The Deck Footing That Landed on the Septic Line

Why this matters

The pipe that carries everything a house flushes to its septic tank is private, shallow, and invisible from the yard. No 811 locate will mark it. It runs from the back wall of the house to the tank, which is usually in the back yard, which is where the deck goes. An auger that crosses its line at any depth below the pipe will go through it, and the crew will usually not know, because a 4 in plastic pipe gives way to a power auger with little more than a kick. This case follows one of those breaks from the morning sewage appeared in the yard back to the footing poured a week earlier. The setbacks a deck must keep from the tank and field are in Septic Fields for Landscapers, Fence and Deck Builders; this case is about the pipe between the house and the tank.

First, stop the exposure

When the homeowner called, the first thing that mattered was not the cause.

• Sewage on the surface: keep children and pets away from the wet area and anything it touches, and rope it off if they cannot be kept away. Do not hose it down; that spreads it and pushes it toward neighbors.
• Stop feeding it: the household stops running water, laundry, the dishwasher and showers, and limits toilet flushing, until the septic contractor has seen it. Every gallon that goes down the drain comes out at the break.
• Contact, not just smell: sewage carries bacteria, viruses and parasites that infect through cuts, the mouth and the eyes. Anyone working near it wears waterproof gloves and boots, keeps hands away from the face, and washes before eating or smoking.
• Nobody enters the tank, ever. A septic tank can hold hydrogen sulfide and too little oxygen to breathe, and the smell is not a guide, because hydrogen sulfide deadens the sense of smell at dangerous concentrations. Looking in through the lid from above is as far as anyone goes. Entry is a permit-required confined space job under 29 CFR 1910.146 (29 CFR 1926 Subpart AA where it is construction work), not part of this work.

What the homeowner saw

The deck had been finished the previous Friday. The following Saturday, eight days later, the homeowner noticed a sewage smell on the back lawn and a soggy patch of grass at the edge of the new deck, near its third footing. By Sunday the patch was wet on the surface and the downstairs toilet was slow.

They assumed the tank was full and called the septic contractor.

What the septic contractor checked, in order

The tank level. The contractor opened the tank's inlet-end lid and looked. The liquid was at its normal working level, right at the outlet pipe, not above it. That one look ruled out the two causes the homeowner expected. A tank that needs pumping, or a drainfield that is no longer taking water, both back the level up above the outlet. A normal level meant the tank and field were working, and the wastewater was not reaching the tank in the first place.

The inlet. With the lid open, the contractor had the homeowner flush the downstairs toilet several times. Almost nothing came out of the inlet into the tank. The waste was leaving the pipe somewhere between the house and the tank.

The camera. The contractor ran a sewer camera from the basement cleanout, on the back wall where the pipe leaves the house. The counter read 7.1 ft when the camera reached broken black plastic and then a gray mass: concrete, filling most of the pipe, with a gap at the top where water was getting past and out into the soil.

The surface. The contractor walked out from the back wall to where the camera said the break was. 7 ft out, under the soggy patch, was the third footing of the new deck.

Why it happened, laid out

 SIDE SECTION, HOUSE TO TANK (not to scale)

 HOUSE |         DECK BEAM
 WALL  |   ========================
       |          |  FOOTING 3 (12 in hole,
 grade |__________|_ 36 in deep, concrete)
       |  ^       |                   tank
 18 in |  |       |                   lid
 below | pipe     |                   [==]
 grade +=====\    |                   |  |
       |      \===X=====\             |  |
       | 4 in   1/4 in   \============+  |
       | ABS    per ft    about 20 in |  |
       |                  deep at the | TANK
       |                  footing     +--+
       |<---- 7 ft ---->|<--- 9 ft -->|

The pipe leaves the foundation 18 in below grade and falls toward the tank at 1/4 in per foot, a common slope for a building sewer. At 7 ft out it is 18 in plus 7 times 1/4 in, which is 19.75 in, call it 20 in deep. The footing hole was 36 in deep. Any hole deeper than the pipe that lands on the pipe's line breaks it, and this one landed dead on it: the pipe runs straight out from the cleanout to the tank, and footing 3 sat 16 ft from the deck's left corner, exactly where the cleanout comes through the wall.

The auger operator remembered the hole. At about 20 in the auger kicked, then went on. The spoil had black plastic chips in it, which the crew took for old landscape edging. They set the form tube and poured. The concrete ran into the broken pipe, and the pipe kept carrying some flow over the top of the plug, which is why nothing showed for a week. Over that week the plug caught paper and solids, flow over it dropped, and more of each flush went out through the break into the soil until it surfaced.

The same strike in other houses

The week of delay came from this pipe's material and from the concrete leaving a gap at the top. Change either and the signs change.

• Cast iron or clay pipe. An auger usually stops hard on iron, and clay shatters with a noise and red or tan shards in the spoil. A crew is far more likely to notice, but clay breaks just as completely.
• Concrete that fills the pipe. If the pour seals the bore, the house backs up the same day, usually first at the lowest drain, a basement floor drain or shower. That is a faster call and a dirtier one.
• A hole that only cracks the pipe. Without concrete in it, a cracked pipe can leak slowly into the soil for months, invite roots, and show up as a recurring slow drain long after the deck crew has gone. Nobody connects it to the deck unless the camera does.
• A pumped line. Some systems pump effluent from a pump tank to the field under pressure. A cut pressure line sprays when the pump runs, on the pump's schedule, often at night, and the leak is effluent from the tank rather than raw sewage. Same contact precautions, same rule against digging near it.

What the locate missed, and why that is the wrong question

The 811 ticket was valid. It marked gas and electric along the side of the house, and nothing in the back yard. That was correct, because the locate service marks the utilities' lines, and the building sewer, the tank and the field all belong to the homeowner.

So the locate did not miss anything. The deck shop's process did. Three clues to the pipe's route were visible on the walk-through: the cleanout and the point where the pipe left the house, inside the basement on the back wall; the plumbing vent stack on the back roof slope above it; and two round tank lids in the lawn 16 ft out, the distance where the diagram above puts the tank. A straight line from the cleanout to the inlet lid crossed the planned footing row at footing 3.

The repair, and who did what

1. The septic contractor excavated by hand and with a small machine around footing 3 to expose the pipe either side of it, wearing the gloves and boots above, with the household still holding water use.
2. The deck shop shored the beam with temporary posts and removed footing 3, breaking the concrete out of the pipe's path.
3. The septic contractor replaced the broken section of pipe with new pipe on proper bedding at the same slope, removed the sewage-saturated soil for disposal as the local health department directed, and checked flow into the tank with the camera and the open lid. A permit for building sewer repair is required in some jurisdictions and handled by the plumbing or health authority depending on the state; the contractor pulled it.
4. The deck shop relocated footing 3 to 2 ft to the side of the pipe's line, hand-dug, which put the two footings either side of it at 6 ft and 10 ft spacing. That changed the beam span on one side, so the shop submitted the revision to the building department under the deck permit, and the inspector signed it off before the beam came off its temporary posts.

The household went back to normal water use only after the septic contractor watched several flushes arrive in the tank at full flow.

What the deck shop checks now

Septic or sewer, asked first. Every deck walk-through starts with the question, and if the homeowner is not sure, the shop checks. See related: How to Find Out Whether a House Is on Sewer or Septic.

The pipe gets drawn before any footing does. The shop finds the cleanout or the point where the pipe leaves the house, the tank lids, and any permit drawing the county health department holds for the system, and draws the line between them on the footing plan. Where the line comes within 3 ft of a footing, the septic contractor locates it with a sonde pushed through the cleanout before any digging.

A kick in the auger stops the hole. Any resistance followed by give, any plastic, clay pipe, gravel bed or wet black soil in the spoil, and the hole is stopped and looked into by hand before anything goes into it. "It was probably edging" is not an identification.

Footings stay off the tank and field entirely, under the state's setback rules, not just off the pipe.

References

• 29 CFR 1910.146, permit-required confined spaces (septic tank entry)
• Your state and county onsite wastewater rules for building sewer repair permits and setbacks
• See related: Septic Fields for Landscapers, Fence and Deck Builders
• See related: Private Wells and Septic for Non-Specialists, Septic System Basics Reference
• See related: How to Find the Private Lines a Utility Locate Will Not Mark