thumb|Old drywell

A dry well or soak is a structure formed underground that disposes of unwanted water, such as surface runoff water and stormwater. In this process, the water is infiltrated into the ground, further merging with groundwater in the local area. Dry wells should typically be anywhere from 30–100 feet deep, with a width of 3–6 feet at the surface. For safety cautions, the dry wells must be placed at a distance away from property lines, basements, and any foundations. They provide high stormwater infiltration capacity while also having a relatively small footprint.

A dry well receives water from entry pipes at its top. It can be used as part of a stormwater drainage network, an agricultural well drainage system or on smaller scales such as collecting stormwater from building roofs. It is used in conjunction with pretreatment measures such as bioswales or sediment chambers to prevent groundwater contamination.

The depth of the dry well allows the water to penetrate soil layers with poor infiltration such as clays into more permeable layers of the vadose zone such as sand.

Simple dry wells consist of a pit filled with gravel, riprap, rubble, or other debris. Such pits resist collapse but do not have much storage capacity because their interior volume is mostly filled by stone. A more advanced dry well defines a large interior storage volume by a concrete or plastic chamber with perforated sides and bottom. These dry wells are usually buried completely so that they do not take up any land area. The dry wells for a parking lot's storm drains are usually buried below the same parking lot. A French drain can resemble a horizontal dry well that is not covered. A larger open pit or artificial swale that receives stormwater and dissipates it into the ground is called an infiltration basin or recharge basin. In places where the amount of water to be dispersed is not as large, a rain garden can be used instead.

See also

References

  • DRYWELLS, Environmental Services, City of Portland, OR
  • New Jersey Stormwater - Best Management Practices Manual, Chapter 9.3 Standard for Dry Wells, February 2004
  • Philadelphia Watershed, Dry Well, Philadelphia Water Department
  • Water Quality Division: Permits: Drywell Registration, Arizona Department of Environmental Water Quality
  • Non-residential drywells are regulated in the U.S. to protect drinking water sources - U.S. Environmental Protection Agency
  • Photos of a reinforced concrete drywell installation
  • Photos of Australian Soakwell Installation