Thursday, June 11, 2009


Here's my latest nugget of new information about septic drain fields. Before I start, I can only encourage people to become informed and educated about septic issues as the future surely holds more potential for being "laid over a barrel" by the generic industry and officialdom.

I realized years ago that there is very little thought or consideration given to the eventual physical degradation occurring to a typical drain field or leach line. The issues are occasionally acknowledged and heads nodded about them, but no one ever seems to look into the what they are nodding about. There is biological degradation or biomat clogging of drain field soils that is inherent in conventional, anaerobic septic effluent that is discharged to a drain field and everyone should understand that issue. There are other physical issues that also reduce some of the potential of a drain field. They are few, but need to be described. Because we introduced the general idea of remediation for drain fields over ten years ago, we have made a serious study of what problems could reduce our success in remediation. We found that there really aren't that many physical issues that can or do occur. I will attempt to describe the most common of these physical issues: siltation.

Over time, silt in the soil will be percolated into the spaces between the drain rock from years of rain and or snow melt; that is if you don't live in Arizona and the Southwest. I was told when I started in construction that siltation spelled the end of a drain field. Well it doesn't. Here's why. An engineering study was done by an engineering group (surprise that an engineering group does engineering studies) here in Northern California. They discovered, with round or spheriod shaped stone, or man made stone replacement, that when you take a cubic foot of space and fill it with any round or spheriod shaped material of any diameter, the material took up approximately 65% or the volume of the cubic foot of space. That left 35% for air space. That includes all diameters from bowling balls to marbles to sand to silt. What was critical was that there be no flat surfaces that can "marry" together eliminating the air space (i.e. crushed aggregate doesn't apply to this study).

This translates to a potential liquid storage volume per cubic foot of drain field as follows: 7.48 gallons per cubic foot minus 65% or 4.86 gallons which equals 2.62 gallons of space for liquid storage per cubic foot of drain field. If one had, say, a 100 foot leach line, with a width of one foot and one foot high of aggregate (natural or a man made synthetic replacement) you would have a total liquid storage capacity of 262 gallons. **This example is for descriptive purposes only and is not meant to indicate anyone's particular drain field.** When siltation occurs, 65% of the air space is filled with spheriod shaped silt particles. There are two issues of importance when siltation occurs.

The first issue to understand is the silt does not become compacted as would be expected in normal soil conditions. Compaction does not occur because the aggregate carries the compressive load to ground around the air spaces now filled with silt. Therefore, there is no pressure on the silt to cause compaction. The silt remains light, airy and permeable to the passage of liquid through it. Being permeable means there is capacity for leaching liquid through the uncompacted silt (liquid that is not filled with biomat producing bacteria).

The second issue is there is still air space between the silt particles. Remember the example above? I'm trying to remember. The silt is spheriod in shape. It therefore takes up only 65% of the air space between the aggregate. What we now have is 35% of 35% of air space and therefore liquid volume for storage. Here it is in numbers. In the example above, we had 262 gallons of storage capacity in the air spaces between the aggregate. Now the air spaces are filled with silt. That means we have 35% of 262 gallons of storage capacity or 92 gallons. There are many more times the cubic foot area within a drain field in a typical septic system.

Let's say we have three hundred linear feet of leach line described above. That would mean we now have a minimum of liquid storage capacity of 276 gallons. For a family of four that is most likely one day's residence time. The aggregate is surrounded with very permeable silt that will not resist the passage of liquid through it. Therefore this example of a drain field (with leach lines) would still be able to function for disposal if we were dealing with rain water or drinking water. We're not dealing with rain water or drinking water so what's the reality?

Anaerobic effluent will carry biomat producing bacteria with it into the drain field. Biomat will fill the voids in the infiltrative soils and clog the voids. These bacteria will also clog the voids between the silt particles with biomat making the silt non-permeable. Remove the biomat from the infiltrative soil voids and the silt and you now have a functional drain field.

Now we have the pitch. But a real solution. This is where the Pirana System comes into play. They both remove biomat from the silt and the infiltrative soils by biologically reducing the viscosity of the biomat slime (liquifying), thus creating permeability, and then the Pirana System will eventually consuming the biomat. The effluent that leaves a septic tank with a Pirana operating within it will not contain the biomat producing bacteria nor a significant amount of organic matter that can clog soil pores or soil voids. The effluent now has nearly the same clogging properties as rain water or drinking water though you absolutely shouldn't drink septic effluent (I know some people I believe should). Which is to say both don't clog pores or voids.

This means that the infrastructure of the drain field has value. We don't need to throw it away; or spend thousands of dollars replacing the drain field; or worry about unknown costs for landscape repair to have a functioning drain field.

I hope I've been clear and informative. I want again to increase your knowledge and widen your perspectives. In these horrific economic times saving every dollar is critical. In normal times spending a dollar that wasn't or isn't necessary should be critical.

Well thanks for stopping by and remember its out there so wipe your feet before you enter a house.


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