Use a Drywell for Graywater or Roof Drainage or Stormwater Disposal
DRYWELL DESIGN & USES - CONTENTS: What is a drywell or "septic drywell", seepage pit, and how is it different from a cesspool?How are drywells or seepage pits constructed? What care is needed for a drywell? Do we need to filter wastewater entering a drywell? What is the failure criteria for a drywell?
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Drywell or seepage pit construction & uses: this document explains what a drywell (or seepage pit) is, describes how drywells are used, gives safety and maintenance advice for drywells, and defines the
criteria for drywell failure.
What are Septic Drywells, What Drywell Maintenance is Needed? How do Drywells Fail?
We warn readers that while installation of a drywell to receive graywater at a property may be a good idea, the use of drywells for this purpose may be a warning about the capacity and remaining life of the septic system.
We use the terms "drywell" and "seepage pit" differently as follows:
DRYWELLS for GRAYWATER - Drywells as Graywater Disposal Facilities
A drywell or seepage pit,
sometimes called a leaching pit, leaching pool, or incorrectly a cesspool,
is a covered pit with an open-jointed or perforated lining through which septic tank
effluent seeps into the surrounding soil.
In other words this is one of the oldest and simplest methods of disposing of gray water or in some cases septic effluent -
a simple pit or hole in the ground, open to soil at its sides and bottoms, intended to receive and dispose of gray water (water from
building non-sewage drains such as laundry, showers, sinks).
A drywell, or "seepage pit" is used at some building sites to receive "gray water" from a laundry, sink, or shower.
may be site-built of stone or dry-laid concrete block, rubble-filled, or constructed of (safer) pre-cast concrete.
may also be sold as pre-designed units constructed of fiberglass or plastic. A drywell design
may be similar to that of a cesspool, but only gray-water and not sewage is discharged into a drywell. The hole or absorption pit is typically 6-8 feet deep and 4-10 feet square (or round) depending on the amount of drainage to be handled and the
percolation rate of the soil.
Some drywells were filled with large rubble. A top of concrete or stone slab is used to keep surface water and children out
of the opening, and is usually covered and graded to be invisible in the yard. Older covers of wood or steel may be very unsafe and
present a child or adult hazard, possibly including the risk of fatality. Mark off, prevent access to, and investigate such systems immediately.
What's the difference between a seepage pit or drywell and a cesspool?
The term "drywell" or "seepage pit" might be used by some people to describe a simple pit
for disposing of septic effluent. Note that I said effluent not sewage.
By contrast, a cesspool holds both solid waste and septic effluent.
I use the term "seepage pit" to refer to a pit used to dispose of septic effluent
which originated as blackwater, the solids having been retained in the septic tank.
I use the term "drywell" to refer to a pit used to dispose of graywater (greywater)
which originated in sinks, laundry facilities, or showers. While their uses and
implications of their presence at a property are quite different, the actual construction
details of a seepage pit or a drywell are about the same. Let's sum up the use
of these terms being rather particular:
Drywell: a hole in the ground intended to receive graywater from sinks, showers, or even roof or surface runoff. It
may be site-built using stone or concrete block, or it may be constructed of pre-cast concrete buried in a pit and surrounded
by gravel to increase its capacity.
Seepage pit: a hole in the ground intended to receive septic effluent such as the outlet from a septic tank.
Seepage pits may be permitted where site space or soil conditions do not permit a conventional leach field. However even
if effluent is successfully "disposed-of" it is probably not being adequately treated if it's coming out of a conventional
septic tank. A Seepage pit might be constructed just as the drywell above but it is likely to require different (larger) site clearance
Cesspool: a hole in the ground intended to receive sewage or blackwater from a building. The cesspool may also
receive graywater, or in order to reduce the loading of the cesspool, some buildings may direct their graywater to a separate
drywell. The cesspool might be constructed just as the two systems above but may have different site clearance
Why are drywells installed?
A drywell is used at a property typically for these reasons
To relieve the liquid load on an onsite waste disposal septic system leach field, particularly in an area where the leach field
is in trouble, at or near the end of its life, or has very limited capacity to dispose of effluent
To receive gray water from a building plumbing fixture (laundry or sink) which has been installed at a location so remote
from the main house drain (to the septic system) that it is more convenient to construct a separate, nearby outside facility
to receive this graywater than to route an indoor or outdoor buried rain to the existing septic system.
(Readers are invited to send additional suggestions)
Tips for Extending Drywell Life
Some experts recommend installing a filter on water entering the drywell. Particularly for a drywell
used to receive water from a clothes washing machine, installing a lint filter between the washing machine
and the drywell can extend the life of the drywell by reducing the moment of soil-clogging particles of
lint and debris into the system.
Intermittent dosing systems such as are used for some alternative septic system designs, can also be adapted
to graywater systems. In simple terms, this means that multiple drywells are used, and graywater is routed
intermittently among them, giving the unused drywell time to recover. A simple valve system on the
graywater drain line can serve
to route greywater (graywater) to alternating drywells.
Cesspools for more in-depth information about those systems.
Using Drywells & Catch Basins for Basement Waterproofing
Reader Question: The drywell at my new home stays full of water and my house floods: who is responsible for the repair?
I bought a new construction home in Staten Island, NY. Unfortunately my garage and side apartment have flooded twice last month due to the heavy rainfall.
The gutter downspouts and sump pump are being led to the drywell however it is overflowing at all times and is not taking on any new water.
Even the catch basin is filled with water and will never completely drain into the drywell. to temporarily try to resolve this issue I have removed all downspouts and sump pumps out of drywell and are now draining onto my property which inevitably is flooding but better outside my home than in my home.
It is new construction and I am basically looking for a little advice on whether this is a structural defect and builder should be responsible for this or is it going to fall on me and how can this be properly fixed.
Staten Island, NY
Reply: For your site the drywell may have never been a workable solution to handling runoff; real estate attorney should review your contract of sale and advise about the new home warranty law
Was the Drywell a Usable Solution for your Building Site?
At ARE DRYWELLS DRY? we express the view that in some areas of high water table and wet soils, a drywell is not likely to be a useful means of collecting and disposing of surface or roof runoff in wet weather. That's because in those areas the "drywell" is in fact wet, or flooded, or at least partially flooded seasonally if not all year long.
From your description it sounds as if one or more of these problems underlies the flooding problem in your new home
The site is one that has a high water table, keeping the drywell flooded - this seems most likely from your description.
The drywell was improperly constructed, too small, or lacking proper site preparation, for example by setting a pre-cast drywell into a pit without adequate pit size or adequate gravel
Groundwater, surface runoff, or roof runoff directed into the drywell are of much larger volume than anticipated.
Who is Responsible for Groundwater, Roof Runoff, or Flooding in a New Home
This question is an ugly morass that is unfortunately all too common in new construction projects, and it is one that needs assistance from an attorney expert in real estate law and familiar with local building codes in your neighborhood.
Our photo ( left) shows a combination that is a near guarantee of a flooded basement: the builder constructed the deck before final site grading, leaving in-slope grade and a virtual pool under the deck and draining towards the home. And gutter improprieties send water running down the house wall during rain.
In general one would expect that proper construction of a new home would include taking whatever means were necessary to protect the home interior from water entry.
And one would wish that initial site investigation (for questions such as where is the water table?) and building code approval would have reviewed any special water or drainage requirements that the builder needed to meet.
Some new home construction contracts excuse the builder from certain home waterproofing steps, explicitly or implicitly leaving those responsibilities up to the homeowner. And unfortunately some new homeowners are unaware that those additional steps are not optional if the home is to be protected from flooding.
When the home floods at the first rain, or when it floods three years later after footing drains have become clogged with silt, the owner and builder end up in a finger-pointing contest that might have originated in the these two basic questions, even if other site water problems are absent:
No gutter system? A common example of ambiguity that leads to home flooding that we encounter is the omission from the construction contract of any provision for roof drainage management: gutters and leaders.
The builder leaves that "detail" up to the homeowner and may even excuse themselves from responsibility for future home flooding if that detail is not addressed by the owner. And it's fair to say that it is a homeowner responsibility to keep the gutters and downspouts clean and working.
Poor final site work? A second common source of new house flooding that crops up is a new home contract that is unclear about what constitutes rough grading versus final landscaping. The builder accepts responsibility for "rough grading" and explicitly leaves "landscaping" to the new owner.
But the new owner and the builder may have different ideas about what those terms mean. A builder might leave the ground around the building very uneven, with local low areas or even in-slope grade that drains towards the building, while the buyer thought that they'd have a properly sloped and graded lawn that just needed a sprinkling of grass seed to be complete.
When a new home site combines both problems 1 and 2 above, there is a very high risk of basement or crawl space water entry and ultimately flooding. Just how quickly flooding appears depends further on other site conditions:
Area water table level
Degree to which surface runoff is directed onto this particular building site
Adequacy of foundation drainage or even, as we find at some homes, its complete omission
The overall terrain shape: is the home in a low spot or depression or at the bottom of a hill? Is the entire area dead flat with no place to send runoff? Is there a storm drain system into which surface and subsurface runoff may be directed?
Some possible solutions to the Flooded Drywell Problem
Your question does not include information about your neighborhood and site nor specifics about the home. But it may be useful to start by asking:
Does an inspection of the drywell show that it is properly constructed?
Is there a storm drain system into which the flooding drywell can be pumped? If so, is that pumping permitted in your municipality?
Exactly where and how is water entering to flood the home?
Is there a working roof drainage system that directs roof spillage well away from the home? Gutters and downspouts might be installed but not working properly, or a mistake like using perforated downspout extensions might be sending water back to the foundation.
Do other homes in the immediate neighborhood also have flooding problems? If not, what's different in the dry homes?
Interior basement de-watering system (photo at left) ? This last resort, if not properly installed, could still leave excessive interior moisture and contribute to a mold contamination problem.
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Biomat Formation in the Septic System Drainfield Absorption System - what leads to drain field clogging and expensive drainfield repairs
TOILETS, DON'T FLUSH LIST these things into a septic system: a list of what's ok and what's not ok to put into septic tanks and building drains
 Pennsylvania State Fact Sheets relating to domestic wastewater treatment systems include
Pennsylvania State Wastewater Treatment Fact Sheet SW-161, Septic System Failure: Diagnosis and Treatment
Pennsylvania State Wastewater Treatment Fact Sheet SW-162, The Soil Media and the Percolation Test
Pennsylvania State Wastewater Treatment Fact Sheet SW-l64, Mound Systems for Wastewater Treatment
Pennsylvania State Wastewater Treatment Fact Sheet SW-165, Septic Tank-Soil Absorption Systems
Document Sources used for this web page include but are not limited to: Agricultural Fact Sheet #SW-161 "Septic Tank Pumping," by Paul D. Robillard and
Kelli S. Martin. Penn State College of Agriculture - Cooperative Extension, edited and annotated by
Dan Friedman (Thanks: to Bob Mackey for proofreading the original source material.)
 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.
 "How to Maintain Your Septic System", Alaska Department of Environmental Conservation, Division of Water, retrieved 8/8/12, original source: http://dec.alaska.gov/water/wwdp/onsite/maintain_septic.htm [copy on file as Alaska_Septic_Care.pdf]
 Installers Manual for Conventional Onsite Domestic Wastewater Treatment and Disposal Systems", Alaska Department of Environmental Conservation, Division of Water, retrieved 1/15/2001, original source: [copy on file as Alaska_Certified_Installer's_Manual.pdf]
US EPA Onsite Wastewater Treatment Systems Manual [online copy, free] 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 Onsite wastewater treatment and disposal systems,
Richard J Otis, published by the US EPA. Although it's more than 20 years old, this book remains a useful reference for septic system designers.
U.S. Environmental Protection Agency, Office of Water Program Operations; Office of Research and Development, Municipal Environmental Research Laboratory; (1980)
"International Private Sewage Disposal Code," 1995, BOCA-708-799-2300, ICBO-310-699-0541, SBCCI 205-591-1853, available from those code associations.
"Manual of Policy, Procedures, and Guidelines for Onsite Sewage Systems," Ontario Reg. 374/81, Part VII of the Environmental
Protection Act (Canada), ISBN 0-7743-7303-2, Ministry of the Environment,135 St. Clair Ave. West, Toronto Ontario M4V 1P5 Canada $24. CDN.
Manual of Septic Tank Practice, US Public Health Service's 1959.
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. 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.
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
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.
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.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
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). 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 I recommend for professionals--DF.
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.
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