Why manganese often remains after iron improves

Had a project recently that had high levels of iron oxides and manganese in a bore and two large pipelines. This is a look at the followup testing on the job.

Manganese is slower to:

1. Oxidise – reactions require higher ORP (oxygen/chlorine demand),

2. Precipitate – forms finer particulates that take longer to purge,

3. Break from biofilm – IRB and Manganese Related Bacteria hold manganese more tightly in structure,

4. Clear from the gravel pack – it is often deeper in the fouling matrix than iron.

So progress is not linear: Iron drops first, manganese follows.

Recommended Adjustments to On-Site Strategy

1. Continue purge cycles

Same approach as before: 2–3 hr purge blocks + field test strip checks.

2. Increase ORP to target manganese

If chlorine was dosed at ~20 mg/L available chlorine, you may consider a top-up dose at 10–15 mg/L to lift oxidation potential for manganese.

If available on site, ask council operators to check ORP (mV):

ORP	Expected Behaviour
+250 to +350 mV	Iron oxidation zone
+400 to +600 mV	Manganese oxidation becomes effective

3. If manganese plateaus, consider:

A short follow-up using either:

• BoreSaver EZ Eco (milder organic acid/chelating removal), or

• BoreSaver Ultra C low-dose (if heavy Mn and biofilm are still evident)

Not required yet—only if manganese refuses to move after the next purge/chlorination cycle.

Manganese Outcomes and Further Management

4.1 Post-treatment results

Following BoreSaver Ultra C PRO rehabilitation, subsequent purging and in-bore chlorination, ALS post-treatment samples indicate:

• Iron (Fe) has been reduced to below the laboratory reporting limit (<0.05 mg/L) in both production bores.

• Manganese (Mn) has significantly reduced compared with pre-treatment values but remains elevated relative to typical drinking-water aesthetic guidelines (0.05 mg/L), with current results in the order of 0.3–0.6 mg/Ldepending on bore and sample timing.

This represents a substantial improvement from the pre-rehabilitation condition (Fe up to ~20 mg/L and Mn up to ~3 mg/L) and confirms that the iron-related fouling within the casing, screen and gravel pack has been successfully mobilised and removed. The remaining manganese signature is now more strongly influenced by the natural aquifer chemistry than by accumulated bore fouling.

Historical water quality data have been requested from the water authority to verify whether manganese has been persistently elevated at this site. This will assist in differentiating between residual post-rehab effects and long-term background conditions in the source aquifer.

4.2 Interpretation

Experience with iron/manganese systems indicates:

• Iron typically responds rapidly to chemical rehabilitation and oxidative purging.

• Manganese is slower to oxidise and precipitate; it often “lags” iron and may remain in solution even when iron has effectively cleared.

• Once major fouling has been removed, residual manganese concentrations are frequently controlled by intrinsic aquifer characteristics rather than the bore condition itself.

On the basis of the available data, the bores now appear to be hydraulically restored and iron-stable, with manganese in the range expected of a naturally manganese-rich groundwater source.

4.3 Recommended short-term actions

1. Additional purge and monitoring run

   • Conduct at least one further extended purge on each bore.

   • Collect “mid-purge” and “late-purge” samples for Fe/Mn to confirm whether manganese is still trending downward or has stabilised around the current levels.

2. Targeted pH-assisted chlorination trial

   • Trial an increase in pH to approximately 8.5–9.0 using soda ash (sodium carbonate), followed by chlorination, to enhance manganese oxidation and precipitation.

   • This should be piloted initially at bench scale (bucket/drum tests) using raw bore water, with comparison between:

     • Chlorine only, and

     • Chlorine plus soda ash (pH 8.5–9.0).

   • If bench results show a clear manganese reduction relative to the chlorine-only control, a controlled in-bore batch treatment can be designed, with treated water pumped to waste and monitored for Fe, Mn, pH and free chlorine.

3. Control limits

   • Maintain pH below 9.0–9.2 to minimise scaling risk and keep chemistry manageable for operators.

   • Ensure appropriate operator PPE, pH monitoring and safe handling procedures for soda ash and hypochlorite.

4.4 Longer-term management options

If, after the above measures, manganese remains persistently elevated (e.g. ~0.3–0.5 mg/L or higher) and historical data confirm that this is a long-standing characteristic of the source, then manganese should be treated as a normal water-treatment issue rather than a bore-rehab defect. In that case, suitable long-term options include:

• Aeration followed by filtration (sand or dual-media) to remove oxidised manganese particulates; and/or

• Oxidising media filters (e.g. manganese dioxide / greensand-type media) operated with chlorine or permanganate support; and/or

• Blending of bore water with lower-Mn sources where available, to achieve acceptable system-wide concentrations.

Under this model, the recent rehabilitation is considered successful in restoring bore performance and iron stability, while manganese management is addressed via above-ground treatment or system design, consistent with normal practice for manganese-bearing groundwaters.