North Texas geology doesn't play predictable. Plano sits right where the Blackland Prairie meets pockets of Austin Chalk, and that mix creates drainage puzzles most standard soil reports miss. Fractured limestone can carry water fast, while the stiff clay layers underneath slow everything to a crawl. A field permeability test (Lefranc or Lugeon) pulls real numbers from the ground—numbers you can use for dewatering design, retention pond sizing, or basement waterproofing. The city's stormwater ordinance ties directly to measured infiltration rates, so guessing with lab values alone risks expensive rework. We run these tests during geotechnical investigation campaigns, often pairing them with in-situ permeability verification in the same borehole to cross-check the formation's behavior under constant-head conditions.
A Lugeon value under 1 doesn't mean zero flow—it means the rock mass will need very little grout to tighten up.
Our approach and scope
Local considerations
IBC Section 1803 requires foundation investigations that account for groundwater conditions, and Plano's enforcement through the Building Inspections division is consistent. Skipping field permeability measurement in fractured Austin Chalk or weathered Eagle Ford shale can lead to two expensive outcomes: a retention pond that never drains and requires a retrofit pump system, or a basement excavation that floods during the first wet season because the dewatering plan underestimated inflow. The chalk-limestone contact around the 33rd parallel often carries solution-enlarged fractures that Lugeon testing reveals clearly—lab permeameters simply can't capture that scale of secondary porosity. An engineer who signs off on a drainage design without site-specific infiltration data carries liability the professional liability carrier won't be happy about. The test costs a fraction of what a failed stormwater installation runs, and the data stays valid as long as the formation isn't reworked.
Relevant standards
IBC 2021 Section 1803 (Geotechnical Investigations), USBR 7000 (Pressure Testing in Rock), USACE EM 1110-2-1901 (Seepage Analysis and Control)
Related services
Lugeon Packer Testing in Rock
For injection galleries, deep foundations socketed into limestone, or tunnel feasibility studies. We use single-packer setups in NQ or HQ boreholes, run five pressure steps, and deliver Lugeon unit plots with a narrative interpreting fracture flow versus matrix permeability.
Lefranc Testing in Soil and Weathered Rock
For stormwater infiltration basins, shallow dewatering, or verifying clay liner performance. We perform constant-head or falling-head tests in open boreholes or inside test pits, measuring steady-state flow with a graduated reservoir and stopwatch.
Typical parameters
Common questions
What does a field permeability test cost in Plano?
Most projects budget between US$640 and US$1,050 per test interval, which includes packer setup, pressure-step data collection, and the interpreted report. The final number depends on depth, access, and whether we combine it with SPT drilling or CPT soundings during the same mobilization.
When does Plano require a Lugeon test instead of a lab permeability test?
The city typically asks for field permeability when a project proposes deep stormwater injection, a basement deeper than one story, or a foundation socketed into rock. Plano's engineering staff wants in-situ values because lab tests on chalk or limestone cores miss fracture flow entirely. We coordinate with the geotechnical engineer of record to decide whether Lefranc or Lugeon fits the stratum.
How long does the test take on site?
A single Lugeon interval takes about 45 to 60 minutes from packer inflation to the final pressure step. A Lefranc constant-head test in soil runs faster—typically 20 to 30 minutes per zone. We can usually complete three to four test intervals in one field day if the drilling crew stays ahead of us.