Tampa's rapid transformation from a late 19th-century phosphate port into a sprawling Gulf Coast metropolis has placed immense pressure on its subsurface infrastructure. The underlying Hawthorne Group and Tampa Limestone formations, riddled with dissolution features and interbedded clay layers, create a hydrogeological puzzle that standard lab tests simply cannot solve. When designing deep foundations, retention systems, or stormwater infiltration galleries, knowing the mass permeability—not just the matrix permeability of a small undisturbed sample—is what prevents costly dewatering failures. Our team runs Lefranc tests in soil and highly weathered rock, and Lugeon tests in fractured limestone, capturing the true hydraulic behavior of the formation under in-situ stress conditions. Because so much of Florida’s geotechnical risk ties directly to water movement through solution-enhanced secondary porosity, we often pair these field measurements with a CPT soil profiling to map the exact stratigraphic boundaries where flow concentrates, ensuring the permeability value is assigned to the correct hydrostratigraphic unit.
A single packer test in Tampa’s limestone can reveal flow paths that render a dry excavation impossible without targeted grouting—ignoring secondary porosity is the fastest route to a flooded site.
Our approach and scope
Site-specific factors
A contractor working on a mid-rise medical office building near the Westshore business district discovered that their dewatering plan, based solely on grain-size correlations from split-spoon samples, was extracting three times the predicted volume of groundwater. The overconsolidated clayey sand they logged actually contained open, dissolution-enlarged joints in the underlying limestone that only a Lugeon test could have identified. Running a stepped-pressure packer test within the zone of fluctuation revealed a hydraulic conductivity two orders of magnitude greater than the lab-derived estimate, leading to a rapid redesign of the sump configuration and the addition of a temporary wellpoint system. Scenarios like this repeat across Tampa Bay’s karst terrain, where the secondary permeability network completely controls the groundwater flow regime. Relying on empirical estimates or remolded laboratory samples, rather than direct in-situ measurement, introduces a margin of error that can swamp a construction budget with change orders, dewatering surcharges, and even regulatory fines for unauthorized off-site drawdown.
Reference standards
ASTM D6391-11 Standard Test Method for Field Measurement of Hydraulic Conductivity Using Borehole Infiltration, ASTM D4630 Standard Test Method for Determining Transmissivity and Storage Coefficient of Low-Permeability Rocks, IBC Chapter 18 (Soils and Foundations) referencing site-specific geotechnical investigation requirements, Florida Building Code Section 1803 for foundation and excavation dewatering design
Other technical services
Lugeon Packer Testing in Limestone
We isolate discrete fractured intervals in the Tampa Limestone using pneumatic packers, applying five pressure stages to determine the hydraulic conductivity and flow regime (laminar, turbulent, or dilation) per the Lugeon methodology.
Lefranc Variable Head Tests in Soils
For sandy and clayey overburden above the bedrock surface, we perform constant or falling head tests within a slotted casing section, recording the rate of water level recovery with pressure transducers for high-resolution data.
Dewatering Feasibility Assessment
Combining in-situ permeability results with the project excavation geometry, we compute steady-state inflow rates and the radius of influence, providing the contractor with defensible numbers for pump specification and discharge permitting.
Grouting Verification Permeability
After curtain or consolidation grouting, we re-test the treated zones using the same packer setup to quantify the reduction in hydraulic conductivity and confirm that the specified residual permeability target has been achieved.
Typical parameters
Common questions
What is the difference between a Lefranc test and a Lugeon test?
Both measure in-situ hydraulic conductivity, but they target different materials. The Lefranc test is designed for soils and very soft, weathered rock, using a simple open borehole section without packers. The Lugeon test specifically evaluates fractured rock by isolating a section of the borehole with inflatable packers and measuring water take at incrementally increasing pressures, which helps identify whether flow is laminar or if joint dilation is occurring under pressure.
How much does a field permeability test package cost in Tampa?
For a typical program involving several Lefranc or Lugeon tests at different depths, the cost generally ranges from US$600 to US$1,040 per test location, depending on the number of intervals tested, the depth to the test zone, and the mobilization requirements for the drill rig and packer assembly.
How long does a Lugeon test take to run on site?
A single Lugeon test interval typically requires about 45 to 60 minutes of actual testing after the packer is set, as we need to run five pressure stages (low-medium-high-medium-low) and maintain stable flow at each stage for a full 10-minute period. Including drilling to depth and packer inflation, a single test consumes roughly one to two hours of rig time, with multiple intervals possible in a single day.