Aquifer Storage and Recovery for the City of Yakima, Washington

The city of Yakima, Washington, is developing an Aquifer Storage and Recovery (ASR) program for municipal water supply and to allow permitting and development of new wells in a sustainable manner.  The city’s experience influenced the development of state ASR rules, which did not exist when the city started their program in 2000.  The quantity aspect of the rule is based on a water balance neutral approach.  However, the rule does not address chlorination disinfection by-products in recharged water, which exceed the criteria for the protection of groundwater, despite meeting Safe Drinking Water Act standards.  This introduces regulatory uncertainty.  Recharge is expected to occur annually, and recovery may only occur occasionally, as needed.  Therefore, ASR will restore aquifer storage, which has displayed depletion, and improve baseflows to the Yakima River, which hosts salmon listed under the Endangered Species Act.
The city has a surface water source as part of their municipal supply to provide recharge water, and backup wells, all connected to the distribution system.  Implementing ASR is almost as simple as modifying valving at wellheads to allow water to flow from the distribution system into the wells.  Permitting primarily involves limiting the recoverable quantity to not more than the residual storage resulting from recharge.  This is estimated with numerical modeling of the aquifer system.  No adverse reactions between the recharged surface water and the groundwater or aquifer materials have been detected.  Because the temperatures of groundwater and surface water are 20 oC and 4 oC, respectively, ASR will improve the aesthetics of drinking water for the customer.  ASR also provides water supply for fire fighting without having to build storage reservoirs that can cost as much as the well installation.  Because ASR is relatively new to Washington State, misconceptions on the part of regulators and project proponents persist.