate system used and the location of each well. A plan sheet is not required for each well installation diagram; multiple wells may be shown on the same sheet.
3.8.7 SURVEY MAPS AND NOTES
Prepare and submit a tabulated list of all monitoring wells and monuments, copies of all field books, maps showing the locations, and elevations of all monitoring wells, and all computation sheets, consisting of the designated number of the well or monument, the X and Y coordinates, and all the required elevations.
RCRA GROUND-WATER MONITORING
DRAFT TECHNICAL GUIDANCE
OFFICE OF SOLID WASTE
U.S. ENVIRONMENTAL PROTECTION AGENCY
401 M STREET, S.W.
WASHINGTON, D.C. 20460
NOVEMBER 19926.6 Well Surveying
The location of all wells should be surveyed by a licensed professional surveyor (or equivalent) to determine their X-Y coordinates as well as their distances from the units being monitored and their distances from each other. A State Plane Coordinate System, Universal Transverse Mercator System, or Latitude/Longitude should be used, as approved by the Regional Administrator. The survey should also note the coordinates of any temporary benchmarks. A surveyed reference mark should be placed on the top of the well casing, not on the protective casing or the well apron, for use as a measuring point because the well casing is more stable than the protective casing or well apron (both the protective casing and the well apron are more susceptible to frost heave and spalling). The height of the reference survey datum, permanently marked on top of the inner well casing, should be determined within å±0.01 foot in relation to mean sea level, which in turn is established by reference to an established National Geodetic Vertical Datum. The reference marked on top of inner well casings should be resurveyed at least once every 5 years, unless changes in ground-water flow patterns/direction, or damage caused by freeze/thaw or desiccation processes, are noted. In such cases, the Regional Administrator may require that well casings be resurveyed on a more frequent basis.
DDSM:clink::beer:
Question; "what's an elephant?"
Answer; "a mouse built to government specifications".
Tom Adams, post: 393363, member: 7285 wrote: Maybe he could just get an elevation @ the very beginning and very end of the system.....;)
Well, the point is that given the nature of the hydraulic modeling of sanitary sewers, the relative elevations of pipe inverts at adjacent nodes in the network is quite a bit more important than those several nodes removed and, unless the line has a slope below 0.5%, the relative accuracy of elevations at even adjacent nodes can tolerate random errors of 0.10 ft. without large errors in flow modeling.
Of course, if the pipes were designed by the physicists at the Cold Fusion Lab at Texas A&M, chances are they are intended to flow uphill and all bets are off.
Kent McMillan, post: 393379, member: 3 wrote: Well, the point is that given the nature of the hydraulic modeling of sanitary sewers, the relative elevations of pipe inverts at adjacent nodes in the network is quite a bit more important than those several nodes removed and, unless the line has a slope below 0.5%, the relative accuracy of elevations at even adjacent nodes can tolerate random errors of 0.10 ft. without large errors in flow modeling.
Of course, if the pipes were designed by the physicists at the Cold Fusion Lab at Texas A&M, chances are they are intended to flow uphill and all bets are off.
I had a few acres in Bayfield before moving to Pueblo. They had a water supply for irrigation that siphoned down in an underground pipline and went uphill to where is spilled out in the drainage ditch above. (I hope I worded that correctly)
