WWrivel
Field soil test

Soil Infiltration Test Calculator

Replace a guessed “sand / loam / clay” assumption with repeated drain-down measurements from the actual location you may use for infiltration.

Measure the place where the water would actually go

Infiltration varies across the same yard. A dry well, rain garden or shallow basin can only use the soil around its proposed location, so test there rather than relying on a county-wide soil label.

Field reading worksheet

Pre-wet the test hole according to the field method you are following, refill it, then record how far the water level drops over a measured time. Wrivel calculates an observed water-level drop rate; it does not convert that observation into saturated hydraulic conductivity, a design infiltration rate or a permit-ready result.

Reading 1
—
Reading 2
—
Reading 3
—

Readings are stored only in this browser.

How the rate is calculated

observed water-level drop rate = water-level drop ÷ elapsed time

Wrivel converts each reading to inches per hour and millimetres per hour, then shows the average and median. Repeated readings matter because a single first-fill measurement can be distorted by unusually dry soil, test-hole geometry, sidewall flow, antecedent moisture or timing error. This simple drain-down rate is an observation from the chosen field method; it is not automatically interchangeable with a formal design infiltration rate.

What the result can—and cannot—tell you

The observed drain-down rate is evidence about this test location. It can help you decide whether infiltration deserves further investigation, but local stormwater rules may require a different test method, safety factor, test depth, seasonal groundwater check or professional design. A fast shallow-hole reading does not prove a dry well is acceptable.

EPA references are not interchangeable tests: EPA's homeowner-oriented Saving the Rain material includes simple rain-garden percolation screens such as a pre-wet/refill observation and complete drainage within 36 hours. Separate EPA Region 8 rain-garden guidance says a rain garden generally needs a soil infiltration rate of about 0.5 in/hr or greater to drain in roughly 6–12 hours. Wrivel does not assume that the water-level drop rate from this simple worksheet equals that design/permeability value. Use the test method and acceptance criteria required locally.

Use the result in the right order

  1. Test the actual proposed infiltration location, preferably with repeated readings.
  2. Check groundwater, bedrock, utilities, septic/well setbacks and any local restrictions.
  3. Size the water you intend to store with the dry-well storage screen.
  4. Keep an overflow route for storms larger than the storage target.