A wireline packer assembly descends into a NX-size borehole on the north bank of the Spokane River, sealing off a five-foot test interval within fractured Priest Rapids basalt. The technician at surface monitors a pressure gauge and graduated reservoir, recording the volume of water accepted by the formation under a constant head. This is the Lugeon test in practice—a direct measurement of rock mass hydraulic conductivity that no laboratory sample can replicate. Across Spokane, where columnar jointing and interflow zones create preferential flow paths, this field equipment provides the hydraulic parameters that foundation dewatering designs and cutoff wall specifications actually require. Complementing the Lugeon method, the test pits technique allows visual inspection of shallow alluvial lenses where packer sealing is problematic.
In Spokane’s fractured basalts, a single Lugeon test at five pressure steps reveals more about the aquifer than a dozen lab perm tests on intact core.
How we work
- Lugeon testing with single or double packer configurations in NX to HQ boreholes.
- Lefranc falling-head and constant-head methods in cased soil horizons.
- Pressure-step analysis to distinguish fracture dilation from matrix flow.
- Real-time data plotting in the field to validate test acceptance criteria.
- Integration with groundwater monitoring wells for long-term hydraulic gradient data.
Local ground factors
A six-story medical office building excavation near the Spokane River encountered artesian conditions in a fractured basalt flow at 28 feet below grade. The preliminary geotechnical report had estimated hydraulic conductivity from grain-size correlations on soil samples—a practice that missed the high-permeability interflow zone entirely. Water inflow overwhelmed sump pumps within hours of reaching the contact, delaying foundation work by three weeks while a dewatering system was redesigned using actual Lugeon test data. The additional cost of a deep well system and treatment for turbid discharge water far exceeded what a pre-construction in situ permeability program would have cost. In Spokane’s layered basalt terrain, packer testing is not an optional extra—it is the difference between a dry excavation and a contractual dispute over unforeseen site conditions. Deep excavations in similar settings demand careful monitoring, which is why we often coordinate testing schedules with excavation monitoring specialists to capture groundwater response during construction.
Applicable standards
ASTM D4630-19 – Standard Test Method for Determining Transmissivity and Storage Coefficient of Low-Permeability Rocks by In Situ Measurements Using the Constant Head Injection Test, ASTM D6391-11 – Standard Test Method for Field Measurement of Hydraulic Conductivity Using Borehole Infiltration, USBR 6525 – Procedure for Performing and Analyzing Lugeon Tests, IBC Section 1803.5.4 – Groundwater Investigation Requirements
Associated technical services
Lugeon Packer Testing in Rock
Constant-head injection testing using single or double pneumatic packers to isolate discrete intervals in basalt, granite, or metamorphic bedrock. Pressure-step analysis quantifies fracture flow, dilation, and hydraulic fracturing potential, providing design parameters for grouting programs and tunnel inflow estimates.
Lefranc Testing in Soils
Falling-head and constant-head permeability tests in cased boreholes through alluvial, glacial, and lacustrine deposits. Suitable for silts, sands, and gravels where packer seating is impractical. Delivers hydraulic conductivity values for dewatering design, infiltration basin sizing, and seepage analysis.
Typical parameters
Quick answers
What is the difference between a Lugeon test and a Lefranc test?
The Lugeon test is a constant-head injection test performed in bedrock using inflatable packers to isolate a section of borehole. Water is injected at stepped pressures, and the flow rate measures fracture permeability. A Lugeon unit is defined as 1 liter per meter of test interval per minute at 10 bars of pressure. The Lefranc test, by contrast, is used in soil; it can be constant-head or falling-head and measures bulk hydraulic conductivity of granular or cohesive materials through an open cavity or screened section. In Spokane practice, Lugeon tests target basalt interflow zones while Lefranc tests characterize the overburden alluvium.
How much does field permeability testing cost in Spokane?
A complete in situ permeability testing program in Spokane typically ranges from US$570 to US$1.130 per test interval, depending on borehole depth, packer configuration, and number of pressure steps required. Mobilization costs and drilling subcontractor rates—which vary seasonally in eastern Washington—are additional. A site with three test intervals in a 60-foot borehole generally falls in the middle of this range per interval.
How many Lugeon pressure steps are required per ASTM D4630?
ASTM D4630 specifies a minimum of five pressure steps following a low-medium-high-medium-low sequence. This cyclic loading pattern distinguishes elastic fracture dilation from permanent hydraulic fracturing. If the flow rate at the final low-pressure step exceeds the initial low-pressure flow by more than 20 percent, the test interval has likely experienced irreversible opening, and the data interpretation must account for this condition.
When is double packer configuration preferred over single packer?
A double packer system isolates a discrete interval between two inflatable seals, preventing water from leaking past the test section into the annulus above or below. This is essential in Spokane’s fractured basalt where vertical joints can transmit injected water far from the intended zone. Single packer testing, which tests everything below the packer, is used only in homogeneous, unfractured rock or as a preliminary screening method before detailed double packer work.