TAMPA — Mystery solved, at least to the satisfaction of those who ponder the long history of the brick-lined tunnels beneath Ybor City.One running theory is that the tunnels, tall enough for an adult to walk through with head slightly bent, were dug by smugglers.Another holds that they might have been a public works project used later by opportunistic smugglers.One tunnel recently unearthed at 12th Street and Sixth Avenue provided an opening onto an answer that finally has historians nodding their heads in agreement.The tunnels were built to dispose of human waste, combining a sanitary sewer and storm drain to flush it all out toward the Ybor Channel.PREVIOUS: Demolition work reveals first opening in 20 years to Ybor City’s infamous tunnels"The curtain has been pulled back," said Tampa Bay History Center curator Rodney Kite-Powell, who recently ventured into the tunnel. "In theory it could have been used as a tunnel to move things, but we know for certain that it was a storm and sanitary sewer."The tunnel, built between 1885 and the late-1890s by Kite-Powell’s estimate, resembles dual-use sewers built in other cities during the 19th Century and has pipes dating back to that period.But newer stormwater pipes also were found there, from as recently as the 1970s or 1980s."It is clearly fairly modern maintenance,” Kite-Powell said. “I am surprised no one has come forward to explain that the tunnel was used as a storm and sanitary sewer."A 1927 plan labels the tunnel as a stormwater sewer, said Carlos Alfonso, managing partner for Alliant Partners, which is developing the property as headquarters for Masonite International.Five foot tall and just as wide, the tunnel has walls and a ceiling made up of three layers of bricks with a flat wood floor. It lies beneath about a foot of earth. The tunnel extends 20 yards south of a railroad track and ends at a concrete wall.Before it was walled off, the tunnel likely ran all the way to the Ybor Channel, Kite-Powell said.In the late-1700s and 1800s, cities along the eastern seaboard built brick storm drains that doubled as sanitary sewers, said Jon Schladweiler, a sewer historian from Arizona, so gravity would do the work of flushing sewage toward an outfall.Chamber pots were used in urban settings, Kite-Powell said, and then dumped into holes that drained into the tunnels."To some degree they depended on storm water to routinely flush away anything that didn't flush away with gravity, like solids," Schladweiler said. The nearby body of water "would then become interesting, depending on the tides."To build these tunnels would have taken "people and horse power," Schladweiler said — first to dig the trench, then to lay the brick and finally to cover it. It's unlikely a smuggler could build one in secret, he said.Still, the tunnels would have provided a clandestine route for smuggling and they were obsolete as sanitary sewers by 1905 or so, when more modern systems were installed around the city, Kite-Powell said.PREVIOUS: From bunkers to tunnels, Mafia history stirs underworld exploration in Ybor City"Their location was certainly well known," he said. "Prohibition was in effect for so long that it would be surprising if someone didn't use" the tunnels "at some point."Still, to historians, this remains a theory until someone steps forward with solid evidence."We have more to learn," Tampa mob historian Scott Deitche said. "But we have learned more in the past few months than in the past 20 years. I hope this inspires people to come forward with stories."Whether someone would be willing to trudge through human waste for smuggling, sewer historian Schladweiler said, would depend on the value of the cargo."It can be done and it has been done," he said, pointing to Polish Jews who escaped Nazi capture through sewer systems.That jibes with a theory that the tunnels were used to smuggle Chinese immigrants from the 1880s through the 1920s, an era when laws made it nearly impossible for Asians to come to the United States.PREVIOUS: Tampa, Cuba once shared network for smuggling illegal aliens into the U.S.One local man was implicated in a Chinese smuggling operation in Ybor in April 1922, Deitche said."There were 30 Chinese brought in from Cuba on a boat."Other tunnels discovered in Ybor included one that ran from the site of an old grocery store at 14th Street and Seventh Avenue, across the street to the former Las Novedades Restaurant. Some believe it may have been used for running moonshine and lottery numbers.For safety reasons, part of the newly discovered tunnel beneath the building site is being demolished. So on Monday, representatives were on site from the University of South Florida Digital Heritage and Humanities Collections Department. Using terrestrial laser scanners, they created digital maps.The portion that will remain is adjacent to a planned courtyard so a glass floor might be installed there so people can see into it, said Darryl Shaw, who is partnering with Alliant Partners on the development."We'd love to. We need to make sure it is safe," Shaw said.If it was a smuggling route, people will want to see it, said sewer historian Schladweiler.If not, he said with a laugh, "some might think it’s like digging a pit under an outhouse and putting a glass cover over it."Contact Paul Guzzo at [email protected] or follow @PGuzzoTimes.