soil sinking over septic tank inlet

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Old 08-19-09, 06:23 PM
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soil sinking over septic tank inlet

Soil has been sinking over the septic tank inlet the past couple years. Slowly the depression has become 8" deep over the lid by 8 feet diameter shallow dish shaped. We had 4.5" rain and washing machine water backflowed into basement.
My question is why did wash water backflow from septic thru pipe sleeve in block wall and as well as over flow washer stand pipe. Do I have a broken inlet pipe into septic and rain water is filling the tank ? Or is sinking ground common and I just need to fill-in more soil ?

Tank was pumped last week for first time in 25 years. Tank is concrete 1500 gal leach field, 3 person house, no garbage disposal, no leaky faucets, 3" PVC straight to tank, 80 feet drain fields on flat loam soil.
 
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Old 08-19-09, 06:43 PM
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Your tank might have a leak allowing the soil to fall or get washed into the tank forming a little sink hole in your back yard. A hole or leak in the tank can allow surface water to enter. All the water entering the tank has to go somewhere and can back flow into the house.

Did the person who pumped your tank examine why the ground was sunken? Did they find dirt inside the tank?
 
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Old 08-21-09, 04:03 AM
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I lost confidence in the person who pumped the tank once they got there. Lots of excuses of why he was going to charge me more $$ for the job. He said the drain field was back washing around the tank and into the house. Since the washwater backflowed out the stand pipe and thru the pipe sleeve at exactly the same time... I think there may be a better explanation. Everything else about the system seems ok, vents appear to be working, drain field is solid, not soggy.
 
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