Although Approximately 35 Million People Obtain Drinking Water From Domestic Wells In U.S., Few Studies Have Investigated The Risk Of Arsenic Exposure From This Source. Excess Lifetime And Annual Risks For Lung And Bladder Cancer Were Calculated Based On The Carcinogenic Potency And Average Arsenic Concentrations In Public And Domestic Water Supplies. Domestic Wells And Public Wells In The Western U.S. Have The Highest Arsenic Levels With Excess Fatality Risks Estimated To Be In The Range Of 1 Per 9,300 To 1 Per 6,600. Monte Carlo Uncertainty Analysis Indicates That Additional Data On Arsenic Concentrations In The New England And Southeast Regions Would Substantially Improve Regional Risk Estimates. Adsorption Of Arsenic On Iron Oxide Surfaces Has Received Significant Attention Because Of Its Effectiveness And Ease In Operation And Handling. Four Types Of Fibrous Materials: Polypropylene, Polyester, Fiberglass, And Cellulose Were Evaluated For Their Ability To Offer A High-Specific Surface Area Alternative To Sand As The Substrate For Iron Oxide Coating And Arsenic Removal From Water. All Fibrous Materials Showed Higher Arsenate Adsorption Densities Than Iron Oxide Coated Sand (0.13-0.23 Mg As/G Versus 0.02-0.1 Mg As/G For 20 G/L Remaining Arsenic Concentration). Arsenate Adsorption Densities Were Highest For Iron Oxide Coated Fiberglass And Cellulose, Suggesting That These Fibrous Materials Would Offer Advantages Over Iron Oxide-Coated Sand. Very Few Studies Have Focused On The Combined Effects Of Ph, Ion Types And Concentrations Typical Of An Arsenic Contaminated Groundwater On Phase Transformation And Arsenic Adsorptive Capacity Of Iron Oxide Media. X-Ray Diffraction Analysis Of Granular Iron Oxide Samples, Incubated For Different Time Periods In The Presence Of Different Ions Typical Of An Arsenic Contaminated Groundwater, Indicated Some Changes In The Peak-Widths Of Media. These Changes Suggest The Possibility Of Structural Changes In Media Over Time. Further Experiments Are Underway To Collect More Information About Changes In Degree Of Crystallinity And Arsenic Adsorption Capacity Of Iron Oxide Media Over Time. These Results Would Be Useful In Understanding The Combined Effects Of Different Environmental Factors On The Stability And Time-Dependent Arsenic Removal Effectiveness Of Iron Oxide Media.