Hydrogeology is the study of the groundwater. There are many monitoring stations located all across the province including this one at Oak Hammock Marsh.
The Oak Hammock Marsh watershed is underlain by bedrock consisting of limestone and dolostone inter-layered with several argillaceous units. The limestone and dolostone form a major fresh water aquifer, called the Carbonate aquifer. This aquifer is the primary source of water supply in the region.
You're looking for a very small magnetic cache attached to the structure.