State of Washington Field Monitoring of Biofilter at City of Portland Maintenance Facility
State of Washington Department of Ecology Technology Assessment Protocol (TAPE)
Field Monitoring of Low Impact Development (LID) Biofiltration System at City of Portland Maintenance Facility
The Washington State Department of Ecology (DOE) Technology Assessment Protocol, known as TAPE, is the stormwater industry’s most stringent and all-encompassing testing protocol worldwide. Unlike other protocols that focus solely on Total Suspended Solids (TSS), the TAPE protocol defines performance goals for TSS, dissolved metals, total phosphorus and oils. The Washington State Department of Ecology TAPE program for evaluating emerging stormwater treatment technologies. Guidance documents for the TAPE program establish specific use designations for emerging stormwater treatment technologies that allow limited application in western Washington to facilitate field testing. If it can be shown through this testing that the treatment technology meets minimum goals for each treatment category, Ecology may issue a General Use Level Designation (GULD) for the technology that permits it’s more widespread use in Washington.
TAPE GULD — Modular Wetland Systems installed and tested a Modular Wetlands System Linear (MWS Linear) stormwater treatment system in Portland, Oregon in order to conduct field monitoring with the intent of applying for a GULD for basic (Total Suspended Solids), phosphorus, oil, and enhanced (dissolved metals) treatment. Pursuant to TAPE requirements, a quality assurance project plan (QAPP) must be prepared to describe the field and laboratory procedures that will be used for this monitoring. The QAPP must then be submitted to and approved by Ecology before initiating the monitoring.
The QAPP specifically describes the procedures that will be used to document the water quality treatment performance of the MWS Linear system that was installed near the end of 2011 at a City of Portland Maintenance Facility. Monitoring of this system initiated in the spring of 2012 and continued until a sufficient number of samples had been collected to demonstrate the system meets the goals specified in TAPE for the treatment categories identified above, and one and one half maintenance cycles were completed. Upon completion in spring of 2013, the monitoring and associated data was analyzed and summarized in a Technology Evaluation Report (TER). This TER was then submitted to Board of External Reviewers (BER) that was established by Ecology to conduct technical reviews for the TAPE program. After considering recommendations from the BER, Ecology can issue GULD for the MWS Linear system for one or more treatment categories identified above.
Based on the Technical Evaluation Report, dated April 1, 2014, Ecology issued the following use level designation for the MWS Linear:
General Use Level Designation (GULD) for the MWS Linear for Basic Treatment (TSS) sized at a hydraulic loading rate of 1.0 gpm/sq ft of wetland cell surface area. For moderate pollutant loading rates, size the Prefilters at 3.0 gallons per minute(gpm)/sq ft of cartridge surface area. For high loading rates size the Prefilters at 2.1 gpm/sq ft of cartridge surface area. In addition, the MWS Linear was able to remove 92% of TSS at concentrations greater than 200 mg/L and a loading rate of 1.21 gpm/sq ft during a single storm event. The maximum removal for a single storm event was 98% with influent concentrations between 100 and 200 mg/L. Average TSS removal for influent concentrations greater than 100 mg/L was 85%.
General use level designation (GULD) for the MWS Linear for Phosphorus treatment (TP) sized at a hydraulic loading rate of 1.0 gpm/sq ft of wetland cell surface area. For moderate pollutant loading rates, size the Prefilters at 3.0 gpm/sq ft of cartridge surface area. For high loading rates size the Prefilters at 2.1 gpm/sq ft of cartridge surface area. More impressively, the MWS Linear was able to remove an average of 67% of ortho-phosphorus. Maximum removal of ortho-phosphorus during a single storm event was 79%. Ortho-phosphorus is the soluble biologically available form of phosphorus that contributes directly to algae blooms and most negatively impacts the environment.
General use level designation (GULD) for the MWS Linear for Enhanced treatment (Dissolved Zinc & Copper) sized at a hydraulic loading rate of 1.0 gpm/sq ft of wetland cell surface area. For moderate pollutant loading rates, size the Prefilters at 3.0 gpm/sq ft of cartridge surface area. For high loading rates size the Prefilters at 2.1 gpm/sq ft of cartridge surface area. In addition, the MWS Linear demonstrated a maximum removal of 90% for dissolved zinc and 60% for dissolved copper during single storm events. Average removal of dissolved zinc was 66% and dissolved copper was 38%. Additional independent laboratory data done at an industrial site in the State of Washington showed dissolved copper removal efficiencies up to 93% at loading rates of 1 gpm/sq ft of wetland cell surface area.
Overall, the MWS Linear proved to be a highly effective and versatile BMP that can provide solutions for various new construction and retrofit applications. The pretreatment chamber and Prefilters effectively protected the wetland cell and prevented any clogging of the WetlandMEDIA over the course of the field evaluation. The MWS Linear demonstrated superior performance and a valuable tool in improving water quality.
|Pollutant||Avg. Infuent (mg/L)||Avg. Effluent (mg/L)||Removal Efficiency|
|Total Suspended Solids (TSS)||75.0||15.7||85%|