Dry well septic could refer to a dry well being transformed into either a cesspool or seepage pit. In most parts of the country, cesspools are prohibited by health regulations and building codes, while seepage pits may be allowed under circumstances. It can also refer to an absorption pit to catch rain runoff to prevent problems with a traditional system.
Cesspools
Cesspools were common many years ago and essentially consist of a cylindrical pit in the ground that is lined with loose brick, stone or concrete and surrounded with gravel, closed, and covered with dirt. Some form of pipe carries sewage into the cesspool where water is allowed to filter out through the gravel. In modern terms, the cesspool functioned as both the tank and the drain field.
As you can imagine, even our modern systems don’t function perfection, so a cesspool was highly prone to failure. Since grease and solids are both allowed into the cesspool, they would quickly clog up the surrounding gravel and soil leading to the necessity of pumping often; however, since waste management wasn’t well understood in the past, a full cesspool might be abandoned in favor of building a new one. Since cesspools are dug straight into the ground, they would typically be too close to the ground water and could lead to serious outbreaks of various diseases.
Currently, some old cesspools are still in use, and if they’re maintained by modern standard, can still function somewhat adequately; however, most local governments aren’t going to permit a dry well septic to cesspool conversion. If a conversion is undertaken, there could be big fines, and the property might be hard to sell in the future. If a cesspool is built from a dry well, at minimum, it shouldn’t be in porous soil, any closer than 4 feet to ground water, and downhill and distance from water supplies.
Seepage Pits
Seepage pits are very similar in construction to cesspools but serve a different function. Similar to the cesspool, the seepage pit has porous walls that are strong enough to maintain the inner space with gravel along the outside to allow only water to penetrate. The main difference is a seepage pit is used in conjunction with a septic tank, while a cesspool is not. In modern terms, whereas the cesspool was tank and drain field; the seepage pit is used with a separate tank and functions as a sort of vertical drainfield.
Seepage pits suffer from the same potential problems as a drainfield, like being clogged with grease and small solids. As opposed to a drainfield, seepage pits use less property and aren’t as heavily affected by rain; however, they’re usually considered inadequate because they don’t make efficient use of surrounding soil and can release contaminated effluent too close to the ground water supply.
Well Conversion
A conversion to a seepage pit might work in arid parts of the US like the southwest where the groundwater is so deep that the effluent from the seepage pit has enough soil to percolate through and disinfect before reaching the groundwater. So far, I haven’t been able to find detailed construction plans for a dry well septic. If I find some I’ll post them, so please check back.