An Introduction to Soils

[Stuart Meade]

Your soils are the foundation of your septic system!  
Here are a couple of general truths regarding soils:

Septic systems need (and require) well drained soils to function.  

Sandy soils are good unless they are too coarse (large sized grains).  Medium and coarse sands are considered poor filters in Indiana and therefor, are not suitable for regular septic systems.

Septic absorption systems sized for sandy soils are smaller than systems in heavier soils (soils with clay).

Clay soils drain very slowly (are poorly drained) and require much larger and sometimes more elaborate septic systems (i.e. mound systems).

Compact till is a layer of impermeable (or almost impermeable), unweathered soil that is sometimes found as shallow as 18" deep in some clay soils.

You cannot install a septic absorption field into compact till.

Filled or compacted soils tend to lose their structure and ability to absorb water.  This is why the current Indiana rule will not allow septic systems to be installed in filled or disturbed soils.

I've written the following on soils for my design website http://www.septicdesign.com/homeowners/soils-and-septic-systems/

[homerj]

Since filled soils are unacceptable for the absorption field, is it permissible to remove all the fill for construction of a new system and replace it with somethink like INDOT Spec 23 sand?  The new St. Joseph, IN Ordinance (No. 58-07) says that in the case of system replacement that "When removal of fill and backfilling the site with INDOT Spec 23 sand is necessary, pressure distribution of effluent shall be required."  If there is unacceptable fill for construction of a new system, can the soil be engineered to meet the specified criteria? It seems like one should be able to design a field to meet what ever kind of permeability is required.

[Dye Queen]

The State Sewage Rule allows the local health department to use best judgement when a setpic system must be replaced due to system defect.  However, the standards of the Rule are required for new construction. If you want to pursue installing a system outside of the Rule parameters for new construction, you must get approval through the State Department of Health.  This process can take some time, but you may be able to develop property that would have otherwise set idle. I would recommend discussing this with your health department first.

[homerj]

thanks dye queen. I don't think my local guys are too inclined to try novel things, but I guess I need to try this in a formal way before I pursue it at the state level.