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

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

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

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

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

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

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

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)

Wendell Conceptual Model Wendell Lagoons

Wendell Conceptual Model Snake River Basalt  Series of basalt flows about feet thick  Interbeds with unconsolidated sediments  Hosts the ESPA and is relatively transmissive  Groundwater about 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

Wendell Conceptual Model Particle Tracking Flow Model Snake River Basalts

Wendell Lagoons W-Canal Recharge Project

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

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

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

Wendell DEQ Considerations Infiltration Basins  Allowed if Rapid Infiltration Land Treatment (RI) is incorporated in treatment process ( IDAPA and )  Groundwater Quality Rule ( IDAPA )  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)

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.

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

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

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.