Even well-constructed drinking water wells lose capacity over time as deposits build up in the filter area and the surrounding formation, especially in groundwater containing iron and manganese where ochre formation can accelerate clogging. This results in reduced specific yield, higher operating costs and longer downtimes when conventional rehabilitation methods such as brushing, swabbing, surge plugging and chemical agents are used. ETSCHEL Brunnenservice GmbH addresses this challenge with a purely mechanical approach that targets deposits where they form: around the screen, filter gravel and the adjacent borehole wall.
Introduced by E+M Bohr (now ETSCHEL Brunnenservice GmbH) in 1991/92, the HPI Process uses water at roughly 100–550 bar, converting the energy into pressure-wave impulses rather than directing a continuous jet at the screen. In the original ‘UNINOZ®’ setup, two eccentrically arranged nozzle pairs rotate in opposite directions at approximately 7,000 rpm, creating impulse effects from pump pulsation and nozzle-arm rotation. Cavitation between the nozzles can also contribute to simultaneous disinfection, and the process is supported by controlled pumping and continuous up-and-down movement to transport the loosened material out of the well. The documented effective depth is said to reach several decimetres into the existing aquifer.
A major step forward was taken in 2017 with the launch of the patented MAXINOZ® rotary nozzle system. Unlike previous designs with fixed nozzle angles (typically 90°), the MAXINOZ® system allows the angles of the nozzle arms to be adjusted to match the geometry of the filter screen material. Using inclined and slanted nozzles increases the effective depth and improves the discharge of dissolved and loosened deposits by creating additional hydraulic waves. These benefits also translate to new-well development, such as filter cake removal and simultaneous desanding, without the need for chemicals.
A clear comparison is documented for well no. 1 Meringerzell (155 m deep, DN 400, steel Hagulit-coated bridge slotted screen with gravel coating), which was affected by ochre formation. In 2007, rehabilitation with UNINOZ® involved the mechanical removal of 251 litres of sand and 5,284 litres of sludge in nine hours, followed by an additional chemical treatment involving the use of approximately two tonnes of hydrochloric acid-based liquid and a gravel washer. In 2017, MAXINOZ® removed 1,200 litres of sand and 14,083 litres of sludge in 7.75 hours — about 4.8 times more sand and 2.7 times more sludge than the earlier mechanical method — while also reducing residual sand (from 1.3 to 1.0 cm³/10 litres) and increasing the specific yield by +61% compared to the 2007 mechanical method and +52% compared to the 2007 mechanical and chemical method. The evaluation concludes that additional chemical rehabilitation can be considered obsolete in this context, while avoiding the water-law approvals typically required for chemical measures.
For operators, the combination of higher solids extraction, stronger yield recovery and reduced administrative and operational burdens translates into tangible savings potential, while maintaining a controlled mechanical process that can be adapted to different well materials and ageing conditions, such as pressure, travel speed, nozzle distance and nozzle type. ETSCHEL Brunnenservice GmbH continues to apply and refine the HPI-Process® as a practical method for the rehabilitation and development of wells across a wide range of designs and deposit scenarios.
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If you would like to assess the rehabilitation potential of your well, ETSCHEL Brunnenservice GmbH can support you as an experienced specialist. Contact us to arrange a consultation and discuss next steps.
