EPSG:7970

COORDINATEOPERATION["NGVD29 height (m) to NAVD88 height (2)",
    VERSION["NGS-US Conus C"],
    SOURCECRS[
        VERTCRS["NGVD29 height (m)",
            VDATUM["National Geodetic Vertical Datum 1929"],
            CS[vertical,1],
                AXIS["gravity-related height (H)",up,
                    LENGTHUNIT["metre",1]],
            ID["EPSG",7968]]],
    TARGETCRS[
        VERTCRS["NAVD88 height",
            VDATUM["North American Vertical Datum 1988"],
            CS[vertical,1],
                AXIS["gravity-related height (H)",up,
                    LENGTHUNIT["metre",1]],
            ID["EPSG",5703]]],
    METHOD["Vertical Offset by Grid Interpolation (VERTCON)",
        ID["EPSG",9658]],
    PARAMETERFILE["Vertical offset file","vertconc.94"],
    OPERATIONACCURACY[0.02],
    USAGE[
        SCOPE["Change of height to a different vertical reference surface."],
        AREA["United States (USA) - CONUS between 89°W and 107°W - onshore - Arkansas; Colorado; Illinois; Iowa; Kansas; Louisiana; Michigan; Minnesota; Mississippi; Missouri; Montana; Nebraska; New Mexico; North Dakota; Oklahoma; South Dakota; Tennessee; Texas; Wisconsin; Wyoming."],
        BBOX[25.83,-107,49.38,-89]],
    ID["EPSG",7970],
    REMARK["In the SE of this area the NGVD29 surface is 0 to 0.1m above the NAVD88 surface; in the W it is 0.6 to 0.9m below the NAVD88 surface. Interpolation in the data file may be made using either NAD27 or any of the NAD83 realizations applicable to US conus."]]

proj4.defs("EPSG:7970","+proj=vgridshift +grids=us_noaa_vertconc.tif +multiplier=1");

{
    "$schema": "https://proj.org/schemas/v0.7/projjson.schema.json",
    "type": "Transformation",
    "name": "NGVD29 height (m) to NAVD88 height (2)",
    "source_crs": {
        "type": "VerticalCRS",
        "name": "NGVD29 height (m)",
        "datum": {
            "type": "VerticalReferenceFrame",
            "name": "National Geodetic Vertical Datum 1929"
        },
        "coordinate_system": {
            "subtype": "vertical",
            "axis": [
                {
                    "name": "Gravity-related height",
                    "abbreviation": "H",
                    "direction": "up",
                    "unit": "metre"
                }
            ]
        },
        "id": {
            "authority": "EPSG",
            "code": 7968
        }
    },
    "target_crs": {
        "type": "VerticalCRS",
        "name": "NAVD88 height",
        "datum": {
            "type": "VerticalReferenceFrame",
            "name": "North American Vertical Datum 1988"
        },
        "coordinate_system": {
            "subtype": "vertical",
            "axis": [
                {
                    "name": "Gravity-related height",
                    "abbreviation": "H",
                    "direction": "up",
                    "unit": "metre"
                }
            ]
        },
        "id": {
            "authority": "EPSG",
            "code": 5703
        }
    },
    "method": {
        "name": "Vertical Offset by Grid Interpolation (VERTCON)",
        "id": {
            "authority": "EPSG",
            "code": 9658
        }
    },
    "parameters": [
        {
            "name": "Vertical offset file",
            "value": "vertconc.94",
            "id": {
                "authority": "EPSG",
                "code": 8732
            }
        }
    ],
    "accuracy": "0.02",
    "scope": "Change of height to a different vertical reference surface.",
    "area": "United States (USA) - CONUS between 89°W and 107°W - onshore - Arkansas; Colorado; Illinois; Iowa; Kansas; Louisiana; Michigan; Minnesota; Mississippi; Missouri; Montana; Nebraska; New Mexico; North Dakota; Oklahoma; South Dakota; Tennessee; Texas; Wisconsin; Wyoming.",
    "bbox": {
        "south_latitude": 25.83,
        "west_longitude": -107,
        "north_latitude": 49.38,
        "east_longitude": -89
    },
    "id": {
        "authority": "EPSG",
        "code": 7970
    },
    "remarks": "In the SE of this area the NGVD29 surface is 0 to 0.1m above the NAVD88 surface; in the W it is 0.6 to 0.9m below the NAVD88 surface. Interpolation in the data file may be made using either NAD27 or any of the NAD83 realizations applicable to US conus."
}

<?xml version="1.0" encoding="utf-8"?>
<Map srs="+proj=vgridshift +grids=us_noaa_vertconc.tif +multiplier=1">
	<Layer srs="+proj=vgridshift +grids=us_noaa_vertconc.tif +multiplier=1">
	</Layer>
</Map>

INSERT into spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext) values ( 7970, 'EPSG', 7970, '+proj=vgridshift +grids=us_noaa_vertconc.tif +multiplier=1', 'None');