Perc Test Hole Specifications for Soil Percolation Tests for Septic Field Design

  • PERC HOLE SPECIFICATIONS - CONTENTS: What are the specifications for soil perc test holes: how deep, what size, etc. What are "perc tests" or soil percolation tests? How do we perform a soil perc test when designing or testing a septic system?
  • POST a QUESTION or READ FAQs about the specifications for septic system test hole tests, deep hole tests, and percolation tests for drainfield qualification and soil testing
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Soil absorption test or percolation rate test hole specifications:

This septic system design chapter provides specifications for soil percolation holes used for testing for septic system absorption system or drainfield design. We explain how to dig a hole for soil percolation tests, deep hole tests, and perc testing where there is rocky soil. We provide perc test safety recommendations.

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Soil perc tests may also be performed in order to evaluate soils when a septic system is believed to have failed, and when repair or septic field replacement are being considered.

Specifications for Digging Holes for Soil Percolation Tests for Septic System Design and Approval

How to Dig a Soil Test Pit

Soil Percolation Test Pit Design Specification GUides

Where to Dig the Soil Test Pit for Septic Systems

Usually two percolation-rate test holes are dug, 50' to 100' apart in order to evaluate the proposed septic leachfield area. Evidence of the seasonal high water table is noted (possibly based on changes in soil color at various depths).

For safety, septic soil drainfield perc test holes must be re-filled after the test is complete. If the hole must be left open and unattended during the test it should be barricaded to prevent anyone from falling in. Here are some hints from Callum County, Washington:

What is the Soil Test Pit Showing and How Does the Percolation Test Impact Septic System Design?

"Soil percolation or perc tests are used to determine the ability of a soil to transmit wastewater effluent through the soil profile.

The soil percolation rate is the amount of time water takes to move through soil, measured in minutes per inch. Finer textured soils have slower percolation rates; it takes longer for water to drain from a test hole. These soil types need larger drainfields than soils with faster percolation rates, such as sandy soils, to handle a given amount of wastewater.

Soils with very slow percolation rates may not be suitable for drainfields. In Nebraska [and other jurisdictions], if soils perc at a rate slower than 60 minutes per inch, consider installing a lagoon system if the lot is at least 3 acres.

Otherwise, an engineer must design a specialized [alternative design] septic system. Soils with very fast percolation rates, less than 5 minutes per inch, must be modified by adding a loamy sand liner to the drainfield, so that proper treatment can occur." [Univ. of Nebraska, Lincoln Extension, Institute of Agricultural & Natural Resources, "Residential Onsite Wastewater Treatment: Site Evaluation]

Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information at other websites, in books or pamphlets for sale is reserved to the author. Technical review by industry experts has been performed and is ongoing - reviewers welcomed and are listed at REFERENCES. This article is part of our series: SEPTIC SYSTEM INSPECTION & MAINTENANCE COURSE an online book on septic systems.

Septic Soil Percolation Test or Wastewater Disposal Field Testing Articles


Continue reading at PERC TEST STANDARDS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see SEPTIC DRAINFIELD SIZE for wastewater application rate tables & septic trench design tables


Readers should also see our example of state-regulated soil percolation tests at the New York State Septic System Design Regulations 75-A.4 - Soil and site evaluation for septic system design page.

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PERC HOLE SPECIFICATIONS at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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