Contech's Filterra is an engineered bioretention system designed to filter pollutants from stormwater runoff. This page provides information on pollutant removal credits for Filterra.
When conditions described in this section are met, applicable Contech Filterra systems are approved for the following pollutant removals.
Applicable configurations (systems) include
To receive the full credit, Filterra systems must comply with the following conditions.
When conditions described in this section are met, applicable Contech Filterra systems are approved for the following pollutant removals.
All conditions must be met for the basic credit, described above. In addition, the following conditions must be met. NOTE: this is to be determined. Examples might be enhanced O&M, some sort of annual assessment, monitoring, etc.
When conditions described in this section are met, applicable Contech Filterra systems are approved for the following pollutant removals.
All conditions must be met for the basic credit, described above. In addition, the following conditions must be met.
NOTE: this is to be determined. Examples might be enhanced O&M, some sort of annual assessment, monitoring, etc.
The base credits are equal to TAPE-approved credits. However, due to differences between Washington State and Minnesota climates, the credits cannot be directly applied as an average annual removal. The applicable treatment volume must be determined using one of the methods described here.
Enhanced credits were determined by analyzing water quality data collected at Bellingham, Washington. The site consisted of residential land use with 0.4 acres of impervious draining to the device. The device was 4 ft by 6.5 ft, with a filter media depth of 1.8 feet and a ponding depth of 0.75 feet.
MPCA compiled data from Appendix K of the report TECHNICAL EVALUATION REPORT - FILTERRA SYSTEM PHOSPHORUS TREATMENT AND SUPPLEMENTAL BASIC TREATMENT PERFORMANCE MONITORING. Summary statistics are shown in the adjacent image. TAPE means and medians represent values meeting TAPE criteria for TP (inflow concentrations of 0.1 to 0.5 mg/L) and TSS (inflow concentrations greater than 20 mg/L). Thus, of the 22 samples, TAPE medians and means represent 10 samples for TP and 18 samples for TSS, while the remaining data in the figure are for all 22 events.
Enhanced Level 1 values of 60% for TP and 85% for TSS are slightly below the median concentrations for all 22 sampling events. The enhanced level 2 value of 65% for TP is below the median TAPE value (78.5%). Since the TAPE median is based on samples with TP concentrations greater than 0.100 mg/L, a criteria for receiving the Level 2 credit for TP is that median average annual inflow concentrations are greater than 0.100 mg/L. This value can be verified with water quality sampling or providing supporting documentation.NOTE - we will have to develop guidance on this.
To link to the Excel spreadsheet containing water monitoring data, click here.