The Best Leach Field

One leach field system beats all of the others.

One leach field system beats all of the others.

Modern Septic Systems

People have been building septic systems since the French Revolution times. For many years there has been a common technological approach: settle out the solids and spread the liquid underground. That still works. The devil is in the details, so to speak. Let’s talk about some newer developments that do the same job as before, but in a far more economical way.

Codes are the controlling factor in any septic system. You have got to deal with soils as you find them, and gravity must be considered. But the way the code is used can make one design cost twice as much as another design.

There is not much change at the start of the septic system: the sewer pipe. It used to be iron or asbestos-cement, but now it is the heavier wall plastic pipe. It flows to a conventional septic tank. The code now requires a minimum of 1500-gallon capacity in Massachusetts, but older tanks can be smaller.

It is suggested, but not usually required, that the septic tank be equipped with an outlet filter. This protects the leaching system from neutral-buoyancy laundry fiber and other floating stuff. But the trade-off is that it requires maintenance, at least bi-yearly, or the system will backup. I always recommend a filter, but in my designs it is removable. An important improvement is having the access hatches to the tank accessible at the surface. Green round covers are installed that are strong and obscure and easy to mow over. These are sealed with stainless steel hardware for safety. Having known access to your tank if far superior that the typical “treasure hunt” where the depth and location are only approximated.

The big savings is in the leach field design. Codes allow for a major reduction in required leach field sizes if modern systems are installed. My favorite system is Eljen (, a “uncomfortable mattress” shaped plastic pad. These are installed on at least 6” of clean sand and covered with a thin fabric film. A foot of topsoil and a low-profile vent are also installed. Massachusetts codes allow at least a 40% reduction in the leaching area requirements, plus a Two Foot reduction in any required mounding, at least for replacement systems. Then too, the typical 5 feet of certified sand surrounding the field is not required with Eljen. The field is much smaller, the mound shorter, and many truckloads of materials are not needed.