HYDROGEOLOGIC INVESTIGATION OF LEAKAGE THROUGH SINKHOLES IN THE BED OF LAKE SEMINOLE INTO AND THROUGH THE FLORIDAN AQUIFER TO ARTESIAN SPRINGS LOCATED DOWNSTREAM FROM JIM WOODRUFF DAM

Jim Woodruff Dam was constructed across the Apalachicola River on the Florida-Alabama border to create Lake Seminole. Polk Lake Spring is located about 244 meters (800 feet) downstream, and a large boil, estimated to be 424,753 liters per second (15,000 cfs), created by water rising from a hole in the river bed, is located in the Apalachicola River about 549 meters (1,800 feet) downstream. This research was initiated by the Mobile District US Army Corps of Engineers to determine if water from the spring and/or boil is leakage from the reservoir, groundwater, or both. EMC, Inc. performed a multi-beam hydrographic survey of the lake bottom topography, identifying five potential leakage sites. The most distant hole identified by the lake bed survey was approximately 434 meters (1,425 feet) upstream from the dam. A dye tracer investigation was conducted to determine if any of these sites was contributing to the discharge at the spring and/or boil located downstream from the dam. After a karst hydrogeologic inventory was conducted, activated charcoal dye receptors were placed at twelve locations, and ISCO automatic water samplers at three locations. `

Three fluorescent dyes were used for the tracer tests. The investigation indicates that lake water sinking into holes in the lake bed is flowing through old solution conduits in the limestone bedrock that existed previous to dam construction. All the leakage confirmed by dye tracing is resurging at the boil located in the river downstream from the dam. However, most of the leakage first resurges at Polk Lake Spring and then sinks at Polk Lake Sink to finally resurge at the boil.

Jim Woodruff Dam was built upon the lower Tampa Limestone, a semi-confining unit for the Upper Floridan Aquifer. The geologic dip in the vicinity is downstream perpendicular to the dam. The Suwannee Limestone, the uppermost geologic unit of the Upper Floridan Aquifer, outcrops under Lake Seminole but dips below the Tampa semi-confining unit in the vicinity of the dam. Additional leakage may be sinking through reactivated sinkholes in the lake where the Tampa semi-confining layer is thin. This leakage may then flow through the Suwannee Limestone (Upper Floridan Aquifer) down dip to resurge at the boil located about 549 meters (1,800 feet) downstream from the dam, where the Tampa is thin due to the downcutting of the Apalachicola River Valley.