2018 model bmp design manual update

SEMINAR AGENDA

Time Agenda Item

8:15-9:00 Check-In and Seating

9:00-9:15 Introduction and Opening Remarks

9:15-9:30 Applicability of Storm Water Requirements

9:30-9:45 Source Control & Site Design Updates

9:45-10:15 Pollutant Control Updates

Biofiltration Sizing Method and Performance Standards Bioretention Soil Media Specification

10:15-10:30 Break

10:30-11:15

Hydromodification Management Updates

Updated Guidance Sizing Factors Regression Equations Critical Coarse Sediment Requirements

11:15-11:30 Infiltration Feasibility Overview

11:30-11:45 Maintenance and Sediment Clogging

11:45-Noon Closing Statements & Final Questions

2018 Model BMP Design Manual Update January 16th, 2018 9:00 a.m. to 12:00 p.m.

5520 Overland Avenue, Conference Center Hearing Room

1/16/2018

2018 Model BMP Manual Public Seminar 1

SAN DIEGO REGIONAL 2018 MODEL BMP DESIGN MANUAL UPDATESPUBLIC SEMINAR

January 16, 2017

1

Welcome

2

Sign-In

Handouts

Refreshments

Break

Q&A and Input

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Introduction and Opening Remarks

Eric Mosolgo - City of San Diego

3

Introduction

4

Model BMP Design Manual is being updated to incorporate: Additional guidance developed by jurisdictions for their

local manuals that are not part of the 2016 edition of the Model BMP Design Manual

Guidance developed to provide additional tools for project applicants and reviewers

Updates in response to questions submitted to the help desk 2 years of local implementation and learning

Draft is posted at the following location: http://www.projectcleanwater.org/download/draft-2018-

model-bmp-design-manual-update-january-2018/

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Model BMP Design Manual Update

5

Model BMP Design Manual is being updated under the direction of the BMP Ad Hoc Workgroup. Members include staff from the following jurisdictions:

City of San Diego

County of San Diego

City of Chula Vista

City of Escondido

BMP Ad Hoc Workgroup met 6 times for development of this update.

BMP Design Manual Timeline

6

Regional MS4 Permit:

May 2013

Model BMP Manual

June 2015

Local Jurisdictional Manuals and

Updated Model BMP Manual

February 2016

Updated Model BMP Manual

April 11, 2018*

Local Jurisdictional

Manuals Updated As Applicable

*Subject to change

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7

Date

Updated Manual Posted for Public Review

January 8, 2018

Public Seminar January 16, 2018

Written Comments Due1 February 8, 2018

Updated Manual Posted2 April 11, 2018

Timeline for Finalizing 2018 Draft Model BMP Design Manual

1Submit via email: [email protected] to change. The updates in the Model BMP DesignManual are not effective until they are incorporated into thelocal jurisdictional BMP Manual.

Presentation Outline

8

Provide an overview of the following updates included in

the January 2018 Model BMP Design Manual:

Applicability of Storm Water Requirements;

Source Control and Site Design Updates;

Pollutant Control Updates;

Hydromodification Management Updates;

Infiltration Feasibility; and

Maintenance Requirements and Sediment Clogging.

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Applicability of Storm Water Requirements

Sheri McPherson - County of San Diego

9

Permanent Storm Water RequirementsModifications to Table 1-2

10

Table 1-2. Applicability of Permanent, Post-Construction Storm Water Requirements lists the types of projects for which storm water requirements and the BMP Design Manual does not apply. Modifications were made based on feedback from the RWQCB as follows:

Removed two items as they are no longer considered routine maintenance: Rebuilding a structure to original design after damage from

earthquake, fire, or similar disasters Routine replacement of damaged pavement, including full depth

replacement, if the sole purpose is to repair the damaged pavement

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Permanent Storm Water Requirements

11

Added three new clarifications: Replacement of impervious surfaces that are part of a

routine maintenance activity, such as:Maintenance activities that are part of a larger master planning

effort (for example, a programmatic effort to bring the City incompliance with ADA requirements).

Installation of ground mounted solar arrays over existingimpermeable surface.

Repair or improvements to an existing building or structurethat do not alter the size: Exterior alterations that do not increase existing impervious

surface footprint and do not expose underlying soil duringconstruction (e.g. roof replacement).

Updates to Hydromodification Management Exemptions

12

Addition of Otay River as HMP exempt water body, as approved by the RWQCB (May 2017)

Potential additional HMP exemptions for the following reaches which have been submitted to the RWQCB for review and are pending approval:

Escondido Creek

Santa Margarita River

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Site Design & Source Control

Nancy Richardson – County of San Diego

13

Source Control Updates

14

Addition of New Fact Sheets

Designation Name Key Components/Requirements

SC-6

A

Large Trash Generating Facilities

Restaurants, Supermarkets, Big-Box Stores, etc.

Provide covers and enclosures to limit potential for dispersion of trash and limit pollution pathways.

SC-6

B

Animal Facilities

Animal shelters, Animal daycare centers, Breeding, boarding, and training centers etc.

Define and identify pollutant sources and limit pollution pathways.

Control dry weather runoff- cover trash enclosures, drain to sanitary sewer/other BMP.

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Source Control Updates

15

Addition of New Fact SheetsDesignation Name Key Components/Requirements

SC-6

C

Plant Nurseries and Gardens

Nurseries, Garden Centers, etc.

Control discharges from watering areas (drain to sanitary sewer/other BMPs).

SC-6

-D

Automotive Facilities

Maintenance/repair centers, Car washes, Retail gasoline outlets

Hydraulic controls to isolate/contain potential pollutants (oils and grease).

Fueling, vehicle washing, maintenance areas with permanent covers.

Activity areas paving requirements

Revised Site Design BMP Naming

16

2016 Model Manual Convention similar to CASQA Stormwater BMP Handbook (SD-##)

2018 Model Manual Updated (SD-A)

CASQA Factsheets are additional reference

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Site Design Updates

17

Updated Fact SheetDesignation Name Key Components/Requirements

SD-A Street Trees/Tree Wells

Pathway for Local Jurisdictions to develop additional sizing guidance allowing DCV reduction beyond 25%.

Example: County of San Diego “Significant Site Design BMPs”

Site Design Updates

18

New Fact SheetDesignation Name Key Components/Requirements

SD-F Amended Soils

Landscaping areas

Impervious area dispersion

• Establish requirements when used to reduce DCV through Runoff Factor Adjustments or Impervious Area Dispersion

• Improve hydrologic characteristics

• Improve vegetation health

• Reduce erosion

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Reminder: Credits for Site Design

19

Implementation of Site Design will reduce the pollutant control BMP obligations for the project applicant.

The 2018 Model BMP Design Manual provides credits for the following site design BMPs:

SD-A: Street Trees/Tree Wells

SD-B: Impervious Area Dispersion

SD-C: Green Roof

SD-D: Permeable Pavement

SD-E: Rain Barrels

Pollutant Control Updates: Biofiltration

Venkat Gummadi – Geosyntec Consultants

20

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Pollutant Control

21

Pollutant Control Updates

Infiltration feasibility (separate agenda item)

Biofiltration sizing methods & performance standards

Bioretention soil media specification

Retention Partial

Retention

Biofiltration

Pollutant Control: Basics Review

22

Pollutant Control BMP Hierarchy

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2016 Biofiltration Sizing

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Requires a Minimum Footprint (3%) for biofiltration BMPs.

If footprint is < 3%, 40% volume reduction is required. This applies to reduced footprint and proprietary biofiltration BMPs.

2018 Biofiltration Sizing

24

2018 Model BMP Design Manual- Two Options City of San Diego Storm Water Standards County of San Diego Supplemental Retention Guidance

Both Options Provide: Biofiltration retention standard – volume reduction

requirements vary based on underlying soil type Additional sizing methods (reduced footprint with upstream

storage, etc.)

No hierarchy if both pollutant control and volume reduction requirements are met.

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2018 Biofiltration Retention Standard

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City Retention Standard: Required retention varies with infiltration rate and is based on a fixed rainfall depth.

2018 Biofiltration Retention Standard

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County Retention Standard: Required retention varies with infiltration rate and 85th Percentile Rainfall Depth. Identical to City for P85 less than 0.61 inches.

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New Volume Reduction Nomographs

27

City Storm Water Standards

Fraction of DCV

Impervious Area Disp.

Evapotranspiration

Biofiltration Sizing: Example

28

Site Scenario Reliable Infiltration Rate: 0.05 in/hr

Due to site grades & layout non-standard or Proprietary biofiltration preferred

DMA Characteristics 1-Acre Impervious

P85: 0.6 inches

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Step 1: Calculate DCV Runoff Coefficient x Area x rainfall depth

0.9 x 1 acre x 43560 ft2/1 acre x 0.6 in x 1 ft./12 in = 1,960 ft3

Step 2: Determine Retention Targets Average annual capture based on infiltration rate

Convert to fraction of DCV


30

City Standard: 15% (from 166.9 x 0.05 in/hr +6.62)

County Standard: 15% (from Automated Worksheet)

See Inset

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Average Annual Retention to Fraction of DCV

15% ≈ 0.11DCV

Required Volume Reduction = 0.11DCV= 0.11*1960 = 216 ft3

Reminder: Credits for Site Design

32

Implementation of Site Design will reduce the pollutant control BMP obligations for the project applicant.

The 2018 Model BMP Design Manual provides credits for the following site design BMPs:

SD-A: Street Trees/Tree Wells

SD-B: Impervious Area Dispersion

SD-C: Green Roof

SD-D: Permeable Pavement

SD-E: Rain Barrels

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Required Volume Reduction = 216 ft3

Impervious Area Dispersion Calculate using adjustment factors from Appendix B.2.1.1 (limited to

4 impervious:1pervious), or Use Dispersion Nomographs from City Storm Water Standards (up to

50 impervious:1pervious) Amended Soil Area: 900 sf. 12”

depth ~2.1% footprint

Dispersion Ratio = 43560/900 = 48

Pore Storage: 225 cf

Fraction DCV: 0.12

Disp. Credit: 0.104

DCV Retained: 222 ft3

Bioretention Soil Media

Max Dugan – Geosyntec Consultants

34

1/16/2018


Bioretention Soil Media (BSM)

35

Roles of BSM

Provides structure, nutrients, and water for vegetation

Filters & Removes pollutants from runoff

Composition is a balancing act between competing roles.

Specifications include ranges for acceptable material properties

Existing BSM Specification

36

Comments on 2016 Specification

Different between City and County

Difficult to review/comply

Nutrient export observed

Clogging

Poor plant health

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Regional BSM Survey

37

Contacted regional suppliers & conducted phone survey

Collected material samples: Sand (5 samples) Topsoil (4 samples) Compost (6 samples) Mixed BSM (8 samples)

Analyzed samples for: Physical and texture parameters Permeability Agronomic properties Water quality: plant available and

water soluble nutrients

SandTopsoil

Com

post

Updated BSM Specification

38

Updated Specification Highlights: Single unified spec

(App. F.3) “Whitebook” format Updated content

ranges High quality material Locally available Limit nutrient exportMaintain plant health

Component White Book Specification

BSM Material Composition

Sand: 60-80%Topsoil: up to 20% Compost: up to 20%

Sand Type Washed Sand

Topsoil Type

Free of hazardous material; decomposed granite and derivatives are not considered to be topsoil

Compost Type

CalRecycle Registered FacilityPreferably Certified by US Composting Council (or equivalent program) Not produced from biosolids feedstock

Alternative Blends Allowed?

Yes, but must comply with testing requirements.

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Break

39

Hydromodification Management Updates: General

Laura Henry - Rick Engineering Company

40

1/16/2018


DMAs Excluded from Flow Control

41

For projects subject to hydromodification management: Protection of critical coarse sediment yield areas

applies to all of the project area (all DMAs) Certain DMAs may be excluded from flow control

Clarification added to Section 6.1 for Self-Mitigating DMAs (defined in Section 5.2.1) De Minimis DMAs (defined in Section 5.2.2) Self-Retaining DMAs (defined in Section 5.2.3)

Self-Mitigating DMAs

42

Self-mitigating DMAs consist of natural or landscaped areas that drain directly offsite or to the public storm drain system

Typically exterior slopes or interior landscape areas that do not drain through a structural BMP

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Self-Mitigating DMAs

43

Must be evaluated on a case by case basis

Self-mitigating DMAs may only be excluded from flow control analyses if the following conditions are met:

The self-mitigating area does not contribute runoff to a flow control POC.

The self-mitigating DMA does not concentrate runoff in a new location where runoff is not concentrated in the pre-development condition.

The self-mitigating DMA does not increase the total area draining to the same discharge point compared to the pre-development condition.

De Minimis DMA

44

De Minimis DMAs: Excluded from flow control requirements

Subtract the de minimis area from both the pre-development and post-project footprint

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Self-Retaining DMAs

45

Self-Retaining DMAs via Qualifying Site Design BMPs: Not Excluded from flow control requirements

DCV reduction is applicable to pollutant control only

Area of Self-retaining DMAs must be included in the flow control analysis

Self-retaining area geometry may be modeled in project-specific continuous simulation modeling

Drainage Layout Guidelines

46

Updated to Section 6.3.1 by adding drainage layout guidelines for effective hydromodification management

Use the existing drainage concentration points for storm water discharge

Avoid creating new concentrated discharge points in locations where drainage is not naturally concentrated

Avoid diversion of flow from one POC to another

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47

Diversion means changing the discharge location of storm water runoff from a given land area from one concentration point to another

For hydromodification management, diversion is measured with respect to each natural drainage system that is subject to erosion (i.e., at each POC), rather than at the property boundary

Diversion is very difficult to mitigate and should be avoided


48

When the proposed project design will create a diversion area:

The project must provide mitigation to match the pre-development runoff from the existing (pre-development) area

Project-specific continuous simulation modeling is required (no Sizing Factors)

For example, if the proposed project will discharge runoff from 5 acres to alocation that had a pre-development drainage area of 4 acres, the proposed projectmust provide mitigation to match the pre-development runoff flow rates anddurations from the pre-development drainage area of 4 acres.

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Hydromodification Sizing Factors

Eric Mosolgo - City of San Diego

49


50

Sizing factors updated to account for changes in: Flow control performance

standard in MS4 Permit BMP geometry Standard overflow structures EPA SWMM Modeling

Compared to 2011 HMP updated sizing factors are smaller

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51

Available Sizing Factors:

Infiltration BMPs

Biofiltration w/Partial Retention

Biofiltration

Cisterns


Partial Retention D, Flat, Lind: 0.16 D, Flat, Ocean: 0.13 D, Flat, Wohl: 0.10

Biofiltration (Lined) D, Flat, Lind: 0.2 D, Flat, Ocean: 0.16 D, Flat, Wohl: 0.11

Partial Retention D, Flat, Lind: 0.05 D, Flat, Ocean: 0.07 D, Flat, Wohl: 0.06

Biofiltration (Lined) D, Flat, Lind: 0.05 D, Flat, Ocean: 0.07 D, Flat, Wohl: 0.06

52

2011 HMP Sizing Factor 2018 HMP Sizing Factor

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53

Limitations on use: Simple studies, i.e.

0.1Q2 Threshold No Diversion No Upstream Offsite Areas Standard BMP Geometries

BMPs with infiltration require minimum design infiltration rate of 0.5”/hour

Sizing Factor footprint represents: Plan view area at surface with no

ponding

Sizing Factor (SF)

Regression Equations

54

Hydromodification Management Flow Control Approved regression equations (USGS 2012) added to Section

6.3 May be used to calculate Q2 and Q10 for Continuous Simulation

Sizing

3.60 . .

6.56 . .

where:

= 2-year recurrence interval discharge in cubic feet per second

=10-year recurrence interval discharge in cubic feet per second

A = Drainage area in square miles

P = Mean annual precipitation in inches

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Hydromodification Updates: Sediment

Max Dugan - Geosyntec Consultants

55

56

A Critical Coarse Sediment Yield Area (CCSYA) is an area that has been identified as an active or potential source of coarse sediment to downstream channel reaches.

Maintaining historic sediment supply is an important component of maintaining channel form.

Critical Coarse Sediment Requirements

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Basic identification, refinement, & mitigation options

Expanded guidance & additional options

4-step compliance process

Numerical performance standard

Mitigation fact sheets

57

2016 Manual 2018 Manual*

Critical Coarse Sediment Requirements

* Guidance was developed through a TAC process

Critical Coarse Sediment Yield Area (CCSYA)

58

Identify

Avoid

Bypass

No Net Impact

Are there CCSYAsUpstream?

Are upstream CCSYAs passed through to the downstream channel?

Yes

Demonstrate No Net Impact

No

No

Are there CCSYAsOnsite?

Yes

Yes

Are onsite CCSYAs passed through to the

downstream channel?

Are onsite impacts avoided?

In Compliance

Yes(both)

No (both)

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Step 1- Identify

59

Identify onsite and upstream CCSYAs Start with Regional WMAA Maps Check for additional local identification methods

(example County Resource Protection Ordinance)

Refine regional maps through site specific process: Depositional analysis Threshold channel analysis Course sediment source area verification Verification of GLUs

Identify

Step 2- Avoid

60

Avoid mapped onsite areas

Minimize footprint

Locate/focus improvements in non CCSYA portions of site

Up to a 5% encroachment may be allowed

If onsite CCSYAs cannot be avoided, PDP must demonstrate No Net Impact

Avoid

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Step 3- Bypass

61

Bypass sediment from Onsite and Upstream CCSYA through/around the site: Maintain minimum velocities,

Route flows containing bed sediment around BMPs, or

Design outlet structures to bypass bed sediments.

Bypass

Step 4- Demonstrate No Net Impact

62

Ep: Erosion Potential Transport Capacity

(Post/Pre)

Sp: Sediment Supply Bed Sediment Supply

(Post/Pre)

.

No Net Impact

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Examples: Scenario 1

63

Identify

Avoid

Bypass

Both onsite and upstream CCSYAs are identified (WMAA Maps)

Project encroaches on 5% of onsite CCSYAs as permitted WMAA mapping.

Project allows CCSYAs to pass through the site unobstructed.

Examples: Scenario 2

64

Identify

Avoid

Bypass

No Net Impact

Both onsite and upstream CCSYAs are identified (WMAA Mapping)

Project encroaches on more than 5% of onsite CCSYAs.

Project allows upstream CCSYA to pass through, but obstructs onsite CCSYA (SpReduction)

Project provides additional flow control to mitigate for reductions in soil loss (Ep Reduction)

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Infiltration Feasibility

Venkat Gummadi - Geosyntec Consultants

65


66

Appendix C and D were simplified by both the County and City of San Diego for their local jurisdictional manuals.

The 2018 Model BMP Manual incorporates both versions as options.

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67

Both versions provide a simple pathway for No Infiltration Condition:

County of San Diego: Basic Infiltration Analysis

City of San Diego: Infiltration Feasibility Condition Letter


68

For the detailed methods:

County of San Diego

Replaced the categorization of infiltration condition worksheet with Advanced Infiltration Analysis

City of San Diego

Revised the categorization of infiltration condition worksheet based on series of meetings with BIA and RWQCB staff

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69

Both the County and City guidance provide standard setbacks for establishing infiltration feasibility

Maintenance Components of Fact Sheets

Laura Henry – Rick Engineering Company

70

1/16/2018


Maintenance Fact Sheets

71

New BMP Maintenance Fact Sheets, created Jan. 2017

Fact sheets contain: Normal expected maintenance

Non-standard maintenance or BMP Failure

Other special considerations

Summary table of maintenance thresholds, maintenance actions, and typical maintenance frequency

Inspection and maintenance checklists

BMP Maintenance Fact Sheet

72

1/16/2018


Compiled into Appendix E Fact Sheets

73

Sediment Loading Analysis

Laura Henry – Rick Engineering Company

74

1/16/2018


Sediment Loading for Maintenance Frequency (Appendix E-27)

75

New Fact Sheet added in Appendix E; SL Sediment Loading (Appendix E-27)

Estimates BMP maintenance frequency based on sediment accumulation

Estimates BMP rehabilitative (major) maintenance and/or replacement frequency

Applicable to:

Structural BMPs

Site design BMPs designed outside the ranges recommended in the fact sheet (i.e., higher loading rate)

Sediment Loading

76

Detailed Clogging Methodology Steps:

Estimate the sediment load discharging to the BMP

Determine available sediment storage in the BMP

Estimate frequency of maintenance

Does not supersede minimum inspection frequency or annual reporting requirements for routine maintenance

Actual maintenance needs are site-specific and must be determined and adjusted as needed based on the results of inspection

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Sediment Loading Worksheets

77

Closing Statements & Final Questions

78

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Closing Statements & Final Questions

79

Review Draft 2018 Model Manual

Manual Download Link: http://www.projectcleanwater.org/download/draft-2018-model-bmp-design-manual-update-january-2018/

Submit written comments

Comments due by February 8, 2018

Submit via email: [email protected]

Address jurisdiction specific comments w/applicable jurisdiction

Contacts

80

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SAN DIEGO REGIONAL 2018 MODEL BMP DESIGN MANUAL UPDATES

81

THANK YOU

January 16, 2017

2018 model bmp design manual update

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