Percolation Testing A.K.A Soils Testing in Arizona for Septic Systems
- 5 days ago
- 5 min read
When planning a new septic system in Arizona, one of the most critical steps is conducting a percolation test. This test, also known as soil testing, determines how well the soil absorbs and filters wastewater. For anyone involved in real estate, land development, or even DIY home improvement projects, understanding percolation testing is essential. It ensures that septic systems function properly, protecting both property investments and the environment.
This article explains what a percolation test is, the licenses required to perform it in Arizona, the general procedure, the cost of a standard percolation test vs. a seepage pit test, and why it is especially important in this state.
What Is a Percolation Test?
A percolation test measures the rate at which water seeps into the soil. This rate helps determine if the soil can handle the wastewater from a septic system without causing contamination or system failure.
The test involves digging holes in the proposed septic drain field area, filling them with water, and measuring how quickly the water drains. The results indicate whether the soil has the right texture and permeability for a conventional or an alternative septic system.
Without this test, installing a septic system risks poor drainage, leading to backups, pollution, and costly repairs.
Licenses Required to Perform Percolation Tests in Arizona
In Arizona, percolation tests must be conducted by licensed professionals to ensure accuracy and compliance with state regulations. The following licenses are typically required:
Registered Environmental Health Specialist (REHS): These specialists are trained in environmental health and often conduct soil testing for septic systems.
Licensed Professional Engineer (PE): Engineers with experience in soil mechanics and wastewater systems can perform or oversee percolation tests.
Geologist: They analyze mineral samples to determine their chemical and physical characteristics, which can reveal significant information about geological processes
Training with the County: A thorough training to help grasp of both the theoretical and practical elements of soil assessment improves understanding of regulatory requirements.
Homeowners or developers should avoid DIY percolation tests unless supervised by a licensed professional. Improper testing can lead to invalid results and legal issues during property transactions or land development.
General Procedure for Conducting a Percolation Test
The percolation test follows a clear, step-by-step process:
Site Selection
Identify the proposed location for the septic drain field. The area should be free of debris, vegetation, and large rocks.
Digging Test Holes
- Standard Soil Test: Standard leach trenches are shallow and horizontally oriented serve as standard gravity-drainfield systems, utilizing the microbiology of the topsoil to filter wastewater. The test holes are dug to match the proposed trench floors, which are approximately 24 to 30 inches deep. Each test hole is excavated to this precise depth to ensure consistent drainage throughout the soil. - Seepage Pit Test: Seepage pits are vertical structures with an overall depth of 50-55 feet penetrating through different layers of soil. Layers ranging from sand and dense clay to gravel. With that being said, testers need to study the soil behavior at depths ranging from 10 to 30+ feet below ground across various verticals to map how drainage changes with depth.
Pre-soaking the Soil
- Standard Soil Test: The holes are filled with water and left to soak for a set period, often 4 to 24 hours. This step saturates the surrounding soil, simulating real septic system conditions. - Seepage Pit Test: Simulating saturation at such depths is significantly more challenging, making the preparation work demanding. To conduct a seepage pit percolation test, a substantial volume of water is required to maintain water pressure across a larger vertical surface. Presoaking a pit must be thoroughly performed to saturate each layer.
Measuring Drainage Rate & Recording Results
- Standard Soil Test: After pre-soaking, refill the holes with water until it is approximately 6 inches above the gravel. The technician times how long it takes for the water level to decrease by a certain distance, typically in minutes per inch. This process is repeated multiple times to calculate an average rate.
- Seepage Pit Test: To evaluate how multiple layers of different soil absorb water under heavy pressure, the pit is completely filled to the brink with water. Then for 2 hours, every 15 minutes, testers will measure the depth of the water drop and record the measurements on a time-versus-drop graph.
Reporting
A detailed Uniformed Site Investigation Report Form is prepared, including test locations, soil conditions, percolation rates, and recommendations. This report is submitted to local health departments or permitting agencies.
The Cost of a Percolation Test with BEST Septic Solutions
The cost of a percolation test varies significantly based on the depth and equipment required to evaluate the soil. For a standard or site-specific percolation test, which typically involves shallower dug holes to assess standard leach fields, property owners can expect it to cost $2,600. However, if the property layout or local regulations necessitate a seepage pit, the price increases to $3,300. This additional expense is driven by the fact that seepage pits require testing at much deeper soil layers, meaning the tester must drive a heavy drill rig to the site to bore the deep test holes.
Why Percolation Testing Is Important for Septic Systems
Septic systems rely on soil to treat and disperse wastewater safely. The soil acts as a natural filter, removing harmful bacteria and nutrients before the water reaches groundwater or surface water.
If the soil drains too slowly, wastewater can pool on the surface, creating health hazards and unpleasant odors. If it drains too quickly, untreated wastewater may contaminate nearby water sources.
Percolation testing ensures:
Proper system design: Knowing the soil’s absorption rate helps engineers design a septic system that fits the site’s conditions.
Environmental protection: Prevents contamination of groundwater and nearby wells.
Compliance with regulations: Many counties in Arizona require percolation test results before issuing septic permits.
Cost savings: Avoids expensive repairs or system failures caused by unsuitable soil.
Why Percolation Testing Is Especially Important in Arizona
Arizona’s unique climate and soil conditions make percolation testing critical for septic system success:
Arid climate: The dry environment affects soil moisture levels, which can impact percolation rates. Testing ensures the soil can handle wastewater despite low rainfall.
Varied soil types: Arizona has sandy, rocky, and clay soils, each with different drainage properties. A percolation test identifies the specific soil characteristics on a property.
Water conservation concerns: Septic systems must be efficient to protect limited water resources. Proper soil testing helps design systems that minimize water contamination.
Strict state regulations: Arizona Department of Environmental Quality (ADEQ) and local health departments enforce rules requiring percolation tests for new septic installations.
Real estate transactions: When buying or selling property with septic systems, percolation tests provide assurance that the system is safe and functional.
Practical Tips for Real Estate and Land Development Professionals
For those involved in real estate or land development in Arizona, percolation testing is a key step in project planning:
Schedule tests early in the development process to avoid delays.
Hire licensed professionals familiar with Arizona’s regulations.
Review percolation test reports carefully before approving septic system designs.
Consider soil testing results when evaluating land for purchase or development.
Educate clients about the importance of percolation testing for long-term property value and safety.
DIY Home Improvement and Percolation Testing
While some homeowners may want to conduct soil testing themselves, percolation tests require precision and knowledge of local codes. DIY efforts often lead to inaccurate results, risking septic system failure.
Homeowners should:
Consult licensed experts for percolation testing.
Use DIY soil testing only for preliminary information, not official permits.
Understand that proper septic system installation depends on professional soil evaluations.
