Assessing Water Quality Improvement and Treatment Effectiveness at a 6-Ha Constructed Wetland in Clackamas County, OR

Stormwater management is an ongoing challenge worldwide. Constructed wetlands (CWs) have been used as aesthetically pleasing, functional solar-powered engines for attenuating pollution delivered by stormwater to rivers and streams. Efficacy of CWs for pollutant attenuation vary by factors beyond design such as flow rate, pollutant loading, maintenance, and weather. In 2018, the Carli Creek Water Quality Project was completed, a 6-ha integrated creek restoration and CW, the latter consisting of a series of a retention pond and 3 bioretention cells. The CW drains a highly industrialized and impervious (~90%) catchment via a combined 0.73 ha of treatment area (1:243 ratio versus catchment ) and 4070 m3 of total runoff storage. A partially complete (n=3) sampling campaign has shown average reduction efficiencies for E. coli, Nitrate-nitrite, Total Zinc, and Total Solids of 89%, 48%, 21%, and 16%, respectively, across the treatment terrace. Concurrent upstream and downstream sites on the receiving creek also show similar reductions for E. coli and Nitrate-nitrite but not Total Solids. These in-stream differences may be due to dilution effects from the treatment terrace so paired mass loading data of these sites will afford a better understanding of the effectiveness of the terrace on improving water quality in the receiving stream of this urbanized catchment. This research shows CWs can effectively reduce certain pollutants from heavily industrialized catchments and that understanding relationships with weather will improve CW design for more effective water quality improvement downstream