Evaluation of Constructed Wetland Treatment Performance for Winery Wastewater Mark E. Grismer, Melanie A. Carr and Heather L. Shepherd Abstract Rapid expansion of wineries in rural California during the past three decades has created contamination problems related to winery wastewater treatment and disposal, however little information is available about performance of on-site treatment systems. Here, the project objective was to determine full-scale, subsurface-flow constructed wetland (CW) retention times and treatment performance through assessment of water quality by daily sampling of TDS, pH, TSS, COD, tannins, nitrate, ammonium, TKN, phosphate, sulfate, and sulfide across operating systems for winery waster treatment. Measurements were conducted during both the fall crush season of heavy loading and the spring following bottling and racking operations at the winery. Simple decay model coefficients for these constituents as well as COD and tannin removal efficiencies from winery wastewater in bench-scale reactors are also determined. The bench-scale study employed upward-flow, inoculated attached growth (pea-gravel substrate) reactors fed synthetic winery wastewater. Inlet/outlet tracer studies for determination of actual retention times were essential to analyses of treatment performance from an operational subsurface flow CW that had been overloaded due to failure to install a pre-treatment system for suspended solids removal. Less intensive sampling conducted at a smaller operational winery wastewater CW that had employed pre-treatment suspended solids removal and aeration indicated that the CW systems were capable of complete organic load removal from the winery wastewater. Keywords: constructed wetlands, winery wastewater, tracer studies, subsurface flow, degradation modeling. 1