Wastewater & Recycled Water

Highlighted Project

Reverse Osmosis Concentrate Management

Valley Water (Santa Clara Valley Water District)

EOA provided technical support to Valley Water in Santa Clara County for management of reverse osmosis concentrate (ROC) from a proposed 10 mgd Advanced Water Treatment Facility designed to produce purified water for indirect potable reuse. The ROC management strategy included discharge of ROC blended with treated effluent from the City of Palo Alto Regional Water Quality Control Plant (RWQCP). EOA conducted a Reasonable Potential Analysis and effluent limit calculations to identify the additional initial dilution credits needed for attainable NPDES permit effluent limits. EOA coordinated a hydrodynamic study conducted by Resource Management Associates to verify the mixing zone sizes associated with the required dilution credits. EOA coordinated chronic toxicity and priority pollutant testing of ROC from a pilot Reveres Osmosis facility. The work demonstrated that ROC could be successfully discharged through the existing RWQCP outfall in compliance with revised NPDES permit effluent limits. Studies supported use of increased dilution ratios allowing less conservative effluent limits. EOA worked with stakeholders to obtain a Letter of Concurrence from the Regional Water Board that the proposed ROC discharge appeared feasible.