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

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

? ? ? ? ? ? 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

ARSENIC > MCL Uranium > MCL Most problematic Manganese & Iron

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

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

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:

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

Swift 1 Mn vs. % recovery

Loss of well efficiency during injection

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

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

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

Pilot-testing two wells with elevated uranium

Uranium trend for pilot tests

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

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

Screened Interval and Injection v. Recovery Rate Maple Hill 2 well Settlers well 47 FT 92 FT GPM GPM 800 GPM 100+ % Recovery GPM 85 % Recovery

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

Multiple completion intervals RECOVERY 500 feet 900 feet RECHARGE Potential for preferential recharge in some zones Pumping rate greater than recharge rate may draw in native water with arsenic

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

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

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

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

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