Question:
I’m taking heat because I told a client that his system was in a state of failure and/or had failed, at least at the point when it backed up into his home. I’m taking more heat from an engineer saying I can’t declare a system failed because I’m only an installer. And more heat from the original installer who surely doesn’t want anyone to say his installation failed. Here are some of the facts and observations I had to work with:
1. The system is only 4 years old.
2. When it was installed, the soils perked at a rate indicating that 190 square feet of absorption area per bedroom was needed.
3. The system is designed for a 4-bedroom home and allegedly was installed to meet the design criteria.
4. The design included a 1,250-gallon tank and a deep-trench leachfield that is about 3 feet wide by 8 feet deep (effective depth below the discharge pipe) by 50 feet long, giving a sidewall surface absorption area of about 800 square feet.
The client called on Friday to say the system was backing up into his home. On Friday a pumper pumped 1,350 gallons out of the tank, noting some backflow from the leach trench into the tank. The leach trench rested for three days. I checked it on Monday. The tank was not back up to operating level yet before I made my observations.
Alaska requires 4 feet of ground cover or equivalent with insulation over all components of a septic system. I measured between 5 and 6 feet of water standing in the leach trench.
An adequacy test done by the engineer on Wednesday or Thursday after nearly a week of rest found the system didn’t fail. He put 600 gallons of water into it, and the trench managed to soak it in without the water backing into the house. I understand they measured 3 feet of water in the trench at the completion of the test.
So, would you consider a system under these conditions either in a state of failure or failed at this point? I may be caught in a losing battle of semantics, but I don’t think it’s wrong to call a more-than-half-full leach trench in a state of failure, and I certainly don’t mind using that term for a system that has already backed up into the house. What do you think?
Answers:
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I have been in this kind of trouble as well. I tell those who are upset to please forgive me for the words I used. Now, let’s get busy on finding out the problem.
1. Do a performance test. Use a water meter or just time how long it takes for a garden hose to fill a 5-gallon bucket. You will need to know how long the leach system has been drying out. Or just refill it to the point of saturation. Now pump the tank dry. Tell the owner to go easy on the water. Come back in 24 or even 48 hours and re- saturate the leach system again, timing the water or using the water meter. This gives you a flow in gallons per day (gpd).
Now do the math. How many bedrooms? For this discussion, assume three. I like to use the U.S. Census numbers that say we each use about 100 gpd. The system should perk 400 to 500 gpd: Mom, Dad and two kids. If the leach system perks out more than this, your owner is using more water than the system was designed for, and it’s not the installer’s problem. If on the other hand it only perks 200 to 300 gpd, you can call this duck anything you want but that sucker failed in my book.
2. Look for leaks. Check toilets, water softeners or any other devices that could be leaking water into the drainfield.
3. Does the home use a cleaning person? Or is Mom a clean freak?
4. Is there is a water softener in the home? You can put a water meter in the loop at this point, because softeners normally only go to the inside fixtures. Check to see if both hot and cold use soft water.
There are more things to do, but this will get you started on doing a good job of truly diagnosing the problem.
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I agree in principle that systems are designed to avoid the growth of a sealing biomat. However, we live in a less than ideal world. There are many variables that affect system life, such as installation techniques, system abuse and soil condition variables.
The unfortunate reality is that the vast majority of systems do form a sealing biomat and they do fail, some in a few years, others after 60 years. I also agree that if the distribution component remains aerobic, a sealing biomat will not form and the aerobic soil bacteria will adequately clean the wastewater.
I believe that the conditions below the trench or field have very low oxygen levels, if any at all. This is especially true in the Midwest and colder climates where the infiltrative surface is 4 to 6 feet below grade. I think everyone would like to believe the conditions are aerobic, but do we have any data to support this?
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I’d have to agree with you if systems were being put 4 to 6 feet below the surface. But, if they are, they would be in violation of most or all codes in Michigan and certainly would violate current recommended practice.
Most codes require between 12 to 24 inches of cover. Most of our designs specify only 8 to 12 inches of soil cover over the stone, and the use of light sandy loam material for backfill. Those are mound specifications.
Many in our regulatory and design community encourage or require contractors to keep the bottom of the stone no more than 18 to 24 inches below existing grade in standard gravity systems. Burying systems more than that is counterproductive. I can tell you for certain that we have been back to look at pressure-dosed mound systems over 20 years old, dug into them, and most do not have any biomat buildup at all.
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System failure begins the first day of use. Or you can just call it aging or maturing. Systems are designed with significant reserve capacity. For example, a 50 percent factor of safety may be included in the daily flow rate, and the sidewall absorption area of the trench may be ignored.
I suspect that these standards were established because we know that every system will eventually fail — it is just a matter of when. Generally speaking, all things being equal, the larger the infiltrative surface, the longer the service life of the system. As the biomat develops, the hydraulic capacity of the system is reduced from the original percolation rate. The biomat slows the percolation rate so it has sufficient time to treat the wastewater as it passes through. Over time, the biomat will literally seal off the bottom of the field or trench, causing ponding below grade.
Sidewall absorption begins as the biomat continues its growth up the sidewalls of the trench or field and eventually to the surface. Visible surface ponding then occurs or tank levels are elevated, or the system backs up into the building.
Any or all of these symptoms can occur depending on site elevations and system configuration. Many states consider a system failed when it creates a health hazard such as surface ponding or backup into the building. Others consider the system failed when any ponding in the system occurs, even sub-grade ponding. A logical definition of failure would be when the average daily hydraulic capacity of the system is exceeded, excluding an unusual event or a system that creates a public health hazard.
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Let’s face it: The Space Shuttle Challenger was designed not to fail and had lots more time, money and expertise dedicated to it than we’ll ever see in onsite wastewater. Design an installation to the very best of our abilities under the circumstances and at the time is the best we’ll be able to achieve.
No one designs for failure, but it is sure to occur on occasion in spite of the best efforts. There are too many variables, including such little things like earthquakes, that can alter the ground structure and water table and destroy the components; chemical compositions introduced by those who don’t have a clue; changes in the environment and society; floods and droughts. The list is endless.
