The problem addressed by the study is a gradual loss of well performance caused by chemical and mechanical clogging. Dissolved iron and manganese in groundwater can precipitate on pump components, screens, gravel packs and surrounding sediments, while fine particles may accumulate at the aquifer–gravel-pack interface. In Finland, these processes are especially relevant because soils can contain abundant iron and manganese, and clay-covered Quaternary aquifers commonly have low oxygen concentrations. Pumping can introduce oxygen-rich water into otherwise reducing conditions, promoting oxidation of dissolved ferrous iron and the formation of poorly soluble ferric oxides and hydroxides. The resulting deposits reduce the flow of water through screen slots and reduce the yield of the intake well.

The four wells investigated in the study had previously produced substantially higher yields and were selected because their performance had declined markedly. The sites differed in their geological setting, construction and degree of blockage. Wells 1 and 2 were located in esker formations, with partly unconfined aquifers containing sand, gravel and locally less permeable layers. Well 3 was situated in a large unconfined esker aquifer with several tens of metres of coarse gravel and sand and numerous kettle holes. Well 4 was located beside a river in an area covered by 5–15 m of clay, where bank infiltration and a sandy, gravelly esker deposit created a distinct hydrogeological environment.

Before treatment, camera inspections showed that the screens of all four wells were almost or completely blocked. Deposit composition was determined by semiquantitative X-ray fluorescence analysis of material collected from the well pipes and screens. Iron oxide represented 68–91.3% of the precipitates, accompanied by silicon dioxide at 4.43–10.6%, manganese oxide at 0.02–13.4% and phosphorus oxide at 0.31–3.96%. Manganese oxide was highest in well 4, at 13.4%, and was detected at only 0.02–1.42% in the sediments from wells 1, 2 and 3. The chemical pattern was consistent with the redox reactions that can immobilize iron and manganese in oxygen-poor groundwater, although the small number of sites means that the relative importance of each component cannot be generalized from these observations alone.

Mechanical rehabilitation came first. A closed-circuit, multi-chamber device circulated water through the well one metre of screen at a time, loosening and removing deposits without the use of a chemical agent. Loose and semi-loose material was pumped out, after which the screens were inspected by camera and the wells were tested again. The process left the screens moderately clean and largely opened their slots, while also reducing the need for chemical treatment. Its effect on well performance varied substantially: specific capacity improved by approximately 10% in well 2 and 59% in well 1 after mechanical cleaning. The larger increases were recorded in wells 3 and 4, where mechanical rehabilitation raised specific capacity by about 137% and 1,483%, respectively, relative to the initial measurements.

Chemical rehabilitation then targeted deposits that remained attached to the screens and extended into the surrounding formation. The treatment used a pH-neutral agent, AIXTRACTOR 2.0, whose reductant is sodium dithionite. By establishing strongly reducing conditions, the agent converts insoluble Fe(III) into soluble Fe(II) and insoluble Mn(III) or Mn(IV) into soluble Mn(II), allowing the precipitates to dissolve and be removed through post-treatment pumping. The working solution was introduced section by section through the circulating-flow system, with a reaction time of about 45 minutes for each section. Camera inspections after this stage showed clean screens, mostly fully open slots and clear water. The additional chemical-stage improvement in specific capacity ranged from 52% in well 2 to 329% in well 4 relative to the mechanically treated wells.

The combined treatment produced marked gains in all four wells. Specific capacity increased by 259% in well 1, 68% in well 2, 623% in well 3 and 6,692% in well 4 compared with the pre-rehabilitation tests. Well 3 provided the only opportunity to compare the measured performance with a documented construction yield: its original yield was 372 cubic metres per hour, but before rehabilitation it had fallen to about 12.5% of the original specific capacity, equivalent to an 87% decline after two years of operation. Mechanical and chemical rehabilitation restored that well to its original performance. Well 4, which had been almost completely blocked and remained unused for a long period, experienced the greatest recovery, supporting the authors’ observation that even severely clogged wells may be worth rehabilitating.

Rehabilitation temporarily altered the chemistry of the pumped water. During chemical treatment, electrical conductivity, sulphate and sulphite concentrations increased, while oxygen levels declined and the redox potential moved from oxidizing values toward zero or negative values. Dissolved iron and manganese also rose sharply as deposits dissolved, with total iron reaching 9,400 micrograms per litre in well 1, 10,400 in well 2, 17,000 in well 3 and 2,900 in well 4 after treatment. The response was not identical at every site: manganese changed little in well 2, decreased in well 3 and increased substantially in well 4. Monitoring at two observation wells near well 4 showed that the rehabilitation solution travelled downward toward the nearby observation well, while no detectable change occurred at a second well approximately 15 metres away.

The altered water was not intended for immediate supply. Post-treatment pumping continued for approximately two to three hours, with field measurements and test strips used to track iron, sulphite and electrical conductivity, until the water approached its pre-treatment condition. Sampling one to two hours after rehabilitation captured the period of greatest chemical impact, while monitoring over the following day showed that water quality returned to baseline levels. The treated water was transferred to a suction tank and sent to a sewage treatment plant. The investigators reported that the depleted treatment solution was not detected in the discharged water, while noting that the water could still contain trace elements released from the deposits during treatment.

The pilot has important limitations. Only four wells were studied, and their differing construction, clogging severity, sediment properties, groundwater chemistry and hydraulic settings prevented the researchers from identifying a single cause for the wide range of recovery rates. No long-term monitoring programme followed the rehabilitation, so the study could not establish how quickly the wells might reclog or how long their recovered performance would persist. The results are most applicable to unconfined, postglacial Quaternary deposits containing permeable sand and gravel, but they should not automatically be transferred to confined aquifers, different sediment structures or contrasting redox environments. The authors call for larger sampling campaigns, consistent pumping tests, longer follow-up and further investigation of how intermittent operation and oxygen influx drive clogging. Even with those qualifications, the pilot provides direct evidence that carefully monitored rehabilitation can recover productive capacity in severely clogged Finnish groundwater wells.

Subject of Research: Rehabilitation of iron- and manganese-clogged groundwater abstraction wells

Article Title: Mechanical and chemical rehabilitation of groundwater abstraction wells clogged by iron and manganese precipitates in Finland

Article References: Nygård-Hämäläinen, M., Korkka-Niemi, K., Kuosmanen, N., Puronpää-Schäfer, P., Hyötylä, S., Sarkonen, K., Friman, T., & Ikäheimo, J. (2026). Mechanical and chemical rehabilitation of groundwater abstraction wells clogged by iron and manganese precipitates in Finland. Hydrogeology Journal. https://doi.org/10.1007/s10040-026-03198-w

Image Credits: AI Generated

DOI: 10.1007/s10040-026-03198-w

Keywords: groundwater wells, well rehabilitation, iron precipitates, manganese precipitates, hydrogeology, mechanical cleaning, chemical treatment, water supply, Finland, redox chemistry, Mechanical, chemical