Iron and Manganese in Ohio Ground Water

Jeff Patzke, DDAGW-CO

Chris KenahMike Slattery

Ambient Ground Water Quality Monitoring Program

• Began in 1973• 200 active / 180 inactive wells, 80% at public water

systems• Purpose is to define source water quality at Ohio’s

ground water-based public water systems, as well as general ground water quality in Ohio.

• Results are available on Ohio EPA-DDAGW web page:http://epa.ohio.gov/ddagw/gwqcp

Technical Papers / Fact Sheets

• Data is useful for water resources planning• Producing technical papers and fact sheets

focusing on specific constituents• Iron and Manganese in Ohio Ground Water

should be available soon.

Iron and Manganese• Addressed together because both:

– Are transition metals that exhibit multiple valence states and are widespread

– Commonly occur in rock-forming minerals or as coatings and cements

– Have concentrations in ground water controlled by:• Distribution in compounds and minerals• Local redox conditions, and • pH, to a lesser extent

– Commonly exceed secondary drinking water standards (nuisance-based) in deeper aquifers

Iron

• Fourth most common element in Earth’s crust.• Exists in a range of oxidation states; the common redox pair

in ground water consists of ferrous (+2; reduced) and ferric (+3; oxidized).

• Ferrous iron is unstable in the atmosphere, so you see minerals rich in ferric iron (e.g., hematite, iron oxides and hydroxides).

• In reduced environments, iron oxides dissolve and ferrous iron is in solution. Pyrite can form if sulfur is present.

• No regulatory drinking water standards for iron; the secondary MCL is 300 ug/L, a guideline for the minimum level for rusty color/staining and metallic taste.

Manganese

• Twelfth most abundant element in Earth’s crust.• Exists in range of oxidation states; +2 (reduced), +3 and

+4 (oxidized) are the most common.• Not in major rock-forming minerals as a primary

constituent, but substitutes for iron, magnesium, and calcium in silicate and carbonate minerals.

• Manganese released by weathering often forms oxides and hydroxides as coatings on fractured rock surfaces.

• In reduced environments, oxides and hydroxides are dissolved, and manganese is released into solution.

• J;

Manganese (continued)

• Manganese can also be mobilized under acidic conditions, so it can be elevated in some industrial waste and mine effluent.

• No regulatory drinking water standards for Mn; the secondary MCL is 50 ug/L, a guideline for the minimum level for black color/staining and metallic taste.

• U.S. EPA non-regulatory lifetime health advisory is 300 ug/L; 1- and 10-day health advisory is 1,000 ug/L.

Iron and Manganese in Ohio Ground Water

• Analysis based on 7,750 results for iron and 7,400 results for manganese.

• Iron >> Manganese• Minimums are likely due to oxidized conditions.• Maximums may be due to turbid samples.• Iron means/medians exceed secondary MCL (300 ug/L) for all aquifer

types.• Manganese means/medians exceed SMCL (50 ug/L) for only

sand & gravel and sandstone.

Parameter Major Aquifer Mean ValueMedian Value

Minimum Value

Maximum Value

Percent Non-Detect

Iron, Total 1

µg/L

Sand and Gravel 1188 687 <20 58400 21

Sandstone 1348 335 <50 31200 24

Carbonate 1095 814 <50 27300 10

Manganese, Total 2

µg/L

Sand and Gravel 195 121 <8.0 5130* 14

Sandstone 225 89 <9.0 2220 19

Carbonate 32 18 <10 300 26

Poor Geographic Correlation for Iron

Higher Iron in Carbonate and Sand and Gravel Aquifers

Higher Manganese in Eastern Ohio

Higher Manganese in Sandstone and Sand & Gravel Aquifers

Elevated Mn Predominantly Occurs in or Above Pennsylvanian Bedrock

Mean Manganese Concentration by Aquifer Geologic Age

• Mn highest in Pennsylvanian Sandstones

• Quaternary aquifers exhibit manganese over entire range of bedrock aquifers

Possible Influence of Acid Mine Drainage on Manganese

• No significant trends over pH 7-7.6

• Manganese is elevated at pH <7 and >7.6

Buried Valley Aquifers with Highest Manganese Overly Pennsylvanian Bedrock

Adjacent Wells Can Have Different Iron Levels

Adjacent Wells Can Have Different Manganese Levels

Local Redox Conditions Influence Iron and Manganese Concentrations

• Redox conditions are controlled by transfer of electrons between donors and acceptors (TEAPS).

• In ground water, organic carbon is usually the donor in redox reactions, with organic carbon oxidized.

• Acceptors are various inorganics that are reduced during reactions that are mediated by microbes.

• As ground water is reduced, the following constituents are progressively consumed as they provide oxygen:

O2 > NO3 > Mn(IV) > Fe(III) > SO42- > CO2

Local Redox Conditions Influence Iron and Manganese (continued)

• Redox conditions can be identified by the presence or absence of the reactants and products.

• Sequence (O2 > NO3 > Mn(IV) > Fe(III) > SO42- > CO2)

indicates that manganese and iron are not soluble until any nitrate is reduced.

• Then, reduction of Mn+4 in Mn oxides or hydroxides to Mn+2

dissolves the minerals and releases Mn+2 into solution.• Once all of the Mn+4 minerals have been reduced, microbes

start reducing the Fe+3 in the iron oxides and hydroxides.• As the iron oxides become unstable in the more reduced

environment, the reduced iron (Fe2+) is released into solution.

Shallow vs. Deep Wells• Shallow:

– Ground water receives surface recharge more quickly, so it is more likely to be young and oxidized.

– Iron and manganese are generally tied up in oxides and hydroxides, so there is little in the ground water.

• Deep:– Ground water is isolated from the atmosphere and

the ground water is more reduced.– Oxide and hydroxide minerals break down and iron

and manganese are released into the ground water.

Manganese and Iron vs. ORP• Fe/Mn increase as the

ground water becomes more reduced.

• Peak Mn occurs at higher ORP than peak Fe (consistent with TEAPS)

• Microbial reduction starts dissolving minerals after oxygen and nitrate are consumed and reduced.

• Mn is mobilized, followed by Fe.

• Ground Water with elevated Fe, but without elevated Mn, supports more reducing conditions than elevated Fe and Mntogether.

Mean Manganese vs. Well Depth• Manganese in solution

increases as well depth increases until about 100’.

• At 100’, manganese starts to drop, because it has all been consumed.

• Iron continues to increase with depth.

• Ground water with elevated iron, but not manganese, suggests more reducing conditions than elevated iron and manganese together.

Conclusions-Iron

• Means and medians exceed secondary MCLs for all aquifer types

• Poor geographic correlation

• Generally highest in sand & gravel and carbonate quifers

Conclusions-Manganese

• Means/medians exceed SMCL for sand & gravel and sandstone, but not carbonate, aquifers

• Highest in eastern Ohio in sandstone and buried valley aquifers overlying Pennsylvanian bedrock

• Levels in eastern Ohio potentially influenced by acid mine drainage

Conclusions- Fe & Mn

Adjacent wells can have different concentrations:

• Shallow wells can have lower levels due to oxidized ground water

• Deep wells can have higher levels due to reduced ground water

Acknowledgements

• Public Water System operators• Ohio EPA Staff

– DDAGW GW staff collect AGWQMP samples– DES completes water quality analysis

• ODNR Map Products

Questions

jeffrey.patzke@epa.ohio.gov614-644-3029

GW Quality Characterization Program (web site)http://epa.ohio.gov/ddagw/gwqcp.aspx