1. Converting a supply well into an ASR well: Case Histories Roger Dittus PG – United Water Idaho Inc

2. United Water Idaho  Serving Boise area  Several pressure zones  80+ supply wells  Two surface water treatment plants Idaho Boise

3. ? ? ? ? ? ? Fine-grained Sediments with sand lenses ? ? ? ? Adapted from cross section by S. Wood, BSU Geosciences C. Petrich Interbedded sand, silt, clay Mudstone Conceptual Cross-Section (Regional Scale) Shallow coarse-grained sediments and basalt Volcanic Rocks 4,0002,0002,0004,000 0 Elevation (feet) WE MunicipalDomestic Municipal

4. ARSENIC > MCL Uranium > MCL Most problematic Manganese & Iron

5. Swift well Maple Hill 2 well Market St. well Settlers well United Water ASR projects As U U Mn

6. Piping Tee 10-inch to 4-inch Flow Meter Cla -valve Flow During Injection

7. Well Drilled in 1978 History of Swift Well: 1986 to 1992: increase from 0.04 mg/L to 0.53 mg/L 1992 to 1996: increase from 0.53 mg/L to 0.94 mg/L 1997: tried to drill out of manganese but deeper water unacceptable United Water Idaho’s first ASR Well Looking for a Solution:

8. 6-inch Private Well in vicinity of Swift well limits injection rate

9. Swift 1 Mn vs. % recovery

12. Loss of well efficiency during injection

13. Swift Well 1 Increase pump capacity injected v. recovered water Swift well

14. Shallow Aquifers Shallow-Intermediate Aquifers Deep Aquifers (Conceptual Model) C. Petrich Terrace Gravels Boise River Low TDS High TDS MediumTDS Vertical Extent of GW-SW Interaction Elevated Uranium SW NE

15. Settlers Well: Native Water has 42 ug/L Recharge water source: deep groundwater Native Water has 40 ug/L Recharge water source: groundwater – mix from two wells Maple Hill 2 Well: Used as non-peak season supply while treatment system shut down

16. Pilot-testing two wells with elevated uranium

18. Uranium trend for pilot tests

21. Recharge Water Native Water Maple Hill 2: Estimated Mixing of native and injected Water 51 Million Gallons 10% Native Water 25% Native Water 50% Native Water

22. Dissolved Oxygen in Recharge Water = 0.25 mg/L Maple Hill 2 well: D.O. in recovered water

23. Screened Interval and Injection v. Recovery Rate Maple Hill 2 well Settlers well 47 FT 92 FT 200 - 230 GPM 175 - 400 GPM 800 GPM 100+ % Recovery 200- 230 GPM 85 % Recovery

24. Market Street Well: Native Water has 13 ug/L arsenic primary recharge water source has some arsenic

25. Multiple completion intervals RECOVERY 500 feet 900 feet 1 2 3 4 5 6 7 RECHARGE Potential for preferential recharge in some zones Pumping rate greater than recharge rate may draw in native water with arsenic

26. Injection rate = 270 gpm Storage Time = 5.9 days Recovery Rate = 775 gpm Pre-ASR Arsenic concentration

28. Second Test Injection rate = 270 gpm Storage Time = 4.2 days Recovery Rate = 665 gpm

29. Third Test Injection rate = 290 gpm Storage Time = 5.1 days Recovery Rate = 690 gpm

30. Market St. well ASR  Pilot testing indicates ASR may be feasible  100% recovery may not be possible  Distribution system manipulation to improve recharge source water/ ASR compatility may be worthwhile  Based on nearby ASR testing: after 1-2 weeks Trihalomethanes increase in this aquifer but decrease to original levels after 2 months storage  Currently storing 15 MG (ten times test volume) for first “production test” of this well

31. Summary & Conclusions  Prior to ASR, several United Water Idaho Supply wells were unusable due to their water-quality  Small-scale ASR test results may only give a rough approximation of actual operations-scale ASR results  ASR at most locations where it has been implemented has proved feasible  ASR wells are more trouble than regular supply wells  Overall, ASR has been cost-effective