The Design Criteria will go into effect April 1, 2023. Until then, it will be optional to adhere to the outlined requirements.

Manufactured treatment devices (MTDs) are devices that may be used in stormwater management plans to specifically target the treatment and removal of pollutants from stormwater runoff to achieve regulatory water quality objectives.

The purpose of the design criteria for MTDs is to ensure continual improvement of stormwater management in the city by providing a consistent basis for evaluating MTD designs and performance claims.

The design criteria for MTDs replace the guidance on oil-grit separators (OGSs), as previously detailed in the City of Toronto’s Wet Weather Flow Management Guidelines (WWFMG). All other requirements of the WWFMG will continue to apply.

The design criteria for manufactured treatment devices (MTDs) will be applied to all Stormwater Management Report submissions to the City. It will be optional until March 31, 2023. During this phase-in period, new development applications with a submission date up to March 31, 2023 can use either the new design criteria for MTDs or Sections 2.2.2.2 (3) and Appendix B of the Wet Weather Flow Management Guideline. As of April 1, 2023, only the new design criteria will be applied to Stormwater Management Reports submitted in connection with new development applications received by the City and dated on or after April 1, 2023.

The design criteria for manufactured treatment devices (MTDs) apply to all Stormwater Management (SWM) Reports submitted to the City as part of Terms of References for new development applications, applications for storm connection exemptions under the Toronto Municipal Code (Chapter 681 – Sewers), and applications requiring Environmental Compliance Approvals (ECA) under the applicable approvals framework from the Ministry of Environment, Conservation and Parks (MECP).

Only the following types of MTDs, as classified and defined by Environmental Technology Verification (ETV) Canada (Bulletin CETV 2022-02-0001), can be proposed to meet water quality control targets (i.e., suspended solids removal) of the City’s Wet Weather Flow Management Guideline:

  • Oil-grit separator (OGS) devices typically target large coarse-particle suspended solids removal through gravity separation, as well as oil and grease removal through phase separation.
  • Filter devices typically target both coarse- and fine-particle suspended solids removal through the use of filtration cartridges, filter media or bio-filtration. These devices may also achieve other target pollutant removal, such as nutrients or metals.

MTDs (other than OGSs and filter devices), including inlet pre-treatment devices (e.g. catch basin inserts/retrofit installations), may only be used as best management practices to protect or optimize operations and maintenance of downstream drainage or stormwater management infrastructure. These MTDs will not be credited for suspended solids removal for water quality compliance.

Stormwater Management Reports proposing the use of oil-grit separators (OGSs) will be required to meet the minimum design criteria below.

Testing and Verification

The OGS will be laboratory tested in accordance with the Procedure for Laboratory Testing of Oil-Grit Separators (TRCA/CETV Program) testing protocol and will have current and valid ISO14034: Environmental Technology Verification (ETV).

Design Treatment Flows

Design treatment flows to the OGS will be estimated based on the Rational Method using design rainfall intensities that correspond to percent average annual rainfall volumes.

Average Year Rainfall Volume-Intensity Data Table
Percentage of Cumulative Annual Volume Captured Percentage of Incremental Annual Volume Design Intensity
[mm/hr]
10% 10% 1.5
20% 10% 2.25
30% 10% 3.0
40% 10% 3.75
50% 10% 4.75
60% 10% 5.75
70% 10% 8.0
80% 10% 10.0
90% 10% 15.5
100% 10% 23.25

Data is sourced from design intensities derived based on 60-min aggregate time duration using five-minute interval rainfall time series data (>1 mm/hr) from 1991 Rain Gauge 4 – Central Station, City of Toronto (Wet Weather Flow Master Plan).

Sizing, Performance Evaluation, Scaling

  • The OGS will be sized to treat design treatment flows ensuring the minimum capture of 90 percent average annual rainfall volume from its contributing drainage area(s), assuming no upstream attenuation of design treatment flows.
  • The OGS performance will demonstrate overall site-wide compliance with applicable suspended solids removal targets as a standalone treatment device or as part of a larger stormwater management plan.
  • The annual suspended solids removal performance claimed for the OGS will be based on the average annual rainfall volume-weighted removal efficiency calculated for design surface loading rates (SLR) from all particle sizes of the ETV-tested particle size distribution. The performance evaluation methodology will:
    • Calculate removal efficiencies for all design SLRs based on the full range of design treatment flows, divided by the OGS surface area.
    • Linearly interpolate the verified removal efficiency for design SLRs, which fall between tested SLRs.
    • Assume a removal efficiency which is identical to the verified removal efficiency for the lowest tested SLR, when the design SLR is less than the lowest tested SLR.
    • Assume a removal efficiency of zero (0) for any incremental increase in design SLR, when the design SLR is greater than the highest tested SLR.
  • The selected model for the OGS device will meet all scaling principles relative to the tested model, as per the applicable testing protocol, including but not limited to:
    • The claimed sediment removal efficiencies for similar manufactured treatment devices (MTDs) are the same or lower than the tested MTD at identical surface loading rates; and
    • The similar MTD is scaled geometrically proportional to the tested unit in all inside dimensions of length and width and a minimum of 85 per cent proportional in depth.
  • Where two or more MTDs are proposed to be installed in series, no additional removal credit may be assumed beyond the removal efficiency of the MTD with the highest removal efficiency.

In-line/Off-line Installation

  • The OGS may be installed off-line when the hydraulic bypass capacity of the upstream flow-diversion structure is greater than the full pipe capacity of the incoming sewer, minus the design treatment flow required for 90 per cent average annual rainfall volume capture.
  • The OGS may be installed in-line when the hydraulic bypass capacity of the internal bypass structure is greater than the full pipe capacity of the inlet sewer, minus the design treatment flow required for 90 per cent average annual rainfall volume capture.
  • The OGS may be installed in-line when the hydraulic bypass capacity of the internal bypass structure is greater than the full pipe capacity of the inlet sewer, minus the maximum tested scour flow rate, and the total suspended solids (TSS) effluent concentration for the maximum tested scour flow rate does not exceed 25 mg/L (Canadian Environmental Quality Guidelines for High Flow) above the tested background influent concentration level.

Operations and Maintenance

The OGS will be sized to target a maintenance interval of one year based on the accumulated annual sediment loading (average event mean concentration of 200 mg/L; sediment wet density of 1230 g/m3) generated from the average annual precipitation volume (840 mm).

Stormwater Management Reports proposing the use of filter devices will be required to meet the minimum design criteria below.

Testing and Verification

The filter device will meet any one of the following conditions:

  1. The device will have Washington State Technology Assessment Protocol-Ecology (TAPE) certification for approved technologies with General Use Level Designation (GULD) and have field testing conducted in accordance with the TAPE protocol, where a minimum of three rainfall events have been captured that exceed the design rainfall intensity and depth corresponding to 90 per cent of the average annual rainfall volume.
  2. The device will be field-tested in accordance with Washington State TAPE protocol and will have current and valid ISO 14034:ETV verification, where a minimum of three rainfall events have been captured that exceed the design rainfall intensity and depth corresponding to 90 per cent of the average annual rainfall volume.

Design Treatment Flow

The design treatment flow to the filter device will be estimated based on the Rational Method using the design rainfall intensity required for 90 per cent average annual rainfall volume capture.

Sizing, Performance Evaluation and Scaling

  • The filter device will be sized to treat the design treatment flow in order to demonstrate compliance with site-wide water quality control targets, assuming no upstream attenuation of design treatment flows.
  • The suspended solids removal claimed from the filter device will be based on the tested average removal efficiency of suspended solids up to a 95 per cent confidence interval for the design treatment flow.
  • The suspended solids removal rate determined for the tested filter device may be applied to other model sizes of that filter device provided that appropriate scaling principles as per the applicable testing protocol are applied, including but not limited to:
    • depth of media, composition of media and gradation of media;
    • the ratio of the design treatment flow rate to effective filtration treatment area (filter surface area) is the same or less than the tested filter device;
    • the ratio of effective sedimentation treatment area to effective filtration treatment area is the same or greater than the tested filter device; and,
    • the ratio of wet volume to effective filtration treatment area is the same or greater than the tested filter device.
  • Where two or more manufactured treatment devices (MTDs) are proposed to be installed in series, no additional removal credit may be assumed beyond the removal efficiency of the MTD with the highest removal efficiency.

In-line/Off-line Installation

  • The filter device may be installed off-line when the hydraulic bypass capacity of the upstream flow-diversion structure is greater than the full pipe capacity of the incoming sewer, minus the design treatment flow required for 90 per cent average annual rainfall volume capture.
  • The filter device may be installed in-line when the hydraulic bypass capacity of the internal bypass structure is greater than the full pipe capacity of the inlet sewer, minus the design treatment flow required for 90 per cent average annual rainfall volume capture.

Operations and Maintenance

The filter device will be sized to target a maintenance interval of one year.

Where manufactured treatment devices (MTDs) are proposed in a stormwater management plan, the following minimum MTD-specific data and information will be attached, as part of the Stormwater Management Report submission for City review and acceptance:

Manufactured Treatment Device Summary Form, including supporting documentation.

Operations and Maintenance Manual – For MTDs proposed within public property, content must include, but not be limited to, the following:

Asset Management

  • Identification description, including dimensions
  • Expected life-cycle period
  • Inspection frequency, including operating assumptions and failure modes
  • Maintenance frequency, including rehab and refurbishment
  • Component and materials list and sourcing (e.g. local, overseas)
  • Complete replacement cost
  • Annual operations and maintenance component and materials cost
  • Personnel requirements for inspection and maintenance e.g. number of staff, certification, labour hours
  • Health and safety considerations (e.g. confined space requirements, materials storage and handling)

Operations and Maintenance

  • Accessibility (e.g. access dimensions, ease of access, confined space)
  • Minimum setback and vertical clearance requirement (for access, equipment laydown, use, etc.)
  • Requirements for water supply access and use
  • Inspection and maintenance equipment list
  • Step-by-step inspection procedures
  • Step-by-step maintenance procedures

General

1. Will further feedback or alternate implementation timelines be considered?

The Design Criteria is now finalized and has progressed to its implementation stage. The City initially released proposed guidance on manufactured treatment devices (MTDs) on its official website in late 2019, providing significant lead time for industry to understand key policy changes and adapt ahead of the final December 2022 release of the Design Criteria for MTDs. Feedback from regulatory agencies, industry experts, manufacturers and suppliers has been best incorporated in this final release to provide greater document clarity and usability in implementation.

2. Was the Design Criteria developed in accordance with Ministry of Environment, Conservation & Parks (MECP) guidelines?

The Design Criteria was developed to be consistent with MECP guidance on MTDs stemming from the Stormwater Management Planning and Design Manual (March 2003) and with MECP authorization conditions for stormwater management systems from the upcoming Consolidated Linear Infrastructure Environmental Compliance Approvals permissions framework.

3. Does the Design Criteria apply to both public and private projects?

Yes, the Design Criteria applies to manufactured treatment devices (MTDs) proposed for private projects, as well as those proposed for installation on City property. The City reserves the right to reject MTDs proposed on City property based on site-specific operational and asset management constraints.

4. Are revisions being proposed to the stormwater quality control target of 80% total suspended solids removal from the Wet Weather Flow Management Guidelines (WWFMG)?

Revisions are not proposed at this time. The Design Criteria only replace Sections 2.2.2.2(3) and Appendix B of the WWFMG as they relate to the design of manufactured treatment devices. All other guidance contained in the WWFMG, including stormwater management control targets, remain valid.

5. Will other manufactured treatment devices (MTDs), such as pre-treatment devices, be accepted when they have ISO14034: ETV verification statements?

Performance claims of MTDs (including pre-treatment devices) with ISO14034: ETV verification statements alone will not be recognized for stormwater quality control. The City will only recognize performance claims for stormwater quality control from MTDs (i.e., oil-grit separators and filter devices) which have been tested using well-established, standard laboratory and field-testing protocols; and have been third-party verified/certified, as described in the Design Criteria.

At the discretion of the applicant and property owner, pre-treatment devices may be proposed in addition to MTDs to optimize operations and maintenance of other stormwater management measures. These devices can provide protection of the treatment system but cannot be considered as a treatment system intended to achieve City stormwater quality objectives.

6. Does the Design Criteria apply to treatment technologies such as bio-retention features?

The Design Criteria applies only to manufactured treatment devices, specifically oil-grit separators and filter devices proposed to meet stormwater quality objectives identified in a Stormwater Management Report. The design of treatment technologies, such as low development impact and/or green infrastructure features (e.g., bio-retention) are beyond the scope of the Design Criteria and subject to other applicable regulatory guidance.

7. Why has the City adopted field-testing protocols for filter devices?

The performance testing protocols adopted for both oil-grit separators and filter devices were informed by guidance from local regulatory agencies and independent, third-party, peer-reviewed recommendations (ETV-Bulletin-CETV-2022-02-0001).

For filter devices specifically, field-testing protocols were adopted to best assess performance claims that account for impacts of filter clogging and flow restriction from non-silica-based cohesive sediments, simulated under “real-world” urban runoff conditions.

Technical Requirements

8. Can hydrologic modelling be used to determine design treatment flows instead of the Rational Method?

The Rational Method has been adopted to ensure a conservative and standard approach for sizing manufactured treatment devices (MTDs) across all application types. For larger sites greater than 2 hectares, applicants may delineate smaller sub-catchment areas draining to MTDs and apply the Rational Method for sizing. Hydrological modelling or detention routing will not be accepted for the sizing of specific MTDs but may be used for modelling/sizing of other stormwater management features.

9. Does the 1991 rainfall data provide appropriate design storm information to size manufactured treatments devices (MTDs)?

Typical return-period “design storms” used in peak flow estimations are not appropriate for sizing MTDs, which target stormwater runoff from “first flush”, lower intensity rainfall events. As per the Wet Weather Flow Management Guidelines (2006), 1991 is the representative year for average annual rainfall conditions that govern stormwater balance and stormwater quality control targets for the City. Therefore, the design rainfall intensity data in the Design Criteria provides a reasonable and standard basis to determine design treatment flows for stormwater quality control via the Rational Method. Note that the design rainfall intensities derived from the 1991 data are comparable to those analyzed using longer-term, multi-year rainfall data.

10. Are there any calculation tools to evaluate performance claims from oil-grit separators?

Applicants are responsible for ensuring that any third-party calculation tools (e.g., TRCA-STEPP OGS Review Sheet) proposed for use in performance evaluation, sizing, and decision-making, meet all requirements of the Design Criteria, and verified for accuracy of data and methodology.

11. Will the City recognize oil-grit separator (OGS) performance claims greater than 50% total suspended solids (TSS) removal?

The City will credit the evaluated performance claim (e.g., percentage TSS removal) from a proposed OGS device when it is designed in accordance with the requirements of the Design Criteria. Depending on site-specific conditions, this may be lower or higher than 50%. A default 50% TSS removal credit for OGS devices will no longer be applicable.

12. Is the minimum rainfall capture requirement a proposed change to Washington state Technology Assessment Protocol – Ecology (TAPE) field testing protocols?

The City is not proposing changes to the TAPE field-testing protocols. However, the Design Criteria requires applicants to conduct a conditional check of TAPE tested rainfall events to ensure results from TAPE certifications are applicable to the City’s climate.

13. How should filter devices be sized to ensure a target maintenance interval of 1 year?

It is recognized that maintenance intervals differ between filter devices and can vary depending on site-specific characteristic. As such, the City will rely on the proposed filter device to be designed for a 1-year maintenance interval, as determined and recommended by the manufacturer.

Implementation

14. Will there be a pre-approved list of manufactured treatment devices (MTDs), requiring manufacturers to apply/register for?

No. The City does not require, endorse, or approve the exclusive use of any individual MTD products or brands. The selection of any MTD in a Stormwater Management Report is solely at the discretion of the professional engineer responsible for the report’s preparation, on behalf of their client/applicant and subject to compliance with Wet Weather Flow Management Guidelines (2006) and the Design Criteria for MTDs.

15. Will the manufactured treatment device design drawings need to be sealed separately from the Stormwater Management Report seal?

The City does not regulate Professional Engineer sealing responsibilities. Please refer to relevant guidelines from Professional Engineers Ontario to understand assumed responsibilities from the use of the Professional Engineer seal.