Failing Septic System

[civilman72]

We are in the process of selling our house and the inspector brought up concerns with our septic system. Turns out there's about 8"-12" of standing water in the leech field inspection port. The tank is 3-chambers, 1,500 gallons with a siphon in the last chamber. It appears that the siphon is not working - when you look down the inspection port you can see water trickling out of the outlet pipe, and the siphon is not "burping" when the water level gets high enough. We have dug a hole 4'-5' deep next to the leech field and did not get any water in that hole, so we do not believe it's groundwater, so I'm thinking the biomat has prematurely clogged the leech field.

Background: We hired a local engineer to design the system 10 years ago, which included blasting of the existing shallow granite rock to provide a deep sandy material for the leech field. Excavator installed the infiltrators, backfill, the septic tank and the pipes. We contracted separately with the engineer, excavator, blaster, and tank supplier. Since that time we've had the tank pumped twice and over the last four years we've had the design engineer perform annual inspections of the system, which have not turned up any red flags. So, we feel like we've been diligent as landowners and are aggravated that the potential cost to replace the entire system will fall on our shoulders but not sure how much legal recourse we may have.

I feel like I have a good understanding of the basic issues that can cause premature septic system failure, including: over-compaction of leech field, improper blasting resulting in lower infiltration rates, homeowners discharge of oil, grease, paints, etc. into the system, but it appears that proving what the cause of the failure is can be very difficult or extremely hazardous and costly.

In Colorado, I believe the statute of limitations is around 6-8 years, so not sure I have any legal recourse with the excavator, blaster or tank supplier. But I would like other engineers' opinions on the liability of the design engineer, considering he's been inspecting this system on an annual basis.

So my questions are:
(1) Is it safe to say that if the design engineer was completing thorough inspections of the system, that he should have seen something during those inspections that would have indicated issues with the system?
(2) Even though he completed the design 10 years ago, would the statute of limitations not pertain to him because he's been doing inspection work within the 6 year limit?
(3) Any ideas how to diagnose what caused the leech field to fail?

I appreciate anyone's input and expertise.

 

[dik]

My first guess would be that the water table is too high. If cut into stone, there is no drainage below unless care is taken to provide a dry sump or something of the ilk. You can have anerobic activity or a biomass created. For rock in close proximity to the soil, you might have considered a raised bed of some type or alternatively a proprietary type of system. I've been involved with the design of maybe 50 septic systems... and some can be a challenge.

One that I ran percolation tests for went really well (perc times were great) and in passing I noticed there was a vertical pipe out of the ground with a tap on it and found out from the client that the pipe and tap was for artesian flow. Just below the soil to be the bed, there was an impervious clay layer. I told the client that he was looking at a raised bed, which he didn't want, and he refused to pay for the work done to date. After that, I usually had a test pit dug using a backhoe to get an idea of the soil profile.

Dik

 

[coloeng]

civilman72,

Not sure where in Colorado you are located, but here in SW Colorado we had a very wet winter. This could account for the additional water that you are seeing that the engineer didn't see in previous years. Other than that, I don't have any other ideas.

Good Luck

 

[civilman72]

We dug a hole next to the leach field and did not find any water, so we're fairly certain the culprit is not groundwater.

I've discussed our issues with a lot of other experts in the field and everyone is perplexed. Best assumption is that the leech field is plugged from accelerated biomat growth.

 

[davefitz]

Considering the lack of drainage due to solid rock base, one might consider inserting into the 3rd chamber a MBR "membrane bioreactor". The effluent is considered to be tertiary treatment and suitable for agricultural quality water . Will need small electric power to supply the air bubbling compressor and the waste suction pump.

The replacement soil was supposed to be "select fill" meaning 85% sand and 15% clay- the clay is needed to destroy viruses. If you only received sand then the replacement fill was incorrect.

"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick