A recent excavation just east of the Tacoma Dome hit groundwater three feet above the level indicated in the preliminary geotech report, turning a straightforward foundation pour into a three-week dewatering operation. That kind of surprise is common when working in the Puyallup River valley, where layered alluvium overlies glacial till and the water table fluctuates with the tides of Commencement Bay. The in-situ permeability test using Lefranc fallin- g-head methods in granular zones and Lugeon packer tests in fractured siltstone bedrock provides the direct hydraulic conductivity values that grain-size correlations simply cannot resolve. Our team runs these tests during the investigation phase so contractors in Tacoma have real numbers for wellpoint spacing, sump sizing, and cutoff wall depths before the shovels move in.
A single Lefranc falling-head test at the right depth can save weeks of dewatering guesswork in Tacoma's interlayered glacial deposits.
Service characteristics in Tacoma
Critical ground factors in Tacoma
The soil profile changes dramatically from downtown Tacoma toward the tideflats, and that shift carries real risk for underground construction. Up on the hillside near Stadium District, compact glacial till may show K-values below 10^-6 cm/s, leading teams to underestimate inflow until they punch into a coarser interbed. Down on the Blair Waterway, hydraulic fills and recent alluvium can transmit water at rates ten to a hundred times faster, turning a minor cofferdam leak into a stability problem within hours. Without direct in-situ measurement, the design relies on correlations that often prove optimistic. We have seen projects where the contractor sized pumps for 50 gpm and faced inflows exceeding 200 gpm because the permeability of a thin sand lens was never directly measured. A targeted Lefranc or Lugeon program eliminates that uncertainty before it becomes a change order.
Our services
Our Tacoma-area permeability testing program combines borehole investigation with direct hydraulic measurement, providing a complete picture of subsurface water behavior for your project.
Lefranc Falling/Rising Head Tests
Variable-head tests performed at discrete depths in soil boreholes to determine hydraulic conductivity in granular and cohesive strata across Tacoma's glacial and alluvial formations.
Lugeon Packer Testing in Rock
Pressurized water tests within sealed borehole intervals to evaluate fracture flow in the bedrock underlying Pierce County, essential for grouting design and deep tunnel assessments.
Dewatering Feasibility Studies
Combining measured K-values with groundwater monitoring to design wellpoint, deep well, or eductor systems tailored to Tacoma's tide-influenced water table conditions.
Pumping Test Supervision
Large-scale aquifer pumping tests with observation well monitoring to validate permeability assumptions and determine radius of influence for major excavations near Commencement Bay.
Quick answers
How much does a field permeability test cost in Tacoma?
For a typical investigation including two to three Lefranc tests within standard boreholes or a single Lugeon test interval, budgets in the Tacoma area generally range from US$700 to US$990, depending on depth, access constraints, and whether the testing is combined with SPT drilling on the same mobilization.
When should I choose a Lugeon test instead of a Lefranc test?
The Lugeon test applies when the planned excavation or tunnel encounters fractured rock, such as the siltstone and basalt underlying Tacoma. It measures flow under pressure in isolated intervals, revealing whether fractures are tight, open, or erodible. The Lefranc test remains the standard for soil horizons above bedrock, particularly in the glacial and alluvial deposits common across Pierce County.
How many test intervals do I need for a deep excavation near the Puyallup River?
For a deep excavation in Tacoma's river valley, we typically recommend at least one test per distinct hydrostratigraphic unit. If the borehole log shows a transition from fill to alluvial sand to glacial till, three intervals are a minimum to capture the contrast between the high-permeability sand and the tighter till. Additional tests at the bedrock interface help define the perched water zone.
Can Lefranc tests be performed in the same borehole as SPT sampling?
Yes, and that is standard practice for our Tacoma investigations. After completing the SPT sampler at the target depth, we clean the borehole, install a slotted casing section, and run the falling-head Lefranc test before advancing to the next sampling interval. This avoids a separate mobilization while providing direct K-values alongside the N-value and sample description.
How do tide levels in Commencement Bay affect permeability test results?
In the tideflat areas and lower Puyallup River corridor, groundwater levels fluctuate diurnally with the tide. We install pressure transducers during testing to track these fluctuations and correct the test data, ensuring the computed hydraulic conductivity reflects the formation properties rather than the transient tidal influence. This correction is critical for designing dewatering systems that must handle both the average and the peak tidal conditions.