ANNOUNCE A SEMINAR DEMONSTRATING The BMP … APWA... · ANNOUNCE A SEMINAR DEMONSTRATING The BMP...

November 18, 2014

THE SAN DIEGO AND IMPERIAL COUNTIES CHAPTER OF THE

AMERICAN PUBLIC WORKS ASSOCIATION (APWA)

ANNOUNCE A SEMINAR DEMONSTRATING

The BMP Sizing Spreadsheeet – A Tool to Comply with Hydromodification

Management Requirements(2007 & 2013 MS4 Permits for San Diego Region)

The BMP Sizing Spreadsheet replaces the former on-line San Diego BMP Sizing Calculator

Seminar Logistic Jayne Janda‐Timba

Background & Introduction René Vidales

Example Project to CompareOnline Calculator & Spreadsheet Nobu Murakami

Question & Answer

Example Problem with 2007 MS4 Permitand 2013 MS4 Permit Requirements Brendan Hastie

Question & Answer

Future of Sizing Factor Method 2013 MS4 PermitCompliance Laura Henry

Question & Answer

Closing

AGENDA

Seminar Logistics Housekeeping Please turn cell phones off Sponsors – Thank You! (County of SD, City of SD & APWA) Handouts−Speaker Profile−Bios−Acronyms−PowerPoint Presentation−Sizing Factors Matrix−Example Problem Handouts

Seminar Logistics Survey the audience……….−Design Engineer−Environmental Community−Development Community−Municipality−Regulators

PowerPoint available on Project Clean WaterWebsite: http://www.projectcleanwater.org

SPEAKERS PROFILE

René A. Vidales P.E, QSD, LEED GA, ENV SP

Program Director County of San Diego

Watershed Protection Program Department of Public Works

5510 Overland Avenue, Suite 410

San Diego, CA 92123 Phone: (858) 694-3246

Nobu Murakami P.E Assistant Project Engineer Rick Engineering Company Water Resources Division

5620 Friars Road

San Diego, CA 92110 Phone: (619) 291-0707 Fax: (619) 291-4165

nmurakami@rickengineering.com

Brendan Hastie, P.E., LEED AP Associate

Rick Engineering Company Water Resources Division

5620 Friars Road

bhastie@rickengineering.com

Laura Henry, M.S., P.E. Project Engineer

5620 Friars Road

lhenry@rickengineering.com Jayne M. Janda-Timba, P.E., TOR,

QSD, QSP Associate

5620 Friars Road

San Diego, CA 92110 Phone: (619) 688-1448 Fax: (619) 291-4165 Cell: (619) 540-6855

Jjanda-timba@rickengineering.com

The BMP Sizing SpreadsheetA Tool to Comply with Hydromodification Management Requirements

Background & Introduction

René Vidales, PE, QSD, LEED GA, ENV SPProgram Coordinator, Watershed Protection Program

County of San Diego

November 18, 2014

Overview Background◦ MS4 Permits◦ Trainings

Introduction◦ History and Intent◦ What it is and Purpose◦ Components◦ Mechanics

Background

MS4 Permits 2007 MS4 Permit (R9-2007-0001)◦ Required PDPs to implement Interim Hydromodification

requirements◦ Interim requirements started January, 2008◦ Required Copermittees to develop Final

Hydromodification requirements◦ Final HMP released January, 2011

MS4 Permits 2013 MS4 Permit (R9-2013-0001)◦ Will be implemented December, 2015◦ Will continue to require PDPs to implement

Hydromodification requirements

Trainings Hydrologic Simulation Program Fortran (HSPF)◦ June 2009 Training

Trainings Online BMP Sizing Calculator◦ December 2010 Training

Trainings Online BMP Sizing Calculator◦ March 2011 Training

Trainings San Diego Hydrology Model (SDHM)◦ January 2012 Training

Trainings SCCWRP Hydromodification Screening Tool◦ June 2012 Training

Why this Training? Online BMP Sizing Calculator◦ Expired June 30, 2014

Why this Training? Online BMP Sizing Calculator◦ Expired June 30, 2014◦ Replaced by the BMP Sizing Spreadsheet

This Training BMP Sizing Spreadsheet◦ November 18, 2014 Training

Introduction

History Final Regional HMP includes a table of sizing factors

for various BMPs Online sizing calculator developed based on sizing

factors in HMP Online sizing calculator taken down and replaced

with spreadsheet. July 1, 2014

History Advantages of spreadsheet versus online sizing

calculator (tool)◦ Does not require internet hosting◦ Does not require major updates to maintain compatibility

with latest versions of internet browsers◦ Can easily be downloaded to an individual computer◦ Easy to use and understand

Intent One possible tool for use by applicants (SDHM,

SWMM, etc. can still also be used) Simple and easy to use Conservative results For use with common conditions (unusual designs

will require continuous simulation modeling) Sizes BMPs for treatment of the 85th percentile

event as well as hydromodification management

What it is and Purpose Spreadsheet to facilitate calculations from Final

HMP (Section 7) and Regional Model SUSMP (Chapter 4)◦ Some input parameters are controlled in order to align with the Final

HMP and the SUSMP◦ Some input parameters are determined based on project conditions◦ Spreadsheet output confirms adequacy of design◦ Particularly useful during preliminary design

Why use it? Online BMP Sizing Calculator is no longer online More reports with hand calculations for HMP

BMP Sizing Spreadsheet TabsLet’s look at the components within thespreadsheet…

Controlled selections◦ BMP Type◦ Low Flow Threshold◦ Soil Group◦ Slope Categorization◦ Rain Gauge

Components

Custom User Input◦ DMA name, size, surface type, and runoff factor◦ BMP area and volume◦ Depth of soil matrix◦ Orifice size

Components

Output◦ Minimum area and volume sizing criteria◦ Minimum and maximum allowable depth◦ Drawdown time

Components

Five (5) BMP Options in the Final HMP- Bioretention Facilities (Table 7-1)- Bioretention Plus Cistern Facilities (Table 7-2)- Bioretention Plus Vault Facilities (Table 7-3)- Flow-Through Planters (Table 7-4)- Infiltration Facilities (Table 7-5)

Select a BMP

Variable surface ponding depth Variable soil matrix depth 30-inch gravel storage layer Orifice 12-inch off bottom

Bioretention/Flow-Through Planter

Variable cistern depth and volume Overflow outlet to bioretention Controlled orifice outlet to bioretention

Bioretention Plus Cistern

Variable vault depth and volume Inflow from bioretention Emergency overflow outlet Controlled orifice outlet

Bioretention Plus Vault

Variable depth and volume No orifice discharge

Infiltration

Determined based on stream susceptibility−Per Section 6.2 of the Final HMP−High = 0.1Q2 (default value; no assessment is performed)−Medium = 0.3Q2

−Low = 0.5Q2

Low Flow Threshold

NRCS Hydrologic Soil Group−County Hydrology Manual , Appendix A−NRCS Web Soil Survey−http://websoilsurvey.nrcs.usda.gov/app/WebSoilSurvey.aspx

Soil Group

Average Slope−Flat (< 5%)−Moderate (5% to 15%)−Steep (>15%)

Only three (3) options−Lindbergh−Oceanside−Lake Wohlford

Rain Gauge

Rain gauge information: http://bit.ly/1nHsWJe33

Rain Gauge and Soil Typehttp://bit.ly/1nHsWJe

Click next to point

Rain Gauge and Soil Typehttp://bit.ly/1nHsWJe

Per Tables 7-1 to 7-5 of the Final HMP Expressed as a ratio of the contributing area

Minimum Surface Area

Per Tables 7-1 to 7-5 of HMP Expressed as a ratio of the contributing area−10-inch of surface ponding (for bioretention)−18-inch storage with 40% porosity (for bioretention)

Minimum Volume

Sized to discharge at the same rate as the low flow threshold

Calculated drawdown time must be less than 96 hours

Vector Control Plan required if more than 96 hours◦ County of San Diego Guidelines for Determining Significance ◦ County of San Diego Guidelines for Report Format and Content

Requirements http://www.sandiegocounty.gov/pds/procguid.html#vectors

Outlet Orifice

“Project Info” TAB

Mechanics

“BMP #1” TAB

Mechanics

“Orifice #1” TAB

Mechanics

“Rain Gauge Map” TAB

Mechanics

“Sizing Factors” TAB

Mechanics

To Compare Online Calculator with Spreadsheet

Example Problem

Comparison ofOnline San Diego BMP Sizing Calculator (Retired)

andBMP Sizing Spreadsheet (New)

Nobu MurakamiRick Engineering CompanyWater Resources Division

November 18, 20141

Use an example residential project to compare:1. Online San Diego BMP Sizing Calculator (Retired)

2. BMP Sizing Spreadsheet (New)

Overview

Example Residential Project

Total DMA = 1.22 AC

DMA to LID (w/o self-treating area) = 1.14 AC

Area Reserved for LID BMP

Additional Information / Assumptions:◦ The POC will be at the point where the runoff leaves the

project◦ No channel assessment performed – use low flow threshold

of 0.1Q2

◦ Design goal is to size a LID BMP using a “Cistern to Bioretention” tool

Example Residential Project

Basin Manager Tool:

• “Start” Tab – (Introduction/Overview for Basin Manger)

• “Project” Tab (Define Project Information)

• “Basin” Tab – (Define Basin Properties)

• “POC” Tab – (Low-flow Threshold Calculation)

• “Export” Tab – (Export/Import Project Information files)

LID Sizer Tool:

• “Start” Tab - (Introduction/Overview for LID Sizing)

• “DMA” Tab - (Define/Manage DMA Properties)

• “LID” Tab - (LID BMP Sizing Calculation)

• “Report” Tab - (Provides a summary of the project / LID Sizing)

• “Export” Tab - (Export/Import DMA/LID files)

Basin Manager Tool and LID Sizer Tool

Online San Diego BMP Sizing Calculator (Retired)

“Project” TAB (Basin Manager Tool) – Online San Diego BMP Sizing Calculator

7“Basin” TAB (Basin Manager Tool) – Online San Diego BMP Sizing Calculator

8“POC” TAB (Basin Manager Tool) – Online San Diego BMP Sizing Calculator

9“DMA” TAB (LID Sizer Tool) – Online San Diego BMP Sizing Calculator

10“DMA” TAB (LID Sizer Tool) – Online San Diego BMP Sizing Calculator

Note: All of the DMAs have been defined, including the self-treating areas. However, the Online Calculator would not consider the self-treating DMA in sizing the LID BMP since the DMA did not contribute to the LID BMP.

11“LID” TAB (LID Sizer Tool) – Online San Diego BMP Sizing Calculator

Minimum Bioretention Area = 601.1 sf.

Minimum Cistern Volume (V1) = 6011.4 cf.

Flow Threshold – 0.1Q2 = 0.024 cfs

Orifice Size = 0.6 in.

Available Tabs within the BMP Sizing Spreadsheet

• “Project Info” (Project Information)

• “BMP #1” (BMP Sizing Calculation)

• “Orifice #1” (Orifice Sizing Calculation)

• “Rain Gauge Map” (for reference)

• “Sizing Factors” (Lookup Tables from the 2011 Final HMP)

BMP Sizing Spreadsheet (New)

13“Project Info” TAB – BMP Sizing Spreadsheet

• “Project”, “Basin” and “POC” tabs from the San Diego BMP Sizing Calculator have been consolidated into this “Project Info” Tab in the BMP Sizing Spreadsheet.

“Project Info” TAB – BMP Sizing Spreadsheet

17“BMP #1” TAB – BMP Sizing Spreadsheet

BMP Area = 8276.4 sf * (1.0) * (0.02) = 166 s.f.

Cistern Vol. = 8276.4 sf * (1.0) * (0.2) = 1655 c.f.

“BMP #1” TAB – BMP Sizing Spreadsheet

25“Sizing Factors” TAB – BMP Sizing Spreadsheet

Minimum Bioretention Area = 601.1 s.f. OK

Minimum Cistern Volume (V1) = 6011 c.f. OK

Note: All of the DMAs have been defined except the area for self-treating DMA has been purposefully left blank since this DMA does not drain to the LID BMP.

“BMP #1” TAB – BMP Sizing Spreadsheet

1.14 AC.

28“Orifice #1” TAB – BMP Sizing Spreadsheet

Existing Condition Cover:

• “Scrub” refers to a natural (pervious) cover

• “Urban” refers to a landscaping area with irrigation

• “N/A” applies only when “Impervious” is selected as the Soil Type

User’s Input

“Orifice #1” TAB – BMP Sizing Spreadsheet

“Break”

Example Problem2007 MS4 Permit and 2013 MS4 Permit

Requirements

Brendan HastieRick Engineering CompanyWater Resources Division

November 18, 2014

Purpose

Compare the BMP Sizing Spreadsheet results for the example problem by inputting data based on 2007 MS4 and 2013 MS4 Permit Requirements

Presentation Overview

Goals of Example Problem Example Problem Information/Assumption Example Problem 2007 MS4 Permit Example Problem 2013 MS4 Permit Summary of the results based on the permit

changes that affect structural BMP design

• Identify and describe the required data (2007 MS4 vs. 2013 MS4)

• Describe the data entry procedures• Demonstrate how to operate the BMP Sizing

Spreadsheet by entering data for example problem

Goals of Example Problem

Redevelopment Project• We will examine one Basin draining to a storm drain

system. The POC will be at the point where the runoff leaves the project.

• Design goal is Treatment + Flow Control.• No channel assessment performed – use low flow threshold

of 0.1Q2 (High Susceptibility).• Rainfall Basin, Soil Type, Pre-Project Cover (2007 MS4

Permit), Pre-Project Slope, and DMA Surface Types are shown on the Example Problem-Redevelopment Project.

• Pre-Development Cover used for the 2013 MS4 Permit.

• Goals:

• Design a Flow Through Planter

Example Problem Information/Assumption

Example Problem Information/Assumption(Sheet 1 of 2)

Example Problem Information/Assumption(Sheet 2 of 2)

Available Tabs within the BMP Sizing Spreadsheet

• “Project Info”

• “BMP #1”

• “Orifice #1”

• “Rain Gauge”

• “Sizing Factors”

Example Problem Information/Assumption(BMP Sizing Spreadsheet)

• In the BMP Sizing Szpreadsheet, select the “Project Info” tab• Enter information in highlighted section• Note: “Rain Gauge” has dropdown menu to select either

“Lindbergh”, “Oceanside”, or “Lake Wohlford”. “Channel Susceptibility” has a dropdown menu to select either “High”, Medium” or “Low”.

Example Problem 2007 MS4 Permit

Project Info Tab9

• The Project info tab is completed.

• Next step is to select the “BMP #1” tab in the Spreadsheet

Project Info Tab10

• The “BMP #1” Tab in the Spreadsheet has been selected• Note: The highlighted fields have been automatically

populated from the previously entered information in the “Project Info” tab

BMP #1 Tab

“Start Sizing BMP Footprint”

• Populate “BMP Name”, “BMP Native Soil Type”, and “BMP Type” fields• The selected soil type presents the soil type that the BMP will be located on. • The soil type will be used to determine the “BMP Infiltration Rate” of the BMP.• Note: Field “BMP Infiltration Rate” field has been automatically populated as the

user enters “BMP Native Soil Type” field. The example problem is to design Flow-Through Planter”; therefore, impervious liner has been selected that results in “N/A” BMP Infiltration Rate”.

BMP #1 Tab

“Sizing BMP Footprint”

• “HMP Sizing Factors” and “Minimum BMP Size”fields will be automatically populated/calculated as the user enters information in the highlighted/blue fields for each DMA

• The goal is to obtain the BMP Sizes for “Surface Area”, “Surface Volume”, and “Subsurface Volume”

BMP #1 Tab

• Populate the selected blue fields for each DMA

BMP #1 Tab

• The first DMA has been entered. Continue the same exercise and enter information for the second DMA.

BMP #1 Tab

• The second DMA has been entered. Continue the same exerciseand enter information for the third DMA.

BMP #1 Tab

• The third DMA has been entered. Continue the same exercise and enter information for the fourth DMA.

BMP #1 Tab

• The fourth DMA 4 has been entered. Continue the same exercise and enter information for the fifth DMA.

BMP #1 Tab

• Now all five DMAs has been entered. The final results for theBMP Size are summarized within the box to the right.

-The minimum surface area is 810.216 s.f.-The minimum surface volume is 675 c.f.-The minimum subsurface volume is 468 c.f.

BMP #1 Tab

• Enter the proposed BMP Size equal or close to the to the minimumBMP Size for startNote: To model for 2007 MS4 Permit, all DMAs with imperviousarea in the pre project condition shall be left empty in runoff factor field

BMP #1 Tab

• Enter the Soil Matrix DepthNote: This is only needed for bioretention or flow-through planterdesigns; 18 inches is the minimum depth)

BMP #1 Tab

• Enter the Selected Ponding DepthNote: Assumed 10 inches for start

BMP #1 Tab

“Sizing BMP Footprint Complete”

• The “Orifice #1” Tab in the Spreadsheet has been selected• “Q2 Sizing Factor”, “Orifice Flow - %Q2”, and “Orifice Area”

will be automatically generated as the user enters data in thehighlighted fields

• Note: “DMA Name”, “Rain Gauge” and “DMA Area” columns havebeen automatically populated from the previously enteredinformation in the “BMP #1” Tab.

Example Problem – 2007 MS4 Permit

Orifice #1 Tab

“Start Sizing Orifice”

• “Soil Type”, “Cover”, and “Slope” information for the first DMA has been entered. Continue the same exercise and enter the Example Problem information for the second DMA

Orifice #1 Tab24

“Sizing Orifice”

• “Soil Type”, “Cover”, and “Slope” information for the second DMA has been entered. Continue the same exercise and enter the Example Problem information for the third DMA

Orifice #1 Tab25

• “Soil Type”, “Cover”, and “Slope” information for the third DMA has been entered. Continue the same exercise and enterthe Example Problem information for the fourth DMA

Orifice #1 Tab26

• “Soil Type”, “Cover”, and “Slope” information for the fourthDMA has been entered. Continue the same exercise and enter the Example Problem information for the fifth DMA

Orifice #1 Tab27

• “Soil Type”, “Cover”, and “Slope” information for the ExistingCondition (Pre-Project Condition) for all DMAs has been entered

• Calculated “Max Orifice Diameter” is 0.54 inches. The size of0.54 inches shall be entered.

• Based on the entered 0.54 inches in the Orifice #1 tab, the“BMP Sizing Spreadsheet” will calculate the Drawdown Time.

• Ignore the drawdown time on this tab

Orifice #1 Tab28

“Sizing OrificeCompleted”

• The size of 0.54 inches is entered in the Orifice #1 tab.• The calculated Drawdown Time is 20.1 hours.

Note 1: Check BMP #1 tab if the entered “Selected Ponding Depth” isbetween the required Minimum and Maximum depths.Note 2: If the minimum ponding depth is more than the maximumponding depth, adjust the BMP size, soil matrix depth and/or the selected pondingdepth.

Orifice #1 Tab

“Computing Drawdown TIme”

• The initially assumed “Selected Ponding Depth” of 10 inchesis between the required minimum and maximum ponding depth;therefore sizing of the BMP footprint , Orifice Size, and Drawdown Time is completed.

BMP #1 Tab

“BMP footprint size and

ponding depth check”

• In the BMP sizing spreadsheet, select the “Project Info” tab• Enter information in highlighted section• Note: “Rain Gauge” has dropdown menu to select either

“Lindbergh”, “Oceanside”, or “Lake Wohlford”. “Channel Susceptibility” has a dropdown menu to select either “High”, Medium” or “Low”.

Project Info Tab31

• The Project info tab is completed.

• Next step is to select the “BMP #1” tab in the Spreadsheet

Project Info Tab32

• The “BMP #1” Tab in the Spreadsheet has been selected• Note: The highlighted fields have been automatically

populated from the previously entered information in the “Project Info” tab

BMP #1 Tab

“Start Sizing BMP footprint”

• Populate “BMP Name”, “BMP Native Soil Type”, and “BMP Type”fields. The selected soil type presents the soil type that theBMP will be located on. Since the example problem is forFlow-Through Planter we selected Impervious Liner instead of soil type.

BMP #1 Tab

“Sizing BMP footprint”

• “HMP Sizing Factors” and “Minimum BMP Size”fields will be automatically populated/calculated as the user entersinformation in the highlighted/blue fields in each DMA

• The goal is to obtain the BMP Sizes for “Surface Area”, “Surface Volume”, and “Subsurface Volume”

BMP #1 Tab

“Sizing BPM footprint”

• Populate the selected blue fields for each DMA

BMP #1 Tab

• The first DMA has been entered. Continue the same exercise and enter information for the second DMA

BMP #1 Tab

• The second DMA has been entered. Continue the same exercise and enter information for the third DMA

BMP #1 Tab

• The third DMA has been entered. Continue the same exercise and enter information for the fourth DMA

BMP #1 Tab

• The fourth DMA has been entered. Continue the sameexercise and enter information for the fifth DMA

BMP #1 Tab

• Now all of the DMAs has been entered. The final results for theBMP Size are summarized within the box to the right.

-The minimum surface area is 2291.256 s.f.-The minimum surface volume is 1910 c.f.-The minimum subsurface volume is 1375 c.f.

BMP #1 Tab

• Enter the proposed BMP Size equal to the minimum BMP sizefor start.

• Enter the soil matrix depth and the ponding depth fields

BMP #1 Tab

• The “Orifice #1” Tab in the Spreadsheet has been selected• “Soil Type”, “Cover”, and “Slope” information for the Existing

Condition (Pre-Project Condition) for the first DMA has beenentered

• “Q2 Sizing Factor”, “Orifice Flow - %Q2”, and “Orifice Area” will be automatically generated as the user enters data in the highlighted fieldsNote: “DMA Name”, “Rain Gauge” and “DMA Area” columns have beenautomatically populated from the previously entered information in the “BMP #1” Tab

Orifice #1 Tab

“Start Sizing Orifice”

• “Soil Type”, “Cover”, and “Slope” information for all DMAs hasbeen entered.

• Calculated “Max Orifice Diameter” by the “BMP SizingSpreadsheet” is 0.21 inches. Based on the entered 0.21 inches, which is equal to the maximum orifice diameter, the “BMPSizing Spreadsheet” calculates the Drawdown Time.

• Since the drawdown time exceeds 96 hours, return to BMP tab and adjust the initial BMP size, and/or the soil matrix depth and/or the selected ponding depth.

Orifice #1 Tab

“Sizing OrificeCompleted”

• Proposed BMP Size and Soil Matrix Depth are iteratively increased untilthe Minimum Ponding Depth is less than the Maximum Ponding Depth.

◦ This indicates that a drawdown time less than 96 hours can be provided.◦ The selected ponding depth has been adjusted to 1.54 inches

Example Problem– 2013 MS4 Permit

BMP #1 Tab

“Increase the BMP Footprint and/orSoil Matrix Depth to Reduce DDT”

• After adjusting the BMP size, the soil matrix depth, and selected ponding depth, the drawdown time is now less than96 hours; therefore, sizing of the BMP is complete.

Orifice #1 Tab

“Check if BMP AdjustmentsResult in acceptable DDT”

Summary of the Results based on the permit changes that affect structural BMP design

The changes from the 2007 MS4 and 2013 MS4 have been implemented in the example problem to size the BMP Surface Area, Surface Volume, Subsurface Volume, and Orifice Size, and to calculate the Drawdown Time using BMP Sizing Spreadsheet

2007 MS4 compares proposed project site surface cover with the Pre-Project surface cover

2013 MS4 compares proposed project site surface cover with the Pre-Development project surface cover

Change in the results: 2013 MS4 requires bigger BMP Surface Area, Surface Volume, Subsurface Volume, Soil Matrix Depth, and smaller Orifice Size. Drawdown Time becomes a significant challenge for BMPs with small drainage areas!

Future of Sizing Factor Method2013 MS4 Permit Compliance

Laura HenryRick Engineering CompanyWater Resources Division

November 18, 2014

Purpose How to apply sizing factors developed based on 2007

standards to meet 2013 standards

Presentation Overview Background and new terminology

2013 MS4 Permit changes that affect structural BMP design

Using sizing factors under the 2013 MS4 Permit

Background Standard for design of flow control BMPs for

hydromodification management requires continuous simulation modeling◦ Project-specific modeling (HSPF, SDHM, SWMM);

◦ Sizing factor method (developed based on unit-area modeling)

Background Sizing factor method is static◦ Unit-area modeling prepared one time

◦ Not being revised for 2013 MS4 Permit

◦ BMP Design Manual will incorporate applicable sizing factors, leave out non-applicable sizing factors

New Terminology “BMP Design Manual” (formerly SUSMP)

“Pollutant control BMP” (formerly treatment control BMP)

“Retain” (infiltrate, evaporate, evapotranspire, harvest and use)

New Terminology “Structural BMP” encompasses:◦ Single purpose BMP (pollutant control OR

hydromodification management flow control)

◦ Dual purpose BMP (integrated BMP that combines pollutant control AND flow control)

New Terminology Bioretention (full retention/infiltration)

Bioinfiltration (partial retention/infiltration)

Biofiltration (no retention/infiltration)

Bioretention:No Underdrain

Bioinfiltration:Raised Underdrain

Biofiltration:Underdrain at Bottom

New Terminology “Flow-Thru BMP”◦ Treatment control BMP that does not incorporate significant

biological methods

Vegetated swales, media filters, sand filters, dry extended detention basins

Hydromodification management performance standards

Pollutant control performance standards

Permit Changes forStructural BMP Design

Changes to applicability/exemptions

New requirement to protect critical coarse sediment yield areas

Requirement to control to “pre-development”condition instead of “pre-project” condition

Changes to Hydromodification Management Requirements

“Pre-development” condition means runoff conditions from the project footprint based on:◦ Infiltration characteristics of the underlying soil

◦ Existing grade

◦ No impervious area

Changes to Hydromodification Management Requirements

What “pre-development” condition requirement means for sizing factor method:◦ Unit runoff ratios for “urban” and “impervious” cover types

may not be used to determine pre-development Q2 for low flow orifice sizing under 2013 MS4 Permit

◦ Assume a natural pervious cover (“scrub”) for the pre-development condition

Changes for Sizing Factor Method

2013 Permit Pollutant Control Hierarchy:◦ Retain onsite 85th percentile runoff (infiltrate, evaporate,

evapotranspire, harvest and use) Volume-based sizing – “Design Capture Volume” (DCV)

◦ Biofiltration if infeasible to retain runoff onsite

◦ Flow-thru treatment BMPs AND mitigate (off-site) for the DCV that was not retained onsite, if infeasible to retain or use biofiltration

Changes to Pollutant Control Requirements

How/why do changes to pollutant control requirements relate to the sizing factors?◦ The change to DCV-based sizing and emphasis on retention

makes it impractical to apply some of the sizing factors that included a flow-based treatment component

◦ Names of sizing factor BMPs are not consistent with updated pollutant control terminology

Sizing factor compatibility issues◦ “Bioretention” area sizing factor from “Cistern Plus

Bioretention” BMP

◦ “Bioretention” area sizing factor from “Bioretention Plus Vault” BMP

Mapping of BMP names for integrated pollutant control and flow control BMPs

BMP Sizing SpreadsheetBMP Name

2013 Compatible BMPs

“Infiltration” Full retention category• “Infiltration basins”• “Permeable pavement (without underdrain)”• “Bioretention without underdrain”

“Bioretention” A or B soils:Full retention category• “Bioretention without underdrain”

C or D soils:with dead storage layer:

Partial retention category• “Bioinfiltration”

C or D soils:without dead storage layer:

No retention category• “Biofiltration”

“Flow-Through Planter”

No retention category• “Biofiltration”

◦ *“Cistern” is still useful for hydromodification management flow control volume sizing, but the treatment element of the BMP downstream of the cistern should be designed based on 2013 standards instead of sizing factors

“Bioretention plus Vault”

Not applicable

“Cistern plus Bioretention”

Not applicable*

Evaluate feasibility to retain runoff for pollutant control, determine pollutant control category◦ Full, Partial, or No retention

Select a structural BMP Size the structural BMP for hydromodification

management For integrated BMPs, verify pollutant control

performance (check drawdown time for DCV)

How to

Full retention◦ Sizing factors for “infiltration”

◦ Sizing factors for “bioretention” in A or B soils

Sizing Factors Applicable to Types of Pollutant Control Facilities

Partial retention◦ Sizing factors for “bioretention” in C or D soils*

*retention storage must be provided below the underdrain, sizing factors will not provide credit for the retention storage

No retention◦ Sizing factors for “bioretention” in C or D soils, when there

is no retention storage provided below the underdrain

◦ Sizing factors for “flow-through planter”

◦ Sizing factors for “cistern”

Full Retention BMP

PartialRetention

BMPNo Retention

2013 BMP Infiltration Basin

PermeablePavement Bioretention Bioinfiltration Biofiltration

Sizing Factor

“Infiltration”(A or B soils) X X

“Bioretention”(A or B soils) X

“Bioretention”(C or D soils)

X(with dead storage layer

below underdrain)

X(without dead storage

layer below underdrain)

“Flow-Through Planter”(C or D soils)

“Cistern” X

Why is drawdown different for pollutant control sizing vs. hydromodification management?

Drawdown Time

Sizing factor method is intended for simple projects◦ No diversion◦ No off-site area

Use project-specific continuous simulation model for more complex projects◦ Guidance and parameters will be provided in the BMP

Design Manual

Limitations on use of sizing factors

ANNOUNCE A SEMINAR DEMONSTRATING The BMP … APWA... · ANNOUNCE A SEMINAR DEMONSTRATING The BMP...

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