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Septic distribution box inspection - US EPA Septic System D-Box Covers

Function of the Cover on a Septic System Drop Box; Cover Leaks, Cover Safety

Septic system drop box cover installation, repair, requirements: why we need a safe, water-tight cover over the septic system D-box.

Septic system D box installation, specifications, inspection, diagnosis, and repair: in this article series about septic system drop boxes we describe the best procedures for locating and inspecting, repairing or replacing the septic drainfield distribution box, or the "D-box" or "Splitter box".

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Distribution Box Cover Troubleshooting & Repair

Septic D box in trouble (C) Daniel Friedman N DayQuestion: How to repair a bad D-box lid or cover

My D box is level, it flows nicely and is made of concrete. Unfortunately the lid has failed and the sides are starting to crumble.

Do I have to replace the whole box or could I simply form and pour concrete around the old one? Would this be an acceptable repair method? - Scott 5/1/12

Reply:

Scott, if you can repair the dbox to be water tight in place that's fine, but I worry its a wasted effort ad if it's crumbling the original concrete mix may have been bad - if so the box will continue to crumble - replacement may be in order and not too costly.

Certainly you don't want to pour a new "lid" in place that seals the D-box making it impossible to open, inspect, adjust, in the future.

Question: standing water over the [septic tank?] cleanout covers

Question:

our cleanout access covers get about an inch of water on it when we run the washer and shower in the house. The water comes up quickly on just the cover and then two minutes later it's gone. We have the tank cleaned once to twice a year; we call the company that cleaned it and the are telling us they need to dig up the D box.

I have checked the yard and there is standing water anywhere. Does digging up the D box sound correct. Or should they just check for a clog? - John 6/26/12

Reply:

John if the septic tank or dbox is flooding as you describe it sounds as if the fields are clogged or flooded. Your system is in trouble, needs diagnosis and repair for sure. Because it's easy and quick it's a great quick-check to look into the D-box to see what's going on.

Open the D-box covers, flush a few toilets in the home, or run the washer, and watch in the D-box. If you see effluent entering and flooding the box then we figure the outlet lines and drainfield are either blocked or saturated.

Start a more throughout inspection at the septic tank, include piping to the D-box, the D-box, and the fields. For example if the tank inspection shows us that the tank baffles are gone, we know we've been pushing solids into and ruining the fields.

Question: how to seal the concrete lid on a septic D-Box?

2017/04/26 Ed said:

What do you use to seal the concrete lid on a d box?

Reply: which Septic D-Boxes & D-box covers need a seal?

Ed

The D-Box should be protected from surface runoff & flooding without a special sealing cover

Pre-cast concrete Distribution Boxes are sold usually by local septic tank and system suppliers and typically include gasketed openings for the effluent distribution pipe connections and a flat concrete lid that simply mates with the flat edges of the D-box without a gasket and without use of a sealer. Below I warn that using an effective sealant between the D-box body and D-box cover risks being unable to remove the cover later when needed.

If the septic system distribution -box is protected from surface runoff and local flooding, as it and the rest of the septic system should be if it is to be functional, and if the septic soakbed or drainfield is itself working, then neither groundwater nor septic effluent will make trouble flowing into nor out of the D-box without extravagant gaskets or sealants.

Sealing a Deep Septic D-Box Cover

Really? Well not always. A most-effective septic drainfield is not buried deep into the ground because there's not enough oxygen down at depths more than a couple of feet.

But in cold climates such as Northern Minnesota, the top of a septic tank itself may be four feet below ground and septic soakaway or drainfield beds may be still deeper. It can be more difficult to keep seasonal ground water out of such systems.

If you have an unusual situation that requires actually sealing the septic D-box lid to the box body, and as usual the concrete D-box design doesn't include gaskets and grooves to mate them, you can use butyl sealant on a clean dry surface - it will bond very well - perhaps too well as the D-box won't leak but it can be hard to get the lid off again if you use too much sealant.

For that reason some septic installers often provide a flexible rubber gasket (or a makeshift one using a neoprene gasket material) that will seal the lid of the D-box while making its removal easy when inspection or adjustment are needed.

Sources of Septic D-Boxes with Seal-able Covers

Tuf-Tite makes a plastic D-box that includes built-in seals around the lid as well as around the connecting pipes. [Tufftite]

Polylok makes a plastic D-box with a sealing cover for round Distribution boxes. [Polylock]

Advanced Drainage Systems produces a polyethylene "drain tube distribution box" sold at WalMart stores. This box includes a friction-fit plastic access cover.

Corex provides a polyethylene plastic D-box taht to me looks identical to the Advanced Drainage Systems product. These products are ribbed for structural strength and may be more suitable for surface water drainage.

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Comments

Don · Aug 15, 2022

I went to my local precast company for a replacement D box cover for a 16x30 box. When I was there, saw some covers that had a cast in Polylok riser for access and figured that's the way to go. They told me they use a slightly larger cover for my box size. Not thinking about it at the time, I purchased it and brought it home. Now I wonder if this new cover which is 21x34 and overhangs the outer edge of the box now would get lifted by frost heaves in the winter? Any thoughts?

InspectApedia-911 (mod) · Aug 16, 2022

@Don,

Interesting question.

The answer depends on your soil properties, moisture levels etc. but I'd speculate that if frost heave were a problem at the D-box then the D-box itself ought to have shown movement.

I'd give it a shot, and be sure to direct surface runoff away.

drummerboyent@shaw.ca · Aug 4, 2020

I found the concrete D-Box on our residential 3 bedroom property. It was about 2.5 feet below the ground and took a lot of personal digging to uncover. Now that I have found it I need to cover it all up again but that means that if I have trouble in the future I have to dig it all up again. What is the best way to cover that depth without dirt and keep it safe from freeze and water seepage? ..........Brian

danjoefriedman (mod) · May 11, 2020

Bob

The D-box has the job of receiving liquid effluent from the septic tank and distributing it among several leach lines that make up the septic drainfield or soakaway bed.

To work the box has to be clear, un-blocked, level, and covered to be protected from both soil (that will block or clog the box) and also from surface water (don't want that leaking into the septic system or it'll flood it).

So yes,

All D-boxes need a lid, sides, and bottom that are water tight.

Do NOT fill the box with soil nor gravel.

Do be sure the box is level and clean and clear, then fitted with a lid.

Like you, I suspect the septic system has not actually been working normally for years.

Before closing up the box you might run some water into the septic tank - that ought then to appear in the D-box and to flow out of it into the drainfield.

Bob · May 11, 2020

I have distribution box with no cover. There was pending over it. We dug it out and it was filled with black dirt. The 4 inch lines look like they just had concrete collars. There was the main pipe from the tank and two other 4inch pipes that went to the fields. System is original and is 30 years old. Pipes looked in good shape.do all d boxes have a lid? Is refilling this open dbox with new soil a good idea? Perhaps fill with gravel? I'm not even sure how this worked all these years

danjoefriedman (mod) · Aug 9, 2018

The plastic should be fine. I'd try that as long as you wont' drive over it. The expense is in the digging and connecting.

John Va · Aug 8, 2018

Hi, I just dug up the pipe going from my septic to the D-Box, trying to find a leak (water coming out of the ground).
I found the pipe is ok, but the D-Box has collapsed. Black mud everywhere the D-Box should be. The only thing I could identify is the concrete bottom. The top and sides are gone. The pipes are still in place. I just had the septic pumped out and there was no sign
of any sludge leaving the tank. The D-Box may have been destroyed for years. It is in a part of the yard, that is never used and seldom mowed.
My question is, if I replace the D-Box, how do I clean out the field pipes (of mud) and test to see if they are ok ?
I was planning on cutting the output pipes back and then adding the needed pipe and coupler to get to the D-Box.
The pipes are pvc white pipe (not sure what schedule they are yet, or size (I believe 4", not measured yet)).
I just found the D-Box and it's condition an hour ago. I am sick over what I found and hoping I don't have to have a new drainage filed installed.
Any advice you can give will be greatly appreciated.
Also, I can get a plastic D-Box from nearby suppliers, but I will have to drive to another town to get a concrete box.
I am leaning towards getting the concrete box. What are your thoughts ?
(p.s. There are a lot of tree roots around where the D-Box is located. I am thinking they are what destroyed the D-Box.)

Thank you for your time.
John in Virginia

anthony · June 29, 2017

need a 36 inch by 16 1/2 distribution box lid

 

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