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Septic Systems: Part Two

by Tyler

So far, the quotes we're getting from engineers to take an undeveloped piece of land through the process of soil investigation, percolation testing, land surveying, septic system design and finally, state permitting, have ranged anywhere from three to five thousand dollars. According to the engineer we're working with, there is no way to know if a permit will be obtainable until it has actually been issued!

For obvious reasons, this is a pretty big deal. If we were unable to obtain a septic permit, we wouldn't be able to build a house on the property we'd like to buy. At the moment, everything hinges on this wrinkle, and, given the importance of it, I've been reading about how it works pretty extensively. Below, I've outlined the steps typically involved:

Step 1: Soil Investigation

The first part of the septic design process involves digging test pits at potential leach field sites on the proposed property with a backhoe. The resulting holes allow the soil composition at these locations to be investigated at varying depths. The type of soil, along with other factors like the estimated seasonal high water table, determine what kind of drainage system is appropriate.

Step 2: Percolation Testing

A percolation test determines the ability of soil to absorb liquid. This test is generally performed by excavating a hand-dug hole, filling it with water repeatedly, and measuring the time it takes to drop a specific distance. Using the results, a formula can be applied to calculate the "perc rate" for the surrounding area. This determines how large a leach field must be, and is dependent on how much water the desired system is rated to process daily.

Step 3: Topographic Survey & System Design

Next, a topographic survey of the property must be completed. The resulting contour map is used to design a site plan which shows the proposed location of the house, leach field, and other important features, such as the water supply and septic tank.

Step 4: Permit Application

At long last, the plans must be collected into what Vermont refers to as a "Wastewater and Potable Water Supply System" permit application, ready for state for approval.

Step 5: Construction

If the permit application is approved, construction can begin. We don't know anything about this, yet!

Suggested Reading:

  1. The Humanure Handbook (the first chapter is a bit silly, but persevere, it's worth a read!)
  2. Create an Oasis With Greywater
  3. Builders Greywater Guide