Field Permeability Testing (Lefranc/Lugeon) — St. Paul Subsurface Flow Assessment

The hydrogeology beneath a West 7th Street brownfield behaves nothing like the sandy terraces under a Highland Park residential lot — even when both sit within the same St. Paul city limits. These contrasts in the Mississippi River valley demand more than a desk study; they require direct measurement of hydraulic conductivity through field permeability testing. Our team deploys both the Lefranc method for soil and the Lugeon test for fractured rock, delivering site-specific K-values that drive dewatering plans, cutoff wall specifications, and foundation drainage design. Because St. Paul's subsurface ranges from glacial outwash to Platteville limestone, a single assumed permeability coefficient can cost a project weeks of groundwater delays. We integrate in-situ test results with grain size data to refine seepage models, and we often recommend a CPT sounding to map continuous stratigraphy before selecting test intervals.

A five-stage Lugeon test in fractured St. Peter Sandstone reveals flow paths that lab permeameters never capture.

Service characteristics in St. Paul

With a population exceeding 300,000 and a building stock that dates from the 1880s to today's mid-rise infill along University Avenue, St. Paul's construction environment spans historic fill, buried stream channels, and bedrock within 20 feet of grade in parts of the East Side. These conditions make the Lefranc test — run in a borehole at a constant or variable head — the go-to method for measuring permeability in soil, while the Lugeon test quantifies fracture flow in the Ordovician dolomite and sandstone that underlies downtown. Each test interval is isolated with a pneumatic packer, and we record pressure-step data across five stages following the Houlsby interpretation method. When the results show a Lugeon value above 10 in the upper weathered rock, we know a simple sump won't cut it — and that's precisely the kind of field intelligence that prevents change orders. The data feeds directly into groundwater control design, and we frequently pair it with slope stability analysis when excavation faces intersect water-bearing layers.

Field Permeability Testing (Lefranc/Lugeon) — St. Paul Subsurface Flow Assessment

Parameter	Typical value
Test methods	Lefranc (constant/variable head) for soil; Lugeon (packer test) for rock
ASTM standard	ASTM D6391-11 (reapproved 2020) for borehole permeability
Test intervals	Typically 3 to 10 ft, isolated with pneumatic packer
Rock mass classification	Lugeon values correlated to fracture aperture per Houlsby (1976)
Reporting parameter	Hydraulic conductivity K (cm/s or ft/day) and Lugeon unit (Lu)
Data deliverables	Pressure-step plots, flow vs. time curves, interpreted K-profile
Typical duration	30-60 min per test interval after borehole advancement

Risks and considerations in St. Paul

St. Paul's industrial past along the rail corridors and the Mississippi left a legacy of fill that ranges from cinders to demolition debris — material whose permeability can vary by two orders of magnitude within a single block. Whenever a deep excavation is planned near the old Hamm's Brewery complex or within the Phalen Creek buried valley, groundwater inflows can surprise even experienced contractors. A single Lugeon test in the underlying bedrock reveals whether fractures are tight (less than 1 Lu) or open enough to require pre-excavation grouting. Skipping this step has led to flooded footings, unstable slopes, and six-figure dewatering overruns that no contingency budget absorbs gracefully. The City's Department of Safety and Inspections reviews subsurface drainage plans against actual field data — and a permeability coefficient borrowed from a textbook won't satisfy reviewers who know the local geology.

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Applicable standards: ASTM D6391-11 (reapproved 2020) — Standard Test Method for Field Measurement of Hydraulic Conductivity, ASCE 7 — Minimum Design Loads and Associated Criteria for Buildings and Other Structures, IBC Chapter 18 — Soils and Foundations, USBR Earth Manual — Part 2, Permeability Tests in Boreholes

Our services

Our St. Paul field team runs the following permeability testing services, each adapted to the soil-rock transition typical of the Twin Cities basin:

Lefranc borehole permeameter

Constant-head or falling-head test in soil, performed during conventional drilling. We measure flow rate and apply the Hvorslev shape factor to compute K for each layer.

Lugeon packer test in rock

Five-stage pressure test (low-high-low) in NX-size boreholes, isolating the test zone with a single or double packer. Lugeon values guide grouting decisions and tunnel inflow estimates.

Dewatering feasibility analysis

Using field K-values, we model well spacing, drawdown, and discharge rates for construction dewatering permits. Outputs meet MPCA and City of St. Paul requirements.

Common questions

How much does a field permeability test cost in St. Paul?

A single Lefranc test during a routine boring typically runs between US$700 and US$1,060, depending on depth and the number of intervals. A full Lugeon test sequence in rock, with packer setup and five pressure stages, starts at the upper end of that range due to the additional rig time and instrumentation.

When should I choose a Lugeon test instead of a Lefranc test?

The Lugeon test applies when the ground is rock — limestone, sandstone, or dolomite — and you need to know how much water moves through fractures. The Lefranc test is for soil. In St. Paul, where bedrock is often within 15 to 30 feet of grade, many projects require both: Lefranc in the overburden and Lugeon in the underlying Platteville or St. Peter formations.

How many test intervals does a typical St. Paul project need?

We space intervals every 5 to 10 feet vertically, depending on stratigraphic changes observed during drilling. A 40-foot borehole might yield four Lefranc tests in soil and one or two Lugeon tests in rock. The exact number follows the site-specific investigation plan and the depth of the proposed excavation or foundation element.

Can you run permeability tests in existing monitoring wells?

Yes, under certain conditions. If the well is properly constructed with a short screen and an effective filter pack, we can perform a rising-head or falling-head slug test to estimate hydraulic conductivity. However, for design-grade data — especially where cutoff walls or deep dewatering systems are involved — we strongly recommend dedicated Lefranc or Lugeon tests in newly drilled boreholes to eliminate well-construction variables.