At least one permanent benchmark shall be established in each subdivision or development. The number and location of required permanent benchmarks shall be approved by Director of Public Works and Engineering or authorized designee. Permanent benchmarks shall consist of a brass or aluminum disk set in concrete, in compliance with the City of Lockport standard drawings.
Permanent benchmarks shall be tied to the North American Vertical Datum of 1988 (NAVD88) of the National Spatial Reference System (NSRS), as maintained by the United States National Geodetic Survey (US-NGS). Permanent benchmarks shall be established under the supervisions of a Professional Land Surveyor, registered in Illinois. The surveyor shall use one of the following methods to achieve a vertical accuracy of Second Order, Class II, per the US-NGS:
(A) Establish vertical geodetic control at the site using a combination of Global Navigation Satellite System (GNSS) measured ellipsoid heights and calculated orthometric heights using a reputable geoid model. GNSS-derived ellipsoid heights shall be determined by processing GPS field measurements through the NGS GPS Online Positioning System - Rapid Static Service (OPUS-RS).
(B) Establish vertical geodetic control at the site by differential leveling surveying, using NGS specifications for Second Order, Class II vertical surveys. All vertical leveling shall be measured relative to at least two NSRS vertical geodetic control monuments of second-order or better accuracy.
Iron rods, one-half inch in diameter, shall be set at all corners, angle points, and points of curvature on property lines and rights-of-way under the supervision of a Professional Land Surveyor, registered in Illinois.
All set or found iron pipes, iron rods and permanent benchmarks shall be shown and described on the final plat. The developer shall replace or verify the existence of all iron pipes, iron rods and permanent benchmarks after the completion of all construction and before initial acceptance of the subdivision or development by the corporate authorities.
(Ord. 18-008, passed 2-7-18)