You will be near a bridge on Howland Avenue. Look at the sign 'OUTFALL STRUCTURE No.OS-9-31'. There is quite a bit of information here, from the outfall identifier to the fact that this is a 24-inch corrogated metal pipe at this culvert. "NAD83" stands for 'North American Datum of 1983', a geodetic reference system common across America to measure vertical height. The coordinates you see are just that, using the 'US State Plane Coordinate System', which would convert to the GPS coordinates you are using now to find this cache.
"NGVD 1929" refers to the 'National Geodetic Vertical Datum' system finalized in 1929, established by using 21 tide gauges in the US and 5 in Canada, with sea heights measured over time and averaged out. With the advent of better systems, including our beloved GPS, 'NAVD 1988' (North American Vertical Datum) was rolled out in 1988. Owing to increased accuracy and more-detailed science, there is an average difference in elevation of one foot, as you see here in the NGVD value of 'EL 26.5' versus the NAVD value of 'EL 25.5' So, no: while there may indeed be some settling of the earth in New Jersey, we have not really lost a foot here. Keep Calm, and Cache On.