Perc Test Standards: Soil Percolation Soil Percolation Rate Standards for Septic Drainfields

  • PERC STANDARDS - CONTENTS: What soil percolation rates are required for septic system leach fields or drain fields? How do we perform a soil perc test when designing or testing a septic system? Specifications and guidelines for soil percolation testing
  • POST a QUESTION or READ FAQs about the standards for septic system test hole tests, deep hole tests, and percolation tests for drainfield qualification and soil testing

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This article discusses soil percolation rate specifications - what are the required soil perc rates when testing for septic system absorption system or drainfield design or repair.

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PERC TEST STANDARDS - What are the soil percolation rate standards and other soil requirements for septic systems?

The Massachusetts Title 5 Septic Inspection criteria does a great job of defining a (at least possibly) what is required to assure a functional septic drainfield. The text explains the role of the biomass below the absorption bed, sets soil depth requirements, and recognizes the importance of keeping the bottom of the working biomass area in well drained soil sufficiently above the seasonal high water table.

Here is an example of soil requirements for a functional drainfield. This version is particularly clearly written and is for residents of Ohio but the principles apply anywhere. 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.

In Ohio, soil absorption systems can be used in areas where the percolation rate of the soil is between 3 and 60 minutes per inch (soil permeability between 1 and 20 inches per hour).

At least 4 feet of suitable soil is required under the soil absorption system to provide adequate treatment of the septic tank effluent. To accommodate the construction of the system and provide adequate soil cover to grade, a minimum of 5 1/2 to 6 1/2 feet of suitable soil is needed above the limiting layer.

A limiting layer may be bedrock, an impervious soil layer (hardpan, fragipan) or a seasonally high water table (gray soil or mottles). The soil absorption system must be at least 8 feet from any drain line on the lot, 50 feet from a water supply, and 10 feet from the property line, right-of-ways and the house.

Septic systems cannot be placed on the flood plain and are limited to areas with less than a 15 percent slope. Reference: Ohio State University Fact Sheet Septic Tank - Soil Absorption Systems

Our separate article by Lockwood includes a description of the calculations to answer the question: How Big Should the Leach Field Be? our article SEPTIC DRAINFIELD SIZE includes a practical example using sample calculations as well as a table of soil percolation rate vs. the necessary leach field size.


Continue reading at SOIL CONDITIONS or select a topic from the More Reading links shown below.

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


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

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