Oil and Grit Separator

Overview

Oil and Grit Separators (OGS) are Manufactured Treatment Devices (MTDs) used for water quality treatment of stormwater runoff through the removal of large particle suspended solids and associated pollutants, and debris. Some devices can also trap light liquids such as oil and other floatables. These MTDs are typically installed underground within the stormwater sewer system in an on-line or off-line configuration. They are distinguished from Filtration-based MTDs by their removal of solids through settling rather than filtration.

Application

Oil and Grit Separators are suitable as pre-treatment to other downstream treatment systems such as ponds or LID features. Cost effective application of OGS for LID typically requires that the practice have a single inlet with a drainage area larger than 0.2 ha.

OGS normally require maintenance every year to function as designed. The cost and level of effort required to undertake the maintenance program over the full life cycle of the practice should be carefully considered when implementing this water quality treatment solution.

Testing and Verification

Several agencies across Canada require ISO 14034 Environmental Technology Verification (ETV) as a condition of technology acceptance. For OGS, the ISO 14034 verification process in Canada consists of two parts:

1. Third party laboratory testing of MTDs in accordance with the TRCA’s Procedure for Laboratory Testing of Oil Grit Separators and associated bulletins, and
2. Third party verification of the test in accordance with the 14034 ETV standard.

The ISO 14034 verification process is currently administered by Globe Performance Solutions and Verify Global. Completed ISO 14034 verification statements for OGS are posted to the former Canadian ETV website, here.

Note that ISO 14034 verification is a necessary, but not sufficient condition for approval agencies using the ISO/ETV process for technology acceptance. The technology must also be classified as an Oil Grit Separator (i.e. not include a filter) for the Procedure for Laboratory Testing of OGS to have been properly applied. This ETV Bulletin helps to provide clarification on this requirement: See table below for a list of current ISO 14034 verified OGS MTDs.

List of OGS MTDs

Verification Year (Initial)	Technology Name	Company Name	Fact Sheet
2022	RWM-DM-1200 & DM-1200-OS Stormwater Systems	Rainwater Management LTD.	Fact Sheet
2019	Hydro International Downstream Defender® OGS	Hydro International	Fact Sheet
2019	SciCLONE™ Hydrodynamic Separator	Bio Clean Environmental Inc. (A Forterra Company)	Fact Sheet
2018	Hydro International First Defense® OGS	Hydro International	Fact Sheet
2018	Hydroworks® HydroStorm (HS) OGS	HydroWorks, LLC	Fact Sheet
2017	Stormceptor® EF and EFO Oil-Grit Separators	Imbrium Systems, Inc.,	Fact Sheet
2017	CDS Hydrodynamic Separator®	CONTECH Engineered Solutions LLC	Fact Sheet
2016	SDD3 Oil Grit Separator®	Next Stormwater Solutions (8091200 Canada Inc.)	Fact Sheet

Performance Test Results

The Procedure for Laboratory Testing of Oil Grit Separators provides performance testing for the following performance measures based on a standard sediment particle size distribution:

1. Sediment removal performance: Mass balance testing at seven surface loading rates to determine the capacity of MTDs to retain solids
2. Sediment scour and re-suspension test: Sediment is pre-loaded into the unit and effluent concentrations are measure at five surface loading rates to determine how well the units retain captured sediment.
3. Light liquid capture and retention test: An optional test in which beads with a density similar to motor oil are pre-loaded into the unit and the number of beads in the effluent are measured to assess the capacity of the unit to trap and retain light liquids.

There are currently eight OGS vendors with ISO 14034 verifications (as shown in the table above). The list of manufacturers and test results of all OGS products and other verified technologies can be found here. Sediment removal performance results were relatively consistent across different MTD designs, with slightly more variation at higher surface loading rates (see Graph below).
*Note: Oil Grit Separators do not achieve the 80% removal efficiency required for stand alone application in Ontario, even at very low flow rates.

In lab testing of a Stormceptor OGS device, here seen testing discharge rates and sediment effluent loads at St. Anthony Falls Laboratory, Minneapolis, Minnesota. (Saddoris, et al. 2010)

The graph above shows the average, minimum and maximum sediment removal efficiencies for ISO 14034 verified OGS at seven surface loading rates (n = 10).

Scaling

The ISO 14034 ETV sediment removal rate data for the tested model at specified surface loading rates may be applied to similar MTDs of smaller or larger size by proper scaling. Scaling the performance results of the tested MTD to other model sizes without completing additional testing is acceptable provided that:

1. The claimed sediment removal efficiencies for the similar MTD are the same or lower than the tested MTD at identical surface loading rates; and
2. The similar MTD is scaled geometrically proportional to the tested unit in all inside dimensions of length and width and a minimum of 85% proportional in depth.

Ensuring the unit is scaled appropriately in all dimensions also helps to ensure that the recommended maintenance intervals for the unit can be achieved.

Sizing

It is recommended that a standard sizing approach be used for all OGS units to ensure they are evaluated based on a consistent methodology. The attached OGS Review Calculator has been developed to facilitate application of ISO 14034 ETV test data through a standard approach applicable to all OGS MTD designs. The following methods and processes are built into the tool:
Rational Method used as a basis for flow calculations:
$Q=CiA$

• • $C$ is the site runoff coefficient,
  • $i$ is the rainfall intensity, and;
  • $A$ is the drainage area)
• Target treatment is based on capture and treatment of the average annual runoff volume for the site using ISO 14034 verified sediment removal test results for 7 surface loading rates
• Linear interpolation is used to calculate sediment removal efficiencies between the ISO/ETV tested surface loading rates
• Surface loading rates below the lowest ISO/ETV tested surface loading rate are assigned a sediment removal efficiency equal to that of the lowest tested rate
• Hourly historical rainfall data (minimum 20 years) are used to generate the rainfall intensity distribution curve.
• Capacity to add historical rainfall record is provided in order to generate the relationship between hourly rainfall intensities vs average annual rainfall volume for the meteorologic station of choice.

Associated Documents Submitted with OGS Review Calculator

Other documents typically submitted with the OGS Review Calculator would include:

• Signed Stormwater Management (SWM) Report, engineering drawings, and specifications by the design engineer (Professional Engineer in Ontario) on behalf of their respective clients/owners
• Applicable third-party testing and verification/certification statements and documentation supporting performance claims
• Manufacturer-provided letter/documentation confirming proposed and tested MTD model details (i.e., diameter, depth, treatment depth, max storage depth, sediment storage capacity, hydraulic capacity for bypass), and compliance with sizing and scaling provisions, as per the OGS Procedure scaling provisions
• Operations and Maintenance Manual indicating the inspection and maintenance frequencies, methods of maintenance, health and safety considerations and other relevant information.

ISO 14034 verified OGS vendor websites

#RWM-DM-1200 & DM-1200-OS Stormwater Systems - Developed by: Rainwater Management LTD. #Hydro International Downstream Defender® OGS - Developed by: Hydro International. #SciCLONE™ Hydrodynamic Separator - Developed by: Bio Clean Environmental Inc. (A Forterra Company). #Hydro International First Defense® OGS - Developed by: Hydro International #Hydroworks® HydroStorm (HS) OGS - Developed by HydroWorks LLC. #Stormceptor® EF and EFO Oil-Grit Separators - Developed by: Imbrium Systems, Inc., #CDS Hydrodynamic Separator® - Developed by: CONTECH Engineered Solutions LLC #SDD3 Oil Grit Separator® - Developed by: Next Stormwater Solutions (8091200 Canada Inc.)

Systems designed to remove trash, debris and some amount of sediment, oil and grease from stormwater runoff based on the principles of sedimentation for the grit and phase separation for the oil.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

The technique of removing pollutants from runoff as it infiltrates through the soil.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

The total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

The total mass of a pollutant entering a waterbody over a defined time period.

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

This formula is used to calculate peak rates of runoff when designing drainage LID BMPs in urban area. It is useful in estimating runoff on relatively small areas (roofs, parking lots, medians, road right-of-ways, etc.)

The rate of rainfall in millimeters per hour.

Stormwater Management