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The County of DuPage
Wheaton, Illinois
 

Physical Monumentation Network

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About DuPage County Survey Control

Horizontal Control Network (Monuments)

The horizontal control network is comprised mostly of section and 1/4 section corner markers throughout the county. These locations were first determined as a result of the nationwide PLSS (Public Land Survey System) Program, which was a cornerstone to the Federal Land Grant Program in the mid 1800s. The PLSS was intended to simplify the defining and documenting of land ownership in the handover of federal lands to private ownership. At the time, the corners were marked with a variety of things, including stones, spikes, iron posts or nails in pavement.

From 1979 to 1984, DuPage County initiated a county-wide re-monumentation program with specific objectives. Questionable corner markers were replaced with more durable and permanent monuments, mostly Harrison Ferro-Magnetic Survey Monuments that still exist today. And most importantly, for the first time the DuPage County PLSS was spatially referenced to the NGS (National Geodetic Survey) control network. Prior to this, there had been no coordinates assigned to the section corners. The level of precision is less than 1 ft variance for every 20,000 ft traveled, or second order class II.

Vertical Control Network (Benchmark)

Notice as of: April 25, 2012

DuPage County has completed upgrading its vertical control network from the North American Geodetic Vertical Datum of 1929 (NGVD29) to the North American Vertical Datum of 1988 (NAVD88).  DuPage County (Benchmarks NAVD88) 

History: 

The DuPage County network of vertical control points was established primarily between the years 1983-86. All level runs were specified to meet the (NGS) National Geodetic Survey Second Order, Class Two level run requirements, and all runs began and ended on what was then classified by National Geodetic Survey as a First Order vertical control point.  

The first run completed on this project was submitted to National Geodetic Survey in Blue Book form, and was accepted by National Geodetic Survey and included in the National Geodetic Survey database for readjustment to the NAVD of 1988 (see attached .pdf NGS letter). The purpose of this submittal to National Geodetic Survey was to receive acceptance of our methodology. Subsequent level runs were not submitted to National Geodetic Survey due to budgetary constraints.  

During the 1988 NAVD readjustment, National Geodetic Survey downgraded a number of the First Order vertical control points we had used as the start/end points of our level runs. As a result, the run we had submitted to them was reclassified to Third Order in the NAVD88 database.  

Since the 1980’s the vast majority of vertical control points (benchmarks) installed have been disturbed or destroyed. The few that remain, the datum they were published on (NGVD29) North American Geodetic Vertical Datum 1929 is obsolete and has been replaced with (NAVD88) North American Vertical Datum 1988. In 2005 the County of DuPage started working on components of a Height Modernization Program.

These components consisted of the following:

  A.    Installing (CORS) Continuously Operating Reference Stations.

  B.    Work was contracted to a local engineering firm to install new vertical control points (benchmarks) for leveling.

  C.    Leveling of vertical control points (benchmarks) to 2nd Order Class I standards per (FGCC) Federal Geodetic Control Committee guidelines to relate the CORS to existing 1st and 2nd Order benchmarks.

  D.    GPS of suitable vertical control points (benchmarks) to establish accurate horizontal and ellipsoidal heights.

All leveling work was submitted to (NGS) National Geodetic Survey for inclusion into the (NSRS) National Spatial Reference System.

The new network of NAVD88 vertical control points (benchmarks) has a spacing of approximately five miles between runs. Several new vertical control points (benchmarks) were installed where existing benchmarks were disturbed\destroyed or additional control was required in the County of DuPage.  

Please report any benchmarks disturbed or destroyed. Send an email to benchmarks@dupageco.org