Local Soil and Site Evaluation for a Conventional Septic System in Redmond, WA

Conventional septic systems are simpler compared to aerobic systems, a mound system or a pressure distribution system, for example. 

In these systems, heavy solids settle at the bottom of the septic tanks as sludge, while liquid waste floats to the top, forming scum. They are prevented from exiting through an outlet baffle. 

Local Soil and Site Evaluation for a Conventional Septic System in Redmond, WA

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Understanding the Soil Type

In the beginning stages of constructing a septic system, one of the key aspects is gaining a comprehensive understanding of the soil on the property. Soil is critical in treating wastewater levels and a fundamental septic system element. 

In assessing the compatibility of different soil types for conventional septic systems, we must consider their impact on system functionality and efficiency. With the information about the soil, the system designer can make informed decisions regarding the most suitable type and size of the septic system for optimal performance.

Redmond’s Soil Types

Redmond, WA, sits in the Pacific Northwest region of the United States, renowned for its varied geological formations and soil types.

Here’s how they correspond to conventional septic systems:

  • Glacial Till – Optimal for septic systems, combining diverse particle sizes for effective drainage and filtration.
  • Loam The premier choice for gravity systems, featuring a mix of sand, silt, and clay for good wastewater treatment.
  • Sandy Loam Feasible for septic use but faster drainage than regular loam; advantageous for swift wastewater dispersion.
  • Clay – Unsuitable for typical septic systems due to impaired drainage; poses health and environmental risks.
  • Peat Generally unfit for conventional septic systems; excessive organic content and poor drainage hinder proper wastewater treatment.
  • Gravel – High permeability may lead to insufficient final treatment; limited filtration might enable groundwater pollution.

Percolation Tests

Septic systems are designed to handle household wastewater disposal in areas without access to municipal sewer systems. The basic components of a conventional septic system include a tank, a drain field (also known as a leach field) and the soil itself.

A Percolation Test assesses soil suitability for on-site wastewater disposal systems like septic systems. It measures the soil’s ability to absorb water at an acceptable rate. Environmental or civil engineers usually conduct the test as part of a generalized septic service.

Here’s how to perform one yourself:

  • Dig holes in the area where the soakaway system will be installed.
  • Roughen the sidewalls and bottom of the holes to promote water absorption.
  • Presoak the soil in the holes to ensure it is fully saturated.
  • Measure the time it takes for the water to percolate or drain away completely.
  • Calculate the percolation rate based on the time measured.
  • Calculate the overall field percolation rate using the results from multiple test holes.
  • Determine the site’s suitability for the soakaway system based on the obtained percolation rates.
  • Кeep the soil percolation test data on the premises for future reference and documentation.

Site Suitability Factors

The site’s suitability for septic systems depends on various factors:

  • Slope – Slope should not exceed 30% for standard systems or 45% for steep slope systems.
  • Landscape features – Avoid areas with swales, depressions, or floodplains that retain or concentrate water.
  • Bottomlands – Poor subsurface drainage makes them unsuitable.
  • Rock outcrops – Limited soil cover may be a concern.
  • Vegetation – Different vegetation indicates soil conditions. Some may not be ideal for septic systems.
  • Avoid future traffic – Ensure no vehicular traffic passes over the system.

Drain Field Design Considerations

Designing a septic system drain field requires careful consideration of key factors to ensure its longevity and minimal environmental impact. 

Local Soil and Site Evaluation for a Conventional Septic System in Redmond, WA

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Here are three crucial aspects to keep in mind:

  • Soil Permeability – Conduct a soil percolation test to assess drainage rate and suitability. Sandy or gravelly soils are preferred, while clayey soils may pose challenges due to slow drainage.
  • Site and Space – Choose a suitable location with a proper slope and no water pooling. Maintain adequate distance from buildings, wells, and water bodies to protect water quality.
  • Wastewater Volume and Load – Calculate expected wastewater volume based on occupants and water usage patterns. Ensure proper sizing for efficient treatment and to avoid overloading.

Regulatory Requirements and Local Codes

You will need a building permit if you plan a new residential or commercial septic system installation in Redmond, WA, or remodeling an old one. We at FreshNClean Septic have experience in working with the local authority of King County and the Washington State Department, so we’re here for your questions.

In short, heres what you need:

  • First, have the city notified of your plans.
  • Applicants must accurately describe the system’s location and obtain an as-built drawing.
  • The application is reviewed by an inspector, who considers the system’s age, condition, type, and relation to the remodel. 
  • Depending on the scope and condition, a licensed septic professional may need to evaluate the system, and upgrades may be required.

Working with Soil and Site Evaluation Professionals

Collaborating with proficient soil and site evaluation professionals for an efficient septic system design is indispensable to any construction or development endeavor. 

Our seasoned professionals possess specialized acumen in assessing natural soil conditions, drainage patterns and environmental influences all of which significantly impact project design and feasibility. Through meticulous evaluations, they ascertain the site’s appropriateness for construction.

Fresh and Clean Septic is a septic company that has a lengthy experience working with conventional septic systems. We can assist you with various types of septic service in Redmond, WA, including such related to assessment, design and installation.

Frequently asked questions

What type of soil is suitable for a conventional septic system in Redmond, WA?

Sandy, loamy, and gravelly soils as they provide adequate drainage and efficient filtration as the effluent wastewater enters the drain field for further processing before reaching the groundwater.

What site is suitable?

It depends on various factors but as long as it is not too steep and not too rocky and there are no plans for a road construction – it might be suitable.

How far should the septic system be from my well or water source?

As per recommendations from the EPA and the HU, a minimum distance of 50 feet between a septic tank and a well used for drinking water is advised. This measure helps safeguard water quality and prevent potential contamination.