1 / 25

Almost Everywhere: Naturally Occurring Arsenic in Wisconsin’s Aquifers

Investigating naturally occurring arsenic in Wisconsin aquifers, focusing on eastern WI's arsenic concentrations and cycling behavior under different pumping conditions. Research highlights the impact of groundwater extraction on arsenic mobilization, redox conditions, and flow paths, emphasizing the importance of controlling these factors for managing exposure. Strategies discussed include well construction methods to prevent oxygen introduction, extending community water supplies, and routine testing and treatment. Findings emphasize the complex cycling of arsenic influenced by pumping rates, volumes, and well disinfection practices. Implications underscore the need to understand and address arsenic contamination for sustainable groundwater management in the region.

steve
Download Presentation

Almost Everywhere: Naturally Occurring Arsenic in Wisconsin’s Aquifers

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Almost Everywhere: Naturally Occurring Arsenic in Wisconsin’s Aquifers Madeline Gotkowitz Wisconsin Geological and Natural History Survey

  2. Arsenic concentrations in Wisconsin % samples > 5 ppb > 10 % 2 to 10% <2 % 1 sample > 5ppb insufficient samples

  3. Study area: eastern Wisconsin > 10 ppb contour

  4. <2 ppm As 4 ppm As 133 ppm As

  5. Eastern Wisconsin Stratigraphy

  6. Quarry on Leonard Pt Road dolomite Sulfide-cement horizon sandstone

  7. Pre-development Pumped system confined

  8. Pumped system Managed system

  9. Mandatory well casing depth based on regional hydrogeology

  10. Geochemistry indicates sulfide oxidation at high-arsenic wells, FeOH reduction at others Fe SO4 A = < 2 mg/L B = 2-10 mg/L C = 10-100 mg/L D = >100 mg/L pH High Fe High SO4 Low pH Schreiber et al. 2003

  11. Without pumping, the well becomes strongly reducing ORP DO Gotkowitz et al. 2004

  12. Arsenic, iron and sulfate within a well, non-pumping conditions

  13. Effect of pumping rate and volume on redox 200 gallons every hour 100 gallons every 8 hours Gotkowitz et al. 2004

  14. Residences transferred to public water supply

  15. In situ disinfection

  16. In situ disinfection treatments Gotkowitz et al. 2008

  17. Arsenic cycling following sulfide exposure to DO, chlorine As-bearing Pyrite Cl2 Cl2 Primary reservoir O2 (minor) O2 (minor) Fe(II) SO4 As species Release from primary reservoir Fe(III) As(V) HFOs w/adsorbed As Secondary reservoir Release from secondary reservoir Desorption of As (pH) or reductive dissolution of HFOs (microbially mediated) West et al. In Review

  18. Arsenic in bedrock aquifers • High concentrations of solid-phase arsenic are associated with sulfide minerals • Arsenic mobilized under oxiding conditions but can become sequestered on iron-oxide minerals • Iron-oxide minerals become a secondary source of arsenic to groundwater under reducing conditions • Complex cycling of arsenic is affected by the water table, pumping rates and volumes, and well disinfection

  19. Southeastern Wisconsin Arsenic > 10 µg/l in 10% of wells Arsenic > 10 µg/l in 20% of wells

  20. Discontinuous sand and gravel lenses provide groundwater; these may be overlain by low-conductivity glacial tills aquifer Low As Moderate As High As Root et al. 2009

  21. Organic carbon triggers arsenic-iron-oxide dissolution Low As Moderate As High As Arsenic, mg/kg Organic matter, % Root et al. 2009

  22. Arsenic in glacial deposits • Low concentrations of solid-phase arsenic is associated with iron and manganese oxide minerals , within all stratigraphic units • Solubility of the solid-phase arsenic results from reducing conditions along deep groundwater flow paths; driven in part by organic carbon leading to reductive dissolution of Fe- and Mn- oxides

  23. Implications of arsenic cycling for managing exposure to arsenic… • Groundwater extraction affects arsenic mobilization • Alters flowpaths • Alters redox conditions • Rate and frequency of pumping impacts biogeochemistry • Strategies must control redox conditions • Well construction: prevent introduction of oxygen, controls flowpath • Extend community water supplies (avoids well disinfection, provides routine testing and /or treatment)

  24. Q&A

More Related