What is a Percolation Test?
A percolation test, commonly known as a “perc test,” is a procedure used to assess the drainage characteristics of the soil. This test is crucial for determining whether a property can accommodate a septic system, which depends on the soil’s ability to absorb and filter wastewater.
How is a Percolation Test Conducted?
- Drilling or Digging Testing Holes: Several holes, typically around 4–12 inches in diameter and about 2 feet deep, are dug or drilled in the area where the septic system is planned.
- Pre-Soaking the Soil: Water is poured into each hole and allowed to saturate the soil for approximately 24 hours. This pre-soaking step helps to replicate conditions during continuous rain or water usage.
- Conducting the Test: Water is then added again to the holes, and the rate at which the water level drops is measured at regular time intervals. This rate indicates how quickly the soil absorbs water.
- Analyzing the Results: The results (inches of water drop per hour) determine the soil’s suitability for a septic system. If the drainage is too fast or too slow, the soil may be unsuitable for septic purposes without modification.
Importance of Percolation Tests
Percolation tests are essential for:
- Septic System Design: Ensuring proper septic tank drainfields to avoid system failures and contamination.
- Compliance: Meeting local health and environmental regulations for waste management.
- Property Valuation: Affecting the usability, and thereby the value, of the land for residential or commercial development.
Examples
- Residential Development: Caroline is planning to build a house in a rural area. She conducts a percolation test to ensure that the soil can support a septic system given the absence of a municipal sewer system.
- Subdivision Planning: Carter is developing a new subdivision. As part of site preparation, Carter runs percolation tests on the soil across different lots, helping the engineer to determine the proper size of the lots and placement of septic tanks.
Frequently Asked Questions (FAQs)
What soils are most suitable for percolation?
Sandy soils generally offer the best drainage and are most suitable for percolation. Clay soils tend to have the poorest drainage capabilities, making them less desirable for septic systems.
Can poor percolation results be improved?
Yes, in some cases, measures such as soil replacement, installation of modern septic systems, or engineered drainage solutions can be taken to improve soil that has failed a percolation test.
How long does a percolation test take?
The fieldwork for a percolation test can usually be completed within one or two days. However, the pre-soaking period adds an additional day to this timeframe.
Is a percolation test required everywhere?
Requirements for percolation tests vary depending on local regulations. Rural areas without access to a municipal sewer system often mandate these tests for building permits.
Related Terms
Permeability
Permeability refers to the ability of the soil to transmit water and air through its pores. High permeability indicates better soil drainage characteristics.
Septic System
A septic system is an underground wastewater treatment structure most commonly used in areas lacking centralized sewer systems. It uses a combination of nature and technology to treat wastewater from household plumbing.
Drainfield
A drainfield, also known as a leach field, is a network of perforated pipes laid in underground trenches filled with gravel. It disperses wastewater from the septic tank into the surrounding soil for aerobic treatment.
Soil Texture
Soil texture defines the percentages of sand, silt, and clay in the soil. The soil texture significantly influences both permeability and the percolation rates.
Online Resources
- Environmental Protection Agency (EPA): Comprehensive guides and regulations on septic systems.
- The National Environmental Services Center: Articles and resource materials related to water and wastewater management.
- Soil Science Society of America: Educational materials and research on soil properties and management.
References
- U.S. Environmental Protection Agency (EPA)
- National Onsite Wastewater Recycling Association (NOWRA)
- Local Health Department guidelines on septic systems
- Soil Survey Manuals for Perc Testing
Suggested Books for Further Studies
- “The Septic System Owner’s Manual” by Lloyd Kahn and John Hulls
- “Soils and Foundations” by Cheng Liu and Jack Evette
- “Handbook of Soil Analysis: Mineralogical, Organic and Inorganic Methods” by Marc Pansu and Jacques Gautheyrou
