53Karst Studies in West Central Florida SINKHOLE FORMATION AT

Lake Grady was created by the damming of Bell Creek in 1969. In March 2000, water quality at residential drinking wells east of Lake Grady, near Riverview Florida, began to decline. Approximately 200 residential wells in the area were contaminated with coliform bacteria. The cause of the contamination was a sinkhole that was activated beneath Lake Grady approxi-mately 200 feet from its southeast corner. Analysis of the hydrologic and hydrogeologic con-ditions during 1999-2001 shows that conditions were favorable for sinkhole development. Prolonged drought, early spring rainfall, and an abnormally low potentiometric surface com-bined to create a condition favorable for loading and flushing sinkholes beneath the lake. PURPOSE Past investigations (Cardinale, 2000) deter-mined sinkholes were the cause of well con-tamination in Lake Grady. None of these in-vestigations, however, sought to determine the cause of the sinkholes. In 2000, Ann Tihansky