Wildlife flourished on the fringes of an old Largo landfill. So, the city followed through on a plan to transform the 31-acre site off Highland Avenue into a nature preserve.
But soon, officials learned that an observation tower built to give patrons a wonderful view of otters, alligators and other wildlife may have brought an unwelcome guest — high levels of arsenic.
Recent soil tests near the tower showed one spot measured 138 parts per million, more than 11 times Florida's target level for clean-up of arsenic in industrial areas.
The Florida Department of Environmental Protection typically uses a value of 5.5 parts per million as a soil cleanup target level for recreational areas. And the industrial soil cleanup target level is 12 parts per million.
Parts of the preserve have been sealed off to protect the public.
The city plans to do additional groundwater tests at the Largo Central Park Nature Preserve to determine how far and how deep arsenic and other contamination has spread and whether the contaminants have found their way into nearby waterways.
"Nothing so far has indicated any off-site impacts," said Leland Dicus, city engineer.
The DEP is reviewing a report Largo sent to the agency, said Ana Gibbs, a DEP spokeswoman.
"We're kind of on hold from moving forward until we hear back from the DEP," Dicus said.
Arsenic was found throughout the preserve at varying levels, but the tower area was identified as the "hot spot."
"What we've been able to conclude, looking at the data, is that it appears contamination in the area of the tower is due to the construction of the tower," Dicus said.
The tower was built with pressure-treated wood, which historically contained arsenic.
Dicus said he's confident that contamination at the preserve is manageable once the city comes up with a plan to deal with high levels of arsenic near the tower.
The city expects to spend about $1 million to clean up the preserve and the old landfill.
Arsenic in other areas throughout the site is most likely associated with naturally occurring background levels or prior uses, such as agriculture, Dicus said.
For many years, arsenic was broadly used as an herbicide in Florida, said Christopher Teaf, a toxicologist at Florida State University.
Arsenic can be toxic, but the likelihood and the degree of harm is related to the exposure, Teaf said. The mere presence of arsenic does not mean there's a health risk, he said.
The northern part of the preserve was used as a landfill from the 1960s through about 1984. Recent soil tests also show elevated levels of benzo(a)pyrene, mostly in the northwest part of the site. The levels are apparently linked to former landfill activity, which also took place west of the preserve, according to the report.
Benzo(a)pyrene is suspected of causing cancer in humans, according to the U.S. Environmental Protection Agency. Generated by various combustion sources, it's also found in materials like tar and asphalt.
"It's a relatively commonly encountered petroleum constituent," Teaf said. "We see it almost everywhere that samples are collected in urban environments."
The landfill site has been the target of environmental studies for years. In 1978, groundwater tests found elevated levels of chromium and lead there, according to a site inspection report for EPA. Later tests also found high levels of other contaminants, including acetone, benzene, mercury, cadmium and selenium.
A decade ago, the EPA began researching the site to evaluate whether it should be listed as a high-priority toxic site on the National Priorities List. No, the agency decided. But it found elevated levels of numerous contaminants and sent its findings to the state DEP.
In 2002, a city study found elevated arsenic measurements around the observation tower. And in February 2003, the DEP sent Largo a letter asking the city to address elevated arsenic levels. The following month, the preserve opened to the public.
In 2004, Largo officials sent a letter to the DEP listing actions the city had taken to protect the public from arsenic. They included installing signs warning the public to stay on trails, putting dirt caps with vegetation over contaminated areas and fencing off land near the observation tower and another area.
Officials didn't hear back from the DEP and thought the matter was closed. But it wasn't.
In 2008, the city got a letter from the DEP, saying Largo must further assess arsenic contamination at the preserve. The state had specific concerns, it said, including the EPA's finding of extensive contamination beyond arsenic, high levels of arsenic near the tower, limited information about how far and how deep arsenic contamination has spread and the potential for arsenic to leach into waterways.
In late 2008, the city fenced off access to the tower and to a walking path to limit public exposure. And since October, the entire preserve has been closed to complete a project to make sure a stormwater treatment pond on the property is working effectively, Dicus said. The preserve is scheduled to open in July, but portions of the park will remain blocked.
"The trail and observation tower will be closed until we finish site assessment and cleanup," Dicus said.
Lorri Helfand can be reached at firstname.lastname@example.org or (727) 445-4155.