Easterly Wastewater Treatment Plant – Water Quality Studies

RBI served the City of Vacaville (City) as the lead consultant in preparing and directing seven special studies to evaluate effluent and receiving water quality conditions for the City’s Easterly Wastewater Treatment Plant (EWWTP). The objectives of the special studies were to collect data to support renewal of the EWWTP‘s National Pollutant Discharge Elimination System (NPDES) permit. RBI also assisted the City in communicating to the public and interested agencies the degree to which water quality and beneficial uses were affected by discharge from the EWWTP. The seven special studies addressed the following topics:

• Effluent dilution in downstream receiving waters
• Discharge effects of pathogens in EWWTP effluent on risks to human health at downstream drinking water intakes
•  Receiving water turbidity trends and discharge effects on receiving water turbidities
•  Presence of pyrethroids in EWWTP effluent and fate and effects of discharged pyrethroids in the receiving waters
• Fate and effects of discharged nitrate, TOC, and dissolved organic carbon (DOC)

• Discharge contributions of priority pollutants to receiving waters
• Presence and concentrations of constituents of emerging concern in EWWTP effluent and receiving waters

To implement this project, RBI used numerous techniques including designing a flow monitoring regime, using weir equations for calculation of flow over dams, developing an approach to assure adequate calibration of previously collected flow data, characterizing flows during the period of the year for which data were unable to be collected due to flow meter failure, and refining the dilution ratio determined in a previous study by the City. RBI also worked with Flow Science, Inc. to conduct dye studies to evaluate far-field effluent dilution and dispersion characteristics. The dilution ratio studies, along with the fate and transport characteristic studies, successfully supported the NPDES permit renewal in June 2014.