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Septic system D box inspection, diagnosis, and repair: here we descr ibe the best procedures for locating and inspecting, repairing or replacing the septic drainfield distribution box, or the "D-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?

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INSPECTING THE D-BOX - Inspecting the Septic System Distribution Box

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.

Signs of D-Box Trouble, Advice on Repairs

Question: Tipped septic effluent distribution box, standing water at end of one leach line

I am being told that my D box is bad. When no levelers are in place all effluent runs into only one port. I have been told that the way that fitting is angled down low and how it comes in angled is bad. It is making me worried. I am essentially being old that it should be redone. We have Type III soils, very sandy with 2 - 75' long infiltrators. Three years ago during the wet season I noticed some standing water at the end of one of the laterals. It was the lateral that receives all the effluent when no levelers are in place. - Nicholas Day

Reply:

We were not sure from the two photos but the D-box looks small, and as if it has been invaded by sewage (suggesting the tank was not pumped on schedule or your tank baffles may be bad).

It also looks as if there are 2 effluent outlets, one with an adjustable flow limiter - that cap with a small opening, and a second with an elbow pointing down.

It looks as if the elbowed line was supposed to take more effluent or take it first - as an attempt to control how different drainfield sections were loaded.

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 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.

1. The soils around the septic field may be saturated with groundwater, flooding the drainfield and backing up and out through the D-box cover. Just sealing the cover wouldn't fix anything in this case. You'd need to divert groundwater away from the drainfield.
2. The septic drainfield or leaching beds may be saturated from having become clogged - at end of life. If this is the case the backup of effluent is occurring because the soil is no longer absorbing effluent. You'll need to investigate to decide if the problem is a blocked or damaged or clogged drainfield line or if the whole field needs replacement.

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:

- running a snake or probe from the septic tank outlet until it stops will give the distance to the D-box (probably)

- look for a depression in the ground a couple of feet in diameter and between the septic tank and the drainfield.

- Look at the site layout for where the D-box could possibly be located. For example, if the drainfield site is level and rectangular, the D-box would typically be at or near the edge of the drainfield closest to the septic tank.

See SEPTIC DRAWINGS for some sketches that give an idea where the distribution box is typically found.

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.

A "kiltered" Dbox is lingo for a "tipped distribution box". As you can read above, the D-box is basically a plumging junction box that receives incoming effluent from the septic tank and routes it out to multiple drainfield lines where the effluent can be further treated and absorbed into the ground. If the D-box is "tipped" that means it's sending too much effluent down just one line (perhaps flooding it) and not enough effluent down other lines (not using them).

Also if surface runoff or ground water is leaking INTO your D-box, that water will add to the septic effluent liquid load and risks flooding and ruining the drainfields.

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?
I have excavated the box and there is a plastic bottom to it, the waste water is flowing into the fields evenly - Dave Brannen

Reply: yes but just in emergency - it's better to replace and set the D-box properly

Dave,

While you could just connect the effluent line from the septic tank directly to one or more drainfield lines using tees and elbows, what is lost by that approach is the ability to

- adjust or change the amount of effluent flow among drainfield lines in order to rest a line, avoid a low line that tends to flood, or otherwise balance effluent flow

- inspect the system for signs that one or more leachfield lines is in trouble

- assure that flow is properly balanced among the various drainfield lines

You have to figure that builders and septic installers don't waste time and money on components - there was a reason for the D-box in the first place. So while I agree that in an emergency, to keep the septic system in use, it's ok to make a TEMPORARY connection such as you describe.

But because your D-box is not deeply buried, because D-boxes are not expensive, and because they serve a useful purpose, the proper repair is to replace the damaged distribution box, set the new one to the proper depth, make sure it's level, and then install and set effluent flow balancing devices at the entry to each of the leach lines fed out of the D box.

Questions & Answers regarding this article

Questions & answers about septic system D-box installation, inspection, troubleshooting, and repair or replacement.

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  SEPTIC D-BOX INSPECTION

• Readers of this page should also see System Design Regulations 75-A.7 Distribution lines, distribution boxes, gravity flow, pressure distribution, dosing, siphons design specifications for septic systems.
• Thanks to reader Nicholas Day for discussing D-box troubles and repairs, September 2010

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
• Inspecting Septic Systems: Online Book, Inspection, Test, Diagnosis, Repair, & Maintenance: our Online Septic Book: Septic Testing, Loading & Dye Tests, Septic Tank Pumping, Clearances, details of onsite waste disposal system inspection, testing, repair procedures.


• Advanced Onsite Wastewater Systems Technologies, Anish R. Jantrania, Mark A. Gross. Anish Jantrania, Ph.D., P.E., M.B.A., is a Consulting Engineer, in Mechanicsville VA, 804-550-0389 (2006), Advanced Onsite Wastewater Systems Technologies. Outstanding technical reference especially on alternative septic system design alternatives. Written for designers and engineers, this book is not at all easy going for homeowners but is a text we recommend for professionals--DF.
• AEROBIC SEPTIC SYSTEMS
• Builder's Guide to Wells and Septic Systems, Woodson, R. Dodge: $ 24.95; MCGRAW HILL B; TP; Quoting from Amazon's description: For the homebuilder, one mistake in estimating or installing wells and septic systems can cost thousands of dollars. This comprehensive guide filled with case studies can prevent that. Master plumber R. Dodge Woodson packs this reader-friendly guide with guidance and information, including details on new techniques and materials that can economize and expedite jobs and advice on how to avoid mistakes in both estimating and construction. Chapters cover virtually every aspect of wells and septic systems, including on-site evaluations; site limitations; bidding; soil studies, septic designs, and code-related issues; drilled and dug wells, gravel and pipe, chamber-type, and gravity septic systems; pump stations; common problems with well installation; and remedies for poor septic situations. Woodson also discusses ways to increase profits by avoiding cost overruns.
• Country Plumbing: Living with a Septic System, Hartigan, Gerry: $ 9.95; ALAN C HOOD & TP; Quoting an Amazon reviewer's comment, with which we agree--DF:This book is informative as far as it goes and might be most useful for someone with an older system. But it was written in the early 1980s. A lot has changed since then. In particular, the book doesn't cover any of the newer systems that are used more and more nowadays in some parts of the country -- sand mounds, aeration systems, lagoons, etc.
  

Onsite Wastewater Disposal Books

• Onsite Wastewater Disposal, R. J. Perkins; Quoting from Amazon: This practical book, co-published with the National Environmental Health Association, describes the step-by-step procedures needed to avoid common pitfalls in septic system technology. Valuable in matching the septic system to the site-specific conditions, this useful book will help you install a reliable system in both suitable and difficult environments. Septic tank installers, planners, state and local regulators, civil and sanitary engineers, consulting engineers, architects, homeowners, academics, and land developers will find this publication valuable.
• Onsite Wastewater Treatment Systems, Bennette D. Burks, Mary Margaret Minnis, Hogarth House 1994 - one of the best septic system books around, suffering a bit from small fonts and a weak index. (DF volunteers to serve as indexer if Burks/Minnis re-publish this very useful volume.)While it contains some material more technical than needed by homeowners, Burks/Minnis book on onsite wastewater treatment systems a very useful reference for both property owners and septic system designers. We refer to it often. While Minnis says the best place to buy this book is at Amazon (our link at left), you can also see this book at Minnis' website at http://web page .pace.edu/MMinnisbook
  
• Septic Tank/Soil-Absorption Systems: How to Operate & Maintain [ copy on file as /septic/Septic_Operation_USDA.pdf ] - , Equipment Tips, U.S. Department of Agriculture, 8271 1302, 7100 Engineering, 2300 Recreation, September 1982, web search 08/28/2010, original source: http://www.fs.fed.us/t-d/pubs/pdfimage/82711302.pdf
• Soil Percolation Tests soil perc testing guide and instructions
• Percolation Testing Manual, CNMI Division of Environmental Quality, PO Box 501304, Saipan, MP 96950
• Planting Over Septic System Component", Daniel Friedman (author/editor, InspectAPedia.com), The Innovator, Winter/Spring 2008, BCOSSA, British Columbia OnSite Sewage Association, 201-3542 Blansard St., Victoria BC V8X 1W3 Canada
• Save the Septic System - Do Not Flush These Items Down the Toilet, Daniel Friedman, InspectAPedia.com - PDF document, printable
• SEPTIC STANDARDS
• SEPTIC MAGAZINES
  
• Septic System Owner's Manual, Lloyd Kahn, Blair Allen, Julie Jones, Shelter Publications, 2000 $14.95 U.S. - easy to understand, well illustrated, one of the best practical references around on septic design basics including some advanced systems; a little short on safety and maintenance. Both new and used (low priced copies are available, and we think the authors are working on an updated edition--DF. Quoting from one of several Amazon reviews: The basics of septic systems, from underground systems and failures to what the owner can do to promote and maintain a healthy system, is revealed in an excellent guide essential for any who reside on a septic system. Rural residents receive a primer on not only the basics; but how to conduct period inspections and what to do when things go wrong. History also figures into the fine coverage.
• Test Pit Preparation for Onsite Sewage Evaluations, State of Oregon Department of Environmental Quality, Portland OR, 800 452-4011. PDF document. We recommend this excellent document that offers detail about soil perc tests, deep hole tests, safety, and septic design. Readers should also see Soil Percolation Tests and for testing an existing septic system, also see Dye Tests
• Grass is Always Greener Over the Septic Tank, Bombeck, Erma: $ 5.99; FAWCETT; MM; This septic system classic whose title helps avoid intimidating readers new to septic systems, is available new or used at very low prices. It's more entertainment than a serious "how to" book on septic systems design, maintenance, or repair. Not recommended -- DF.
  
• US EPA Onsite Wastewater Treatment Systems Manual Top Reference: US EPA's Design Manual for Onsite Wastewater Treatment and Disposal, 1980, available from the US EPA, the US GPO Superintendent of Documents (Pueblo CO), and from the National Small Flows Clearinghouse. Original source http://www.epa.gov/ORD/NRMRL/Pubs/625R00008/625R00008.htm
• Water Wells and Septic Systems Handbook, R. Dodge Woodson. This book is in the upper price range, but is worth the cost for serious septic installers and designers. Quoting Amazon: Each year, thousands upon thousands of Americans install water wells and septic systems on their properties. But with a maze of codes governing their use along with a host of design requirements that ensure their functionality where can someone turn for comprehensive, one-stop guidance? Enter the Water Wells and Septic Systems Handbook from McGraw-Hill.
  Written in language any property owner can understand yet detailed enough for professionals and technical students this easy-to-use volume delivers the latest techniques and code requirements for designing, building, rehabilitating, and maintaining private water wells and septic systems. Bolstered by a wealth of informative charts, tables, and illustrations, this book delivers:
  * Current construction, maintenance, and repair methods
  * New International Private Sewage Disposal Code
  * Up-to-date standards from the American Water Works Association
  
• Wells and Septic Systems, Alth, Max and Charlet, Rev. by S. Blackwell Duncan, $ 18.95; Tab Books 1992. We have found this text very useful for conventional well and septic systems design and maintenance --DF. Quoting an Amazon description:Here's all the information you need to build a well or septic system yourself - and save a lot of time, money, and frustration. S. Blackwell Duncan has thoroughly revised and updated this second edition of Wells and Septic Systems to conform to current codes and requirements. He also has expanded this national bestseller to include new material on well and septic installation, water storage and distribution, water treatment, ecological considerations, and septic systems for problem building sites.
  
• The NSFC Products List has an excellent list of design manuals/modules available from their website or by telephone 800-624-8301
• Submissions welcome. send us a suggested document link or request an exchange of website links
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