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TARPON SPRINGS - In the second of three new reports, a consultant to Stauffer Management Co. has concluded that most of the Stauffer Superfund toxic waste site is sinkhole-free and geologically stable.
Therefore, the consultant concludes, "there is no reason" that Stauffer shouldn't go ahead with a plan to pile up contaminated dirt on the property and cover the mounds with a watertight cap.
Now it's up to the U.S. Environmental Protection Agency to study that report and determine whether its conclusions are valid.
"Just because they say certain things in here, that doesn't mean that's the absolute truth," said Nestor Young, the EPA's project manager for the Stauffer cleanup.
"We may look at the data and not agree with some of those conclusions, who knows?" Young said Wednesday. "That's what we need to do now. Our experts need to take it apart to make sure they're making the correct conclusions based on the data that they collected."
Stauffer's consultants, O'Brien & Gere Engineers, concluded that 120 acres, or about 92 percent of the site, show no signs of past sinkholes.
The remaining 10 acres show signs of sinkholes that took place more than 40,000 years ago. Engineers used carbon-dating to determine the age of the sinkholes and concluded those areas "appear to be very stable with an extremely low risk" of further collapse.
"We're extremely satisfied that we've done a very comprehensive and complete geophysical study and indeed it does demonstrate that we should be in a position to safely and effectively implement the (mound-and-cap) remedy," Stauffer Management president Brian Spiller said.
The Stauffer plant processed phosphate ore into elemental phosphorus from 1947 to 1981. The site was put on EPA's Superfund list in 1994 after officials found high levels of arsenic, lead and radium-226, as well as other contaminants known to or suspected of causing lung cancer.
The EPA was poised to let Stauffer go ahead with the mound-and-cap plan until three years ago. That's when residents and local, state and federal officials, including U.S. Rep. Mike Bilirakis, R-Tarpon Springs, convinced EPA officials to pause and study the risk of sinkholes and groundwater contamination.
Since then, Stauffer has spent $3-million on three new studies, and got ideas and advice on the work from a variety of agencies before starting, Spiller said.
Along with finding little risk of sinkholes, O'Brien & Gere concluded that a continuous layer of clay and clayey materials extends over 92 percent of the site. That's the same 92 percent untouched by old sinkholes. The layer varies from 1 to 24 feet thick but is 8 feet thick on average, according to the report. The layer is an important barrier between the site's contamination and the drinking water below.
Also, after using electromagnetic and other high-tech equipment, consultants found five areas on the property "that might potentially contain significant amounts of buried metal debris," the report said.
But they said they didn't find anything like a large cache of buried metal drums - something that some Tarpon Springs residents have long suspected.
The report does say there are "potential triggering mechanisms" for sinkholes on the property. It recommends using "reasonable practices" such as minimizing vibration and keeping sudden changes in surface water flow to a minimum if the mound-and-cap cleanup goes forward.
Those triggering mechanisms are "large piles of material," such as lime sludge and other discarded material, in areas of historic sinkhole activity, said Frank McNeice, Stauffer's site manager. There are not large amounts of slag, a radioactive byproduct of phosphate ore processing, in those areas, he said.
The consultants said they found no reason why the mound-and-cap cleanup couldn't be "safely implemented and remain effective over the life of the remedy," a period lasting hundreds of years.
No one outside Stauffer or the EPA has seen a copy of the report yet, but a local critic of both remained skeptical.
"What they're doing over there is just absolutely bogus," said longtime activist Mary Mosley. In particular, she questioned the consultant's conclusions about the thickness of the clay under the property. She also said, "once there's been a sinkhole, there is no clay liner. It's been breached."
Stauffer delivered its geophysical study to the EPA on Tuesday. Young said he will circulate the report among agencies and individuals with a stake in the site or expertise in geology.
That group will include a citizens group known as the Pinellas-Pasco Technical Advisory Grant, or Pi-Pa-TAG, the Pinellas County Health Department and county department of environmental management, Pasco County School District, Army Corps of Engineers and University of South Florida geology professor Mark Stewart.
It also will include an EPA geological consultant, the firm of Black & Veatch, which said three years ago that the area around the Stauffer site "is prone to sinkhole formation."
Young said he will compile questions and comments from those groups, as well as interested residents, and have Stauffer respond to them. The goal is to get a document on which EPA can confidently base a decision.
Once it has a final report, the EPA will hold a public meeting, possibly in the fall, Young said.
Stauffer's first report, done by another firm and released early this month, concluded that there is a thick enough underground layer of clay to keep the site's contamination from reaching the deeper aquifer that supplies most Floridians with their drinking water.
A third report, which is due by the end of the year, will study which cementlike substance would best stabilize the material inside the mound.
- Richard Danielson can be reached at 727 445-4194 or danielson@sptimes.com