This is a bonus cache for the Hummelstown Adventure Lab.
Hummelstown is located by the Swatara Creek (aka Swattie). This creek has a reputation for frequent flooding when there's major rainfall. Considerable damage to bridges and houses has been experienced in the past. This parking lot has a sign concerning information about the Duke Street Bridge and provides access to one of the Nature Trails in Hummelstown. Nearby (see the reference waypoint) are High Water marks for Swattie flooding!
The coordinates for the final are:
N40 16.ABC W76 43.XYZ
Currently Hurricane Agnes has achieved the highest High Water mark on June DE, 1972. It did considerable damage and was extremely costly. Use the waypoint to find the value of DE.
A = E-D
B, C, X, Y, and Z can be found in the Adventure Lab.