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===Step 1: Review Project Goals & Site Conditions===
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[http://stormwater.pca.state.mn.us/index.php/Using_the_treatment_train_approach_to_BMP_selection Stormwater treatment trains] combine multiple stormwater treatment processes and/or practices in a manner that ensures management of all pollutants that could affect a [[Glossary#R|receiving water]]. To provide guidance for stormwater managers, hypothetical treatment trains were developed for five common stormwater management scenarios. This page provides information on implementing a stormwater [[Glossary#B|Best Management Practice]] (BMP) treatment train for an [http://stormwater.pca.state.mn.us/index.php/Glossary#U ultra-urban setting]. To see other scenarios, see [[Scenario for developing a stormwater treatment train for an ultra-urban setting#Related articles|related articles]] at the bottom of this page.
  
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The Ultra-Urban site is characterized by high impervious cover in the form of residences, parking, or commercial development. For the purposes of this scenario, the drainage conditions for a single building on a city block in downtown Minneapolis, Minnesota were considered. A single city block covers an average area of 3 acres and generally contains 2-4 buildings. For this scenario, it is assumed that a single building, including its frontage, sidewalk and half of the road covers a drainage area of 1 acre, as shown in the Ultra-Urban Scenario Base schematic below.
+
==Step 1: Review project goals and site conditions==
 +
[[File:Ultra-Urban Scenario Base.PNG|thumb|300 px|alt=schematic illustrating Ultra-Urban Scenario Base |<font size=3>Site layout for an ultra-urban setting. For this example the site consists of a single building on a 1 acre drainage area. (source: CDM Smith).</font size>]]
  
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[[File:Ultra-Urban Scenario Base.PNG|thumb|300 px|alt=schematic illustrating Ultra-Urban Scenario Base |Ultra-Urban Scenario Base<font size=3></font size>]]
+
The ultra-urban site is characterized by high impervious cover in the form of residences, parking, or commercial development. For the purposes of this scenario, the drainage conditions for a single building on a city block in downtown Minneapolis, Minnesota were considered. A single city block covers an average area of 2 to 3 acres and generally contains 2 to 4 buildings. For this scenario, it is assumed that a single building, including its frontage, sidewalk and half of the road covers a drainage area of 1 acre, as shown in the schematic to the right.
  
−
The basic site conditions for the Ultra-Urban setting are summarized in Ultra-Urban Scenario Site Condition table below
+
The basic site conditions for the ultra-urban setting are summarized in the table below.
  
 
{| class="wikitable"
 
{| class="wikitable"
 +
|+Site conditions for a hypothetical site in an ultra-urban setting
 
|-
 
|-
 
| Site || Ultra-Urban (Downtown Minneapolis)
 
| Site || Ultra-Urban (Downtown Minneapolis)
Line 22: Line 24:
 
|}
 
|}
  
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High imperviousness results in high velocity and erosive stormwater flows that can damage building integrity and overwhelm stormwater infrastructure. The soil type, although fairly well draining, is assumed to be compacted due to high urbanization. Lack of vegetation and infiltration opportunities also prevent pollutant removal which leads to reduced water quality. The goal of this project is to install a BMP treatment train to reduce runoff volume and pollutant loads for the Water Quality Event.
+
High imperviousness results in high velocity and erosive stormwater flows that can damage building integrity and overwhelm stormwater infrastructure. The soil is assumed to be compacted due to high urbanization. Lack of vegetation and infiltration opportunities also prevent pollutant removal which leads to reduced water quality. The goal of this project is to install a BMP treatment train to reduce runoff volume and pollutant loads for the [http://stormwater.pca.state.mn.us/index.php/Glossary#W Water Quality Event].
  
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===Step 2: Review Pollutant Removal Processes & Identify Potential Practices===
+
==Step 2: Review Pollutant Removal Processes & Identify Potential Practices==
 +
The BMPs selected for this site must achieve the goals of decreased runoff volume and pollutant removal, as well as fit within the site constraints. The following table summarizes the BMP categories and their applicability to this site.
  
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The BMPs selected for the Ultra-Urban site, must achieve the goals of decreased runoff volume and pollutant removal, as well as fit within the site constraints. the Ultra-Urban Scenario BMP Practice Selection table summarizes the BMP categories and their applicability to this site.  
+
{| class="wikitable sortable"
 +
|+BMP practice selection options for an ultra-urban site
 +
|-
 +
! Practice !! Applicability !! Reason
 +
|-
 +
| [https://stormwater.pca.state.mn.us/index.php?title=Pollution_prevention Pollution prevention and public education] ||  || Pollution Prevention will be implemented during site maintenance.
 +
|-
 +
| Source controls ||  || Additional maintenance for source controls is not intended for this site; this is not an applicable practice.
 +
|-
 +
| [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_infiltration_Best_Management_Practices Infiltrators] || X || Allows for total stormwater and pollutant capture and aesthetically pleasing for pedestrians.
 +
|-
 +
| [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_filtration_Best_Management_Practices Swales and strips] ||  || Not applicable for a highly urbanized city block.
 +
|-
 +
| [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_filtration_Best_Management_Practices Filters] || X || Allows for reduction of stormwater volume and pollutant loads and easy diversion to other BMPs.
 +
|-
 +
| [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_sedimentation_Best_Management_Practices Constructed basins] ||  || Too large to meet space constraints.
 +
|-
 +
| Manufactured devices [https://stormwater.pca.state.mn.us/index.php?title=TP_and_TSS_credits_and_guidance_for_manufactured_treatment_devices_(mtds)], [https://stormwater.pca.state.mn.us/index.php?title=Pretreatment] ||  || Applicable, however more aesthetically pleasing options should be pursued first.
 +
|-
 +
| [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_and_rainwater_harvest_and_use/reuse Storage, harvesting and reuse] ||  || Applicable depending on available space and building function. However, stormwater storage for re-use is not necessary for this scenario.
 +
|}
  
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{{:Ultra-Urban Scenario BMP Practice Selection}}
+
Infiltrator and filter BMPs are determined to best address the goals of this project. The process of selecting and placing BMPs on a site is typically iterative, working between the site constraints, project goals, and available budget. The approach and considerations for this scenario are discussed in the following sections.
  
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Infiltrator and Filter BMPs are determined to best address the goals of this project for the Ultra-Urban scenario. The process of selecting and placing BMPs on a site is typically iterative, working between the site constraints, project goals, and available budget. The approach and considerations for this scenario are discussed in the following sections.
+
==Step 3: Determine site constraints and BMP placement==
 +
An [[Glossary#U|ultra-urban setting]] can pose a unique set of site constraints due to limited space for development and high pedestrian traffic. Specific site constraints for a typical city block in Minneapolis include:
  
 +
[[File:Ultra-Urban Scenario Street Level BMP Placement Schematic.PNG|thumb|400 px|alt=schematic illustrating Ultra-Urban Scenario Street Level BMP Placement  |<font size=3>Proposed site layout for a hypothetical site in an ultra-urban setting (Source: CDM Smith).</font size>]]
  
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===Step 3: Determine Site Constraints & BMP Placement===
+
*Available space – In the ultra-urban setting the location of BMPs is restricted to rooftops and the narrow corridor between buildings and city streets. Impervious surfaces in the drainage area are necessary for supporting high foot and vehicle traffic, as well as structural support of buildings. Selected BMPs must be able to effectively reduce the adverse effects of stormwater while maintaining the function of the existing impervious surfaces.
 +
*Public integration – Ultra-urban settings are usually characterized by high volumes of pedestrian and vehicular traffic. Selected BMPs must be resistant to degradation due to constant use. BMP aesthetics should also be a consideration.
 +
*Utilities – when working in a downtown or ultra-urban setting, there is often little flexibility in the location and movement of utilities. BMP sizing and location should try to avoid major impact utilities.
 +
*Regulatory Requirements - All local, state, and federal regulatory requirements must be met. The [http://stormwater.pca.state.mn.us/index.php/Category:Design_criteria design criteria and recommendations] from the Minnesota Stormwater Manual will be followed.
  
−
The Ultra-Urban Setting can pose a unique set of site constraints due to limited space for development and high pedestrian traffic. Specific site constraints for a typical city block in Minneapolis include:
+
To meet space allotments and reduce degradation due to interaction with people and vehicles, the most viable locations for BMPs are the building rooftop, the pedestrian sidewalk and parking/bike lane. For reference, the street level areas are depicted in the schematic to the right.
  
−
*Available Space – In the Ultra-Urban setting the location of BMPs is restricted to rooftops and the narrow corridor between buildings and city streets. Impervious surfaces in the drainage area are necessary for supporting high foot and vehicle traffic, as well as structural support of buildings. Selected BMPs must be able to effectively reduce the adverse effects of stormwater while maintaining the function of the existing impervious surfaces.
+
Further considerations for placement of BMPs on the street level are the required minimum dimensions for high capacity roads, curbs, sidewalks and planting and furnishing zones as well as the 10 foot minimum [http://stormwater.pca.state.mn.us/index.php/Stormwater_infiltration_and_setback_%28separation%29_distances setback] from a building foundation.
−
*Public Integration – Ultra-Urban settings are usually characterized by high volumes of pedestrian and vehicular traffic. Selected BMPs must be resistant to degradation due to constant use. BMP aesthetics should also be a consideration.
 
−
*Utilities – when working in a downtown or Ultra-Urban setting, there is often little flexibility in the location and movement of utilities. BMP sizing and location should try to avoid major impact utilities.
 
−
*Regulatory Requirements - All local, state, and federal regulatory requirements must be met. The design criteria and recommendations from the Minnesota Stormwater Manual will be followed.
 
  
−
To meet space allotments and reduce degradation due to interaction with people and vehicles, the most viable locations for BMPs are the building rooftop, the pedestrian sidewalk and parking/bike lane. For reference, the street level areas are depicted in the Ultra-Urban Scenario Street Level BMP Placement Schematic below
+
==Step 4: Select individual BMPs and evaluate range of performance==
 +
[[File:Ultra-Urban Scenario BMP Layout.PNG|right|thumb|400 px|alt=schematic illustrating Ultra-Urban Scenario BMP Layout|<font size=3>Example of a suitable BMP layout for an ultra-urban setting (Source: CDM Smith).</font size>]]
 +
[[File:MIDS Green Roof Configuration.PNG|left|thumb|300 px|alt=schematic illustrating MIDS Green Roof Configuration|<font size=3>[http://stormwater.pca.state.mn.us/index.php/Requirements,_recommendations_and_information_for_using_green_roofs_as_a_BMP_in_the_MIDS_calculator Green roof configuration used for the MIDS calculator]. Needed inputs are the media depth and surface area of the green roof. (Source: CDM Smith).</font size>]]
 +
[[File:MIDS Tree Trench - Box System Configuration.PNG|right|thumb|300 px|alt=schematic illustrating MIDS Tree Trench - Box System Configuration|<font size=3>MIDS tree trench configuration. In addition to surface areas and media depth, required inputs include soil storage information, soil type, drawdown time, and tree information.</font size>]]
 +
[[File:Ultra-Urban Green Roof Design.PNG|thumb|left|300 px|alt=schematic illustrating Ultra-Urban Green Roof Design.PNG|<font size=3>Ultra-Urban Green Roof Design</font size>]]
 +
[[File:Tree Trench System Design.PNG|right|thumb|300 px|alt=schematic illustrating Tree Trench System Design|<font size=3>Tree trench system design.</font size>]]
 +
[[File:Typical Permeable Pavement Configuration.PNG|thumb|left|300 px|alt=schematic illustrating Typical Permeable Pavement Configuration|<font size=3>Typical configuration for permeable pavement (Source: CDM Smith).</font size>]]
 +
[[File:Permeable Pavement Layout.PNG |thumb|right|300 px|alt=schematic illustrating Permeable Pavement Layout|<font size=3>Layout for permeable pavement.</font size>]]
  
−
[[File:Ultra-Urban Scenario Street Level BMP Placement Schematic.PNG|thumb|300 px|alt=schematic illustrating Ultra-Urban Scenario Street Level BMP Placement  |Ultra-Urban Scenario Street Level BMP Placement Schematic<font size=3></font size>]]
+
[http://stormwater.pca.state.mn.us/index.php/Scenario_for_developing_a_stormwater_treatment_train_for_an_ultra-urban_setting#Step_2:_Review_Pollutant_Removal_Processes_.26_Identify_Potential_Practices Step 2] introduced the practices that would best address the goals and site constraints for the ultra-urban setting as infiltrators and filters. Infiltration is a hydraulic process that serves to reduce runoff volume and pollutant loads by complete abstraction of runoff. Physical, chemical and biological processes remove pollutant loads as water moves through the media mix. In contrast, filtration is a physical process that uses the same physical, chemical and biological principles to reduce pollutant loads as water moves through the media. However, excess water is drained through an [[Glossary#U|underdrain]].
  
−
Further considerations for placement of BMPs on the street level are the required minimum dimensions for high capacity roads, curbs, sidewalks and planting and furnishing zones as well as the 10 foot minimum setback from a building foundation.
+
:'''Filter: Green Roof'''
 +
*[[Green roofs]] are primary treatment BMPs which act as [http://stormwater.pca.state.mn.us/index.php/Stormwater_filtration_Best_Management_Practices filters]. Installing a green roof substantially reduces impervious cover and the volume and rate of water draining to the street level. Green roofs have a median [http://stormwater.pca.state.mn.us/index.php/Total_Suspended_Solids_%28TSS%29_in_stormwater total suspended solid] (TSS) removal of 85 percent. Although green roofs do not have high rates of [http://stormwater.pca.state.mn.us/index.php/Calculating_credits_for_green_roofs#Total_phosphorus_.28TP.29_calculations total phosphorus] (TP) removal, in a northern temperate region such as Minnesota a green roof can reduce runoff volume by 50 percent to 70 percent. Volume and rate reduction will reduce loading on downstream BMPs allowing for more effective pollutant reduction. Studies show that green roofs actually [http://stormwater.pca.state.mn.us/index.php/File:Green_roof_pollutant_removal.docx become more effective over time]. As vegetation becomes more established, water quality may improve due to mature plants ability absorb and filter more pollutants. A green roof will allow for reduction in runoff volume, peak discharge, delay peak runoff, and divert excess water to downstream BMPs for further pollutant reduction.
  
−
===Step 4: Select Individual BMPs & Evaluate Range of Performance===
+
:'''Infiltrator: Tree Trench/Box System'''
 +
*[[Trees|Tree trenches and boxes]] on the street level between the sidewalk and street can capture and reduce runoff from the road, sidewalk, and underdrain outlet from the green roof. Tree trenches/boxes act as [http://stormwater.pca.state.mn.us/index.php/Stormwater_infiltration_Best_Management_Practices infiltrators] where the soil media, trees and microbes work in conjunction to absorb, filter or transform pollutants. The media in tree trenches/boxes also [http://stormwater.pca.state.mn.us/index.php/Calculating_credits_for_tree_trenches_and_tree_boxes holds pollutants] to be utilized by vegetation or microbes during periods of low rainfall. [http://stormwater.pca.state.mn.us/index.php/Design_criteria_for_bioretention#Mix_D Soil Media Mix D] is recommended for tree BMPs. Together they provide the most effective design for nutrient and pollutant removal because of the interplay of physical, chemical and biological processes. [http://stormwater.pca.state.mn.us/index.php/Infiltration_basin Infiltration basins] could provide similar runoff volume and pollutant reductions, however because this was an area with high pedestrian interaction, tree trenches/boxes provide a higher aesthetic value.
  
−
Step 2 introduced the practices that would best address the goals and site constraints for the Ultra-Urban setting as infiltrators and Filters. Infiltration is a hydraulic process that serves to reduce volume runoff and pollutant loads by complete abstraction of runoff. Physical, chemical and biological processes remove pollutant loads as water moves through the media mix. In contrast, filtration is a physical process that uses the same physical, chemical and biological principles to reduce pollutant loads as water moves through the media. However, excess water is drained through an underdrain.
+
:'''Infiltrator: Permeable Pavement'''
 +
*[[Permeable pavement]] acts as a final filter to remove phosphorus and other pollutants and to reduce road and storm sewer flooding. Although permeable pavements can be prone to clogging in areas of high TSS loading, the preceding BMPs will reduce pollutant loading from the sidewalk and buildings, and allow for more effective pollutant removal from the adjacent impervious street. Permeable pavement offers structural stability to allow for traffic loading from cars and bikes, while allowing water to infiltrate through voids in the surface. The aggregate storage media under the permeable pavement and tree boxes will be a single unit as shown in the figure to the right, allowing for captured stormwater and pollutants to be available for vegetation in the tree trenches/boxes.
  
−
'''Filter: Green Roof'''
+
A multitude of infiltrator or filter BMPs may be considered for an Ultra-Urban setting where the goals of stormwater management are the reduction of runoff volumes and pollutant loads. A green roof, tree trenches, and permeable pavement were selected as plausible treatment train BMPs for this scenario.
−
*Green roofs are primary treatment BMPs which act as filters. Installing a green roof substantially reduces impervious cover and the volume and rate of water draining to the street level. Green roofs have a median TSS removal of 85%. Although green roofs do not have high rates of TP removal, in a northern temperate region such as Minnesota a green roof can reduce runoff volume by 50% to 70%. Volume and rate reduction will reduce loading on downstream BMPs allowing for more effective pollutant reduction. Studies show that green roofs actually become more effective over time. As vegetation becomes more established, water quality may improve due to mature plants ability absorb and filter more pollutants. A green roof with an underdrain will allow for reduction in runoff volume, peak discharge, delay peak runoff, and divert excess water to downstream BMPs for further pollutant reduction.
 
  
−
'''Infiltrator: Tree Trench/Box System'''
+
==Step 5: Size BMPs and assess performance==
−
*Tree trenches and boxes on the street level between the sidewalk and street can capture and reduce runoff from the road, sidewalk, and underdrain outlet from the green roof. Tree trenches/boxes act as infiltrators where the soil media, trees and microbes work in conjunction to absorb, filter or transform pollutants. The media in tree trenches/boxes also holds pollutants to be utilized by vegetation or microbes during periods of low rainfall. Soil Media Mix D is recommended for tree BMPs. Together they provide the most effective design for nutrient and pollutant removal because of the interplay of physical, chemical and biological processes. Infiltration basins could provide similar runoff volume and pollutant reductions, however because this was an area with high pedestrian interaction, tree trenches/boxes provide a higher aesthetic value.  
+
For the ultra-urban setting, space is a significant site constraint. BMP sizing must be strategic to allow for maximum BMP efficiency while meeting performance goals. Assumptions included an annual phosphorus event mean concentration (EMC) of 0.3 milligrams per liter, and an annual TSS EMC of 54.5 milligrams per liter. The following table summarizes the existing site runoff, volume and pollutant retention goals. The [[MIDS calculator]] provides a performance goal requirement based on the site conditions for the treatment train which is shown in the table below.
  
−
'''Infiltrator: Permeable Pavement'''
+
{| class="wikitable"
−
*Permeable pavement acts as a final filter to remove phosphorous and other pollutants and to reduce road and storm sewer flooding. Although permeable pavements can be prone to clogging in areas of high TSS loading, the preceding BMPs will reduce pollutant loading from the sidewalk and buildings, and allow for more effective pollutant removal from the adjacent impervious street. Permeable pavement offers structural stability to allow for traffic loading from cars and bikes, while allowing water to infiltrate through voids in the surface. The aggregate storage media under the permeable pavement and tree boxes will be a single unit as shown in Figure 3.2.3, allowing for captured stormwater and pollutants to be available for vegetation in the tree trenches/boxes.
+
|+Ultra-urban scenario performance goal
−
 
+
|-
−
[[File:Ultra-Urban Scenario BMP Layout.PNG|thumb|300 px|alt=schematic illustrating Ultra-Urban Scenario BMP Layout|Ultra-Urban Scenario BMP Layout<font size=3></font size>]]
+
! Annual runoff volume (acre-feet !! Annual particulate phosphorus load (lbs) !! Annual dissolved phosphorus load (lbs) !! Annual total suspended solids load (lbs) !! Performance goal volume retention requirement (ft<sup>3</sup>
−
 
+
|-
−
A multitude infiltrator or filter BMPs may be considered for an Ultra-Urban setting where the goals of stormwater management are the reduction of runoff volumes and pollutant loads. A green roof, tree trenches, and permeable pavement were selected as plausible treatment train BMPs for the Ultra-Urban setting in downtown Minneapolis.
+
| 2.15 || 0.96 || 0.79 || 319 || 3793
−
 
+
|}
−
===Step 5: Size BMPs & Assess Performance===
 
−
 
 
−
For the Ultra-Urban setting, space is a significant site constraint and therefore BMP sizing must be very strategic to allow for maximum BMP efficiency while meeting performance goals. Assumptions included an annual Phosphorus EMC of 0.3 mg/l, and an annual TSS EMC of 54.5 (mg/l). Table 3.4.3 summarizes the existing site runoff, volume and pollutant retention goals. The MIDS calculator provides a performance goal requirement based on the site conditions for the treatment train which is shown in the Ultra-Urban Scenario Performance Goal table .below.
 
−
 
 
−
{{:Ultra-Urban Scenario Performance Goal}}
 
  
 
BMP Sizing for each component of a treatment train is an iterative process where available space, performance goals and regulatory requirements must be considered.  
 
BMP Sizing for each component of a treatment train is an iterative process where available space, performance goals and regulatory requirements must be considered.  
  
−
====Green Roof====
+
===Green roof===
 +
{| class="wikitable" style="float:right; margin-left: 10px; width:350px;"
 +
|+'''Event runoff volume performance summary'''
 +
|-
 +
! Parameter !! Value
 +
|-
 +
| Runoff Volume from Direct Watershed (ft<sup>3</sup>) || 2832
 +
|-
 +
| Runoff Volume from Upstream BMPs (ft<sup>3</sup>) || 0
 +
|-
 +
| Retention Volume Provided by BMP (ft<sup>3</sup>) || 2734
 +
|-
 +
| Outflow Volume from BMP (ft<sup>3</sup>) || 98
 +
|-
 +
| Percent Performance Goal Achieved (%) || 97
 +
|}
  
−
The design of a green roof is based around the input parameters needed for the MIDS program and the MIDS calculator requirements for green roofs. The MIDS calculator is able to determine the performance of the Green Roof BMP based on the parameters shown in the MIDS Green Roof Configuration schematic.
+
{| class="wikitable" style="float:right; margin-left: 10px; width:250px;"
 +
|+Ultra-urban green roof sizing input parameters
 +
|-
 +
! Roof area (ft<sup>2</sup>) !! Media depth (in)
 +
|-
 +
| 24852 || 4
 +
|}
  
 +
The design of a green roof is based around the [http://stormwater.pca.state.mn.us/index.php/Requirements,_recommendations_and_information_for_using_green_roofs_as_a_BMP_in_the_MIDS_calculator input parameters needed for the MIDS calculator for green roofs]. The MIDS calculator is able to determine the performance of the green roof BMP based on the parameters shown in the schematic to the right.
  
−
[[File:MIDS Green Roof Configuration.PNG|thumb|300 px|alt=schematic illustrating MIDS Green Roof Configuration|Ultra-MIDS Green Roof Configuration<font size=3></font size>]]
+
The surface area of a green roof is controlled by the available area on the building rooftop. The rooftop size is dictated by the space available on the existing building. The sizing input parameters for the green roof are shown in the table below.
  
−
The surface area of a green roof is controlled by the available area on the building rooftop. The rooftop size is dictated by the space available on the existing building. The sizing input parameters for the green roof are shown in the Ultra-Urban Green Roof Sizing Input Parameters table below.
+
For this setting, space was allotted for a 6 foot walkway around the perimeter of the green roof to provide maintenance access to the BMP without hindering its functionality and the performance. To route excess water to the downstream BMPs on the south and west side of the building, two 4-inch downspouts were included. Two downspouts reduce the risk of clogging and provides an extra outlet for water if one downspout is undergoing maintenance. A schematic of the green roof design is shown to the right.
  
−
{{:Ultra-Urban Green Roof Sizing Input Parameters}}
+
These parameters were entered into the MIDS calculator to evaluate performance of the green roof BMP for runoff volume and pollutant load reductions. These results are summarized in the adjacent tables.
  
−
For this setting, space was allotted for a 6 foot walkway around the perimeter of the green roof to provide maintenance access to the BMP without hindering its functionality and the performance. To route excess water to the downstream BMPs on the south and west side of the building, two-4 inch downspouts were included. Two downspouts reduce the risk of clogging and provides an extra outlet for water if one downspout is undergoing maintenance. A schematic of the green roof design is shown in the Ultra-Urban Green Roof Design schematic.  
+
{| class="wikitable" style="width:1000px;"
 +
|+'''Annual performance goal summary'''
 +
|-
 +
! Pollutant !! Parameter !! Value
 +
|-
 +
| rowspan="5" | Volume
 +
| Runoff from Direct Watershed (acre-ft.) || 0.00
 +
|-
 +
| Runoff from Upstream BMPs (acre-ft.) || 1.59
 +
|-
 +
| Retention Volume Provided by BMP (acre-ft.) || 0.79
 +
|-
 +
| Outflow Volume from BMP (acre-ft.) || 0.87
 +
|-
 +
| Percent Performance Goal Achieved (%) || 45
 +
|-
 +
| rowspan="5" | Particulate phosphorus
 +
| Particulate P from Watershed (lbs.) || 0.72
 +
|-
 +
| Particulate P from Upstream BMPs (lbs.) || 0
 +
|-
 +
| Particulate P Load Reduction (lbs.) || 0
 +
|-
 +
| Particulate P Outflow || 0.72
 +
|-
 +
| Total Percent Particulate P Reduction || 0
 +
|-
 +
| rowspan="5" | Dissolved phosphorus
 +
| Dissolved P from Watershed (lbs.) || 0.58
 +
|-
 +
| Dissolved P from Upstream BMPs (lbs.) || 0
 +
|-
 +
| Dissolved P Load Reduction (lbs.) || 0
 +
|-
 +
| Dissolved P Outflow || 0.58
 +
|-
 +
| Total Percent Dissolved P Reduction (%) || 0
 +
|-
 +
| rowspan="5" | Total suspended solids (TSS)
 +
| TSS from Watershed (lbs.) || 236
 +
|-
 +
| TSS from Upstream BMPs (lbs.) || 0
 +
|-
 +
| TSS Load Reduction (lbs.) || 226
 +
|-
 +
| TSS Outflow || 10
 +
|-
 +
| Total Percent TSS Reduction (%) || 96
 +
|}
  
−
[[File:Ultra-Urban Green Roof Design.PNG|thumb|300 px|alt=schematic illustrating Ultra-Urban Green Roof Design.PNG|Ultra-Urban Green Roof Design.PNG<font size=3></font size>]]
+
===Tree trench/Box system===
 +
{| class="wikitable" style="float:right; "width:1000px;"
 +
|+'''Annual performance goal summary'''
 +
|-
 +
! Pollutant !! Parameter !! Large trench !! Small trench
 +
|-
 +
| rowspan="5" | Volume
 +
| Runoff from Direct Watershed (acre-ft.) || 0.05 || 0.03
 +
|-
 +
| Runoff from Upstream BMPs (acre-ft.) || 0.44 || 0.00
 +
|-
 +
| Retention Volume Provided by BMP (acre-ft.) || 0.49 || 0.03
 +
|-
 +
| Outflow Volume from BMP (acre-ft.) || 0.00 || 0.00
 +
|-
 +
| Percent Performance Goal Achieved (%) || 100 || 100
 +
|-
 +
| rowspan="5" | Particulate phosphorus
 +
| Particulate P from Watershed (lbs.) || 0.02 || 0.01
 +
|-
 +
| Particulate P from Upstream BMPs (lbs.) || 0.36 || 0.00
 +
|-
 +
| Particulate P Load Reduction (lbs.) || 38 || 0.01
 +
|-
 +
| Particulate P Outflow || 0.00 || 0.00
 +
|-
 +
| Total Percent Particulate P Reduction || 100 || 100
 +
|-
 +
| rowspan="5" | Dissolved phosphorus
 +
| Dissolved P from Watershed (lbs.) || 0.02 || 0.01
 +
|-
 +
| Dissolved P from Upstream BMPs (lbs.) || 0.29 || 0.00
 +
|-
 +
| Dissolved P Load Reduction (lbs.) || 0.31 || 0.01
 +
|-
 +
| Dissolved P Outflow || 0.00 || 0.00
 +
|-
 +
| Total Percent Dissolved P Reduction (%) || 100 || 100
 +
|-
 +
| rowspan="5" | Total suspended solids (TSS)
 +
| TSS from Watershed (lbs.) || 7 || 4
 +
|-
 +
| TSS from Upstream BMPs (lbs.) || 5 || 0
 +
|-
 +
| TSS Load Reduction (lbs.) || 12 || 4
 +
|-
 +
| TSS Outflow || 0 || 0
 +
|-
 +
| Total Percent TSS Reduction (%) || 100 || 100
 +
|}
  
−
These parameters were entered into the MIDS calculator to evaluate performance of the green roof BMP for a runoff volume and pollutant load reductions. These results are summarizes in the Green Roof Performance Summary table below.
+
{| class="wikitable" style="float:right; margin-left: 10px; width:500px;"
 +
|+'''Event runoff volume performance summary'''
 +
|-
 +
! Parameter !! Large trench !! Small trench
 +
|-
 +
| Runoff Volume from Direct Watershed (ft<sup>3</sup>) || 80 || 48
 +
|-
 +
| Runoff Volume from Upstream BMPs (ft<sup>3</sup>) || 49 || 0
 +
|-
 +
| Retention Volume Provided by BMP (ft<sup>3</sup>) || 419 || 209
 +
|-
 +
| Outflow Volume from BMP (ft<sup>3</sup>) || 0 || 0
 +
|-
 +
| Percent Performance Goal Achieved (%) || 100 || 100
 +
|}
  
−
{{:Green Roof Performance Summary}}
+
{| class="wikitable" style="float:right; margin-left: 10px; width:400px;"
 +
|+Ultra-urban green roof sizing input parameters
 +
|-
 +
! Top surface area (ft<sup>2</sup>) !! Bottom surface area (ft<sup>2</sup>) !! Media depth (ft) !! Number of trees !! Required drawdown time (hrs)
 +
|-
 +
| 420 || 420 || 3 || 2 || 48
 +
|-
 +
| 210 || 210 || 3 || 1 || 48
 +
|}
  
−
===Tree Trench/Box System===
+
The design of a tree trench BMP is based around the [http://stormwater.pca.state.mn.us/index.php/Requirements,_recommendations_and_information_for_using_trees_as_a_BMP_in_the_MIDS_calculator input parameters needed for the MIDS calculator for tree trenches without underdrains]. The MIDS calculator configuration for the tree trench BMP is illustrated in the figure to the right.
  
−
The design of a Tree Trench System BMP is based around the input parameters needed for the MIDS program and the MIDS calculator requirements for tree trenches without underdrains. The MIDS calculator is able to determine the performance of the tree trench BMP based on the parameters shown in Figure 3.2.6.
+
Two types of tree trenches were designed for this setting. Two large tree trenches were placed at the outlets of each downspout to account for flow from the upstream green roof BMP as well as runoff from the adjacent sidewalk. Four small tree trenches were added to intercept runoff from the sidewalk, preventing flow into the street. Sizing of the tree trenches is limited by pedestrian zone spacing requirements. Installations in the pedestrian zone should conform to all local rules and regulations. This Ultra-Urban scenario was set in downtown Minneapolis, MN and as such, sizing for the frontage, sidewalk and planting zones are determined based on the [https://nacto.org/docs/usdg/pedestrian_facility_design_access_minneapolis.pdf Minneapolis Public Works Pedestrian Facility Design Guidelines]. The required [http://stormwater.pca.state.mn.us/index.php/Minimum_setback_requirements 10 foot minimum setback] for infiltration practices from a building foundation and [http://stormwater.pca.state.mn.us/index.php/Design_guidelines_for_soil_characteristics_-_tree_trenches_and_tree_boxes soil volume requirements] for the chosen tree type also factored into tree trench sizing. The tree trench sizing input parameters are summarized in the table below.  
  
−
====Tree Trench/Box System====
+
The [http://stormwater.pca.state.mn.us/index.php/Plant_lists_for_trees tree types] and sizes for the tree trench system BMPs are restricted by the available soil volume. Deciduous trees are most suitable for the ultra-urban design as they provide more clearance for pedestrian passage around the trees. The table below shows the tree inputs for the MIDS calculator.
  
−
The design of a Tree Trench System BMP is based around the input parameters needed for the MIDS program and the MIDS calculator requirements for tree trenches without underdrains. The MIDS calculator is able to determine the performance of the tree trench BMP based on the parameters shown in Figure 3.2.6.
+
The MIDS calculator also accounts for soil media within the tree trench system, underlying soils, and tree types. As previously stated, Media Mix D is highly recommended for best results with a tree BMP. The selected media mix dictates the MIDS inputs for soil-water storage properties, including a media field capacity of 0.09 cubic feet per cubic foot and a media porosity of 0.31 cubic feet per cubic foot. Although the area’s underlying Hydrologic Soil Group B is relatively well-draining with an infiltration rate of 0.45 inches per hour, high soil compaction was assumed because of the intense urbanization. Therefore an overflow structure was included in the tree trench for larger storm bypass and reduced infiltration capacity over time. The figure to the right displays the overall layout for the tree trench system.
  
−
[[File:MIDS Tree Trench - Box System Configuration.PNG|thumb|300 px|alt=schematic illustrating MIDS Tree Trench - Box System Configuration|MIDS Tree Trench - Box System Configuration<font size=3></font size>]]
+
These parameters were entered into the MIDS calculator to evaluate performance of the tree trench BMPs for runoff volume and pollutant load reductions. These results are summarized below.
  
−
Two types of tree trenches were designed for the Ultra-Urban setting. Two large tree trenches were placed at the outlets of each downspout to account for flow from the upstream Green Roof BMP as well as runoff from the adjacent sidewalk. Four small tree trenches were added to intercept runoff from the sidewalk, preventing flow into the street. Sizing of the tree trenches is limited by pedestrian zone spacing requirements. Installations in the pedestrian zone should conform to all local rules and regulations. This Ultra-Urban scenario was set in downtown Minneapolis, MN and as such, sizing for the frontage, sidewalk and planting zones are determined based on the [http://www.minneapolismn.gov/www/groups/public/@publicworks/documents/webcontent/convert_256028.pdf Minneapolis Public Works Pedestrian Facility Design Guidelines]. The required [http://stormwater.pca.state.mn.us/index.php/Minimum_setback_requirements 10 foot minimum setback] for infiltration practices from a building foundation and [http://stormwater.pca.state.mn.us/index.php/Design_guidelines_for_soil_characteristics_-_tree_trenches_and_tree_boxes soil volume requirements] for the chosen tree type also factored into tree trench sizing. The tree trench sizing input parameters are summarized in the Ultra-Urban Tree Trench Sizing Input Parameters table below.  
+
===Permeable pavement===
 +
{| class="wikitable" style="float:right; "width:1000px;"
 +
|+'''Annual performance goal summary'''
 +
|-
 +
! Pollutant !! Parameter !! Value
 +
|-
 +
| rowspan="5" | Volume
 +
| Runoff from Direct Watershed (acre-ft.) || 0.29
 +
|-
 +
| Runoff from Upstream BMPs (acre-ft.) || 0..00
 +
|-
 +
| Retention Volume Provided by BMP (acre-ft.) || 0.29
 +
|-
 +
| Outflow Volume from BMP (acre-ft.) || 0.00
 +
|-
 +
| Percent Performance Goal Achieved (%) || 100
 +
|-
 +
| rowspan="5" | Particulate phosphorus
 +
| Particulate P from Watershed (lbs.) || 0.13
 +
|-
 +
| Particulate P from Upstream BMPs (lbs.) || 0.00
 +
|-
 +
| Particulate P Load Reduction (lbs.) || 0.13
 +
|-
 +
| Particulate P Outflow || 0.00
 +
|-
 +
| Total Percent Particulate P Reduction || 100
 +
|-
 +
| rowspan="5" | Dissolved phosphorus
 +
| Dissolved P from Watershed (lbs.) || 0.11
 +
|-
 +
| Dissolved P from Upstream BMPs (lbs.) || 0.00
 +
|-
 +
| Dissolved P Load Reduction (lbs.) || 0.11
 +
|-
 +
| Dissolved P Outflow || 0.00
 +
|-
 +
| Total Percent Dissolved P Reduction (%) || 100
 +
|-
 +
| rowspan="5" | Total suspended solids (TSS)
 +
| TSS from Watershed (lbs.) || 43
 +
|-
 +
| TSS from Upstream BMPs (lbs.) || 0
 +
|-
 +
| TSS Load Reduction (lbs.) || 43
 +
|-
 +
| TSS Outflow || 0
 +
|-
 +
| Total Percent TSS Reduction (%) || 100
 +
|}
  
−
{{:Ultra-Urban Tree Trench Sizing Input Parameters}}
+
{| class="wikitable" style="float:right; margin-left: 10px; width:500px;"
 +
|+'''Event runoff volume performance summary'''
 +
|-
 +
! Parameter !! Large trench !! Small trench
 +
|-
 +
| Runoff Volume from Direct Watershed (ft<sup>3</sup>) || 518
 +
|-
 +
| Runoff Volume from Upstream BMPs (ft<sup>3</sup>) || 0
 +
|-
 +
| Retention Volume Provided by BMP (ft<sup>3</sup>) || 3469
 +
|-
 +
| Outflow Volume from BMP (ft<sup>3</sup>) || 0
 +
|-
 +
| Percent Performance Goal Achieved (%) || 100
 +
|}
  
−
The [http://stormwater.pca.state.mn.us/index.php/Plant_lists_for_trees tree types] and sizes for the tree trench system BMPs are restricted by the available soil volume. Deciduous trees are most suitable for the Ultra-Urban Design as they provide more clearance for pedestrian passage around the trees. The Ultra-Urban Tree Trench Tree Selection Parameters table below shows the tree inputs for the MIDS calculator.
+
{| class="wikitable" style="float:right; margin-left: 10px; width:400px;"
 +
|+Ultra-urban green roof sizing input parameters
 +
|-
 +
! Top surface area (ft<sup>2</sup>) !! Surface area at subgrade (ft<sup>2</sup>) !! Storage depth (ft) !! Required drawdown time (hrs)
 +
|-
 +
| 4818 || 4818 || 1.8 || 48
 +
|}
  
−
{{:Ultra-Urban Tree Trench Tree Selection Parameters}}
+
The design of a permeable pavement parking/bike lane is based around the input parameters needed for the MIDS calculator for permeable pavement. A typical permeable pavement configuration is shown in the figure to the right.
  
−
The MIDS calculator also accounts for soil media within the tree trench system, underlying soils, and tree types. As previously stated, Media Mix D is highly recommended for best results with a Tree BMP. The selected media mix dictates the MIDS inputs for soil-water storage properties, including a media field capacity of 0.09 ft3/ft3 and a media porosity of 0.31 ft3/ft3. Although the area’s underlying Hydrologic Soil Group B is relatively well-draining with an infiltration rate of 0.45 in/hr, high soil compaction was assumed because of the intense urbanization. Therefore an overflow structure was included in the tree trench for larger storm bypass and reduced infiltration capacity over time. Figure 3.2.7 displays the overall layout for the tree trench system.
+
The sizing of the permeable pavement parking/bike lane varies depending on the scenario and available space and should conform to all local rules and regulations for transportation zones. This ultra-urban scenario was set in downtown Minneapolis, MN and as such local sizing guidelines for traffic ways, parking lanes and bike lines were considered. The [https://nacto.org/docs/usdg/pedestrian_facility_design_access_minneapolis.pdf Minneapolis Public Works Street and Sidewalk Design Guidelines] offers desired minimum lane widths for urban roads, parking and bike lanes. These recommendations conform to the minimum design standards set forth by the [https://www.revisor.mn.gov/rules/?id=8820.9936 Minnesota Administrative Rules]. The dimensions for the permeable pavement lane, including space for parking and bike passage, were designed to be 12 feet wide and extend the length of the block. This meets the [Minneapolis Public Works Design Guidelines for Streets and Sidewalks Minneapolis Public Works Design Guidelines for Streets and Sidewalks] requirements for the minimum functional lane widths.
  
 +
Additional considerations for permeable pavement sizing are depth of the aggregate reservoir and the required drawdown time. The sizing input parameters for the permeable pavement BMP are summarized below.
  
−
[[File:Tree Trench System Design.PNG|thumb|300 px|alt=schematic illustrating Tree Trench System Design|Tree Trench System Design<font size=3></font size>]]
+
Although the underlying [[Glossary#H|Hydrologic Soil Group]] B is considered to be well draining with an infiltration rate of 0.45 inches per hour, high soil compaction was assumed because this is a highly urbanized area. In addition, the permeable pavement BMP will need to support vehicular loads and therefore further compaction of underlying soils may be required. For this reason, an existing inlet will be maintained directly downstream of the permeable pavement for bypass and overflow from larger storm events. The porosity of the aggregate media was assumed to be 0.4 cubic feet per cubic foot. These parameters were input into the MIDS calculator to evaluate the pollutant removal and volume reduction performance of the BMP. The results of the MIDS credit calculations for volume reduction and pollutant loading are shown below.
  
−
These parameters were entered into the MIDS calculator to evaluate performance of the tree trench BMPs for a runoff volume and pollutant load reductions. These results are summarizes in the Tree Trench Performance Summary table below.
+
===Overall ultra-urban BMP treatment train performance===
 +
[[File:Ultra-Urban BMP Treatment Train MIDS Calculator Schematic.PNG |thumb|300 px|alt=schematic illustrating Ultra-Urban BMP Treatment Train MIDS Calculator|<font size=3>Ultra-Urban BMP Treatment Train MIDS Calculator Schematic</font size>]]
  
−
{{:Tree Trench Performance Summary}}
+
The overall performance of the BMP treatment train was evaluated using the [[MIDS calculator]]. The treatment train configuration consisting of a green roof, 2 large tree trenches, 4 small tree trenches and a permeable pavement parking/bike lane is shown on the right.
  
−
===Permeable Pavement===
+
This treatment train was able to significantly reduce the volume and pollutant loadings in this ultra-urban setting. The treatment train achieved removal efficiencies of 97 percent for each of the components of interest: runoff volume, total phosphorus and TSS. The results from the MIDS calculator run are summarized in the following table.
  
−
The design of a permeable pavement parking/bike lane is based around the input parameters needed for the MIDS program and the MIDS calculator requirements for permeable pavement. A typical permeable pavement configuration is shown in Figure 3.2.8.
+
{| class="wikitable sortable"
 +
|+Annual stormwater BMP treatment train performance summary
 +
|-
 +
| rowspan="3" | Volume
 +
| Performance Goal Runoff Volume (acre-ft.) || 2.15
 +
|-
 +
| Retention Volume Provided by BMPs (acre-ft.) || 2.09
 +
|-
 +
| Percent Runoff Volume Removed (%) || 97
 +
|-
 +
| rowspan="5" | Total phosphorus
 +
| Performance Goal Particulate P Load (lbs.) || 0.96
 +
|-
 +
| Performance Goal Dissolved P Load (lbs.) || 0.79
 +
|-
 +
| Particulate P Load Removed by BMPs (lbs.) || 0.93
 +
|-
 +
| Dissolved P Load Removed by BMPs (lbs.) || 0.77
 +
|-
 +
| Percent TP Removed (%) || 97
 +
|-
 +
| rowspan="3" | Total suspended solids
 +
| Performance Goal TSS Loads (lbs.) || 319
 +
|-
 +
| TSS Load Removed by BMPs (lbs.) || 309
 +
|-
 +
| Percent TSS Removed (%) || 97
 +
|}
  
−
[[File:Typical Permeable Pavement Configuration.PNG|thumb|300 px|alt=schematic illustrating Typical Permeable Pavement Configuration|Typical Permeable Pavement Configuration<font size=3></font size>]]
+
==Step 6: Review Construction & Operations Criteria==
 +
Each of the BMPs included in the treatment train have unique criteria for construction and operations. Information regarding construction and operations should be reviewed in detail before design and construction of the BMPs take place. Available information for each of the BMPs is provided below.
  
−
The sizing of the permeable pavement parking/bike lane varies depending on scenario, available space and should conform to all local rules and regulations for transportation zones. This Ultra-Urban scenario was set in downtown Minneapolis, MN and as such local sizing guidelines for traffic ways, parking lanes and bike lines were considered. The [http://www.minneapolismn.gov/www/groups/public/@publicworks/documents/webcontent/convert_283657.pdf Minneapolis Public Works Street and Sidewalk Design Guidelines] offers desired minimum lane widths for urban roads, parking and bike lanes. These recommendations conform to the minimum design standards set forth by the [https://www.revisor.mn.gov/rules/?id=8820.9936 Minnesota Administrative Rules]. The dimensions for the permeable pavement lane, including space for parking and bike passage, were designed to be 12 ft. wide, and extend the length of the block. This meets the [http://www.minneapolismn.gov/www/groups/public/@publicworks/documents/webcontent/convert_283657.pdf Minneapolis Public Works Design Guidelines for Streets and Sidewalks] requirements for the minimum functional lane widths. The Permeable Pavement Layout schematic displays the overall layout for the permeable pavements.
+
{| class="wikitable"
−
 
+
|+Construction and Operations Guidance for parking lot scenario
−
 
+
|-
−
[[File:Permeable Pavement Layout.PNG |thumb|300 px|alt=schematic illustrating Permeable Pavement Layout|Permeable Pavement Layout<font size=3></font size>]]
+
! Green roof !! Tree trench !! Permeable pavement
−
 
+
|-
−
The additional considerations for permeable pavement infiltration BMP sizing are depth of the aggregate reservoir and the required drawdown time. The sizing input parameters for the permeable pavement BMP are summarized in Table 3.2.9.
+
| [https://stormwater.pca.state.mn.us/index.php?title=Construction_specifications_for_green_roofs Construction] || [https://stormwater.pca.state.mn.us/index.php?title=Construction_guidelines_for_tree_trenches_and_tree_boxes Construction] || [https://stormwater.pca.state.mn.us/index.php?title=Construction_specifications_for_permeable_pavement Construction]
−
 
+
|-
−
{{:Ultra urban Permeable Pavement Sizing Input Parameters}}
+
| [https://stormwater.pca.state.mn.us/index.php?title=Operation_and_maintenance_(O%26M)_of_green_roofs Maintenance] || [https://stormwater.pca.state.mn.us/index.php?title=Operation_and_maintenance_(O%26M)_of_tree_trenches_and_tree_boxes Maintenance] || [https://stormwater.pca.state.mn.us/index.php?title=Operation_and_maintenance_of_permeable_pavement Maintenance]
−
 
+
|}
−
Although the underlying Hydrologic Soil Group B is considered to be well draining with an infiltration rate of 0.45 in/hr., high soil compaction was assumed because this is a highly urbanized area. In addition, the Permeable Pavement BMP will need to support vehicular loads and therefore further compaction of underlying soils may be required. For this reason, an existing inlet will be maintained directly downstream of the permeable pavement for bypass and overflow from larger storm events. The porosity of the aggregate media was assumed to be 0.4 ft3/ft3. These parameters were input into the MIDS calculator to evaluate the pollutant removal and volume reduction performance of the BMP. The results of the MIDS credit calculations for volume reduction and pollutant loading are given below in the Permeable Pavement Performance Summary table below.
 
−
 
 
−
{{:Permeable Pavement Performance Summary}}
 
−
 
 
−
===Overall Ultra-Urban BMP Treatment Train Performance===
 
−
 
 
−
The overall performance of the BMP Treatment Train was evaluated by the MIDS Calculator. The treatment train configuration consisting of a green roof, 2 large tree trenches, 4 small tree trenches and a permeable pavement parking/bike lane is shown in Figure 3.2.10.
 
−
 
 
−
[[File:Ultra-Urban BMP Treatment Train MIDS Calculator Schematic.PNG |thumb|300 px|alt=schematic illustrating Ultra-Urban BMP Treatment Train MIDS Calculator|Ultra-Urban BMP Treatment Train MIDS Calculator Schematic <font size=3></font size>]]
 
−
 
 
−
This treatment train was able to significantly reduce the volume and pollutant loadings in the Ultra-Urban setting. The treatment train achieved removal efficiencies of 97% for each of the components of interest: runoff volume, Total Phosphorous and Total Suspended Solids. The results from the MIDS Calculator Ultra-Urban BMP Treatment Train is summarized in the Ultra urban Annual BMP Treatment Train Performance Summary table below.
 
−
 
 
−
{{:Ultra urban Annual BMP Treatment Train Performance Summary}}
 
−
 
 
−
===Step 6: Review Construction & Operations Criteria===
 
  
−
Each of the BMPs included in the treatment train have unique criteria for construction and operations. Information regarding construction and operations should be reviewed in detail before design and construction of the BMPs take place. Available information for each of the BMPs used in this Ultra-Urban Treatment Train are provided in the Construction and Operations Guidance for Ultra-Urban BMPs table below.
+
==Related articles==
 +
*[[Using the treatment train approach to BMP selection]]
 +
*[[Scenario for developing a stormwater treatment train for a parking lot]]
 +
*[[Scenario for developing a stormwater treatment train for an ultra-urban setting]]
 +
*[[Scenario for developing a stormwater treatment train for a site with limited infiltration capacity]]
 +
*[[Scenario for developing a stormwater treatment train for a retrofit site]]
 +
*[[Scenario for developing a stormwater treatment train for constructed ponds in new development]]
 +
*[[Case studies for stormwater treatment trains]]
  
−
{{:Construction and Operations Guidance for Ultra-Urban BMPs}}
+
<noinclude>
 +
[[Category:Level 2 - Management/Watershed scale and treatment train]]
 +
<noinclude>

Latest revision as of 13:33, 12 February 2023

Stormwater treatment trains combine multiple stormwater treatment processes and/or practices in a manner that ensures management of all pollutants that could affect a receiving water. To provide guidance for stormwater managers, hypothetical treatment trains were developed for five common stormwater management scenarios. This page provides information on implementing a stormwater Best Management Practice (BMP) treatment train for an ultra-urban setting. To see other scenarios, see related articles at the bottom of this page.

Step 1: Review project goals and site conditions

schematic illustrating Ultra-Urban Scenario Base
Site layout for an ultra-urban setting. For this example the site consists of a single building on a 1 acre drainage area. (source: CDM Smith).

The ultra-urban site is characterized by high impervious cover in the form of residences, parking, or commercial development. For the purposes of this scenario, the drainage conditions for a single building on a city block in downtown Minneapolis, Minnesota were considered. A single city block covers an average area of 2 to 3 acres and generally contains 2 to 4 buildings. For this scenario, it is assumed that a single building, including its frontage, sidewalk and half of the road covers a drainage area of 1 acre, as shown in the schematic to the right.

The basic site conditions for the ultra-urban setting are summarized in the table below.

Site conditions for a hypothetical site in an ultra-urban setting
Site Ultra-Urban (Downtown Minneapolis)
Drainage Area 1.0 acre
Impervious Area 95%
Soil Conditions Hydrologic Soil Group ‘B’, silty sands and silty gravelly sands. Permeability ranges between 0.30- 0.45 inches per hour at a depth of 3 feet. Bedrock was not observed in borings conducted on site.
Topography & Drainage Rooftop runoff drains down to street level through downspouts. Street level runoff drains to the southwest corner of the city block.
Project Goals Reduce stormwater runoff volume and pollutant loads by decreasing impervious cover to promote infiltration and nutrient uptake.

High imperviousness results in high velocity and erosive stormwater flows that can damage building integrity and overwhelm stormwater infrastructure. The soil is assumed to be compacted due to high urbanization. Lack of vegetation and infiltration opportunities also prevent pollutant removal which leads to reduced water quality. The goal of this project is to install a BMP treatment train to reduce runoff volume and pollutant loads for the Water Quality Event.

Step 2: Review Pollutant Removal Processes & Identify Potential Practices

The BMPs selected for this site must achieve the goals of decreased runoff volume and pollutant removal, as well as fit within the site constraints. The following table summarizes the BMP categories and their applicability to this site.

BMP practice selection options for an ultra-urban site
Practice Applicability Reason
Pollution prevention and public education Pollution Prevention will be implemented during site maintenance.
Source controls Additional maintenance for source controls is not intended for this site; this is not an applicable practice.
Infiltrators X Allows for total stormwater and pollutant capture and aesthetically pleasing for pedestrians.
Swales and strips Not applicable for a highly urbanized city block.
Filters X Allows for reduction of stormwater volume and pollutant loads and easy diversion to other BMPs.
Constructed basins Too large to meet space constraints.
Manufactured devices [1], [2] Applicable, however more aesthetically pleasing options should be pursued first.
Storage, harvesting and reuse Applicable depending on available space and building function. However, stormwater storage for re-use is not necessary for this scenario.

Infiltrator and filter BMPs are determined to best address the goals of this project. The process of selecting and placing BMPs on a site is typically iterative, working between the site constraints, project goals, and available budget. The approach and considerations for this scenario are discussed in the following sections.

Step 3: Determine site constraints and BMP placement

An ultra-urban setting can pose a unique set of site constraints due to limited space for development and high pedestrian traffic. Specific site constraints for a typical city block in Minneapolis include:

schematic illustrating Ultra-Urban Scenario Street Level BMP Placement
Proposed site layout for a hypothetical site in an ultra-urban setting (Source: CDM Smith).
  • Available space – In the ultra-urban setting the location of BMPs is restricted to rooftops and the narrow corridor between buildings and city streets. Impervious surfaces in the drainage area are necessary for supporting high foot and vehicle traffic, as well as structural support of buildings. Selected BMPs must be able to effectively reduce the adverse effects of stormwater while maintaining the function of the existing impervious surfaces.
  • Public integration – Ultra-urban settings are usually characterized by high volumes of pedestrian and vehicular traffic. Selected BMPs must be resistant to degradation due to constant use. BMP aesthetics should also be a consideration.
  • Utilities – when working in a downtown or ultra-urban setting, there is often little flexibility in the location and movement of utilities. BMP sizing and location should try to avoid major impact utilities.
  • Regulatory Requirements - All local, state, and federal regulatory requirements must be met. The design criteria and recommendations from the Minnesota Stormwater Manual will be followed.

To meet space allotments and reduce degradation due to interaction with people and vehicles, the most viable locations for BMPs are the building rooftop, the pedestrian sidewalk and parking/bike lane. For reference, the street level areas are depicted in the schematic to the right.

Further considerations for placement of BMPs on the street level are the required minimum dimensions for high capacity roads, curbs, sidewalks and planting and furnishing zones as well as the 10 foot minimum setback from a building foundation.

Step 4: Select individual BMPs and evaluate range of performance

schematic illustrating Ultra-Urban Scenario BMP Layout
Example of a suitable BMP layout for an ultra-urban setting (Source: CDM Smith).
schematic illustrating MIDS Green Roof Configuration
Green roof configuration used for the MIDS calculator. Needed inputs are the media depth and surface area of the green roof. (Source: CDM Smith).
schematic illustrating MIDS Tree Trench - Box System Configuration
MIDS tree trench configuration. In addition to surface areas and media depth, required inputs include soil storage information, soil type, drawdown time, and tree information.
schematic illustrating Ultra-Urban Green Roof Design.PNG
Ultra-Urban Green Roof Design
schematic illustrating Tree Trench System Design
Tree trench system design.
schematic illustrating Typical Permeable Pavement Configuration
Typical configuration for permeable pavement (Source: CDM Smith).
schematic illustrating Permeable Pavement Layout
Layout for permeable pavement.

Step 2 introduced the practices that would best address the goals and site constraints for the ultra-urban setting as infiltrators and filters. Infiltration is a hydraulic process that serves to reduce runoff volume and pollutant loads by complete abstraction of runoff. Physical, chemical and biological processes remove pollutant loads as water moves through the media mix. In contrast, filtration is a physical process that uses the same physical, chemical and biological principles to reduce pollutant loads as water moves through the media. However, excess water is drained through an underdrain.

Filter: Green Roof
  • Green roofs are primary treatment BMPs which act as filters. Installing a green roof substantially reduces impervious cover and the volume and rate of water draining to the street level. Green roofs have a median total suspended solid (TSS) removal of 85 percent. Although green roofs do not have high rates of total phosphorus (TP) removal, in a northern temperate region such as Minnesota a green roof can reduce runoff volume by 50 percent to 70 percent. Volume and rate reduction will reduce loading on downstream BMPs allowing for more effective pollutant reduction. Studies show that green roofs actually become more effective over time. As vegetation becomes more established, water quality may improve due to mature plants ability absorb and filter more pollutants. A green roof will allow for reduction in runoff volume, peak discharge, delay peak runoff, and divert excess water to downstream BMPs for further pollutant reduction.
Infiltrator: Tree Trench/Box System
  • Tree trenches and boxes on the street level between the sidewalk and street can capture and reduce runoff from the road, sidewalk, and underdrain outlet from the green roof. Tree trenches/boxes act as infiltrators where the soil media, trees and microbes work in conjunction to absorb, filter or transform pollutants. The media in tree trenches/boxes also holds pollutants to be utilized by vegetation or microbes during periods of low rainfall. Soil Media Mix D is recommended for tree BMPs. Together they provide the most effective design for nutrient and pollutant removal because of the interplay of physical, chemical and biological processes. Infiltration basins could provide similar runoff volume and pollutant reductions, however because this was an area with high pedestrian interaction, tree trenches/boxes provide a higher aesthetic value.
Infiltrator: Permeable Pavement
  • Permeable pavement acts as a final filter to remove phosphorus and other pollutants and to reduce road and storm sewer flooding. Although permeable pavements can be prone to clogging in areas of high TSS loading, the preceding BMPs will reduce pollutant loading from the sidewalk and buildings, and allow for more effective pollutant removal from the adjacent impervious street. Permeable pavement offers structural stability to allow for traffic loading from cars and bikes, while allowing water to infiltrate through voids in the surface. The aggregate storage media under the permeable pavement and tree boxes will be a single unit as shown in the figure to the right, allowing for captured stormwater and pollutants to be available for vegetation in the tree trenches/boxes.

A multitude of infiltrator or filter BMPs may be considered for an Ultra-Urban setting where the goals of stormwater management are the reduction of runoff volumes and pollutant loads. A green roof, tree trenches, and permeable pavement were selected as plausible treatment train BMPs for this scenario.

Step 5: Size BMPs and assess performance

For the ultra-urban setting, space is a significant site constraint. BMP sizing must be strategic to allow for maximum BMP efficiency while meeting performance goals. Assumptions included an annual phosphorus event mean concentration (EMC) of 0.3 milligrams per liter, and an annual TSS EMC of 54.5 milligrams per liter. The following table summarizes the existing site runoff, volume and pollutant retention goals. The MIDS calculator provides a performance goal requirement based on the site conditions for the treatment train which is shown in the table below.

Ultra-urban scenario performance goal
Annual runoff volume (acre-feet Annual particulate phosphorus load (lbs) Annual dissolved phosphorus load (lbs) Annual total suspended solids load (lbs) Performance goal volume retention requirement (ft3
2.15 0.96 0.79 319 3793

BMP Sizing for each component of a treatment train is an iterative process where available space, performance goals and regulatory requirements must be considered.

Green roof

Event runoff volume performance summary
Parameter Value
Runoff Volume from Direct Watershed (ft3) 2832
Runoff Volume from Upstream BMPs (ft3) 0
Retention Volume Provided by BMP (ft3) 2734
Outflow Volume from BMP (ft3) 98
Percent Performance Goal Achieved (%) 97
Ultra-urban green roof sizing input parameters
Roof area (ft2) Media depth (in)
24852 4

The design of a green roof is based around the input parameters needed for the MIDS calculator for green roofs. The MIDS calculator is able to determine the performance of the green roof BMP based on the parameters shown in the schematic to the right.

The surface area of a green roof is controlled by the available area on the building rooftop. The rooftop size is dictated by the space available on the existing building. The sizing input parameters for the green roof are shown in the table below.

For this setting, space was allotted for a 6 foot walkway around the perimeter of the green roof to provide maintenance access to the BMP without hindering its functionality and the performance. To route excess water to the downstream BMPs on the south and west side of the building, two 4-inch downspouts were included. Two downspouts reduce the risk of clogging and provides an extra outlet for water if one downspout is undergoing maintenance. A schematic of the green roof design is shown to the right.

These parameters were entered into the MIDS calculator to evaluate performance of the green roof BMP for runoff volume and pollutant load reductions. These results are summarized in the adjacent tables.

Annual performance goal summary
Pollutant Parameter Value
Volume Runoff from Direct Watershed (acre-ft.) 0.00
Runoff from Upstream BMPs (acre-ft.) 1.59
Retention Volume Provided by BMP (acre-ft.) 0.79
Outflow Volume from BMP (acre-ft.) 0.87
Percent Performance Goal Achieved (%) 45
Particulate phosphorus Particulate P from Watershed (lbs.) 0.72
Particulate P from Upstream BMPs (lbs.) 0
Particulate P Load Reduction (lbs.) 0
Particulate P Outflow 0.72
Total Percent Particulate P Reduction 0
Dissolved phosphorus Dissolved P from Watershed (lbs.) 0.58
Dissolved P from Upstream BMPs (lbs.) 0
Dissolved P Load Reduction (lbs.) 0
Dissolved P Outflow 0.58
Total Percent Dissolved P Reduction (%) 0
Total suspended solids (TSS) TSS from Watershed (lbs.) 236
TSS from Upstream BMPs (lbs.) 0
TSS Load Reduction (lbs.) 226
TSS Outflow 10
Total Percent TSS Reduction (%) 96

Tree trench/Box system

Annual performance goal summary
Pollutant Parameter Large trench Small trench
Volume Runoff from Direct Watershed (acre-ft.) 0.05 0.03
Runoff from Upstream BMPs (acre-ft.) 0.44 0.00
Retention Volume Provided by BMP (acre-ft.) 0.49 0.03
Outflow Volume from BMP (acre-ft.) 0.00 0.00
Percent Performance Goal Achieved (%) 100 100
Particulate phosphorus Particulate P from Watershed (lbs.) 0.02 0.01
Particulate P from Upstream BMPs (lbs.) 0.36 0.00
Particulate P Load Reduction (lbs.) 38 0.01
Particulate P Outflow 0.00 0.00
Total Percent Particulate P Reduction 100 100
Dissolved phosphorus Dissolved P from Watershed (lbs.) 0.02 0.01
Dissolved P from Upstream BMPs (lbs.) 0.29 0.00
Dissolved P Load Reduction (lbs.) 0.31 0.01
Dissolved P Outflow 0.00 0.00
Total Percent Dissolved P Reduction (%) 100 100
Total suspended solids (TSS) TSS from Watershed (lbs.) 7 4
TSS from Upstream BMPs (lbs.) 5 0
TSS Load Reduction (lbs.) 12 4
TSS Outflow 0 0
Total Percent TSS Reduction (%) 100 100
Event runoff volume performance summary
Parameter Large trench Small trench
Runoff Volume from Direct Watershed (ft3) 80 48
Runoff Volume from Upstream BMPs (ft3) 49 0
Retention Volume Provided by BMP (ft3) 419 209
Outflow Volume from BMP (ft3) 0 0
Percent Performance Goal Achieved (%) 100 100
Ultra-urban green roof sizing input parameters
Top surface area (ft2) Bottom surface area (ft2) Media depth (ft) Number of trees Required drawdown time (hrs)
420 420 3 2 48
210 210 3 1 48

The design of a tree trench BMP is based around the input parameters needed for the MIDS calculator for tree trenches without underdrains. The MIDS calculator configuration for the tree trench BMP is illustrated in the figure to the right.

Two types of tree trenches were designed for this setting. Two large tree trenches were placed at the outlets of each downspout to account for flow from the upstream green roof BMP as well as runoff from the adjacent sidewalk. Four small tree trenches were added to intercept runoff from the sidewalk, preventing flow into the street. Sizing of the tree trenches is limited by pedestrian zone spacing requirements. Installations in the pedestrian zone should conform to all local rules and regulations. This Ultra-Urban scenario was set in downtown Minneapolis, MN and as such, sizing for the frontage, sidewalk and planting zones are determined based on the Minneapolis Public Works Pedestrian Facility Design Guidelines. The required 10 foot minimum setback for infiltration practices from a building foundation and soil volume requirements for the chosen tree type also factored into tree trench sizing. The tree trench sizing input parameters are summarized in the table below.

The tree types and sizes for the tree trench system BMPs are restricted by the available soil volume. Deciduous trees are most suitable for the ultra-urban design as they provide more clearance for pedestrian passage around the trees. The table below shows the tree inputs for the MIDS calculator.

The MIDS calculator also accounts for soil media within the tree trench system, underlying soils, and tree types. As previously stated, Media Mix D is highly recommended for best results with a tree BMP. The selected media mix dictates the MIDS inputs for soil-water storage properties, including a media field capacity of 0.09 cubic feet per cubic foot and a media porosity of 0.31 cubic feet per cubic foot. Although the area’s underlying Hydrologic Soil Group B is relatively well-draining with an infiltration rate of 0.45 inches per hour, high soil compaction was assumed because of the intense urbanization. Therefore an overflow structure was included in the tree trench for larger storm bypass and reduced infiltration capacity over time. The figure to the right displays the overall layout for the tree trench system.

These parameters were entered into the MIDS calculator to evaluate performance of the tree trench BMPs for runoff volume and pollutant load reductions. These results are summarized below.

Permeable pavement

Annual performance goal summary
Pollutant Parameter Value
Volume Runoff from Direct Watershed (acre-ft.) 0.29
Runoff from Upstream BMPs (acre-ft.) 0..00
Retention Volume Provided by BMP (acre-ft.) 0.29
Outflow Volume from BMP (acre-ft.) 0.00
Percent Performance Goal Achieved (%) 100
Particulate phosphorus Particulate P from Watershed (lbs.) 0.13
Particulate P from Upstream BMPs (lbs.) 0.00
Particulate P Load Reduction (lbs.) 0.13
Particulate P Outflow 0.00
Total Percent Particulate P Reduction 100
Dissolved phosphorus Dissolved P from Watershed (lbs.) 0.11
Dissolved P from Upstream BMPs (lbs.) 0.00
Dissolved P Load Reduction (lbs.) 0.11
Dissolved P Outflow 0.00
Total Percent Dissolved P Reduction (%) 100
Total suspended solids (TSS) TSS from Watershed (lbs.) 43
TSS from Upstream BMPs (lbs.) 0
TSS Load Reduction (lbs.) 43
TSS Outflow 0
Total Percent TSS Reduction (%) 100
Event runoff volume performance summary
Parameter Large trench Small trench
Runoff Volume from Direct Watershed (ft3) 518
Runoff Volume from Upstream BMPs (ft3) 0
Retention Volume Provided by BMP (ft3) 3469
Outflow Volume from BMP (ft3) 0
Percent Performance Goal Achieved (%) 100
Ultra-urban green roof sizing input parameters
Top surface area (ft2) Surface area at subgrade (ft2) Storage depth (ft) Required drawdown time (hrs)
4818 4818 1.8 48

The design of a permeable pavement parking/bike lane is based around the input parameters needed for the MIDS calculator for permeable pavement. A typical permeable pavement configuration is shown in the figure to the right.

The sizing of the permeable pavement parking/bike lane varies depending on the scenario and available space and should conform to all local rules and regulations for transportation zones. This ultra-urban scenario was set in downtown Minneapolis, MN and as such local sizing guidelines for traffic ways, parking lanes and bike lines were considered. The Minneapolis Public Works Street and Sidewalk Design Guidelines offers desired minimum lane widths for urban roads, parking and bike lanes. These recommendations conform to the minimum design standards set forth by the Minnesota Administrative Rules. The dimensions for the permeable pavement lane, including space for parking and bike passage, were designed to be 12 feet wide and extend the length of the block. This meets the [Minneapolis Public Works Design Guidelines for Streets and Sidewalks Minneapolis Public Works Design Guidelines for Streets and Sidewalks] requirements for the minimum functional lane widths.

Additional considerations for permeable pavement sizing are depth of the aggregate reservoir and the required drawdown time. The sizing input parameters for the permeable pavement BMP are summarized below.

Although the underlying Hydrologic Soil Group B is considered to be well draining with an infiltration rate of 0.45 inches per hour, high soil compaction was assumed because this is a highly urbanized area. In addition, the permeable pavement BMP will need to support vehicular loads and therefore further compaction of underlying soils may be required. For this reason, an existing inlet will be maintained directly downstream of the permeable pavement for bypass and overflow from larger storm events. The porosity of the aggregate media was assumed to be 0.4 cubic feet per cubic foot. These parameters were input into the MIDS calculator to evaluate the pollutant removal and volume reduction performance of the BMP. The results of the MIDS credit calculations for volume reduction and pollutant loading are shown below.

Overall ultra-urban BMP treatment train performance

schematic illustrating Ultra-Urban BMP Treatment Train MIDS Calculator
Ultra-Urban BMP Treatment Train MIDS Calculator Schematic

The overall performance of the BMP treatment train was evaluated using the MIDS calculator. The treatment train configuration consisting of a green roof, 2 large tree trenches, 4 small tree trenches and a permeable pavement parking/bike lane is shown on the right.

This treatment train was able to significantly reduce the volume and pollutant loadings in this ultra-urban setting. The treatment train achieved removal efficiencies of 97 percent for each of the components of interest: runoff volume, total phosphorus and TSS. The results from the MIDS calculator run are summarized in the following table.

Annual stormwater BMP treatment train performance summary
Volume Performance Goal Runoff Volume (acre-ft.) 2.15
Retention Volume Provided by BMPs (acre-ft.) 2.09
Percent Runoff Volume Removed (%) 97
Total phosphorus Performance Goal Particulate P Load (lbs.) 0.96
Performance Goal Dissolved P Load (lbs.) 0.79
Particulate P Load Removed by BMPs (lbs.) 0.93
Dissolved P Load Removed by BMPs (lbs.) 0.77
Percent TP Removed (%) 97
Total suspended solids Performance Goal TSS Loads (lbs.) 319
TSS Load Removed by BMPs (lbs.) 309
Percent TSS Removed (%) 97

Step 6: Review Construction & Operations Criteria

Each of the BMPs included in the treatment train have unique criteria for construction and operations. Information regarding construction and operations should be reviewed in detail before design and construction of the BMPs take place. Available information for each of the BMPs is provided below.

Construction and Operations Guidance for parking lot scenario
Green roof Tree trench Permeable pavement
Construction Construction Construction
Maintenance Maintenance Maintenance

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This page was last edited on 12 February 2023, at 13:33.