Engineered Leech Lines
Here is an example of an large scale residential engineered septic system with deep leech lines to provide adequate drainage for this area with a lot of hard pan. What you see in this picture are the long trenches called leech lines which are filled with 1 1/2 inch river rock surrounding a horizontal perforated pipe. This allows water to flow from the septic tank and into these trenches. The water then peculates through the rock and back into the ground. This job was done in Fresno CA.