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Water Quality Degradation in Fire Ravaged Watersheds

Water Quality Degradation in Fire Ravaged Watersheds. September 17, 2003 RMSAWWA. Introduction: Rodeo-Chediski Wildfire. Rodeo-Chediski Fire. Largest Arizona wildfire on record Burned nearly 500,000 acres in Salt River Watershed

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Water Quality Degradation in Fire Ravaged Watersheds

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  1. Water Quality Degradation in Fire Ravaged Watersheds September 17, 2003 RMSAWWA

  2. Introduction:Rodeo-Chediski Wildfire

  3. Rodeo-Chediski Fire • Largest Arizona wildfire on record • Burned nearly 500,000 acres in Salt River Watershed • Salt River Watershed is major supply of drinking water for Phoenix Area • Runoff from burn area supplied huge amounts of TOC, turbidity, metals and nutrients to reservoir system

  4. Runoff from Burn Area (Salt River)

  5. Water Quality Comparison

  6. Potential Impacts • High Organic Content=> High DBP Formation Potential • Regulated Carcinogens • Eutrophication/Algal Blooms • Toxicity to Aquatic Organisms in Salt River

  7. Fire Area SRP System

  8. Dilution Scenarios • Fire Residue Water will attenuate (dilute) in reservoirs and canals • Reservoir mixing patterns • 20% Dilution estimated as worst-case scenario

  9. Bench Scale Enhanced Coagulation Testing Conditions Coagulant Dose Coagulant Range (mg/L) pH Aluminum 90 - 130 7.0 Sulfate Ferric Chloride 25-55 7.0 Bench Scale Testing

  10. Jar Test Settling Time Calculation • AWWA Manual 37 • Settling time in jar should correspond to surface overflow rate in full scale basin (not time in basin!) • Surface overflow rate is really a settling velocity: 700 gpd/sf = 2 cm/min • Depth to spout in jar is 10 cm • Settling time = (10 cm)/(2 cm/min) = 5 min (theoretical)

  11. Results... • Turbidity • TOC • DBP Formation Potential

  12. Bench Scale Testing ResultsAlum Turbidity

  13. Bench Scale Testing ResultsFerric Turbidity

  14. Equivalent Alum Dose • Al2(SO4)3 => 16% Al 3+ • FeCl3 => 34% Fe 3+ • Twice as much effective metal ion in ferric • Equivalent dose: 2 ppm alum : 1 ppm ferric • Cost is about 2X for ferric

  15. % Turbidity Removal 20% Fire Water Jar Testing , pHc=7.0 100% Ferric: 10 NTU 98% 96% Alum: 27 NTU 94% 92% Raw Turbidity in ( ) Settled Water % Turbidity Removal Alum (410) 90% Ferric (410) Ferric removed more turbidity 88% at a lower equivalent alum dose (1 ppm ferric = 2 ppm alum) 86% 84% 82% 80% 40 50 60 70 80 90 100 110 120 130 140 Equivalent Alum Dose (ppm) Turbidity Results

  16. Bench Scale Testing ResultsAlum TOC

  17. Bench Scale Testing ResultsFerric TOC

  18. TOC Removal 20% Fire Water Jar Testing, pHc=7.0 5.00 Alum 5 Day THM: 375-330 mg/L 4.50 4.00 Ferric 5 Day THM: 375-315 mg/L 3.50 3.00 Raw TOC in ( ) Alum (12.9) TOC (mg/L) 2.50 Ferric (12.9) Ferric removed more TOC at 2.00 a lower equivalent alum dose (1 ppm ferric = 2 ppm alum) 1.50 1.00 0.50 0.00 40 50 60 70 80 90 100 110 120 130 140 Equivalent Alum Dose (ppm) TOC Results

  19. TOC Performance Comparison

  20. Bench Scale Testing ResultsAlum DBPs

  21. Bench Scale Testing ResultsFerric DBPs

  22. Results Summary

  23. Conclusions • Fire Residue Water • High Turbidity levels • High TOC concentration • High DBP formation potential • High Color content • Difficult to Remove TOC and DBP formation potential to acceptable level with Enhanced Coagulation alone. • Impacts may be felt for years • Treatment Strategies • Blending • Enhanced Coagulation--low pH and high dose • Ferric Chloride may be cheaper and more effective • TOC removal by adsorption (GAC, BAC)

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