Over time, deep wells often become clogged with mineral deposits, which gradually restrict the inflow of water. The most common deposits are iron oxides, followed by manganese (hydric) oxides. These deposits can partially or fully block filter slots, increase drawdown and reduce specific capacity. This means that more energy and time are required to achieve the same yield. In practice, this often manifests as a well that ‘still runs’, but increasingly inefficiently until rehabilitation becomes unavoidable.
The High-Pressure Impulse Process (HPI-Process®) is designed for well development and rehabilitation using high-pressure water. Two pairs of nozzles rotate in two planes via water recoil, creating deep pressure waves that loosen deposits not only at the screen, but also in the filter gravel and the surrounding area. The mobilised material is simultaneously pumped out, enabling cleaning and discharge to occur as a coordinated process rather than as separate flushing steps.
Aichhalden’s municipal deep well 1 (Baden-Württemberg) was constructed in 1962 using OBO synthetic resin pressed wood pipes (DN 350) to a depth of about 98 metres. The well includes multiple filter sections (24–40 m, 45–55 m, 62–89 m and 94–96 m). Prior to rehabilitation, a camera inspection showed that the filter slots were partly or completely closed, primarily due to iron deposits. A short pump test conducted prior to the 2019 rehabilitation works indicated a specific capacity of 0.065 l/s per metre of drawdown, which is consistent with the well’s declining performance over time.
During the subsequent eight-hour HPI rehabilitation process, almost 1,700 litres of deposits were loosened and discharged. The treatment was carried out in three stages, with the withdrawal rate progressively increasing from 4.5 l/s to 7 l/s. To quantify the improvement, a follow-up three-hour short pumping test at 2 l/s was conducted, revealing a drawdown of only 4.64 m (compared to 30.72 m previously), a reduction of more than 26 metres.
Following rehabilitation, the well’s specific capacity increased to 0.431 l/s per metre of drawdown — an improvement of 563% compared to the pre-rehabilitation test. Compared to the original new construction reference of 0.061 l/s per metre in 1962, the performance corresponds to an increase of roughly 607%, i.e. about 600%. Notably, a prior rehabilitation in 1997 involving pistons, high-pressure internal flushing and HPI with gas had only partially restored the ‘new’ condition, highlighting how dosed impulse injection using HPI with high-pressure water can more effectively dissolve hardened deposits, even in older wells with less resistant screen materials.
