What’s a drywell?
A drywell is a type of absorption system (remember that a septic system is made up of a septic tank and then some sort of absorption system).
A drywell is usually a tall concrete cylinder with holes in the side and an open bottom (see above).
Drywell installation and how they work
Drywells are installed by digging a deep hole, usually near the septic tank, and setting the drywell in it. Gravel is usually dumped around the outside of the drywell and a lid put on top.
The drywell is then connected to the septic tank with piping (tile) and the whole thing is covered with soil. Effluent enters the drywell from the septic tank and then exits out the holes in the side and seeps into the soil that surrounds it..
Drywells were also constructed of brick. These were built as upside-down cone shaped structures constructed inside a large hole. Once completed, they were carefully covered up with soil (backfilled). Some have small lids at the top of this cone. This lid is often accessible from the ground surface for pumping, visual inspections or just gazing into for sheer delight.
I have had the pleasure of peering into many of these masonry marvels, some of which are ten feet deep and eight feet across at the bottom. This homemade variety has been known to cave in, sometimes swallowing garden tractors and their riders!
NOT a recommended activity (low fun factor).
Nowadays, drywells are seldom installed for use in septic systems but are often used in parking lots for the disposal of surface water. However, many drywells are still used in existing septic systems. Drywells don’t usually make up the entire field absorption system but instead are used in conjunction with other types of absorption fields like trenches.
No longer the chosen disposal method
Drywells are no longer legal to install in Indiana. Studies have shown that drywells have been big contributors to polluting the groundwater. Many of them were installed in sandy soils with high water tables. This allows the effluent to move directly into the ground water instead of first being treated by well drained soils. Ouch.
Dry wells are often set in parking lots to drain away surface water.