Information: Reference to specific commercial products, processes, or services by trade name, trademark, service mark, manufacturer, or otherwise does not constitute or imply endorsement, recommendation, or favoring by the Minnesota Pollution Control Agency.
CONTECH Engineered Solutions, LLC. MWS-Linear Modular Wetland is an engineered filtration system designed to filter pollutants from stormwater runoff. It is classified as a manufactured treatment device (mtd).
This page provides information on pollutant removal credits for Contech MWS-Linear Modular Wetland, links to supporting information, and links to information on system design, inspection, operation, and maintenance.
TP and TSS credits
When conditions described in this section are met, applicable Contech MWS-Linear Modular Wetland systems are approved for the following removals for total suspended solids (TSS) and total phosphorus (TP).
- TSS: 80 percent removal
- TP: Tier 1
- Credit: 50 percent removal
- Conditions for receiving credit
- Inspect manufactured treatment device a minimum of twice during year 1. Conduct inspections following manufacturer’s instructions/recommendations and any additional instructions listed in this section. Use maintenance indicators provided by manufacturers to determine if maintenance is needed. Maintenance procedures should follow manufacturer’s guidelines. After year 1, follow manufacturers inspection, operation, and maintenance schedule and procedures unless otherwise required or unless year 1 inspections indicate a need for increased inspection and/or operation and maintenance.
- Comply with appropriate configurations and Use conditions from TAPE.
- Comply with appropriate configurations in the Design Manual and Use conditions
- TP: Tier 2
- Credit: 53 percent removal
- Conditions for receiving credit
- Must meet Tier 1 conditions.
- DP should be 25 percent or less of TP. For a discussion of conditions where DP is likely to exceed 25% of TP, link here. TP removal should be adjusted when DP fractions exceed 25%, as described at the link provided above.
- Inspect manufactured treatment device monthly during the frost free season for the first year of operation after construction. Conduct inspections following manufacturer’s instructions/recommendations. Use maintenance indicators provided by manufacturers to determine if maintenance is needed. Maintenance procedures should follow manufacturer’s guidelines. Determine future inspection and maintenance schedules from findings during the first year of operation.
- TP: Tier 3 - no Tier 3 credit at this time
For more information on credits, see TP and TSS credits and guidance for manufactured treatment devices (mtds)
For a discussion of Contech MWS-Linear Modular Wetland configurations see appropriate configurations in the design, installation, and specification documents.
To receive the full credit, Contech MWS-Linear Modular Wetland systems must comply with the following conditions.
- Design, assemble, install, operate, and maintain Contech MWS-Linear Modular Wetland systems in accordance with applicable manuals.
- The maximum flow rates through the devices are specified below.
- Sized at a hydraulic loading rate of:
- 1 gallon per minute (gpm) per square foot (sq ft) of Wetland Cell Surface Area
- Prefilter box (approved at either 22 inches or 33 inches tall)
- 3.0 gpm/sq ft of prefilter box surface area for moderate pollutant loading rates (low to medium density residential basins).
- 2.1 gpm/sq ft of prefilter box surface area for high p
- 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 review before approval of the unit for site installation.
- The applicant tested the Modular Wetlands Linear Stormwater Treatment System with an external bypass weir. This weir limited the depth of water flowing through the media, and therefore the active treatment area, to below the root zone of the plants. This GULD applies to Modular Wetlands Linear Stormwater Treatment Systems whether plants are included in the final product or not.
- MWS-Linear Modular Wetland media shall conform to the specifications described in Specifications and shall be sourced from Contech Environmental Services, Inc. (A Forterra Company) with no substitutions.
- Follow maintenance procedures given in the most recent version of the Operation and Maintenance Manual.
- Install the Contech MWS-Linear Modular Wetland in such a manner that flows exceeding the maximum Contech MWS-Linear Modular Wetland operating rate are conveyed around the Contech MWS-Linear Modular Wetland media and will not resuspend captured sediment.
- Discharges from the Contech MWS-Linear Modular Wetland units shall not cause or contribute to water quality standards violations in receiving waters.
- When applicable, adhere to use conditions provided in Washington State Department of Ecology's report (Ecology's Conditions of Use) For Contech Engineered Solutions, LLC (Contech) Modular Wetlands Linear. Note that some information in this report is specific to Washington State and not applicable to Minnesota.
Credits apply only to the water being treated by a device. The applicable treatment volume must be determined using one of the methods described here.
The Tier 1 credit equals the TAPE-approved credits. Tier 2 credit was determined by analyzing water quality data collected at a transportation maintenance facility in Portland, Oregon. The site consisted of 0.45 acres of impervious surface from parking and roadways areas. The unit size was 4 X 13 feet.
MPCA compiled data from General Use Level Designation Technical Evaluation Report. Below are summary statistics for the device.
- Median TP inflow - 0.103 mg/L
- Median TP removal (all data with concentrations > 0.05 mg/L) - 61.3%
- 95% lower confidence limit TP removal (all data with concentrations > 0.05 mg/L) - 52.5%
- Median TP removal (data meeting TAPE criteria) - 63.3%
- 95% lower confidence limit TP removal (data meeting TAPE criteria) - 54.0%
- Median TSS removal (all data) - 81.9%
- 95% lower confidence limit TSS removal (all data) - 71.2%
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). Of the 24 samples, TAPE medians and means represent 16 samples for TP.
Inspection, operation, and maintenance
Meet the conditions specified for the appropriate TP and/or TSS credit.
Meet the following conditions, unless conditions for the appropriate TP and/or TSS credit are more stringent.
- 2 maintenance visits required annually if annual precipitation exceeds 30 inches; one visit annually if annual precipitation is less than 30 inches