Bowing to state concerns over the increased potential for sinkhole activity near Tampa Bay Water's C.W. "Bill" Young Regional Reservoir in Lithia, Fla., the water utility has scuttled its $41-million, 3-billion-gallon planned expansion of the facility.

Gerald Seeber, Tampa Bay Water general manager, canceled the project after an April 18 letter from the Florida Dept. of Environmental Protection (FDEP) hinted the agency likely would reject TBW's permit application. FDEP cited concerns that an expansion would overload the capacity of the area's geology to resist sinkhole development, noting the rapid drawdown of area water levels due to agricultural well pumping.

The FDEP has grown worried over the area's "dynamic, rather than stable," geological conditions, which the agency believes could reactivate existing sinkholes located near the reservoir. If reactivated, one existing sinkhole "has the potential to undermine the reservoir embankment," writes Lisa Robertson, FDEP environmental administrator. Robertson cited a 2010 sinkhole that opened at a Hillsborough County landfill, located just over one mile from the reservoir.

The reservoir's site was earlier deemed safe from sinkhole activity when the facility was originally constructed. However, the landfill sinkhole, coupled with analysis of newly available data, indicates a greater threat than previously thought.

"Analysis of the data [suggests] that pumping may be generating a groundwater circulation system," wrote Robertson.

In an e-mailed response to a query from ENR, Seeber said that, while the water authority disagrees with FDEP, it understands the agency's concerns and will abide by its findings.

"The reservoir's long-term fix remains our priority, so we are following the permitting agency's direction to proceed with only the renovation," Seeber said.

Asked whether any mitigation measures may be needed for the planned renovation, FDEP's deputy press secretary, Dee Ann Miller, stated by e-mail, "DEP, the Southwest Florida Water Management District and Tampa Bay Water have all committed to work together in identifying potential mitigation measures to address the concerns related to the rapid drawdown; however, we are in the preliminary stages of this process."

Kiewit Infrastructure Group, Omaha, is leading a design-build contract covering the renovation, valued at $121 million.

The move to cancel the expansion may delay the renovation. With Kiewit now revising construction drawings, TBW's Seeber now expects the earliest he might deliver a financing plan for review is August, two months later than previously scheduled.