Source of Water Discharged from Green Cove Spring, Clay County, Florida. Professional Paper SJ2014-PP2.

摘要

Green Cove Spring is a third-magnitude spring located on the west bank of the St. Johns River within the City of Green Cove Springs in Clay County, Florida. This spring is the northern most spring found in the St. Johns River Valley or along the Atlantic coast. Previous investigations have identified diffuse discharge in the St. Johns River, and earlier published investigations suggest the source of this springs water is the Upper Floridan aquifer. There remains some speculation that the source of this springs water is derived from the intermediate aquifer system based upon the dive-able depth of the spring vent and other factors. An investigation by the St. Johns River Water Management District (SJRWMD) was undertaken to determine the source of the water that discharges from this spring. Monitoring well drilling and testing did not indicate the presence of a productive intermediate aquifer system in the Green Cove Spring area. Evaluation of the lithologic and geophysical log data indicate that the top of the intermediate confining unit and the Upper Floridan aquifer have a distinct elevation change west of the spring versus east of the spring, which suggests structural deformation in those units. This deformation may have resulted in fractures in these units that have been enlarged over time by dissolution, thus providing a pathway for upward migration of Upper Floridan aquifer water. In this area, there are upward vertical head gradients that may provide recharge to permeable zones within the intermediate confining unit or surficial aquifer system. Water from this spring and six nearby monitoring wells that penetrate the Upper Floridan, intermediate, and surficial aquifers was collected for chemical analysis. Stiff and Piper tri-linear diagrams of the major chemical constituents were constructed to characterize the quality of water from each of the aquifers and spring. Strontium 87/86 ratios were used to compare the relative age date of water within the Upper Floridan aquifer and water discharge from the spring. The evaluation of current and historical water quality data collected from the spring confirms that the dominate source of discharge water from Green Cove Spring is the Upper Floridan aquifer.