Arsenic in Iowa’s Groundwater—The Unknown Threat: A Pilot Study in Cerro Gordo County

1. Arsenic in Iowa’s Groundwater—The Unknown Threat: A Pilot Study in Cerro Gordo County Douglas J. Schnoebelen, PhD: University of Iowa

2. Acknowledgements Peter Weyer, CHEEC, (Center for Health Effects Env. Con.) Brian Hanft, Cerro Gordo Health Department Daniel Ries, Cerro Gordo Health Department Sophia Walsh, Cerro Gordo Health Department Lorelei Kurimski, UHL Sherri Marine, UHL Pam Mollenhauer, UHL Mike Wichman, UHL Paul Van Dorpe, DNR Gary Shaver, Shaver Well Drilling CDC--Funding

3. Overview Is arsenic in groundwater a new problem? Why Cerro Gordo County? SWRL2 study Background on: Geology and rock types Geochemistry and Redox Geochemical scenarios Using the geology and geochemistry to design the sampling plan Database and communication

4. Does not tell the whole story Map of U.S. showing arsenic concentrations in groundwater Arsenic concentrations found in at least 25% of GW samples within a moving 50km radius (Ryker, 2001)

5. Arsenic in Groundwater Arsenic concentrations may be high groundwater in many areas across the United States & the world The old drinking water standard of 0.05 mg/L (50 ppb) was in the U.S. from 1942 - 2005 New standard for drinking water of 0.01 mg/L (10 ppb) was set in the U.S. in 2006 Arsenic is a carcinogen (skin, lung, bladder cancers) and linked to cardiovascular disease Private wells are unregulated and may be at risk

6. High As levels near Clear Lake/Mason City Map from IDNR, VanDorpe, 2010

7. Arsenic in Cerro Gordo County Arsenic in groundwater can come from a variety of sources: Ruled out anthropogenic sources Arsenic in the Soil and Rock Geochemical and Biogeochemical Reactions Potential redox zones and solubility/mobility Bacterial activity Both are important!

8. Bedrock Units--Lime Creek and Cedar Valley Cedar Valley Group-- (Middle and Upper Devonian in age). Records T-R cycles of the Devonian sea. Carbonates (limestones and dolostones) principle rock types. Wide variety of fossils (ie Devonian Fossil Gorge in Coralville). Lime Creek Formation--(Upper Devonian in age). Other T-R cycles in the Devonian sea. Generally shallower water deposition. Shale, calcareous shale, and argillaceous limestone. Pyrite (FeS) certainly common in the shales of the Lime Creek, but also found in the Cedar Valley as well. Other iron minerals too!

9. Some minerals may contain small amounts of arsenic: iron hydroxides and sulfides Iron hydroxides: are not crystalline (no structured crystal lattice)—also known as hydrous ferric oxides (HFOs) or Hydrous iron oxides (HIOs) or oxhydroxides. Often as grain coatings or weathering deposits. Numerous iron oxides(16 different ones) Iron II hydroxides: Fe(OH)2 Iron III Hydroxides: Fe(OH)3 Examples: Hematite (Fe2O3)---common coating on grains Also Goethite: FeO(OH) Sulides:(Pryrite, FeS2), arsenopyrite (FeAsS), realgar(AsS), marcasite (FeS2)

10. Arsenic and Redox Oxidation and Reduction (Redox) reactions are important in understanding arsenic concentrations and speciation in the groundwater Redox reactions are simply a family of reactions that are concerned with the transfer of electrons between species. Oxidation refers to reactions of an element & oxygen where electrons are lost (ie rust) Reduction refers to reactions to the element or compound where electrons are gained Oxidation—involves an increase in the oxidation number of an atom while Reduction—occurs when the oxidation number of an atom decreases

11. Arsenic Species and Oxygen Arsenic in groundwater can exist with formal oxidation states of III (arsenite) and V (arsenate). Arsenate (As V) would be more typical in oxygen rich waters (DO over 1 mg/L) EPA regulations are for TOTAL arsenic (III and V combined). Most lab analyses report TOTAL arsenic Arsenic III is more toxic than Arsenic V Arsenic III is more difficult to remove (with conventional treatment) than Arsenic V

12. Sulfide Minerals and Oxygen(one of several geochemical scenarios) Fluctuating water levels in the well bore introduce oxygen to the sulfide minerals– resulting in high As concentrations in the groundwater (perhaps Wisc. example Galena/St. Peter Ss) Arsenic (As) concentrations will be highest in wells with flucuating water levels and sulfides at the same level (O2 is the source) However, if sulfides are above OR some distance below the water table then As concentrations are typically lower in the groundwater (but may still be a problem).

13. Iron oxides and Reducing conditions(another geochemical scenario of many) The reducing conditions in the aquifer drives a complex series of Redox reactions with the sequential loss of dissolved oxygenreduction of nitrateMn (IV) and Fe(III)SO4methane produced Microbial activity important in catalyzing reactions and arsenic from iron oxides released (India example) Also can have a change under reducing conditions of Fe(III) to mixed form Fe(II)/Fe(III) oxides that can affect the affinity of the minerals binding the ARSENIC therefore releasing more As to the water

14. Groundwater Sampling Plan—How to design? No plan is perfect---funds are not unlimited (best bang for the buck to achieve our objectives Better understand the arsenic problem: source, geochemistry, causes Improve data to homeowners and drillers Enlarge the data set over a larger geographic area Select wells with complete geology (new wells) Bedrock wells Analysis of rock cuttings from the wells 50 wells per twice per year (wet/dry seasons) for 3 years

15. Groundwater Sampling—What to sample? Dissolved Oxygen and Eh: Redox conditions pH: Sorption and Desorption Temp and SpC: Field parameters Hydrogen sulfide: Redox conditions Major Cations and Anions: Geochemistry Organic Carbon: Geochemistry Fe, Mn and other metals: Reductive vs Desorption Arsenic Species: As III and As V These can test: Aresenic sources, solubility, mobility, potential redox zones, potential bacterial activity

16. Groundwater sampling equipment used

17. Groundwater Sampling Flow through Cell and Sonde (field readings critical) Hach Spectrophotometer (sulfide in the field) Sample Chamber (reduces contamination) Replace tubing each time (no carryover) Series of field readings before final measurement

18. Groundwater Sampling In-house training Data Sheets and good communication with the Lab Field test site with actual sample to track data handling 10% QA/QC samples Lab is measuring Arsenic as total, III and V

19. Database—Goals and Objectives Geochemical modeling of the data Spatial and temporal patterns Any correlation with simple field measurements Trends, patterns, correlation with rock samples Would like to follow-up with lab studies & more targeted samples

20. Thank You!!!! Doug Schnoebelen, The University of Iowa, IIHR—Hydroscience and Engineering: douglas-schnoebelen@uiowa.edu