1. Reuse of Treated water for Aquifer Recharge in the East Snake River Plain Eric Collins, R.G. GSI Water Solutions, Inc. May 1, 2008 Waste

2. Reuse and Aquifer Recharge  News headlines and public awareness  Nationally most reuse projects in four states  Idaho Reuse Conferences and new DEQ guidance documents  ESPA Comprehensive Aquifer Management Plan includes aquifer recharge alternatives

3. Presentation Topics  Wendell, Idaho project  Other related reuse and recharge projects in the region ▲ Wendell Twin Falls ● ● Boise

4. Wendell Project Setting  Groundwater is sole source water supply  Regional water level declines in ESPA  Potential curtailment of water rights for groundwater users - uncertain long-term water availability  City WWTP planned upgrades

5. Wendell Project Objectives  Mitigate potential reductions in the City’s water supply by reuse of treated wastewater for aquifer recharge  GSI invited by J-U-B Engineering to help the City assess the feasibility of two aquifer recharge options: 1) Injection Wells 2) Infiltration Basins

6. Wendell WWTP Overview  Current facilities  Wastewater Facilities Plan (2007)  Target discharge rate 1.5 AF/day Lagoons Wendell

7. Wendell Conceptual Model Geology T Thin soil mantle overlying Snake River Group Basalts

8. Wendell Conceptual Model Shallow Soil  Soil generally consists of loam, clay, silt, and sand  Caliche within soil profile and/or at soil basalt interface  Permeability estimates: moderately slow to rapid  Infiltration Tests: Infiltrometer test near lagoon1.5 inches/hr (JUB 2007) Small scale pilot tests1 - 3 inches/day (JUB 2008) State W-Canal Recharge Site1 foot/day (Blew 2007) State X1 Recharge Site3.6 feet/day (DEQ 2006)

9. Wendell Conceptual Model Wendell Lagoons

10. Wendell Conceptual Model Snake River Basalt  Series of basalt flows about 20-25 feet thick  Interbeds with unconsolidated sediments  Hosts the ESPA and is relatively transmissive  Groundwater about 125 -150 feet deep discharging to the west and south as springs next to the Snake River  Perched water possible from fined-grained sediments in the interbeds

11. Wendell Conceptual Model Particle Tracking Flow Model Snake River Basalts

12. Wendell Lagoons W-Canal Recharge Project

13. Wendell Hydrogeologic Considerations Injection Wells Option  Specific capacity about 150+ gpm/ft  One potential injection well could easily accommodate the target recharge rate of 1.5 AF/day  Direct recharge to the aquifer – timing control  High density of wells and water rights in study area means a small buffer zone

14. Infiltration Basins  Dependent on the vadose zone above aquifer  Shallow soil has high percentage of fines and limited infiltration capacity  Snake River basalts are highly transmissive in the lateral direction but water is expected to travel slower in the vertical direction Wendell Hydrogeologic Considerations

15. Wendell DEQ Considerations Injection Wells Option  Injection wells not allowed under new reuse rules (RO treatment prior to injection was acceptable)  Vadose zone injection wells also not allowed

16. Wendell DEQ Considerations Infiltration Basins  Allowed if Rapid Infiltration Land Treatment (RI) is incorporated in treatment process ( IDAPA 58.01.16 and 58.01.17)  Groundwater Quality Rule ( IDAPA 58.01.11 )  Buffer zone (Well Location Acceptability Analysis) - potential groundwater monitoring  New DEQ guidance available: (Guidance for Reclamation and Reuse of Municipal and Industrial Wastewater Rapid Infiltration Land Treatment, April 2008)

17. Wendell Water Rights Considerations  Does DWR allow reuse aquifer recharge as mitigation for out-of-priority diversions from groundwater?  There are no projects in Idaho where DWR has approved this concept. However, Idaho may follow the trend set by other states.

18. Wendell Project Summary  No injection wells  RI basins for aquifer recharge may be feasible but a few issues still need to be addressed: Shallow soil infiltration capacity Understanding of flow path through basalts Securing mitigation credit from DWR  The City is currently conducting small-scale pilot testing to further assess infiltration rates  Also consulting with DWR regarding mitigation credit

19. Other Projects in the Region  State W-Canal project Wendell area  ASR projects Boise area  Reuse projects Mountain Home AFB  Reuse and aquifer recharge Boise area planned community developments

20. Closing Remarks  With increasing stresses on the water supply in this region of Idaho, treated water reuse and managed aquifer recharge will likely develop as it has in other states.  Legislative funding, regulatory attention, and community perceptions are positive indicators.