Can wells in the vadose zone be backflushed to regain infiltration capacity? Concept and laboratory test.

Vadose zone wells (VZW), or drywells, allow for high infiltration rates combined with small area demand. Nevertheless, they are rarely used for managed aquifer recharge, since turbid water leads to gradual clogging and a reduction in infiltration capacity. Established redevelopment measures require backflushing, which is commonly considered impossible for VZWs, making them "non regenerable". In this study, the possibility of backflushing a VZW is discussed. Key to the underlying approach is isolating the lower (clogged) section of a well and saturating its surrounding with water by infiltration via the upper (unclogged) screen. Subsequently, underpressure sucks water from the surrounding soil into the isolated section. The approach was tested with and without a gravel pack, on laboratory scale, showing a successful reversal of flow direction in both cases. The degree of redevelopment was quantified by measuring the drainage time of the well, which increased from initially 45 s without gravel pack and 40 s with gravel pack to 9,500 and 11,000 s, respectively, after clogging. After backflushing, the well with gravel pack showed a median drainage time of 95 s, which remained stable over ten cycles of clogging and backflushing. In contrast, drainage time of the well without gravel pack increased continuously to >170 s, even after vibrator application. In conclusion, it can be stated that the backflush of a VZW with the presented approach is possible and has an effect on the well's infiltration capacity, though it seems more effective for wells with gravel pack. [ABSTRACT FROM AUTHOR]