Savannah’s growth didn't start at the port—it started with the water table. The city sits on a Pleistocene terrace dissected by tidal creeks, underlain by the Miocene-age Hawthorn Formation and deeper limestone of the Floridan aquifer. Every deep excavation or foundation in downtown Savannah eventually confronts a simple question: how fast does water move through these layers? In our experience, field permeability tests using the Lefranc method in granular overburden or Lugeon tests in weathered limestone give the only reliable answers. We run these tests on active job sites from Bay Street to Pooler, often in combination with in-situ permeability borehole arrays and CPT soundings that map the stratigraphy before we isolate test intervals.
A Lugeon value above 10 in Savannah’s limestone means you’re not just dealing with porosity—you’re dealing with open conduits that can carry tidal head inland.
Method and coverage
Regional considerations
The difference between a site on the sandy Pleistocene terrace near Hunter Army Airfield and one on the alluvial clays of Hutchinson Island is stark. At Hunter, Lefranc tests often show 10^-3 to 10^-4 cm/s—dewatering with wellpoints works, and we can predict drawdown with reasonable confidence. Hutchinson Island, sitting on soft marsh deposits over solution-weathered limestone, is another story. Lugeon tests there sometimes jump from 5 Lu to 60 Lu within a single 10-foot stage, signaling karstic voids connected to the river. The biggest risk in Savannah isn’t the average permeability—it’s the vertical heterogeneity. A design based on a single borehole log misses the thin sand seams that act as hydraulic highways. We’ve seen excavations flood because a 6-inch silty sand lens, invisible in SPT split-spoon samples, connected the bottom of the cut to a tidal creek 200 feet away. That’s why we insist on packer-isolated testing at multiple depths.
Standards that apply
ASTM D6391-11: Standard Test Method for Field Measurement of Hydraulic Conductivity Using Borehole Infiltration, USBR Earth Manual Part 6525: Water Pressure Testing in Rock (Lugeon Method), USACE Savannah District Geotechnical Guidelines: Permeability Testing for Levee and Dam Projects, FHWA-NHI-05-037: Soil Slope and Foundation Design—Dewatering and Permeability
Complementary services
Lefranc Variable-Head Tests
We isolate a screened section in soil and measure rate of water level recovery. Data reduced using Hvorslev or Bouwer-Rice solutions, reported as hydraulic conductivity per interval.
Lugeon Pressure Testing in Rock
Five-stage pressure test (low-high-low-high-low) in fractured limestone or marl. Results plotted as Lugeon value vs. pressure, with interpretation of fracture flow regime—laminar, turbulent, dilation, or washout.
Dewatering Parameter Package
Combined Lefranc tests, lab grain size curves, and CPT pore pressure dissipation data. We deliver transmissivity, storativity estimates, and recommended well spacing for your dewatering contractor.
Typical parameters
Q&A
What is the difference between a Lefranc test and a Lugeon test?
The Lefranc test measures hydraulic conductivity in soil by injecting or recovering water through a screened borehole section, following ASTM D6391. The Lugeon test applies to fractured rock—water is pumped into an isolated interval under controlled pressure, and water take is expressed in Lugeon units. In Savannah, we use Lefranc in the overburden sands and clays, and switch to Lugeon when the bit hits the Hawthorn limestone.
How deep can you run permeability tests in the Savannah area?
Our NQ drill string reaches 120 feet routinely, which covers most foundation and dewatering depths in Chatham County. For deeper investigations into the Floridan aquifer, we can extend with HWT casing, though most projects in Savannah don't need to go below 100 feet unless tunneling or deep well injection is involved.
How much does a field permeability test program cost in Savannah?
A typical program with 3 to 5 Lefranc tests or Lugeon stages runs between US$710 and US$1,010 per test interval, including drill rig time, packer setup, data acquisition, and the engineering report. Total cost depends on depth, number of intervals, and whether we're already on site for SPT drilling. We provide a fixed-price proposal after reviewing your boring logs.
How many test intervals do I need for a dewatering design?
It depends on stratigraphic complexity. In the terrace sands south of Savannah, 3 to 4 Lefranc tests spaced vertically across the proposed excavation depth are usually sufficient. On Hutchinson Island or near tidal creeks, where limestone is shallow and fractured, we recommend 4 to 6 Lugeon stages plus at least 2 Lefranc tests in the overburden to capture the full hydraulic profile.