We ran a Lugeon test last summer on a site off Coral Way where the contractor couldn’t figure out why the dewatering wells weren’t pulling enough drawdown. Turned out the oolite had secondary porosity — vuggy channels that a lab perm from an SPT split spoon completely missed. That’s the reality of working in Miami: the limestone tells a different story every 100 feet. When you’re pushing a deep excavation or designing a permanent cutoff wall for a coastal parking garage, the saturated hydraulic conductivity you get from a textbook isn’t going to cut it. You need in-situ measurements under actual flow conditions. That’s where the Lefranc test in granular layers and the Lugeon test in rock come in — both run during drilling, both giving you formation-scale permeability that a <2-inch sample can’t replicate. We run these tests across Miami-Dade, from the high-rise corridor in Brickell down to the sprawling industrial pads in Medley, and the numbers always surprise the design team.
The Biscayne Aquifer can deliver transmissivity numbers that make a hydrogeologist smile — and a contractor sweat.
Local considerations
Compare a site in Sweetwater with one out in West Kendall and you’ll see two completely different permeability profiles. Sweetwater sits on the eastern edge of the coastal ridge, with thin sand over highly transmissive oolite — water flows laterally through solution channels, and a Lefranc test in a sand lens above the rock can give you a false sense of security if you don’t also test the limestone below. West Kendall, farther inland, often has thicker sands and a deeper, less karstified Fort Thompson formation. The risk isn’t just about dewatering — it’s about cutoff wall toe elevation. If you design for the wrong k, your wall stops short of an impermeable layer and you’re pumping forever. We’ve seen developers in edge zones near the Everglades get surprised by artesian conditions in the deeper Hawthorn Group sediments, where a Lugeon test is the only way to confirm the confining unit’s integrity before excavation starts. Saltwater intrusion along the coast adds another layer — you’re not just measuring how fast water moves, but also checking whether pumping could pull the interface inland, a concern the SFWMD watches closely.
Common questions
How much does a Lefranc or Lugeon test cost in Miami?
For Miami-Dade projects, field permeability testing by either the Lefranc or Lugeon method typically runs between US$660 and US$1,140 per test interval, depending on depth, access conditions, and whether the test is integrated into an existing drilling program or requires standalone mobilization. The price includes the packer setup, data logging, and the interpreted k-value report.
When do I need a Lugeon test instead of a Lefranc test?
A Lugeon test is the right choice when your borehole is advancing through rock — in Miami, that means the Miami Oolite, Fort Thompson, or Key Largo limestone formations. The Lugeon method uses a packer to isolate a section of the rock and applies pressure in stages, which helps identify whether the rock mass has fractures, vugs, or solution channels. A Lefranc test is designed for granular soils — sands, silty sands, and gravel lenses — where you’re measuring matrix permeability rather than fracture flow.
How many permeability tests do I need for a dewatering design in Miami?
For a typical mid-rise excavation in Miami, we recommend at least one test per distinct hydrostratigraphic unit encountered — usually the upper sand (Lefranc), the oolite (Lugeon), and any lower sand lenses within the Fort Thompson (Lefranc). For sites larger than half an acre or with variable geology, spacing tests every 50 to 100 feet across the footprint gives the dewatering engineer enough data to build a reliable groundwater model.
Can you run a Lefranc test in the same boring as an SPT?
We can, and often do. Once the SPT sampler is retrieved and the split spoon data is recorded, we can advance the boring to the target depth, clean the hole, and set up the Lefranc test in the same borehole. This keeps the exploration program efficient — one rig, one mobilization, multiple data types. Just be aware that a test in an SPT borehole needs proper development to remove drilling fluid from the sidewalls, otherwise the readings will underestimate true permeability.
