In Baltimore, the mix of Piedmont saprolite over schist and deeper Coastal Plain sediments creates a tricky permeability profile. We see it often: a contractor starts a basement excavation near the Inner Harbor, groundwater pours in, and nobody ran a field permeability test beforehand. For any cut below the water table or any slope requiring drainage design, a Lefranc test in boreholes tells you the actual hydraulic conductivity in situ — not a lab number on a disturbed sample. We run these tests in both open-hole and packed-off setups depending on the target layer. Before you design a dewatering system, you want to pair the permeability data with a resistivity survey to map preferential flow paths across the site. That combination has saved clients weeks of schedule delays on several Baltimore projects.
In Baltimore, the transition from fill to residual silt to fractured gneiss demands staged permeability tests at different depths — one number won't cut it.
Method and coverage
- Hydraulic conductivity from variable-head Lefranc
- Lugeon value (LU) from constant-head injection
- Flow regime classification (laminar, turbulent, void)
- Effective porosity estimate where applicable
Regional considerations
Much of Baltimore's urban fabric sits on the Fall Line — a geologic boundary where the hard Piedmont rocks dip under the softer Coastal Plain sands and clays. This contact zone is notoriously anisotropic. Water flows fast along joints in the schist but barely moves through the overlying clay. A single well test might miss the problem. If you design a foundation drain or a tieback wall without a series of field permeability tests, you risk underestimating inflow by an order of magnitude. We've seen it happen on Charles Street projects where seepage through a single fracture flooded a shored excavation. The Lugeon test identifies those fracture zones; the Lefranc test quantifies the matrix seepage.
Standards that apply
ASTM D5092-04 (Standard Practice for Design and Installation of Groundwater Monitoring Wells), ASTM D4631-18 (Standard Test Method for Transmissivity and Storage Coefficient of Confined Aquifers by Constant Head Injection), IBC 2021 Chapter 18 (Soils and Foundations), AASHTO T 207-19 (Field Permeability Test in Boreholes)
Related services
Lefranc Variable-Head Test
For low-permeability soils and weathered rock. We install a standpipe in a cased borehole, measure the rate of water-level rise, and compute k using Hvorslev's method. Ideal for foundation drainage design and cutoff wall evaluation.
Lugeon Packer Test (Constant Head)
For fractured rock masses. A double-packer assembly isolates a 1.5–3.0 m test zone. Water is injected at five pressure steps (0 to 1000 kPa), and the flow rate is recorded. The Lugeon value (LU) and flow regime (laminar, turbulent, wash-out) are reported.
Staged Permeability Profiling
When the site has multiple strata (fill, residual silt, saprolite, bedrock), we run a sequence of Lefranc or Lugeon tests in the same borehole. Each stage targets a different depth interval. The result is a vertical profile of hydraulic conductivity that you can use directly in seepage models like SEEP/W or PLAXIS.
Typical parameters
Common questions
When should I choose a Lefranc test instead of a Lugeon test in Baltimore?
Use the Lefranc method when the ground is soil or highly weathered rock with permeability between 1e-5 and 1e-7 m/s — typical of Baltimore's residual silts and saprolite above the Fall Line. Use the Lugeon method when you're testing sound fractured rock (schist, gneiss) where the flow is controlled by joints and you need a Lugeon value (LU) for design. The Lugeon test also reveals whether flow is laminar, turbulent, or washing out infilling material.
How much does a field permeability test cost in Baltimore?
A standard Lefranc or Lugeon test with one packer assembly runs between US$700 and US$940, depending on borehole depth and number of test stages. For a full vertical profile with 3–5 stages in a single borehole, the cost typically falls between US$1,200 and US$1,800. These estimates include on-site supervision, data reduction, and a report with P-Q curves.
What information do I get from the Lugeon test that a lab test cannot provide?
The Lugeon test measures in situ hydraulic conductivity in a rock mass, not on a small laboratory specimen. It captures the effect of joints, fractures, and bedding planes — features that dominate groundwater flow in Baltimore's Piedmont bedrock. The test also classifies the flow regime (laminar, turbulent, wash-out, or void filling), which tells you whether the fracture system is open, infilled, or unstable under injection pressure.
Do I need a field permeability test for a residential basement in Baltimore?
If your basement excavation goes below the water table or into weathered rock, yes. Baltimore's shallow groundwater in many neighborhoods (Fells Point, Canton, Hampden) can cause serious seepage during construction. A Lefranc test in a single borehole at the proposed basement depth will tell you whether dewatering is needed and what the steady-state inflow rate will be. It's a small investment compared to the cost of a flooded excavation.