U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
Datums Page                                                        Page  1 of 12

                                                                                
Station ID: 8545240                         PUBLICATION DATE:  01/14/2013
Name:       PHILADELPHIA (USCG STA.), DELAWARE RIVER          
            PA
NOAA Chart: 12313                           Latitude:   39° 56.0' N (  39.93333)
USGS Quad:  PHILADELPHIA                    Longitude:  75°  8.5' W ( -75.14167)


To reach the tidal bench marks from the toll plaza at the west end of the Walt
Whitman Bridge, proceed 0.2 km (0.1 mi) west to exit 47, bear to the right and
follow signs to Front Street. Turn right and proceed 0.5 km (0.3 mi) north on
Front Street to Oregon Avenue, turn right and continue 1.1 km (0.7 mi) east on
Oregon Street to Christopher Columbus Avenue. Turn left on Christopher Columbus
Avenue and proceed 2.7 km (1.7 mi) north to Washington Avenue, then turn right
and continue to the US Coast Guard Marine Safety Office visitors parking lot.
The bench marks are located on the USCG property, along Christopher Columbus
Avenue, and along Arch Street. The tide house is located along the bulkhead at
the SE corner of the USCG MSO facility.


                         T I D A L   B E N C H   M A R K S


                 PRIMARY BENCH MARK STAMPING:  5530 A 1989
                         DESIGNATION:          854 5240 A

MONUMENTATION:           Tidal Station disk                    VM#:        12904
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Stainless steel rod                   OPUS PID:        
LATITUDE:   39° 56.0' N (  39.93330)          LONGITUDE:  75°  8.5' W ( -75.14170)


The primary bench mark is a disk located along the south edge of the USCG
property on the east side of Columbus Avenue, 33.10 m (108.6 ft) SE of the SW
corner of the main building, 25.79 m (84.6 ft) west of the fiberglass gage
house, 19.87 m (65.2 ft) south of the south face of the main building, 1.22 m
(4.0 ft) north of the chain link fence, and 1.22 m (4.0 ft) east of a light
post. The bench mark is crimped to the top of a stainless steel rod driven 13.4
m (44 ft) to refusal, and encased in a 5 inch PVC pipe with concrete kickblock.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  2 of 12

                                                                                
Station ID: 8545240                         PUBLICATION DATE:  01/14/2013
Name:       PHILADELPHIA (USCG STA.), DELAWARE RIVER          
            PA
NOAA Chart: 12313                           Latitude:   39° 56.0' N (  39.93333)
USGS Quad:  PHILADELPHIA                    Longitude:  75°  8.5' W ( -75.14167)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  5530 B 1989
                         DESIGNATION:          854 5240 B

MONUMENTATION:           Tidal Station disk                    VM#:        12905
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Stainless steel rod                   OPUS PID:        
LATITUDE:   39° 56.1' N (  39.93469)          LONGITUDE:  75°  8.5' W ( -75.14250)


The bench mark is located near the NW corner of the USCG property, near the
intersection of Coumbus Avenue and Christian street, 31.88 m (104.59 ft) west of
the NE corner of the fence post, 12.62 m (41.40 ft) north of the curved concrete
curb of the USCG personnel parking lot, 3.53 m (11.6 ft) south of the traffic
signal post at the SE corner of Columbus Avenue and Christian Street
interesection, 7.16 m (23.49 ft) SE of the eastern curb of Columbus avenue, and
4.10 m (13.5 ft) west of the NE corner of the black metal fence post. The bench
mark is set 0.20 cm (0 inches) below the ground, crimped to a stainless steel
rod driven 11.0 m (36.1 ft) to refusal, and encased in a 5 inch PVC pipe with
concrete kickblock.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  3 of 12

                                                                                
Station ID: 8545240                         PUBLICATION DATE:  01/14/2013
Name:       PHILADELPHIA (USCG STA.), DELAWARE RIVER          
            PA
NOAA Chart: 12313                           Latitude:   39° 56.0' N (  39.93333)
USGS Quad:  PHILADELPHIA                    Longitude:  75°  8.5' W ( -75.14167)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  5530 C 1989
                         DESIGNATION:          854 5240 C

MONUMENTATION:           Tidal Station disk                    VM#:        12906
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Stainless steel rod                   OPUS PID#: BBDC10
LATITUDE:   39° 56.0' N (  39.93330)          LONGITUDE:  75°  8.6' W ( -75.14330)


The bench mark is a disk located near the front lawn of the USCG property, 45.90
m (150.6 ft) NW of the flagpole at the entrance of the main building, 9.20 m
(30.2 ft) NNE of the north curb of Washington Avenue leading into the base, 8.50
m (27.9 ft) SE of the eastern curb of Columbus Avenue, and 8.20 m (26.9 ft) east
of the traffic signal post at the NE corner of Washington and Columbus Avenues.
The bench mark is set 0.18 m (0.6 ft) below ground, crimped to a stainless steel
rod driven 12.2 m (40 ft) to refusal, and encased in a 5 inch PVC pipe with
concrete kickblock.



                         BENCH MARK STAMPING:  5530 D 1989
                         DESIGNATION:          854 5240 D

MONUMENTATION:           Tidal Station disk                    VM#:        12907
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Stainless steel rod                   OPUS PID:        
LATITUDE:   39° 56.1' N (  39.93500)          LONGITUDE:  75°  8.6' W ( -75.14330)


The bench mark is a disk located in the NW corner of the U.S. Park Service's
Gloria Dei - Old Swedes Church property on the west side of Columbus Avenue,
19.51 m (64.0 ft) west of the centerline of the church driveway at Christian
Street, 19.29 m (63.3 ft) SW of the SW corner of the brick garage at the church
entrance gate, 16.61 m (54.5 ft) east of the brick wall along Water Street, and
16.48 m (54.1 ft) south of the brick wall along Christian Avenue. The bench mark
is crimped to a stainless steel rod driven 14.6 m (48 ft) to refusal, and
encased in a 5 inch PVC pipe with concrete kickblock.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  4 of 12

                                                                                
Station ID: 8545240                         PUBLICATION DATE:  01/14/2013
Name:       PHILADELPHIA (USCG STA.), DELAWARE RIVER          
            PA
NOAA Chart: 12313                           Latitude:   39° 56.0' N (  39.93333)
USGS Quad:  PHILADELPHIA                    Longitude:  75°  8.5' W ( -75.14167)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  5530 E 1989
                         DESIGNATION:          854 5240 E

MONUMENTATION:           Tidal Station disk                    VM#:        12908
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Stainless steel rod                   OPUS PID:        
LATITUDE:   39° 56.2' N (  39.93670)          LONGITUDE:  75°  8.6' W ( -75.14330)


The bench mark is a disk located on the west side of Columbus Avenue near the
intersection of Columbus Avenue and Queen Street, 14.29 m (46.9 ft) south of the
south curb of Queen Street, 8.90 m (29.2 ft) SW of a fire hydrant, 6.61 m (21.7
ft) west of the western curb of Columbus Avenue, and 1.80 m (5.9 ft) east of the
east face of a brick wall surrounding townhouses. The bench mark is crimped to
the top of a stainless steel rod driven 3.4 m (11 ft) to refusal, and encased in
a 5 inch PVC pipe with concrete kickblock.



                         BENCH MARK STAMPING:  5530 F 1993
                         DESIGNATION:          854 5240 F

MONUMENTATION:           Tidal Station disk                    VM#:        12909
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Concrete bulkhead                     OPUS PID:        
LATITUDE:   39° 56.0' N (  39.93330)          LONGITUDE:  75°  8.5' W ( -75.14170)


The bench mark is a disk set in the concrete bulkhead near a mooring cleat on
the SE side of the USCG property, 16.60 m (54.5 ft) SSW of the NW corner of the
bulkhead for the boat lift, 14.43 m (47.3 ft) SE of the face of the USCG main
building, 0.42 m (1.4 ft) ESE of the center of a yellow bollard, 0.18 m (0.6 ft)
NW of the SE face of the bulkhead, and 0.3 m (1 ft) above the parking lot.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  5 of 12

                                                                                
Station ID: 8545240                         PUBLICATION DATE:  01/14/2013
Name:       PHILADELPHIA (USCG STA.), DELAWARE RIVER          
            PA
NOAA Chart: 12313                           Latitude:   39° 56.0' N (  39.93333)
USGS Quad:  PHILADELPHIA                    Longitude:  75°  8.5' W ( -75.14167)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  5530 G 1993
                         DESIGNATION:          854 5240 G

MONUMENTATION:           Tidal Station disk                    VM#:        12910
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Concrete wash drain foundation        OPUS PID:        
LATITUDE:   39° 56.1' N (  39.93500)          LONGITUDE:  75°  8.7' W ( -75.14500)


The bench mark is a disk set in a concrete wash drain foundation west of Water
Street under the north bound lane of I-95, 25.51 m (83.7 ft) WNW of the NW edge
of the fence surrounding the U.S. Park Service's Gloria Dei - Old Swedes Church,
16.61 m (54.5 ft) NW of light pole #64533D, 2.99 m (9.8 ft) SSW of the fourth
concrete support for I-95 when counting from the northern end of the overpass,
and 0.46 m (1.5 ft) above the road.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  6 of 12

                                                                                
Station ID: 8545240                         PUBLICATION DATE:  01/14/2013
Name:       PHILADELPHIA (USCG STA.), DELAWARE RIVER          
            PA
NOAA Chart: 12313                           Latitude:   39° 56.0' N (  39.93333)
USGS Quad:  PHILADELPHIA                    Longitude:  75°  8.5' W ( -75.14167)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  U 237 1959
                         DESIGNATION:          U 237

MONUMENTATION:           Bench Mark disk                       VM#:        13161
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:  JU0722
SETTING CLASSIFICATION:  Concrete bulkhead                     OPUS PID:        
LATITUDE:   39° 57.2' N (  39.95330)          LONGITUDE:  75°  8.4' W ( -75.14000)


The bench mark is a disk set in the top of a concrete bulkhead between Pier No.
11 and Pier No. 9 on the east side of Christopher Columbus Avenue, 36.3 m (119.0
ft) north of the NW corner of Pier No. 9, 19.6 m (64.3 ft) east of the
centerline of northbound Christopher Columbus Avenue, 8.8 m (28.9 ft) south of
the SW corner of building on Pier No. 11, and 4.0 m (13.1 ft) SSE of the center
of a large water pump intake valve.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  7 of 12

                                                                                
Station ID: 8545240                         PUBLICATION DATE:  01/14/2013
Name:       PHILADELPHIA (USCG STA.), DELAWARE RIVER          
            PA
NOAA Chart: 12313                           Latitude:   39° 56.0' N (  39.93333)
USGS Quad:  PHILADELPHIA                    Longitude:  75°  8.5' W ( -75.14167)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  23 1922 ELEV. 7.894 FT.
                         DESIGNATION:          854 5530 TIDAL 23
                         ALIAS:                TIDAL 23 STA 1

MONUMENTATION:           Tidal Station disk                    VM#:        13162
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:  JU0721
SETTING CLASSIFICATION:  Granite step                          OPUS PID:        
LATITUDE:   39° 57.2' N (  39.95330)          LONGITUDE:  75°  8.4' W ( -75.14000)


The bench mark is a disk set in top of a granite step at the main entrance to
the city pumping station at the SW corner of Race Street and Christopher
Columbus Avenue, 30.5 m (100.0 ft) SSW of the centerline of Race Street, 11.6 m
(38.1 ft) WNW of the centerline of Christopher Columbus Avenue, 6.3 m (20.7 ft)
NNE of the SE corner of the building and 5.8 m (19.0 ft) SW of a fire hydrant,
and 0.2 m (0.7 ft) above ground level.



                         BENCH MARK STAMPING:  35 1931
                         DESIGNATION:          854 5530 TIDAL 35

MONUMENTATION:           Bench Mark disk                       VM#:        13163
AGENCY:                  US Coast and Geodetic Survey
                         (USC&GS)                              IDB PID#:  JU2225
SETTING CLASSIFICATION:  Granite sill                          OPUS PID:        
LATITUDE:   39° 57.2' N (  39.95330)          LONGITUDE:  75°  8.4' W ( -75.14000)


The bench mark is a disk set in top of the north end of a granite sill of the
most southerly of three doorways on the west side of Christopher Columbus Avenue
just north of Race Street near the Benjamin Franklin Bridge foundations, 44.8 m
(147.0 ft) south of the centerline of a closed I-95 ramp, 38.2 m (125.3 ft)
north of the centerline of Race Street, and 12.1 m (39.7 ft) west of the
centerline of Christopher Columbus Avenue southbound.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  8 of 12

                                                                                
Station ID: 8545240                         PUBLICATION DATE:  01/14/2013
Name:       PHILADELPHIA (USCG STA.), DELAWARE RIVER          
            PA
NOAA Chart: 12313                           Latitude:   39° 56.0' N (  39.93333)
USGS Quad:  PHILADELPHIA                    Longitude:  75°  8.5' W ( -75.14167)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  5240 H 1997
                         DESIGNATION:          854 5240 H

MONUMENTATION:           Tidal Station disk                    VM#:        13813
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Concrete bulkhead                     OPUS PID:        
LATITUDE:   39° 56.0' N (  39.93330)          LONGITUDE:  75°  8.5' W ( -75.14170)


The bench mark is a disk set in the concrete bulkhead cap located on the north
side of the USCG property, near the aluminum ramp to the small boat dock, 41.70
m (136.8 ft) NE of the NE corner of the brick two story administration building,
9.84 m (32.3 ft) NE of the NE corner of the brick two story Naviagation
Department building, and 2.25 m (7.4 ft) SE of the middle of the aluminum ramp
leading to the floating docks.



                         BENCH MARK STAMPING:  5240 J 1997
                         DESIGNATION:          854 5240 J TIDAL

MONUMENTATION:           Tidal Station disk                    VM#:        13814
AGENCY:                  National Ocean Service (NOS)          IDB PID#:  AJ2129
SETTING CLASSIFICATION:  Concrete bulkhead                     OPUS PID:        
LATITUDE:   39° 56.0' N (  39.93330)          LONGITUDE:  75°  8.5' W ( -75.14170)


The bench mark is a disk set in the concrete bulkhead cap located on the north
side of the USCG property, 56.67 m (185.9 ft) ENE of the NE corner of the
Navigation Department building, 9.17 m (30.1 ft) WNW of the NE corner of the
concrete bulkhead, 0.25 m (0.8 ft) SSW of the north face of the concrete
bulkhead, and 0.20 m (0.7 ft) NNE of the yellow cleat bolted to the concrete
deck.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page  9 of 12

                                                                                
Station ID: 8545240                         PUBLICATION DATE:  01/14/2013
Name:       PHILADELPHIA (USCG STA.), DELAWARE RIVER          
            PA
NOAA Chart: 12313                           Latitude:   39° 56.0' N (  39.93333)
USGS Quad:  PHILADELPHIA                    Longitude:  75°  8.5' W ( -75.14167)


                         T I D A L   B E N C H   M A R K S


                         BENCH MARK STAMPING:  5240 K 1997
                         DESIGNATION:          854 5240 K

MONUMENTATION:           Flange-encased Rod                    VM#:        13815
AGENCY:                  National Ocean Service (NOS)          IDB PID#:        
SETTING CLASSIFICATION:  Stainless steel rod in sleeve         OPUS PID:        
LATITUDE:   39° 56.0' N (  39.93330)          LONGITUDE:  75°  8.7' W ( -75.14500)


The bench mark is a flange-encased rod located in the south end of the property
of the U.S. Park Service's Gloria Dei - Old Swedes Church, 21.95 m (72.0 ft)
south of a 0.76 m (2.6 ft) diameter elm tree, 20.15 m (66.1 ft) ESE of a brick
wall on the west side of the property, and 8.80 m (28.9 ft) NNE of the south
wall of the property along Washington Avenue. The datum point is the top of a
stainless steel rod driven 8.5 m (28 ft) to refusal, and encased in a 5 inch NOS
logo cap.



                         BENCH MARK STAMPING:  5240 L 2011
                         DESIGNATION:          854 5240 L

MONUMENTATION:           Survey disk                           VM#:        19988
AGENCY:                                                        IDB PID#:        
SETTING CLASSIFICATION:  Concrete bulkhead                     OPUS PID:        
LATITUDE:   39° 56.0' N (  39.93317)          LONGITUDE:  75°  8.5' W ( -75.14192)


The benchmark is a disk set in the concrete footing for a yellow cleat, behind
the first cleat on the east end of a concrete finger pier next to the ramp for
the fire boats, 16.60 m (54.5 ft) SE of the SE corner of a brick building, 12.70
m (41.7 ft) east of the east side of the noaa tide house, 4.90 m (16.1 ft) NE of
the first light on the finger pier, 0.03 m (0.1 ft) SW of a yellow cleat, set
flush in the concrete.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page 10 of 12

                                                                                
Station ID: 8545240                         PUBLICATION DATE:  01/14/2013
Name:       PHILADELPHIA (USCG STA.), DELAWARE RIVER          
            PA
NOAA Chart: 12313                           Latitude:   39° 56.0' N (  39.93333)
USGS Quad:  PHILADELPHIA                    Longitude:  75°  8.5' W ( -75.14167)


                            T I D A L   D A T U M S 


Tidal datums at PHILADELPHIA (USCG STA.), DELAWARE RIVER based on:

     LENGTH OF SERIES:      17 YEARS
     TIME PERIOD:           April 1995 - March 2012
     TIDAL EPOCH:           1983-2001
     CONTROL TIDE STATION:  8551910 REEDY POINT, C&D CANAL


Elevations of tidal datums referred to Mean Lower Low Water (MLLW), in METERS:

     HIGHEST OBSERVED WATER LEVEL (10/30/2012)         =  3.238
     MEAN HIGHER HIGH WATER                     MHHW   =  2.039
     MEAN HIGH WATER                            MHW    =  1.917
     MEAN SEA LEVEL                             MSL    =  1.063
     MEAN TIDE LEVEL                            MTL    =  0.987
     North American Vertical Datum              NAVD88 =  0.945
     MEAN LOW WATER                             MLW    =  0.058
     MEAN LOWER LOW WATER                       MLLW   =  0.000
     LOWEST  OBSERVED WATER LEVEL (12/31/1962)         = -2.079

North American Vertical Datum (NAVD88)

Bench Mark Elevation Information                In METERS above:

     Stamping or Designation                    MLLW        MHW

     5530 A 1989                                 3.523    1.606
     5530 B 1989                                 3.549    1.632
     5530 C 1989                                 4.234    2.317
     5530 D 1989                                 5.252    3.335
     5530 E 1989                                 2.965    1.048
     5530 F 1993                                 4.638    2.721
     5530 G 1993                                 5.846    3.929
     U 237 1959                                  2.962    1.045
     23 1922 ELEV. 7.894 FT.                     2.973    1.056
     35 1931                                     2.637    0.720
     5240 H 1997                                 4.684    2.767
     5240 J 1997                                 4.645    2.728
     5240 K 1997                                 6.513    4.596
     5240 L 2011                                 4.626    2.709


                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page 11 of 12

                                                                                
Station ID: 8545240                         PUBLICATION DATE:  01/14/2013
Name:       PHILADELPHIA (USCG STA.), DELAWARE RIVER          
            PA
NOAA Chart: 12313                           Latitude:   39° 56.0' N (  39.93333)
USGS Quad:  PHILADELPHIA                    Longitude:  75°  8.5' W ( -75.14167)


Foot Notes:

Benchmarks 23 1922 ELEV. 7.894 FT, 35 1931, 5240 L 2011, and U 237 1959 are
based on one differential leveling connection and do not meet the quality
control standards of the NOS.  Therefore, caution should be used when deriving
elevations for these marks.

                          U.S. DEPARTMENT OF COMMERCE
                National Oceanic and Atmospheric Administration
                            National Ocean Service
                                                                   Page 12 of 12

                                                                                
Station ID: 8545240                         PUBLICATION DATE:  01/14/2013
Name:       PHILADELPHIA (USCG STA.), DELAWARE RIVER          
            PA
NOAA Chart: 12313                           Latitude:   39° 56.0' N (  39.93333)
USGS Quad:  PHILADELPHIA                    Longitude:  75°  8.5' W ( -75.14167)


                             D E F I N I T I O N S


Mean Sea Level (MSL) is a tidal datum determined over a 19-year National Tidal
Datum Epoch.  It pertains to local mean sea level and should not be confused
with the fixed datums of North American Vertical Datum of 1988 (NAVD88).

NAVD88 is a fixed datum derived from a simultaneous, least squares, minimum
constraint adjustment of Canadian/Mexican/United States leveling observations.
Local mean sea level observed at Father Point/Rimouski, Canada was held fixed as
the single initial constraint.  NAVD88 replaces NGVD29 as the national
standard geodetic reference for heights.  Bench mark elevations relative to
NAVD88 are available from NGS through the World Wide Web at 
National Geodetic Survey.

NGVD29 is a fixed datum adopted as a national standard geodetic reference for
heights but is now considered superseded.  NGVD29 is sometimes referred to as
Sea Level Datum of 1929 or as Mean Sea Level on some early issues of Geological
Survey Topographic Quads.  NGVD29 was originally derived from a general
adjustment of the first-order leveling networks of the U.S. and Canada after
holding mean sea level observed at 26 long term tide stations as fixed.
Numerous local and wide-spread adjustments have been made since establishment in
1929.  Bench mark elevations relative to NGVD29 are available from the National
Geodetic Survey (NGS) data base via the World Wide Web at 
National Geodetic Survey.

NAVD88 and NGVD29 are fixed geodetic datums whose elevation relationships to
local MSL and other tidal datums may not be consistent from one location to
another.

The Vertical Mark Number (VM#) and PID# shown on the bench mark sheet are unique
identifiers for bench marks in the tidal and geodetic databases, respectively.
Each bench mark in either database has a single, unique VM# and/or PID# assigned.
Where both VM# and PID# are indicated, both tidal and geodetic elevations are
available for the bench mark listed. The NGS's Integrated Data Base (IDB PID)
provides geodetic datum based on traditionally leveled and bluebooked ties to
the National Spatial Reference System(NSRS) https://www.ngs.noaa.gov/datasheets/.
The NGS Online Positioning User Service (OPUS PID) provides geodetic datum based
on GPS position & tie it to the NSRS https://www.ngs.noaa.gov/OPUS/.

The NAVD88 elevation is shown on the Elevations of Tidal Datums Table Referred
to MLLW only when two or more of the bench marks listed have NAVD88 elevations.
The NAVD88 elevation relationship shown in the table is derived from an average
of several bench mark elevations relative to tide station datum.  As a result of
this averaging, NAVD88 bench mark elevations computed indirectly from the tidal
datums elevation table may differ slightly from NAVD88 elevations listed for
each bench mark in the NGS database.