This document explains why drywells or seepage pits in many areas simply do not work, or do not work reliably all year round due to seasonal high water tables and flooding.

We include suggestions on protecting seepage pits and drywells from ground water and flooding in order to extend their life. This material is a chapter of our Septic Systems Online Book: This document explains septic system inspection procedures, defects in onsite waste disposal systems, septic tank problems, septic drainfield problems, checklists of system components and things to ask. Septic system maintenance and pumping schedules.

Are "Drywells" really "Dry"? - Flooding Seepage Pits Stop Working

No. In many areas "drywells" are a misnomer since during wet weather as water tables rise, the drywell "pit" is not very dry and in fact may fill up with water and simply stop working.

In wet areas of the Northeastern U.S., for example, we disagree with the practice of "solving" a roof drainage disposal problem at a flat site by building a "drywell" since in our experience these fail rather soon and in some cases even fill up and work backwards, sending water back to a building footing drain or roof drainage system where water then leaks into the building!

Worse, if the "drywell" was buried close to the building foundation wall it may actually serve as a conduit, sending water against the building foundation and actually into the building.

If soil and site conditions are adequate for absorption trenches, seepage pits shall not be used.

A minimum three foot vertical separation must exist between the bottom of any pit and the high groundwater level, bedrock, or other impervious layer.

Below we suggest keeping surface runoff and subsurface groundwater away from your seepage pit or drywell to keep it working.

More Reading:

• Biomat Formation in the Septic System Drainfield Absorption System - what leads to drain field clogging and expensive drainfield repairs
• SEPTIC & CESSPOOL SAFETY Septic System, Septic Tank, & Cesspool Safety Warnings for Septic Inspectors, Septic Pumpers, and Homeowners
• Cesspools for onsite wastewater disposal
• Drywells for onsite wastewater or graywater disposal
• 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
• Tank Location - How to Find the Septic Tank, how deep will the cover be, how to document its location - these methods also apply to locating a cesspool or drywell at a property.
• Inspecting & Testing 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.
• Dye Tests: how to perform a Septic Loading and Dye Test - septic dye testing procedures in complete detail, a septic function test - a chapter in the above book.

Tips for Extending a Drywell or Seepage Pit Life & Protecting them from Flooding

Direct surface runoff away from the seepage pit or drywell, including both on-surface water that can be controlled by a swale or intercept drain, and also ground-water that may require a deeper intercept drain conducting surrounding groundwater to a safe destination at least 20' away from the pit.

Also see Clearances for Septic Components Required - Well distance to Septic, Septic clearance from well, trees, lakes, streams, property boundary, etc.

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.

Also see SINKHOLES, WARNING SIGNS.

Citation of this article by reference to this website and brief quotation for the sole purpose of review are permitted. Use of this information in electronic form, in books or pamphlets for sale is reserved to the author.

Key Drywell & Cesspool Articles

• CESSPOOLS
• CESSPOOL FAILURE CRITERIA
• CESSPOOL AGE ESTIMATES
• CESSPOOL SAFETY WARNINGS
• CISTERNS, WATER STORAGE
• DRYWELL DESIGN & USES
  • DRYWELL SAFETY CONCERNS
  • DRYWELLS ARE THEY ACTUALLY DRY?
  • DRYWELL / SEEPAGE PIT SPECIFICATIONS
  • DRYWELL / SEEPAGE PIT CONSTRUCTION DETAILS
  • DRYWELL / SEEPAGE PIT COLLAPSE or FAILURE
• GREYWATER SYSTEMS
• SEEPAGE PITS
• SEPTIC TANKS - home

...

Continue reading  at DRYWELL / SEEPAGE PIT SPECIFICATIONS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

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DRYWELLS ARE THEY ACTUALLY DRY? at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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