Test page Filterra
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.
Contents
Basic credit
When conditions described in this section are met, applicable Contech Filterra systems are approved for the following pollutant removals.
- Total suspended solids - 80% of the runoff volume treated
- Total phosphorus – 50% of the runoff volume treated
Configurations
Applicable configurations (systems) include
- Filterra Internal Bypass - Pipe (FTIB-P)
- Filterra Internal Bypass – Curb (FTIB-C)
- Filterra® Shallow
Use conditions
Filterra systems shall comply with the following conditions:
- Design, assemble, install, operate, and maintain the Filterra systems in accordance with applicable Contech Filterra manuals.
- The maximum flow rates through the devices are specified below. Use the lowest applicable Infiltration Rate depending on the level of treatment required.
- 175 inches per hour for TSS
- 100 inches per hour for TP
- Systems are designed to treat a specified water quality volume or annual average runoff volume. The annual average runoff treated can be determined using methods that are specified here.
- Each site plan must undergo Contech Filterra review before approval of the unit for site installation.
- Filterra media shall conform to the specifications described in Bioretention System Specifications - JUN17.pdf?ver=2018-05-16-083614-343 Filterra Bioretention System Specifications and shall be sourced from Contech Engineered Solutions, LLC with no substitutions.
- Follow maintenance procedures given in the most recent version of the Guides/Filterra OM Packet.pdf?ver=2018-05-31-143300-750 Filterra Operation and Maintenance Manual (summarized below).
- Install the Filterra in such a manner that flows exceeding the maximum Filterra operating rate are conveyed around the Filterra mulch and media and will not resuspend captured sediment.
- Discharges from the Filterra units shall not cause or contribute to water quality standards violations in receiving waters.
Enhanced credit - 1
When conditions described in this section are met, applicable Contech Filterra systems are approved for the following pollutant removals.
- Total suspended solids - 85% of the runoff volume treated
- Total phosphorus – 60% of the runoff volume treated
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.
Enhanced credit - 2
When conditions described in this section are met, applicable Contech Filterra systems are approved for the following pollutant removals.
- Total phosphorus – 65%
All conditions must be met for the basic credit, described above. In addition, the following conditions must be met.
- TP inflow concentrations must be greater than 0.100 mg/L.
NOTE: this is to be determined. Examples might be enhanced O&M, some sort of annual assessment, monitoring, etc.
Derivation of credits
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.