The Sulfur Springs area includes about 56 square miles in west-central Hillsborough County, Florida. The north-central part of the city of Tampa is highly urbanized; the north-west part of the area is rural or undeveloped. The area has numerous sinkholes, two of which are used as retention basins for urban storm runoff. An intermittent stream discharges into a sinkhole that is hydraulically connected with the Floridian aquifer. A well-developed cavity system occurs in the upper part of the aquifer in the southwestern and southeastern parts of the area. Groundwater velocities of 4,200 to 9,200 feet per day were determined from dye tests conducted in a sinkhole area north of Sulfur Springs. Sulfur Springs provides the city of Tampa a supplemental water supply of 20 million gallons per day. Periodically, the spring pool is closed to swimming because of the high bacteria counts in the water. The source of bacteria appears to be an internally drained sinkhole area north of the spring. In 1980, groundwater use in the study area, excluding withdrawals from Sulphur Springs, was 7.2 million gallons per day, largely for public water supplies. The city of Tampa pumped an average of 48.5 million gallons per day from the Tampa Dam Reservoir on the Hillsborough River. (USGS)