Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
SEPTIC SYSTEM INSPECT DIAGNOSE REPAIR
SEPTIC CARE INSTRUCTIONS
SEPTIC D-BOX INSPECTION
SEPTIC DRAINFIELD FAILURE DIAGNOSIS
SEPTIC DYE TEST PROCEDURE
SEPTIC FAILURE SIGNS
SEPTIC INSPECTION & TEST GUIDE
SEPTIC LIFE EXPECTANCY
SEPTIC SUPPLIES & PARTS
SEPTIC SYSTEM DESIGN ALTERNATIVES
SEPTIC SYSTEM DESIGN BASICS
SEPTIC SYSTEMS, HOME BUYERS GUIDE to
SEPTIC SYSTEM SAFETY WARNINGS
SEPTIC TREATMENTS & CHEMICALS
SEWAGE BACKUP PREVENTION
SEWAGE EJECTOR / GRINDER PUMPS
SEWER GAS ODORS
SEWER LINE REPLACEMENT
SINKHOLES, WARNING SIGNS
SOAKAWAY BED FAILURE DIAGNOSIS
SULPHUR & SEWER GAS SMELL SOURCES
TOILETS, INSPECT, INSTALL, REPAIR
TRAPS on PLUMBING FIXTURES
TREATMENTS & CHEMICALS, SEPTIC
VIDEO GUIDES: Septic Videos
WASHING MACHINES & SEPTIC SYSTEMS
WATER SOFTENERS & CONDITIONERS
WATER SUPPLY & DRAIN PIPING
WASTEWATER TREATMENT BASICS
WATER, WELLS, WATER TANKS: TESTING GUIDE
WINTERIZE A BUILDING
Septic system D box inspection, diagnosis, and repair: here we describe the best procedures for locating and inspecting, repairing or replacing the septic drainfield distribution box, or the "D-box" or "Splitter box". This series of articles discusses Inspection and Reporting the Condition of Private Residential Waste Disposal Systems - or - Where Does it Go When I Flush? and ... Will We Meet Again?
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved.
The distribution box (more than one may be in use) connects a single effluent line from the septic tank to a network of absorption system components such as drainfield leach lines or to a network of seepage pits or galleys.
The photo (left) shows the adjustable weir outlets that permit balancing flow among drainfield lines. (Source EPA who used photo from Ayres Associates.) More sketches of D-box layouts and configurations are shown in this EPA drawing.
Regulating effluent distribution: In good system design the outlet openings from the distribution box to each drainfield line can be adjusted to regulate the flow among the various absorption lines.
Elegantly simple, a plug with an eccentric hole is inserted into the end of each leach line fed from the D-box. By turning the plug in the end of the leach line pipe one can place the eccentric hole higher or lower with respect to the bottom of the distribution box, thus compensating for a slightly tipped box, differences in leach line length, or differences in leach line condition.
Uneven effluent distribution: If a distribution box becomes tipped (or clogged) effluent may be routed to only a portion of the absorption system, thus overloading it and leading to a "breakout" of effluent at the surface or to clogging and system backup.
An examination of the septic system distribution box interior may show flood lines in the box if the drain field has been clogged or saturated in the past even if at the time of inspection the box is not flooded.
If the septic drainfields have been flooded you should be pessimistic about the remaining life of the absorption system.
If the septic drainfield distribution box is tipped and/or septic system effluent arriving from the septic tank has not been uniformly distributed among the drainfield lines (assuming they are of equal length and in equally good soils), only a simple adjustment of the outflow may be needed.
Round plugs with eccentric openings may be present or can be inserted in the D-box outlet openings to regulate flow among the individual absorption lines. (C)Trap Daniel Friedman Copyright Protected text. Also see ALTERNATING BED SEPTIC SYSTEMS.
Tipped or flooded distribution boxes, resulting in uneven loading of soil absorption system lines. This condition can flood one or two lines leading to early field failure.
Question: Tipped septic effluent distribution box, standing water at end of one leach line
With thanks to clarifications from reader Doug (March 2013), we recap the effluent distribution piping connections to this D-box as follows:
Without the elbow, effluent flows more forcibly across the box and into the opposing outlet, but very little effluent will make the 90-degree turn into the perpendicular outlet. This is a very common installation practice
If you knew for example that one of your lines was much longer than the other, you'd send more effluent to the longer line - presuming they are both working ok.
As you report that one of the laterals showed a sign of failure during wet weather several years ago, you might want to try to re-balance the effluent flow sending more (or perhaps temporarily, most) of the effluent into the other drainfield line. But to have an accurate idea of the condition of the drainfield sections or leach lines before adjusting the effluent flow in your D-Box, the best step would be to carefully excavate near the end of each of the two leach lines (presuming you don't already have inspection ports installed). Look at the condition of the soils there, particularly, look for standing water or effluent.
Because the D-box is a small thing and not deep, it shouldn't be a big job nor too costly to dig it out, install a larger one, make sure the D-box is not tipped, and that effluent is flowing as desired into both of the drainfield lines.
But you should also check the septic tank condition, especially the outlet baffle, and the scum/sludge levels, to be sure the tank is pumped on schedule (SEPTIC TANK PUMPING SCHEDULE) and that the baffles are in place and working. (SEPTIC TANK BAFFLES).
Another problem that could send sludge into the D-box would be a septic tank that floods from groundwater leaking into it, so you will want to check that too. At also see SEPTIC TANK INSPECTION PROCEDURE, and SEPTIC TANK INSPECTION PROCEDURE, and finally, see Septic Tank Leaks.
Frequently Asked Questions (FAQs) about septic system distribution box (D-box) troubleshooting
Question: water is leaking out of my distribution box. Should the lid be sealed?
I have septic water leaking out of my distribution box. I the lid suppose to be sealed or does it just sit on top?? My system is is pumped up hill to a ditribution box - Robert
Reply: water leaking into or out of a D-box is a sign of trouble that needs investigation and repair;
Water leaking out of the distribution box
If you see "water" leaking out of the septic drainfield D-box it's a sign of trouble. I suspect one of two typical causes.
Water leaking into the distribution box
You don't want surface or ground water leaking into the D-box since in any quantity that water will flood the drainfield. If the D-box cover fits pretty flush and smooth atop the distribution box, the amount of water that leaks in through the top should be trivial. If the top is quite uneven and leaky, and if you can't correct surface drainage to keep water away from the distribution box you might need to add a compressible rubber or foam gasket between the D-box lid and the edges of the distribution box itself to reduce leaks there. Don't cement the distribution box lid in place or you won't be able to open it for inspection, adjustment, or repair.
Question: distance from the septic tank to the D-box?
how far away from the septic tank is the dbox?? - Kristin Clary
How far from the main tank is the D box located on average? - Fishass
Reply: Distance from the Septic tank to the D-Box:
Kristin & Fishass: there is not a fixed distance from the septic tank to the distribution box; rather, its location depends on the space for and layout of the septic drainfield. But you can often get a fair idea where the D-box is likely to be by any of several means:
Question: are the pipes from the D-box solid or perforated?
are the pipes leading from the dboxI have a drywell system) solid or perferated, , one side of the yard is very wet, the other side seems bone dry, could one the pipes either clogged or the other broken, not sure which one to dig up 1st - Joe M
Reply: It depends on septic drainfield layout
Joe the use of solid vs. perforated pipes downstream from the D-box would depend on the septic field layout, but typically from the D-box there will be a solid effluent-carrying pipe serving as a manifold that then feeds individual perforated lines in drainfield trenches.
In theory in my OPINION there is nothing preventing the beginning of gravel-trenches quite close to the d-box, in which case wherever the pipe is running in a gravel trench intended to absorb effluent, the pipe would be perforated. But I would NOT run perforated effluent piping through mere soil backfill (i.e. not a gravel-filled trench) as you'd be inviting soil infiltration and clogging of the line.
Question: during a septic test the trenches "took on water" - they think the D box is kiltered. What does that mean and how do I fix it?
I had a Hydraulic Load test done and the trenches were taking on water...they think the D box is kiltered. Can you explain this and what are the recommendations to have it fixed? - Reen
Reply: a tipped d-box does not distribute effluent evenly among the drainfield lines and can cause flooded drainfields
Sure Reen: someone is making things sound like rocket science instead of simple ditch-digging.
Question: The d-box is not distributing effluent evenly among my three drywells. Is it likely to be a tipped d box or a clog?
I have an old 3-drywell system fed from a d-box in the center of the 3 drywells (laid out on 3 points of an equilateral triangle). The system has had minimal use but one drywell is full and the other 2 are bone dry. Should they all be being fed in parallel or in series (one fills before the next)? Is there likely a tip or a clog? - Jeff O
Reply: Drywells are often installed and fed in series; if yours are in parallel, set the D box to send effluent to all of them.
Often drywells were installed in series - not in parallel. If that's how yours were piped, then if you can confirm that the full drywell has an outlet pipe that drains into the next (dry) one in the series you should be OK. If that connection is missing I'd add it.
Question: My d box is damaged, can I just eliminate it and plumb directly to the leach field lines?
My d- box is only covered by 2" of dirt, I think the harsh winter last year did it in. Is it possible to just plumb the outlet from wetlands to the two drain field pipe?
Reply: yes but just in emergency - it's better to replace and set the D-box properly
What is the difference in splitter box and a D box? - T.C.
Reply: why we might need a Zoeller Tru-Flow Splitter inplace of a conventional Septic D-box - alternating drainfields & effluent flow balancing
Basically there is no difference in function between a D-box and a Splitter box. All D-boxes have some capability of adjusting the flow of effluent among different D-box outlets - a techique that can extend drainfield life by giving some drainfield sections a rest for two years or so between services. In some literature the control that permits diverting effluent among drainfield segments, or shutting it off entirely, is called a splitter valve. In other installations, a simple manual plug or cap is inserted or adjusted at each outlet opening inside the distribution box.
Some "splitter" boxes such as Zoellers are more sophisticated than the simple concrete or plastic Distribution Boxes illustrated in the article above.
In a convenational concrete D-box, it's just that: a plastic or concrete or fiberglass "box" into which one pipe delivers septic effluent from the septic tank, and from which two or more pipes carry effluent to drainfield trenches, galleys, or other disposal sysems. The box routes effluent among the various lines and if properly installed we hope effluent is distributed evenly. Some D-boxes include a round cover with an eccencrtic hole that can be rotated up or down to balance the efflent load among different drainfield sections.
Higher velocity pumped septic effluent may require careful effluent distribution control in the D-box - the Splitter
Zoeller's Splitter uses a series of internal baffles to control the routing of effluent among drainfield lines. One rason we might need the baffles and more precise control of effluent distribution through the D-box (or Splitter) is that Zoeller, who manufacture sewage grinder pumps and septic effluent pumps, (we pose) may have found that pumped septic effluent arrives in the Splitter (or D-box) at a higher velocity than effluent that drains into the box from a septic tank by gravity.
At high velocity, effluent entering a conventional D-box may not flow uniformly among the multiple box outlets - instead it would charge across the box and flow mostly into the effluent line directly across from the inlet pipe. Zoeller's baffles appear intended to prevent that problem by diverting flow uniformly among the various Splitter box outlets.
Zoeller's Tru-Flow [D-box] Splitter system includes diverter adjustments that help you fine tune and balance the effluent flow among various drainfield sections. The system can handle varying septic flow rates depending on the number of openings in use in the "box" - that is, depending on the number of outlets and drainfield sections that are in use.
See our contact information for Zoeller at the reviewers section at the end of this article for a link to the Zoeller D-Box-Splitter for septic effluent distribution system information.
Watch out: Zoeller warns that if you use this device, which does a more careful job of routing effluent among the different drainfield branches, it is clog-prone if you don't include a septic filter in the system at the effluent outlet end. Indeed, an effluent filter will protect and extend the life of any drainfield and its components.
Question: Clogged D-box Repair Procedures?
I have a system with a pump station that pumps gray water uphill about 50 yards. Today I noticed water percolating out of the ground near my drain field. I started digging and found what I assume is the d box. It was packed full of roots and the plastic seal around the pipe coming from the pump had been pushed out by the roots. I removed the roots but I could not remove the seal from the box. It has 5 more holes in it which 4 are closed and the other has a pipe leading to another concrete box 4-5 feet further out. The second box is much deeper than the first. It appears that the pipes T out after the first box. More digging tomorrow. I ran the pump after replacing the lid and packing dirt around the pipe but it just came out of the box instead of going through the system. The downstream pipe is open.
Question: one side of my fields never dries out, we installed speed levelers and a new D-box. Should we cap off the wet area lines?
I have 8 lines coming off my d box. my yard is slightly pitch to one side. that side also sees most of the rain water. The surface never seems to fully dry like my other lines. speed levelers were installed when the dbox was replaced. should those 2 lines be capped and shut off for a while to regain a better saturation point? i you, JB 5/10/12
Question: 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
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
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 chedk the yard and there is standing water anywhere. Does diging up the D box sound correct. Or sholuld they just check for a clog? - John 6/26/12
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 efflent entering and flooding the box then we figure the outlet lines and drainfield are either blocked or saturated.
Start a more throughou 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: Repairman says hard water will ruin my water treatment system and drainfield
xI have hard water and treat it with a culligan system. My neighbor had a title five and needed to have his D-box replaced to pass. The repairman said the whole street will have the same problem because of hard water will my treated water system help or hurt my system - Kevin 9/29/12
How do they test for Title 5?
And it doesn't quite make sense to me for your repairman to say that hard water will damage your water softener. The purpose of the water softener is to treat hard water. That's its job.
Questions & answers or comments about septic system D-box installation, inspection, troubleshooting, and repair or replacement.
Ask a Question or Enter Search Terms in the InspectApedia search box just below.
Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.