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===3. Treatment trains designed to enhance overall treatment system performance===
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→Treatment trains with runoff volume reduction facilities
[[File:(LSRCA Logo) Atherley Narrows annual chloride concentrations (1971 - 2020).png|thumb|650px|A graph showing increasing average levels of chloride found in Atherley Narrows, (a rural sampling location, between Lake Couchiching and Lake Simcoe), over the past few decades, due in part to increased use of rock salt in parking lots, roadways and commercial and residential properties. From 2005 - 2020 the amount of chloride increase per year has doubled when compared to 1971 - 1986 (1.26 mg/L per yr. vs. 0.63 mg/L per yr.) (LSRCA, 2021). It is estimated that by 2120 the average level of chloride within the the Lake Simcoe watershed will exceed the 120mg/L guideline set by CWQG. (LSRCA, 2018)<ref name="example7">LSRCA. 2018. Parking Lot Design Guidelines: Municipal Policy Templates to Promote Salt Reduction in Parking Lots. https://www.lsrca.on.ca/Shared%20Documents/Parking-Lot-Design-Guidelines/Parking%20Lot%20Design%20Guidelines.pdf.</ref>]]
[[File:Treatmenttrain TRCA.JPG|thumb|600px|Example of a generalization of utilizing a “Treatment Train Approach” illustrated here. Using [[permeable pavement]] as a source control/lot control on your business/residential property, effluent then flows into conveyance control such as an [[Exfiltration trench|exfiltration system]], used in conjunction with the minor stormwater system as shown above. and then flowing into a stormwater management pond (wet pond) for additional erosion and flood control (TRCA, n.d. Understand - Stormwater Management. Accessed: https://trca.ca/conservation/stormwater-management/understand/</ref>]]
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==Overview==
==Overview==
A treatment train uses a combination of source (LID), conveyance and/or end-of-pipe practices to meet water quality, water quantity, water balance, and erosion design criteria for the site. These may be implemented to reduce the burden of facility maintenance, address a broader range of design criteria, increase overall treatment system performance, and/or control the rate of flow through downstream facilities.
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A treatment train uses a combination of lot-level or source (LID), conveyance and/or end-of-pipe practices to meet water quality, water quantity, water balance, and erosion design criteria for the site. These may be implemented to reduce the burden of facility maintenance, address a broader range of design criteria, increase overall treatment system performance, and/or control the rate of flow through downstream facilities.
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{|class="wikitable"
|+Types of Treatment Train Practices<ref>Ministry of the Ontario Conservation & Parks (MECP). 2021. Understanding Stormwater Management: An Introduction to Stormwater Management Planning and Design. Major concepts and environmental concerns to consider in the Ministry of the Environment’s Stormwater Management Planning and Design Manual 2003. Updated: July 15, 2021. Accessed: https://www.ontario.ca/page/understanding-stormwater-management-introduction-stormwater-management-planning-and-design</ref>
|-
!Type of Control/Practice
!Lot-Level Source Controls & Conveyance Practices
!End-Of Pipe Facilities
|-
|'''Storage'''
|
*Rooftop storage
*[[Blue roof]]
*[[green roof]]
*[[rain barrel|Cistern]]
*Temporary Parking lot storage
*Oversized storm sewer storage
|
|-
|'''Infiltration'''
|
*Flatter and gently sloped lot grading
*[[Bioretention]]
*[[Bioswales]]
*[[Soakaways]]
*[[Infiltration trenches]]
*[[Exfiltration trench]]
*[[Infiltration chambers]]
*[[Enhanced swales]]
*[[swales]]
*[[Vegetated filter strips]]
|
|-
|'''Pretreatment'''
|
*[[Sand filters]]
*[[Filter Media]]
*[[Vegetated filter strips]]
*[[Oil and Grit Separators]]
*[[Grassed Swales]]
*[[Vegetated Filter Stripes]]
*[[Filter Media Additives for Phosphorus Removal|Media Filters]]
*[[Pretreatment#concentrated underground flow|Proprietary concentrated underground flow features]]
|
|-
|'''End-of-Pipe / Flood & Erosion Control'''
|
|
*[[Wet ponds]]
*[[Wetlands]]
*[[Dry ponds]]
*[[Filter Media Additives for Phosphorus Removal|Media Filters]]
*[[Pretreatment#concentrated underground flow|Proprietary concentrated underground flow features]]
*[[Infiltration chambers|Infiltration basins]]
*[[Stormwater tree trenches]]
|}
==Types of Treatment Train Designs==
==Types of Treatment Train Designs==
These are the most common types of treatment trains. They typically involve installation of one or more [[pretreatment]] devices upstream or at the [[inlet]] of the primary stormwater treatment facility.
These are the most common types of treatment trains. They typically involve installation of one or more [[pretreatment]] devices upstream or at the [[inlet]] of the primary stormwater treatment facility.
[[File:Treatment train air force.JPG|thumb|800px|An example of a stormwater treatment train approach at Tyndall Air Force Base in Florida, in a coastal environment. This example includes source controls of [[bioretention]] parking islands, [[permeable pavement]], and conveyance controls of[[swales]], a natural infiltration basin in a forested woodlot, and end-of-pipe controls of [[dry ponds]], [[constructed wetlands]] and coastal dunes. All of these features help to reduce traditional SWM features' maintenance, treatment and rehabilitation coasts, while also reducing pollutants into the receiving waterbody. (U.S Air Force, 2020)<ref>U.S. Air Force. n.d. LANDSCAPE MASTER PLAN - C. Site Development Criteria. CO4. Stormwater - C04.3.2 Stormwater at Individual Building Sites. Accessed: https://www.tyndallifs.com/images/LMP_pdf/TAFB_Final_LandscapeMasterPlan_2020-09-24_SectionC04.pdf</ref>]]
'''Example''': Runoff into larger treatment practices such as [[bioretention]] or [[stormwater tree trenches]] may be pretreated by [[Inlet sumps: Gallery|concrete sumps]] at [[curb cut]] inlets, [[forebays]] or catch basin inserts, which are designed to capture coarse sediment, debris and trash. Centralizing sediment and trash captured at the inlet or entrance to the facility reduces maintenance by preventing [[filter media]] [[clogging]] and limiting the area over which sediment and trash needs to be removed. In some cases, pre-treatment device clean-outs may be incorporated into existing municipal catch basin cleaning programs.
'''Example''': Runoff into larger treatment practices such as [[bioretention]] or [[stormwater tree trenches]] may be pretreated by [[Inlet sumps: Gallery|concrete sumps]] at [[curb cut]] inlets, [[forebays]] or catch basin inserts, which are designed to capture coarse sediment, debris and trash. Centralizing sediment and trash captured at the inlet or entrance to the facility reduces maintenance by preventing [[filter media]] [[clogging]] and limiting the area over which sediment and trash needs to be removed. In some cases, pre-treatment device clean-outs may be incorporated into existing municipal catch basin cleaning programs.
[[File:Sump inelt to chamber system.JPG|thumb|500px|Example of a [[Pretreatment#Concentrated underground flow|overland flow sump inlet]] allowing sediment to settle out of influent stormwater before entering a large infiltration chamber housed under a parking lot/ The outlet control device can then drain into a [[dry pond]] furthu downstream or offsite (Source: Philadelphia Water Department. 2020)<ref>Philadelphia Water Department. 2020. Stormwater Management Guidance Manual: Version 3.2. Accessed from: https://www.pwdplanreview.org/upload/manual_pdfs/PWD-SMGM-v3.2-20201001.pdf</ref>]]
===2. Treatment trains designed to address one or more design criteria===
===2. Treatment trains designed to address one or more design criteria===
These types of treatment trains combine practices that address different [[Screening LID options|design criteria]], in recognition that most individual stormwater facility types do not meet all design criteria as stand-alone facilities. For instance, [[SWM ponds|stormwater wet ponds]] may provide [[water quality]], erosion and flood control but not water balance control (i.e. [[Runoff volume control targets|runoff volume control]]). [[Bioretention]] provides good water quality and water balance control but are rarely designed for flood control.
These types of treatment trains combine practices that address different [[Screening LID options|design criteria]], in recognition that most individual stormwater facility types do not meet all design criteria as stand-alone facilities. For instance, [[SWM ponds|stormwater wet ponds]] may provide [[water quality]], erosion and flood control but not water balance control (i.e. [[Runoff volume control targets|runoff volume control]]). [[Bioretention]] provides good water quality and water balance control but are rarely designed for flood control.
'''Example''': [[Pretreatment#Concentrated underground flow|Proprietary filtration treatment device]] (providing water quality) draining to an underground [[infiltration trench]] or [[Infiltration chambers|chamber system]] (providing water balance control). Overflows from the trench or chamber system could drain to a [[dry pond]] or other flood control facility to provide water quantity and erosion control). Another example may be to direct low flows from a stormwater management pond [[outlet]] to an infiltration practice.
'''Example''': [[Pretreatment#Concentrated underground flow|Proprietary filtration treatment device]] (providing water quality) draining to an underground [[infiltration trench]] or [[Infiltration chambers|chamber system]] (providing water balance control). Overflows from the trench or chamber system could drain to a [[dry pond]] or other flood control facility to provide water quantity and erosion control). Another example may be to direct low flows from a stormwater management pond [[Overflow|outlet]] to an infiltration practice.
'''Performance calculation''': Treatment trains designed to address multiple design criteria may improve overall water quality performance by, for example, reducing water quality concentrations in the first facility and reducing water quality loads (through infiltration/evapotranspiration) in a second facility. Even if the effluent concentration from facility one and facility two are the same, the overall load reduction of the treatment train may be greater than provided by any one of the facilities alone.
'''Performance calculation''': Treatment trains designed to address multiple design criteria may improve overall water quality performance by, for example, reducing water quality concentrations in the first facility and reducing water quality loads (through infiltration/evapotranspiration) in a second facility. Even if the effluent concentration from facility one and facility two are the same, the overall load reduction of the treatment train may be greater than provided by any one of the facilities alone.
===3. Treatment trains designed to enhance overall treatment system performance===
[[File:Storm bmps rev3.png|thumb|400px|An example of a treatment train approach used to enhance treatment performance in an area with limited surface area due to parking and the adjacent municipal roadway. In this example water is able to be collected and then conveyed from a [[green roof]] system, a [[bioswale]] and [[permeable pavement]] parking lot, through an [[OGS|oil and grit separator]] and then to an [[Infiltration chamber]] or an underground [[Rainwater harvesting|cistern]] tank. Clean water can then be reused onsite or overflow out to the municipal storm sewer and receiving waterbody (City of Saskatoon, 2023).<ref>City of Saskatoon. 2023. Storm Water Management Credit Program. Image courtesy of the City of Mississauga. Accessed: https://www.saskatoon.ca/services-residents/power-water-sewer/storm-water/storm-water-management-credit-program</ref>]]
The design intent of these treatment trains is to enhance overall system performance. The previous category of treatment train may enhance performance, but the objective may not always be to address a broader range of stormwater criteria.
The design intent of these treatment trains is to enhance overall system performance. The previous category of treatment train may enhance performance, but the objective may not always be to address a broader range of stormwater criteria.
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Of course, the real world is not black and white, and it is possible to blend these categories to meet a variety of different site stormwater management objectives. The purpose of categorizing the treatment train types into design priorities is to highlight the need to consider different objectives, while recognizing that if the design priority of the treatment train is narrowly focused, objectives other than those targeted may not be met.
Of course, the real world is not black and white, and it is possible to blend these categories to meet a variety of different site stormwater management objectives. The purpose of categorizing the treatment train types into design priorities is to highlight the need to consider different objectives, while recognizing that if the design priority of the treatment train is narrowly focused, objectives other than those targeted may not be met.
==Calculating [[Water Quality]] Performance of Treatment Trains==
==Calculating Performance of Treatment Trains==
The performance of a treatment train will vary based on the type of stormwater treatment practices implemented and their arrangement within the treatment train. Various changes occur as [[Runoff volume control targets|runoff]] moves through the treatment train. Key changes that need to be considered when [[Low impact development treatment train tool|calculating treatment train performance]] including:
The performance of a treatment train will vary based on the type of stormwater treatment practices implemented and their arrangement within the treatment train. Various changes occur as [[Runoff volume control targets|runoff]] moves through the treatment train. Key changes that need to be considered when [[Low impact development treatment train tool|calculating treatment train performance]] including:
Removal efficiency calculations are sensitive to influent concentration because facility effluent concentrations cannot be reliably reduced beyond a certain level, which varies by facility type. For example, a pond may have an ‘irreducible’ effluent concentration of 30 mg/L for an average rainfall year. If the TSS influent concentration to the pond is 200 mg/L, the pond removal efficiency would be 85%. If the treatment practice(s) upstream of the pond reduce the pond influent concentration to only 100 mg/L, the TSS removal efficiency of pond would only be 70%. This value may be even lower if the 100 mg/L contains a higher percentage of fine particles than untreated runoff (which is often the case).
Removal efficiency calculations are sensitive to influent concentration because facility effluent concentrations cannot be reliably reduced beyond a certain level, which varies by facility type. For example, a pond may have an ‘irreducible’ effluent concentration of 30 mg/L for an average rainfall year. If the TSS influent concentration to the pond is 200 mg/L, the pond removal efficiency would be 85%. If the treatment practice(s) upstream of the pond reduce the pond influent concentration to only 100 mg/L, the TSS removal efficiency of pond would only be 70%. This value may be even lower if the 100 mg/L contains a higher percentage of fine particles than untreated runoff (which is often the case).
===3. Changes in [[Runoff volume control targets|runoff volume]]===
===3. Changes in runoff volume===
Where runoff is being reduced along the treatment train through infiltration and evapotranspiration, there will be a change in [[water quality]] loading that needs to be considered.
Where runoff is being reduced along the treatment train through infiltration and evapotranspiration, there will be a change in [[water quality]] loading that needs to be considered.
The water quality load is the product of runoff concentrations and runoff volumes. Hence, a change in either of these variables will result in a change in load. As concentrations and volumes are affected by different variables it is best to consider the components separately, and then combine them to calculate overall load based performance for the treatment train under consideration.
The water quality load is the product of runoff concentrations and runoff volumes. Hence, a change in either of these variables will result in a change in load. As concentrations and volumes are affected by different variables it is best to consider the components separately, and then combine them to calculate overall load based performance for the treatment train under consideration.
==Calculations for Load Based Performance==
==Calculations for Load Based Performance==
*''A'' = Flow proportioned influent concentration (mg/L)
*''A'' = Flow proportioned influent concentration (mg/L)
*''B'' = Flow proportioned effluent concentration (mg/L)}}
*''B'' = Flow proportioned effluent concentration (mg/L)}}
Simple treatment train equations that apply the pollutant removal efficiency of the downstream treatment practice to the fraction of load remaining after passing through the upstream treatment practice, or those that assign downstream practices half the removal efficiency of the upstream practice '''are not recommended'''. Instead, the configuration and type of treatment train should be considered on a case by case basis, with consideration for changes in influent runoff concentration/composition and runoff volume as water drains through the different practices. Some examples are provided in the sections below.
==Treatment trains without runoff volume reduction==
As noted above, non-infiltrating stormwater facilities are often designated as enhanced or basic treatment based on their capacity to remove total suspended solids (TSS). Enhanced level facilities are credited with 80% TSS removal while basic level facilities are credited with 60% TSS removal or less.
Basic level facilities are typically placed upstream of enhanced level facilities in treatment trains because enhanced level facilities remove the coarse sediment particles that would otherwise be removed by the basic level facility, as well as finer sediment particles. Placing the level two facility downstream of the level one facility would, therefore, not enhance TSS removal, although it may enhance removal of other pollutants depending on the design components.
Since basic level facilities remove TSS particles that are effectively removed by enhanced level facilities, the removal efficiency of a treatment train consisting of two non-infiltrating facilities would be equal to the removal efficiency of the highest performing facility (i.e. 80% TSS removal), assuming that the facilities are sized appropriately.
Examples of this type of treatment train would include: (i) [[Pretreatment features|catch basin inserts]] (aka water quality inlets) upstream of a filtration facility (e.g. lined [[bioretention]], [[Pretreatment|proprietary filtration system]], [[Media filters|sand filter]]); (ii) [[OGS]] upstream of a wet pond; (iii) [[Infiltration chambers|temporary parking lot or pipe storage]] upstream of a filtration facility. If an OGS is placed upstream of a [[dry pond]], the overall treatment performance would be equal to that of the dry pond since the finer particle size fraction of TSS is not captured. As mentioned above, the major benefit of these types of treatment trains is to reduce long term maintenance cost and effort by centralizing sediment in the upstream practice where it is easier to clean out.
In some cases, it may be advantageous to include two level one facilities in a treatment train. An example may be a lined [[bioretention]] with pre-treatment upstream of a [[Pretreatment#Concentrated underground flow|filter with media designed to enhance phosphorous uptake]]. The overall [[Phosphorus#Limiting excess phosphorus|phosphorus removal rate]] for the treatment train would be equivalent to that of the downstream filter, assuming that it is sized appropriately for the site in question. The bioretention facility in this instance would help to control flow rates to the downstream facility while also filtering out sediments that would otherwise cause pre-mature [[clogging]] of the downstream [[filter media]].
==Treatment trains with runoff volume reduction facilities==
[[File:72208733 sustainable drainage 624.jpg|thumb|650px|A treatment train example of source controls in a housing development neighbourhood with [[vegetated filter strips]], [[swales]] and [[permeable pavement]] driveways and roadways achieving water balance requirements during a 90th percentile event and then overflows can be conveyed to a [[dry pond]] / [[wet pond]] and then into receiving [[constructed wetlands]] and water courses (Susdrain/CIRIA, 2014)<ref>Susdrain/CIRIA. 2014. Sustainable Urban Drainage Systems (SUDS) in Flood Prevention. DuratexUK Rubber & Plastics Ltd. Accessed: https://www.duratex.co.uk/company-blog/industry-news/sustainable-urban-drainage-systems-suds-in-flood-prevention</ref>]]
These types of treatment trains are becoming more common because they can achieve multiple [[Runoff volume control targets|stormwater control]] and [[water quality|treatment objectives]]. Since wet ponds alone do not achieve stormwater water balance criteria, they must be supplemented with facilities providing runoff volume reductions to meet regulatory requirements. If site water balance objectives require control of the 90th percentile event (roughly 25 – 30 mm in most jurisdictions), the same infiltration facilities may also be used to treat the water quality storm (typically 25 mm), allowing for a [[dry pond]] or similar temporary detention facility to be used at the end-of-pipe to meet flood and erosion control criteria.
In the example of LID practices upstream of a wet pond, the overall treatment train would meet the 80% TSS reduction target, since both facilities achieve enhanced level water quality targets. The wet pond may be downsized to account for the upstream reduction in runoff volumes, but the overall volume of water treatment to the enhanced level target (80% TSS removal) would be equal to the volume treated by the LID plus that treated by the wet pond, which together would exceed the 90th percentile water quality requirement.
In cases where the 90th percentile storm volume is fully retained (i.e. infiltrated or evapotranspired), the wet pond may be substituted with a dry pond. In this scenario, the water quality and water balance volumes are provided by the upstream facilities, and the dry provides flood and erosion control. Runoff volumes exceeding the 90th percentile storm volume would be treated at a more basic level. Lower maintenance costs would be the primary advantage of substituting a dry pond for a wet one, although the dry pond may also provide opportunities for multiple uses in some contexts.
One final and relatively common example of infiltration practice treatment trains on smaller sites would be a [[Pretreatment#Concentrated underground flow|non-infiltrating filter]] used as pre-treatment to an infiltration practice such as a [[infiltration trench|trench]] or [[Infiltration chambers|chamber]] system. The upstream facility is sized to treat the water quality volume (or higher) and the downstream infiltration trench or chamber is sized to meet water balance criteria (e.g. infiltration of the 90th percentile storm). If the entire water quality volume is infiltrated by the downstream practice, the TSS load reduction for the treatment train would be 100%. If only 80% is infiltrated in the downstream facility, the TSS load reduction would be 96% since 80% of TSS is reduced in the first facility and 80% of the volume is reduced in facility two (0.8 + (0.8 x 0.2) = 0.96 x 100). The second facility would not further reduce TSS concentrations because only fine unfilterable sediments are left once the runoff has passed through facility one. Therefore, facility two reduces water quality loads only by reducing the volume of runoff (which was assumed to be 80% in this example).
==References==
==References==