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Bill93

Right area, right stamping, wrong disk

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The topic comes up occasionally about careless logging by people who don't check the stamping to see they have the right disk.

 

One of my first few NGS logs turned out to be WRONG despite having the right agency and stamping. I guess the lesson is that you need to understand civil engineering terminology to be sure something hasn't been rebuilt. I thought the road had just been raised over the old bridge but it seems this is a new culvert, with a new disk that somebody in their questionable wisdom decided should have the same stamping.

 

NJ0584 STATION RECOVERY (2014)

NJ0584

NJ0584'RECOVERY NOTE BY NATIONAL GEODETIC SURVEY 2014

NJ0584'THIS REPORT WAS SUBMITTED BY STEVEN MILLIGAN. THERE IS STILL A

NJ0584'MONUMENT WITH A DISK STAMPED LINN CO ENG DEPT 1402, BUT IT IS NOT

NJ0584'IN THE SAME STRUCTURE AS DESCRIBED IN THE 1934. IN 1934, THE DISK

NJ0584'WAS IN THE TOP OF THE CENTER OF THE SOUTH CONCRETE GUARD RAIL OF A

NJ0584'TWIN 5 BY 12 FOOT HIGHWAY BRIDGE, AND NOW IT IS IN THE CENTER OF

NJ0584'THE TOP OF THE SOUTH HEADWALL OF A TWIN 6 BY 12 FOOT RCB. A +2.75

NJ0584'HOUR OPUS SESSION SHOWS A DIFFERENCE FROM THE PUBLISHED

NJ0584'ORTHOMETRIC HEIGHT OF THE DISK OF -1.013 METER. I CONTACTED LINN

NJ0584'COUNTY AND FOUND THAT THE ROAD WAS RELOCATED IN 1968, AND THE

NJ0584'BRIDGE WAS REPLACED BY A CULVERT. ALSO, LINN COUNTY SHOWS TWO BM'S

NJ0584'WITH A DISK STAMPED 1402 WITH A ORTHOMETRIC DIFFERENCE OF -3.15

NJ0584'FEET.THE 2004 GEOCACHER DID NOT FIND THE 1934 DISK, BUT INSTEAD

NJ0584'FOUND THE POST 1968 DISK.

Edited by Bill93

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We had a similar confusion once on a bridge replacement project. The mark in the bridge had the elevation preserved by us (with several TBM's nearby) before the start of the project, rebuild and widen one lane of bridge at a time. We got a new disk from NGS state advisor that was pre-stamped. The project inspector was to set it when they poured the abutment and set it in the same location, NE abutment near level with deck. But he reset the original mark (had it jack-hammered out) instead and never told anyone. After the project was done (took a almost a year) I went back to level to the new mark and discovered what he did. We then had to re-stamp the original disk before leveling. This could have easily been overlooked because at that time we had lost several Survey tech's due to retirement and I was the only one left who was there when we preserved the elevation. The project engineer could have cared less about the bench mark.

 

As I recall the difference between the original elevation and the new reset was less than 1 foot.

Edited by Z15

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