TAMPAA century ago, water flowed freely from the Hillsborough River down into Tampa Bay. The millions of gallons of freshwater used to keep the bay's salinity in check, which was important for the health of the snook and other fish living there. But in 1897, Tampa dammed the river, creating a reservoir to supply its drinking water. Since then, freshwater has continued to spill out of the dam into the riverbed, but during dry seasons there is sometimes no water to spare.Under pressure to fix that situation, Tampa officials now plan to restore the flow into Tampa Bay — but not with river water. Instead, the city plans to pump up to 2 million gallons a day from Blue Sink, a complex of sinkholes in Sulphur Springs, then pipe that water to the base of the dam and pour it out.To the people who live in the suburbs around Blue Sink, this is a Rube Goldberg solution that can only lead to further problems — for them. They fear pumping water from the sinkholes will create even more sinkholes, not to mention draining their lakes and sucking their private wells dry."When our lakes go dry, who pumps the water back into our lakes?" one resident asked in an email to the agency in charge of permitting the project.During a recent community meeting that drew more than 100 people, Jim Wilson of the North Forest Hills Neighborhood Association said he told city officials "we were worried about our water and our quality of life."After all, he pointed out, the sinkholes, nearby Sulphur Spring and the neighborhood's lakes all connect underground to the aquifer, so "all this stuff is tied together."But Tampa Water Department boss Brad Baird said the homeowners shouldn't worry. Any impacts to the aquifer and lakes, he predicted, "will be minimal."For one thing, the pump won't be running all the time, only as needed. The city's engineers, in their application for a 30-year pumping permit, estimate that at most that would be 287 to 318 out of 365 days. "In some years we won't need it at all," Baird said.The city's studies say none of the 800 wells within a 1-mile radius "is expected to be significantly impacted" by that amount of pumping. At most they might drop two-tenths of a foot, the city's engineers predict.They've based those conclusions on a pair of 30-day pumping tests and a computer model. The neighbors are not buying the test results. "I don't know how you can look at 30 days and project out 30 years," Wilson said. "If you can tell me from 30 days what's going to happen over the next 30 years, you're smarter than I am."They have not questioned the computer model, but others have. Hydrologists know that for years Florida officials have based all their water permitting decisions on computer models that use a false assumption. The models assume that the aquifer flows at a steady rate through layers of sand and gravel.Actually, what's beneath our feet isn't sand. It's called karst — a landscape made of limestone that's full of holes both big and small, where water sometimes shoots through as if sprayed by a firehose.As a result, the computer models are so far off base "they shouldn't be used to make decisions," David Still, former executive director of the Suwannee River Water Management District, said in an interview earlier this year.Both the model and the pump tests for Blue Sink were provided by the Southwest Florida Water Management District, more commonly known as Swiftmud. Swiftmud is Tampa's partner on the Blue Sink project, paying half of the $11 million bill. Swiftmud also happens to be the regulator that pushed for restoring the river's flow into Tampa Bay and is now overseeing how Tampa carries out that order. The state agency issued Tampa a construction permit in October, but has yet to approve the city's water-use permit. That's slated for a decision next month. Baird said the city hopes to begin work near year and finish in 2015.Swiftmud began pressing Tampa to restore the river flow in 1999, setting a goal that was challenged by a nonprofit group, Friends of the River. The Friends group sued, saying Swiftmud's goal didn't provide enough freshwater to support snook, baby manatees and other wildlife, and settled for a five-year study. Ultimately Swiftmud set a new river flow goal that was twice as much as its original one, about 13 million gallons a day. Friends of the River hoped the city would use the water in the 1,300-acre reservoir to meet that goal."The most elegant option is to release water at the dam," Rich Brown, a member who as an engineer had worked on water quality issues for the Navy, said in 2007. "You just turn a button, crank the gate open."Rather than give up drinking water, the city instead picked something far more complicated. The Blue Sink project is only the fourth of five projects Tampa has planned for supplementing the river, Baird said. Other sources include the Tampa Bypass Canal and the Morris Bridge Sink northeast of Temple Terrace.That the city is now looking to Blue Sink as a water source for environmental restoration marks a turnaround in its attitude. A 2004 study found that the city had been funneling polluted stormwater into the sinkhole complex for years, and some sinks had become blocked by people dumping in old refrigerators, car parts, tires and battery casings.Times staff researcher Caryn Baird contributed to this report. Craig Pittman can be reached at [email protected] or on Twitter @craigtimes.