Abstract
This study focuses on the treatment performance of two full-scale treatment wetlands constructed by BP for groundwater remediation. The first is in Casper, Wyoming (commissioned in 2003); the second is located in Wellsville, New York (commissioned in 2008). Treatment wetlands were selected in both cases due to low operating costs, which result in favorable life-cycle costs when managing legacy contaminants associated with former refining operations.
Both treatment systems have been highly effective and have met regulatory compliance objectives. System performance can be measured by a first-order, area-based rate coefficient (k), that can be applied to future wetland design projects. For the full-scale Casper wetland, rate coefficients were measured as 0.66, 0.96, and 0.89 m/d for benzene, BTEX and gasoline-range organics, respectively. The wetland system removes essentially 100% of these constituents, with non-detect concentrations in the effluent.
For the full-scale Wellsville wetland, rate coefficients were measured as 0.37 and 0.33 m/d for aniline and nitrobenzene. The wetland system has removed 94% of the aniline and 93% of the nitrobenzene (based on mean influent and effluent concentration values over the period of record). Treatment performance has been very stable after the initial winter start-up period. Excursions above non-detect concentrations typically occur during the winter months when water temperatures are at a minimum and the wetlands are partially iced over. The Wellsville system has also been very effective in iron removal, removing 98% of the iron (based on mean concentration values), despite relatively high influent concentrations (mean value of 33.3 mg/L).
Both systems operate under cold climate conditions. The Casper wetland operates at temperatures as low as -35°C; the Wellsville wetland operates at temperatures that can drop below -20°C. The multi-year performance history of these two wetland systems demonstrates that wetlands are a viable and cost-effective treatment alternative, even under cold climate conditions.
