PilgrimNuclear’Power’Station’Elevation’Analysis ... · PilgrimNuclear’Power’Station’Elevation’Analysis’|JonesRiverWatershedAssociation’ Northeastern!Geospatial!Research!Professionals,!Inc.!

Pilgrim Nuclear Power Station Elevation Analysis | Jones River Watershed Association Northeastern Geospatial Research Professionals, Inc.

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Introduction:

The Pilgrim Nuclear Power Station (PNPS), located in Plymouth County, Massachusetts on the shores of Cape Cod Bay was commissioned on December 9, 1972. The power station design included development of near-‐shore revetments and other engineered reinforcements intended to protect the site from wave action emanating from Cape Cod Bay . Over the operational history of the power station, there have been dredging operations to ensure that the water intake and outlet remain operational and that engineering design meets current standards.

Resulting from a perceived shortfall in response to global climate change and sea-‐level rise evidence on the part of PNPS, it has come to the attention of the Jones River Watershed Association (JWRA) that the Pilgrim Nuclear Power Station site and its assets may be at risk. Specifically, with the advent of outdoor storage of high level radioactive waste in the form of spent fuel rods contained in casks engineered for such containment in close proximity to Federal Emergency Management Administration (FEMA) flood zones.

This elevation analysis has been conducted using the best available, civilian accessible geospatial data in a comparative study to determine where the location of spent fuel casks are in regard to FEMA modeled flood zone data.

Method:

Elevation data from the following agencies have been acquired (Appendix A):

Entergy: PNPS Site map (2006)

United States Geological Survey (USGS): Terrestrial Light Detection and Ranging (LIDAR) measurements (2011)

National Oceanic and Atmospheric Administration (NOAA): Bathymetric survey (2007)

United States Army Corps of Engineers (USACE): Topographical (LIDAR) and Bathymetric product (2012)

Bathymetric data were used for visualization and analysis purposes. Terrestrial elevation data were utilized to compare original site plan spot elevation measurements. Bathymetric data were also used to show overwash potential of the engineered shoreline reinforcement in addition to the inundation (or partial inundation) of revetments designed to protect the site.


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Analysis:

Using tools for datum conversion, provided through NOAA (Appendix B), we find the results listed in Table 1 (Appendix C). Locations labeled C, D, and E show the greatest vertical variation on site. The variation may exist due to measurements taken off of the ground surface where no offset calculation was provided, as these locations appear to be used for construction purposes and therefore temporary survey elevation points. Location RM14 is measured at 64.72 Feet (NGVD 29), and deviates from the LIDAR data significantly.

Survey elevations for this site as provided on the Entergy site drawing (Appendix A) appear to be specifically for the layout of buildings on the site, and not for providing an accurate, relevant comparison between where buildings rest relative to elevations on the ground. With the exception of perhaps location RM14, the other surveyed elevations cannot be used with any significant level of accuracy to determine existing, on the ground elevations elsewhere on the site.

Conclusion:

The PNPS site map shows several surveyed locations that do not match current modeled elevation data. Although the survey locations on the PNPS map are in a known, disparate vertical datum and are compared to the current modeled elevation data, in some cases, there is a discrepancy in elevations that is too great to determine precisely where the modeled FEMA flood zone impacts the site. The data collected and produced by Entergy have been referenced to and modeled for the NGVD29 datum while all other data are referenced and modeled to the newer NAVD88 datum. Although it is possible to convert between NGVD29 and NAVD88 datums, it is standard practice to use data that are all modeled to the same datum (horizontal and vertical, respectively). This eliminates potential misrepresentation of a given location on site plans, and other planimetric data (including flood hazard data), which may also be projected in a different datum. While it appears that the top of engineered elevation per the PNPS site map is nearly identical to the modeled LIDAR elevation data, the discrepancy in vertical elevations when survey data are compared to the FEMA flood zone data confounds the analysis.

Recommendation:

The recommendation based on this analysis is to undertake a site survey of PNPS grounds using known, measured benchmarks. Additional reference locations should also be plotted and measured throughout the PNPS site for an accurate elevation data set that is surveyed to the NAVD88 datum. This will provide the public (regulators, residents, etc.) with a clearer picture of how sea level rise resulting from our changing climate impacts current, potentially hazardous conditions at PNPS. Further, a new data set will enable decision-‐makers the ability to more accurately assess on-‐site assets and contingencies for future planning.


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Appendicies

Appendix A

Pilgrim Nuclear Power Station Site Map, NGVD29, C2 Revision 10 (Entergy, December 2006)

(named Site Plan with file path: AMM:\CIVIL-‐STRUCTURAL\C2.DWG)


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USGS LIDAR Coverage, NAVD88 (2011):

NOAA Bathymetric Survey, NAVD88 (2007)


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USACE Topographical (LIDAR) and Bathymetric Product, NAVD88 (2012)


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Appendix B

National Oceanic and Atmospheric Administration VERTCON process:

http://www.ngs.noaa.gov/cgi-‐bin/VERTCON/vert_con.prl

Converts vertical measurements between NGVD 1929 coordinates and NAVD 1988.

National Geodetic Survey (NGS) Height Conversion Methodology

http://www.ngs.noaa.gov/TOOLS/Vertcon/vert_method.html

This process is designed to provide datum shift between the NAVD 88 and NGVD 29 vertical datums at specified geographic position.

Dennis G. Milbert, Ph.D.

05/12/1999

METHOD

Program VERTCON computes the modeled difference in orthometric height between the North American Vertical Datum of 1988 (NAVD 88) and the National Geodetic Vertical Datum of 1929 (NGVD 29) for a given location specified by latitude and longitude.

The VERTCON 2.0 model was computed on May 5, 1994 using 381,833 datum difference values. A key part of the computation procedure was the development of the predictable, physical components of the differences between the NAVD 88 and NGVD 29 datums. This included models of refraction effects on geodetic leveling, and gravity and elevation influences on the new NAVD 88 datum. Tests of the predictive capability of the physical model show a 2.0 cm RMS agreement at our 381,833 data points. For this reason, the VERTCON 2.0 model can be considered accurate at the 2 cm (one sigma) level. Since 381,833 data values were used to develop the corrections to the physical model, VERTCON 2.0 will display even better overall accuracy than that displayed by the uncorrected physical model. This higher accuracy will be particularly noticable in the eastern United States.

It should be emphasized that VERTCON 2.0 is a datum transformation model, and can not maintain the full vertical control accuracy of geodetic leveling. Ideally, one should process level data using the latest


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reduction software and adjust it to established NAVD 88 control. However, VERTCON 2.0 accuracy is suitable for a variety of mapping and charting purposes.

Most horizontal positions of the bench marks used to generate VERTCON were scaled from USGS topographic maps. The estimated uncertainty of the scaled positions, 6", is greater than the differences between NAD 27 and NAD 83. Therefore, the latitude and longitude provided to VERTCON can be on either the NAD 27 or NAD 83 datum.

The VERTCON 2.0 model expresses datum differences between NAVD 88 and NGVD 29 due to removal of distortions in the level data, as well as due to the physical differences in the height systems. In some rare cases, these local NGVD 29 distortions could be 20 cm or more. If both ends of your old vertical survey were tied to one of these "problem" lines, then the datum difference of the problem line is appropriate to use to transform the survey data. If both ends of a vertical survey are tied to "undistorted lines", then it is appropriate to use a slightly distant point to compute the transformation, no matter how close your survey data may approach a given problem line. The possible presence of a problem NGVD 29 line in the vicinity of your survey will become evident if dramatically different datum transformation values are computed within a small area.

It must also be emphasized that VERTCON 2.0 is not to be considered reliable beyond the boundaries of the lower 48 United States. Future versions of VERTCON may be extended into neighboring countries. The National Imagery and Mapping Agency (NIMA -‐ previously the Defense Mapping Agency) has been of immense help in this endeavor. NIMA has provided a major portion of the NGS land gravity data set. NIMA has also been instrumental in the creation of the various 30" elevation grids in existence. Although the work of the NIMA generally precludes public recognition, their cooperation in this work is gratefully acknowledged.


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Appendix C: Table 1. Elevation comparison, NGVD29 and NAVD88 for survey elevations on Entergy 2006 site plan.

Column1 Column2 Column3 Column4 Column5 Column6 Column7Benchmark Longitude, DD Latitude, DD Elevation (NGVD 1929) Elevation (NAVD88) Units NAVD88 -‐ NGVD29A -‐70.579736 41.944086 19.58 19.92 Feet 0.34B -‐70.577345 41.943638 22.83 20.24 Feet -‐2.59C -‐70.579503 41.94443 28.67 22.46 Feet -‐6.21D -‐70.579701 41.944291 30.15 20.76 Feet -‐9.39E -‐70.578975 41.943962 24.24 20 Feet -‐4.24RM 14 -‐70.573297 41.939861 64.72 49.69 Feet -‐15.03Chiseled Square -‐70.579533 41.946788 13.92 10.44 Feet -‐3.48

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PilgrimNuclear’Power’Station’Elevation’Analysis ... · PilgrimNuclear’Power’Station’Elevation’Analysis’|JonesRiverWatershedAssociation’ Northeastern!Geospatial!Research!Professionals,!Inc.!