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Soil Analysis and Percolation Tests

What is a Perc Test? 

Whenever land is purchased, transferred, or transformed, it may be essential to conduct a perc test to assess the soil's drainage rate. Perc tests play a critical role in legal and safe property transfers or improvements, especially when it comes to installing or upgrading septic systems.

In a nutshell, a perc test measures the soil's moisture absorption rate by determining how long it takes for the soil to drain water added to the ground. This information helps identify suitable locations for installing septic system elements such as drains, leach fields, and other components.

Qualified Environmental Health professionals specializing in septic system design or land surveying typically conduct perc tests. They assess factors like soil slope, sand and gravel content, and other elements to gauge its drainage potential. Soils with high clay or rock content are usually unsuitable for septic systems due to their low drain rates.

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When do I need a Perc Test?

What is the Perc Test Process? 

You need to get a perc test when you're improving a property and planning to install a new septic system. It is required in Iowa before building new septic systems or replacing existing ones. For rural sites without access to municipal sewage systems, perc tests are crucial as they determine where houses can be built.

While some perc tests are straightforward, involving the measurement of water drainage from holes, others may follow a more advanced process with pre-soaking and regular measurements.

The cost of a standard perc test is 300 dollars.

It's best to conduct perc tests during the driest parts of the year, typically towards the end of summer or the beginning of winter, to obtain more accurate results.

Perc test reports are official documents that detail the soil's percolation rate, providing crucial information for septic system planning and renovations. Failed perc tests indicate issues with drainage, but alternative options and solutions can be explored, such as changing the test location, or considering alternative septic systems.

  • The specialist may dig one or more holes into the soil of a proposed drain field

  • After digging the holes, loosened soil is scraped away and a specialist fills the holes with gravel up to about 2 inches

  • The soil is pre-soaked to mimic the saturation conditions of a typical septic system

  • 12 inches of water are placed in the hole for at least four hours during pre-soaking

  • The specialist returns the next day, then tests the holes by filling them with water (usually covering the gravel by at least 6 inches)

  • The specialist then takes measurements every 15 to 30 minutes or so to determine the percolation rate

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