We ran a series of Lugeon tests last August for a detention basin expansion off Coffee Road, just south of the Kern River. The owner had assumed uniform sandy gravels based on a few exploratory borings, but the packer test data told a different story—interbedded clay lenses at 25 feet were holding water tight, while the surrounding gravels were losing 12 Lugeon units in the same interval. That’s Bakersfield’s subsurface for you: channel deposits that can flip from impermeable to freely draining in five vertical feet. In projects where water management drives the design, a test pit investigation gives us the visual stratigraphy, and we pair it with the in-situ test to get a hydraulic conductivity value the civil engineer can actually put into a seepage model. Without that number, you’re guessing on cutoff depths and pump sizing.
A single Lugeon profile through Bakersfield’s alluvial fans can reveal permeability contrasts of two orders of magnitude within a 20-foot interval.
How we work
Local considerations
Bakersfield sits at 404 feet elevation on the Kern River fan, a landform built by episodic flooding over millennia. That history shows up in the borehole logs as cobble lenses, paleochannels, and abrupt clay plugs—features that make permeability predictions from grain-size correlations unreliable. We’ve seen groundwater recharge projects where the infiltration rate was overestimated by 300% because no one accounted for the Corcoran Clay’s lateral continuity. A Lefranc test at the design invert catches those low-permeability layers before the bulldozers arrive. In dam and levee work along the Kern River, a Lugeon value above 25 signals potential internal erosion risk; below 3, you’re looking at grouting or a positive cutoff. The California Division of Safety of Dams reviews these numbers closely, and they’ll ask for the raw pressure-flow plots if the permeability seems too convenient. Field testing eliminates the argument.
Relevant standards
The applicable standards include ASTM D6391-11 (in situ hydraulic conductivity), USBR Earth Manual Designation E-18 (Lugeon), and CFR Title 23, Division 1, Chapter 1 (DSOD review).
Associated technical services
Lefranc variable-head test
Ideal for sandy alluvium above the water table. We install a slotted PVC screen, surround it with filter sand, seal with bentonite, and measure water level recovery with a pressure transducer logged at 1-second intervals.
Lugeon packer test in rock
Applied in the foothills east of Highway 99 where granitic and metamorphic bedrock appears. Five-stage pressure cycle per USBR E-18, with flow measured at steady state using a calibrated flowmeter.
Borehole infiltration test
For retention basin and pond sites. Constant-head method with a Mariotte bottle maintaining a fixed water level in the borehole; K calculated from intake rate and borehole geometry per the Hvorslev solution.
Typical parameters
Common questions
How much does a field permeability test cost in Bakersfield?
Which test is more appropriate for a recharge basin in the Bakersfield area—Lefranc or Lugeon?
Lefranc, almost always. Recharge basins in Kern County are typically sited in the unconsolidated alluvium above the Corcoran Clay, where you can auger or wash-bore to the test depth without hitting rock. The Lefranc method gives you a hydraulic conductivity representative of the granular formation in its natural, undisturbed state. We’ll run it at the proposed basin invert and again 10 feet deeper to catch any permeability drop-off.
How long does a Lugeon test take on site?
Plan on two to three hours per test interval once the borehole is drilled and cleaned. The five-stage pressure cycle (1-3-5-3-1 bar) requires steady-state flow at each pressure step, which can take 10 to 20 minutes per stage in moderately permeable rock. We record pressure and flow every 30 seconds, and we won’t sign off until the Lugeon value between the last two stages agrees within 15 percent.
Do you report the Lugeon value or the hydraulic conductivity?
We provide both. The raw Lugeon unit (liters per meter per minute at 10 bar) goes on the field log, and we convert it to an equivalent hydraulic conductivity in cm/s using the Moye equation for the final report. Engineers in California often prefer the Lugeon value for dam design because it’s directly comparable to the grouting threshold, while the K value feeds into groundwater models.