City of Redmond Stormwater Infiltration System Assessment

(Redmond, WA)  Landau Associates assisted the City of Redmond in assessing the risk to the City's shallow unconfined drinking water aquifer from infiltration of stormwater through existing stormwater infiltration systems constructed throughout the City's wellhead protection zone. The City obtains 40 percent of its drinking water from municipal wells that draw groundwater from the shallow aquifer, which at some locations is only five feet below ground surface. During meetings with the industrial property owners and the City, we developed assessment criteria and procedures to allow property owners to evaluate their own infiltration systems and to allow the City to rank individual properties with regard to the risk they pose to the aquifer. Landau Associates developed requirements for infiltration system owners to modify their systems or, for owners of properties that pose less risk, to adopt certain best management practices to further reduce the risk of introducing pollutants to the aquifer. We also facilitated a series of meetings with a citizen technical advisory group to reach consensus on the assessment criteria and modification requirements.