The Importance of a Detailed Site Evaluation

One of the common questions we get from homeowners is,” How much does a septic system cost?”  That is difficult to say for sure, we tell them. First you need to have a site and soil evaluation performed to see what types of systems might work for your property. A detailed explanation of what characteristics are assessed in the soils profile entails, following which, the homeowner invariably says, “I already sent my soils samples to the lab.”

When a homeowner says they have sent soils samples to the lab, we ask where they took the samples from? This question is usually answered with a random depth or the basic, 3, 5 and 8 feet.  The next question we ask is, ‘why did you take the samples from those depths?” to which the response is typically dead silence.

What makes us think that if we have a problem soil in our soils profile, it will be at a prescribed depth like 3 feet or 5 feet? What if the problem soil is located at two and a half feet or four feet? Can we just ignore the problem in the soil profile because it doesn’t appear at the prescribed depth?

Performing a detailed site evaluation will help to ensure that a problem soils horizon isn’t missed because we didn’t examine the soils profile closely enough to determine where our restricting and limiting layers are located.

Renovation of effluent requires seven days of retention or travel time in the soil. Different soils textures and structures impact how quickly or slowly the effluent will travel through the soil prior to re-entering the water table.  The rate of travel is also impacted by coarse fragments, roots, and other items that create void spaces in the soil, like gopher holes.

Prior to selecting a loading rate and sizing the system, performing a detailed site evaluation will ensure that all factors that will impact the soils treatment component (field or mound) of the septic system are taken into consideration.

Texture alone should not be used to determine a loading rate. A good texture can be negatively impacted by a poor structure, while a poor texture can be positively impacted by a strong structure. If texture is the only parameter used to determine the loading rate, there is a potential for constructing a system that is much smaller than it should be or larger than it has to be.

The Saskatchewan Onsite Wastewater Disposal Guide provides the criteria for a detailed site evaluation in Section 4 on page IV-5. While the information in the Guide prescribes soils depths for sampling, be aware that the Guide is a minimum standard.  Best practice should prevail. Taking samples from the restricting layer and limiting (design) layer will provide more accurate information on the capability of the soil to treat and disperse the effluent.

At the end of the day, performing a detailed site evaluation provides the information needed to design and install an onsite wastewater system that protects and serves the homeowner for many years to come, while protecting our precious groundwater resources. That’s a win for everyone.


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