A vadose zone recharge well works like a condensed drainage pit.

Adapted from the concept of dry wells that collect and disperse stormwater runoff in parking lots and other large paved areas to the underground, vadose zone recharge wells are dug in the unsaturated zone of sand and gravel material above the groundwater table, commonly known as the vadose zone. From there, reclaimed water percolates through clay, sand, gravel, and silt layers laterally and vertically into the groundwater aquifer (see drawing).

“While they require less space and are more cost-effective than surface infiltration basins, the wells can't be rehabilitated like other recharge technologies,” says Floyd Marsh, water resources manager and practice leader for the Phoenix office of Lockwood, Andrews & Newnam Inc. Well lifespan is estimated at five to 10 years.

Therefore, the water that's injected into the wells must be treated to very high levels—preferably Class A+ quality—to prevent clogging from particulates such as total suspended solids and total organic carbons. In addition to slowing infiltration, these materials lessen the well's effective life.

“The reclaimed water has a high nutrient load, which allows bacteria already in the soil to flourish,” says Gary Small of Phoenix-based HydroSystems Inc., which specializes in developing recharge solutions. “Disinfecting and filtrating at the surface helps to ensure that the water injected into these wells is of a very high quality.”

To achieve this objective, the project team recommended a filter that has 98% particle removal efficiency and provides a cost-effective solution with a small footprint.

Instead of a membrane, the AFR Series-8 internal backflushing filter from Eaton Filtration of Portage, Mich., uses a stainless steel wire mesh screen to filter suspended solids and micro-organisms down to 2 microns. Filters used in Surprise, Ariz.'s project will remove 5-micron particles at a removal efficiency of 98.6%.

Source: HydroSystems Inc.

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