Residential Septic Systems

A review of common septic system designs:

I love it when I can use septic designs for a land development project and the reason is simple - I do not have to run expensive sewer lines! The soil conditions must be favorable however and this, most definitely, is not always the case. I provide an approved septic design for my septic projects and it is up to the lot buyer to do the installation. The conventional gravity system is an ideal outcome for all since smart buyers may factor the cost of complex septic systems into their offer price. The septic systems described below vary in complexity, installation cost and maintenance. Here’s a look at some, but not all, of the common septic systems in use today.

Conventional Septic System:

Effluent is distributed from the septic tank to a gravel drainfield lined with geofabric.

Chamber Septic System:

A septic system that uses a gravelless drainfield. Large plastic pipes or synthetic materials are used in place of gravel.

Drip Distribution System:

Influent goes to the septic tank. As effluent it is sent to a pump tank and is delivered in timed doses to the drip laterals in the drainfield.

Aerobic Unit:

An aerobic system is like a mini sewage treatment plant. Oxygen is injected into the treatment tank to enhance aerobic bacterial treatment of influent. Typically used when there is lack of space or poor soil conditions. Regular maintenance required.

Mound Septic System:

A constructed sand mound contains the drainfield lines. Effluent from the tank is pumped to the mound in measured doses. Treatment occurs as the effluent filters through the sand mound.

Sand Filter Septic System:

Drainfield can be above or below the ground surface. The septic tank sends effluent to a filter pump chamber filled with a sand material. The effluent is pumped under low pressure through at the top of the filter and when treated, is discharged to the drainfield.

Evapotranspiration Bed System:

Unlike other systems, the final process is evaporation of treated waste water that is not discharged to the ground water. Typically used in arid climates and where native soil conditions are shallow.

Constructed Wetland Septic System:

Mimics natural wetlands. Wastewater flows from the septic tank to an impervious wetland chamber of pea gravel within sand and gravel below. Appropriate wetland vegetation is planted on the chamber surface and minor residual treatment water is discharged to a drainfield for treatment in the soil.

Cluster (Community) Septic:

A system that serves common ownership - multiple dwellings.

Septic Systems - Additional:

In my experience, especially in the Pacific Northwest, agencies of interest tend to lean in the direction of supporting land development projects that use septic systems. One reason is a concern for ground water absorption with resulting aquifer recharge. In a sewer system, treatment of wastewater is done miles away in a sewage treatment plant and discharge also occurs miles distant from the source. Agencies tend to prefer local absorption and let’s face it, sewage treatment plants are expensive to build and maintain. I closely follow the progress of project soil studies to determine the types of septic designs I will most likely see and make sure that during project marketing the buyers are aware of the design approved by the Health Department and it’s affect on installation cost.

Blog photos courtesy of - United States Environmental Protection Agency - Thank you!

Contact me at: ldr@landdevelopmentrealities.com