DYE TRACE AND BACTERIOLOGICAL TESTING OF SINKHOLES - SULFUR-SPRINGS, TAMPA, FLORIDA

This paper summarizes over four years of studies and testing of a sink hole/spring system in north Tampa. Sulphur Springs Pool delivers an av erage of 95 million l/d to the Hillsborough River, which is tributary to Tampa Bay. In 1986, owing to increasingly erratic bacterial levels at the natural bathing area adjacent to Sulphur Springs, the Hillsboro ugh County Health Department closed the pool for swimming. The City of Tampa, Southwest Florida Water Management District (SWFWMD), Hillsbor ough County Environmental Protection Commission, and the United States Geological Survey have gathered data in an attempt to better understa nd the system and possible sources of contamination. The Sulphur Sprin gs Action League is a civic group in the area, which has an objective of reopening the pool for recreational purposes. Environmental Enginee ring Consultants, Inc. provided pro bono technical assistance and expe rtise in assisting the Action League with its goal. The Action League obtained a grant from SWFWMD to outfit underwater divers for sinkhole exploration as well as water quality and dye trace analysis. The main suspects for bacterial contamination of the pool were two significant sinkholes located 1950 and 2300 m north of the spring. A series of dye tests and water-quality tests were performed. It was estimated that t he underground velocity of water was between 90-100 m/h. Using a dye t race, bacteria testing, and travel time estimating, a new source of co ntamination was found in a Department of Transportation (DOT) stormwat er retention basin in which a sinkhole had opened up and was receiving stormwater. The two significant sinkholes received stormwater from co mmercial and residential areas, and this stormwater brings a large amo unt of bacteria into the sinkhole, which funnels into the underground system and induces a bacteria spike at Sulphur Springs pool that excee ds the bathing water standards. The City of Tampa has constructed an e xperimental initial flush capture basin that will sand-filter stormwat er to see if this will favorably affect bacteria levels. A mayor's tas k force in Tampa has recommended ultraviolet disinfection as an interi m solution to the contamination problem.