Anchorage sits on a complex mix of glacial till, outwash sands, and silty clays from the Cook Inlet basin, with seasonal permafrost remnants still influencing shallow groundwater in some hillside neighborhoods. Running an infiltration test here means accounting for that variability, especially when designing septic drainfields or stormwater infiltration basins under the strict Alaska Department of Environmental Conservation (ADEC) regulations. The double-ring infiltrometer method isolates vertical flow into the soil matrix, while the Porchet approach works well for the coarser outwash deposits common along the Turnagain Arm corridor. We pair this field data with a permeability lab test on undisturbed samples to cross-verify rates before finalizing your system sizing. Whether you are looking at a residential lot in Eagle River or a commercial pad in Midtown, getting an accurate infiltration number early avoids costly redesigns once excavation reveals unexpected layering.
A single infiltration test location in Anchorage’s glacial till can miss 200% lateral variability — three locations minimum per ADEC guidance.
Methodology and scope
- Seating both steel rings 6 inches into the ground to prevent lateral seepage
- Constant-head or falling-head readings depending on expected soil texture
- At least 3 test locations per site to capture lateral variability in the glacial deposits
Local considerations
Anchorage’s February 2023 winter storm dumped 28 inches of snow in 48 hours, and when spring thaw arrives, those same soils determine whether your stormwater basin overflows or drains properly. If the infiltration test is skipped or done in a single pit, you risk designing a system that fails during the May melt period, leading to ponding, slope saturation, and potential foundation seepage in the Hillside zone. ADEC requires a minimum of two test pits for septic systems, but in the heterogeneous glacial deposits of the Upper Huffman Road area, three to five tests per acre give you the confidence to specify the right drainfield size without overbuilding or underperforming. Our field crew records soil texture, moisture content, and any ice lens presence — because a thawing silt layer can produce wildly different rates than a summer reading.
Applicable standards
ASTM D3385-18 (Standard Test Method for Infiltration Rate of Soils in Field Using Double-Ring Infiltrometer), ADEC 18 AAC 72 (Wastewater Disposal Regulations — Subsurface Sewage Disposal Systems), ASCE/EWRI 12-13 (Standard Guidelines for the Design of Urban Stormwater Systems)
Associated technical services
Borehole Permeability Testing
Constant-head and falling-head tests in cased boreholes for deep drainage or dewatering design, especially relevant in the Ship Creek valley where water tables sit within 5 feet of the surface.
Soil Classification & Gradation
Full sieve and hydrometer analysis per ASTM D6913 and D7928 to correlate infiltration rates with grain-size distribution, helping you predict which soil layers will drain fast and which will retain water.
Compaction Testing (Sand Cone / Nuclear Density)
Field density and moisture checks on compacted fills for stormwater basins and septic mounds, ensuring the placed material matches the infiltration assumptions used in design.
Typical parameters
Frequently asked questions
How many infiltration test locations does ADEC require for a new septic system in Anchorage?
ADEC 18 AAC 72 requires at least two percolation tests per proposed drainfield area, but in the heterogeneous glacial soils common in Anchorage, we recommend three to five test locations. The Hillside and Abbott Loop areas often show significant lateral variability, and a single test may overestimate the design rate.
What is the typical infiltration rate range for Anchorage soils?
Clean sands in the Muldoon and Fairview areas can yield rates of 2–5 in/hr, while glacial till in the Hillside zone often drops below 0.5 in/hr. Silty outwash deposits near Ship Creek give rates around 0.3–1.0 in/hr. These values guide the size of your septic drainfield or stormwater infiltration basin.
How much does an infiltration test cost in Anchorage?
A standard double-ring infiltrometer test in Anchorage ranges from US$350 to US$450 per location, including field setup, 2–6 hours of monitoring, and a written report with Ksat values and soil descriptions. Additional locations or deeper Porchet tests add US$200–US$350 each.
Can I do an infiltration test in frozen ground during winter?
No, ASTM D3385 requires unfrozen soil because ice lenses block water flow and produce artificially low rates. We typically run infiltration tests from May through October in Anchorage. For winter projects, we recommend scheduling early or using a thawed test pit if ground temperature is above 32°F at the test depth.