introductory module technical guidance document

Introductory ModuleTechnical Guidance Document

New Development and Significant Redevelopment Program Roll-out Training

July 2011

Training Modules

Surface Water vs. Groundwater

(and Evapotranspiration!)3

Surface water regulators/Environmental Groups want to push stormwater into the ground as much as possibleGroundwater regulators and users are concerned about this

Surface Water Regulators/NRDC

Groundwater Regulators / Water Agencies

Runoff

Infil

tratio

n

Evapotranspiration

LID Gallery: Hydrologic Source Controls

HSC-1: Localized On-Lot Infiltration

HSC-2: Impervious Area Dispersion


HSC-3: Street Trees/Canopy Cover

HSC-4: Residential Rain Barrels


HSC-5: Green Roof/Brown Roof

HSC-6: Blue Roof

LID Gallery: Infiltration

INF-1: Infiltration Basin

INF-2: Infiltration Trench


INF-3: Bioretention without Underdrains

INF-3: Bioinfiltration (Bioretention with Elevated

Underdrains)


INF-5: Dry Well

INF-6: Permeable Pavement


INF-7: Underground Infiltration

LID Gallery: Harvest and Use

HU-1: Above Ground Cisterns

HU-2: Underground Cisterns

LID Gallery: Biotreatment

BIO-1: Bioretention with Underdrains (Planter box)


BIO-2: Vegetated Swale


BIO-3: Vegetated Filter Strip

BIO-4: Wet Detention Basin


BIO-6: Dry Extended Detention Basin

BIO-5: Constructed Wetland


BIO-7: Proprietary Biotreatment

Purpose of TGD

Provide technical guidance for developing Project WQMPs

Assist in practical, objective interpretation of permit-based requirements

Provide recommended processes for developing plans and demonstrating conformance

Provide technically-based feasibility criteria

Provide supporting information for BMP selection, analysis, and design

TGD Feasibility Criteria

Deeper infiltrationUnderdrains discharge to storm pipe

Retention Biotreatment

Under what conditions should I pass through this gate? How should I evaluate this?

TGD Preparation Challenges

The TGD needs to:

Provide rigorous technical defense for criteria

Attempt to accommodate all foreseeable project scenarios

Bridge separate requirements in NOC and SOC permit areas

But it needs to be usable!

TGD Approach

Focus intensive guidance on several common project scenarios

Locate supporting technical material in appendicesExamples: groundwater protection criteria, BMP sizing calculation methods

Try to distill feasibility criteria to simple tables and thresholds where possible (example: TUTIA)

Break out separate appendices for NOC and SOC permit areas

Role of Documents

Role of Documents: Example

Organization of TGD

Main body of TGD (109 pages)Relatively streamlined reference How to develop compliant plans How to complete the WQMP Template

Appendices (259 pages)Provides modular guidance on specific topicsIntended to be referenced only as needed for project-specific factors

Organization of TGD

Section 1. IntroductionDescribes role and organization of TGD

Section 2. Technical Guidance for Preparing Project WQMPs

Mirrors the structure of the WQMP and Template Subheadings are intended to provide guidance for how to prepare WQMPs. For example:

• 2.1. Discretionary Permits and Water Quality Conditions• 2.2 Project Description

2.2.2 Expected Stormwater Pollutants

Key highlights of TGD Section 2

Site and watershed characterization

BMP selection flowchart

Feasibility criteria and worksheet

Guidance on demonstrating conformance with BMP sizing and selection requirements for a variety of common scenarios

Guidance on incorporating USEPA Green Streets into WQMPs

Figure 2.1: LID BMP Selection

Flow ChartConsider HSCs first

(green roofs are here)If self-retaining, then

nothing further

Retain remaining DCV to the MEP with infiltration and/or harvest and use

Biotreat remaining DCV if feasible; enter alternative compliance

for remainder

Section 2.4.3: Conformance Analysis for Typical Scenarios

Scenarios:

1. The project is able to feasibly retain the DCV

2. The project cannot feasibly retain the full DCV, but can biotreat the remaining volume

3. The project cannot feasibly retain the full DCV and cannot feasibly biotreat the remaining volume

4. The project cannot feasibly retain the entire DCV because there are not any feasible retention BMPs

Organization of TGD

Section 3. Site Design Principles and Techniques

Narrative elements of LID related to site layout and planningMinimal overlap with Section 4

Section 4. LID and Treatment Control BMP Design

Inventory of LID and Treatment Control BMPsSelecting BMPs to address pollutants of concernBMP Performance Tables

Table 4.1. Categories of LID BMPs and Treatment Control BMPs

HSCs InfiltrationHarvest and

Use ET BiotreatmentTreatment

Control

Localized on-lot infiltration

Impervious area dispersion (e.g. roof top disconnection)

Street trees(canopy interception)

Residential rain barrels (not actively managed)

Green roofs/ brown roofs

Blue roofsImpervious area

reduction (permeable pavers, site design)

Infiltration basins

Infiltration trenches

Bioretention without underdrains

BioinfiltrationDrywellsPermeable

pavementUnderground

infiltration

Storage options:

Above-ground cisterns and basins

Underground detention

Potential demand:

IrrigationToilet flushingVehicle/

equipment washing

Evaporative cooling

Industrial processes

…

ET is a significant volume reduction process in:

All HSCsSurface-based

infiltration BMPsBiotreatment

BMPs

Bioretention with Underdrains

Vegetated Swale

Vegetated Filter Strip

Wet Detention Basin

Constructed Wetland

Dry Extended Detention Basin

Proprietary Biotreatment

Sand Filters (media bed filters)

Cartridge Media Filters

Pretreatment

Hydrodyn. Separators

Catch Basin Inserts

Biotreatment BMPs

Table 4.2 Relative Treatment Performance Ratings of Biotreatment BMPs

Unit Operations and Process Assumed Principal Unit Operations and Processes Provided S

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Bioretention system

• Particulate Settling • Size Exclusion • Inert Media Filtration • Sorption/Ion Exchange • Microbial Competition/Predation • Biological Uptake • Volume loss (via infiltration, ET)

H L L H M H M H

Bioretention system with internal water storage zone and nutrient sensitive media design

Bioretention UOPs, plus: • Microbially Mediated Transformations (if

designed with internal water storage zone) H M M H M H M H

Dry extended detention basin

• Particulate Settling • Size Exclusion • Floatable Capture • Vegetative Filtration (with low-flow channel) • Volume loss (via infiltration, ET)

M L M M L M L H

Dry extended detention basin with vegetated sand filter outlet structure

Dry extended detention basin UOPs, plus: • Inert Media Filtration H L M M M M L H

Vegetated Swale • Vegetative Filtration • Sorption/Ion Exchange • Volume loss (via infiltration, ET)

M L L M L M M M

Vegetated Filter Strip • Vegetative Filtration • Sorption/Ion Exchange • Volume loss (via infiltration, ET)

M L L M L M M L

Organization of TGD

Section 5. Hydromodification Control DesignHydromodification design conceptsDescription of hydromodification controlsDesign process for NOC and SOC

Section 6. Source Control MeasuresStructuralNon-structuralMunicipal

Organization of TGD

Section 7. Operations and Maintenance Planning

Developing maintenance agreementsDeveloping BMP maintenance activities

Contents and Roles of Appendices

Appendix I. Summary of BMP Sizing Requirements for North Orange County

Describes role of various BMPs Condensed guidance on selection and sizing for various project scenariosPlain-language “cheat sheet”

Appendix II. Summary of BMP Sizing Requirements for South Orange County

Same role and contents as Appendix I


Appendix III. Hydrologic Calculations and Sizing Methods For LID BMPs

Describes various methods for calculating the Design Capture Volume (DCV)Includes worksheets and examplesProvides guidance for sizing of BMPs in seriesDescribes basis for percent capture criterion

More info on Appendix III will be provided in the Technical Focus Modules

Appendix III contains methods, examples, worksheets, and supporting figures


Appendix IV. Approved Methods for Quantifying HCOCs (North Orange County)

Describes hydrologic methods for 2-year peak runoff volume and peakDescribes hydrologic methods for time of concentrationExamples using on TR-55 Model


Appendix V. Approved Methods for Quantifying HCOCs (South Orange County)

Provides introduction to flow duration control standards Includes links to references

• Interim Hydromodification Sizing Tool and Memo

• Guidance for Site-Specific IHC Analysis

• SOC HMP (future)


Appendix VI. Approved Methods for Calculating Alternative Compliance Volume for LID

Provides instructions for calculating the alternative compliance volumeDescribes approach for applying water quality creditsProvides instructions for calculating remaining treatment volume/flowrate


Appendix VII. Infiltration Rate Evaluation Protocol and Factor of Safety Recommendations

Introduces the different roles of infiltration rate evaluationDescribes various methods for evaluating infiltration rateProvides guidance on selecting a factor of safetyMethods coordinated with Riverside County BMP Manual

Appendix VII provides sample forms and worksheets


Appendix VIII. Groundwater-related Infiltration Feasibility Criteria

Provides guidance on:• Depth to groundwater and mounding potential• Presence of groundwater plumes• Wellhead protection and septic systems• Contamination risks from land use activities• Consultation with applicable groundwater agencies

Includes technical requirements for conducting site specific studiesDeveloped in coordination with OCWD


Appendix IX. Technical Basis for Green Roof Design Criteria

Provides criteria to assist in design, review, and approval of green roofs

Appendix X. Harvest and Use Demand Calculations and Feasibility Screening

Provides guidance for computing harvested water demandIncludes pre-computed thresholds for feasibility screening based on project characteristics

Example: Harvest and use demand threshold table

Table X.7: Minimum TUTIA for Minimum Partial Capture

Project Type Residential Retail and

Office Commercial

Industrial Schools1

Basis of Toilet User Calculation Resident Employee (non-visitor)

Employee (non-visitor)

Employee (non-student)

Design Capture Storm Depth, inches

Minimum TUTIA Ratio Required for Minimum Partial Capture

(toilet users/impervious acre) 0.6 74 98 125 21

0.65 80 106 135 23

0.7 86 114 145 24

0.75 92 122 155 26

0.8 98 130 165 28

0.85 104 138 176 30

0.9 110 146 186 31

0.95 117 154 196 33

1 123 162 206 35 1 – based on employees only; assumes approximately 5 students per employee.


Appendix XI. Criteria for Designing BMPs to Achieve Maximum Feasible Retention and Biotreatment

“If it is not feasible to retain the entire DCV, what is the maximum portion that is feasible?”

Describes biotreatment design elements to achieve maximum feasible incidental infiltration and ET

Provides recommended percent of site to dedicate to BMPs

Provides objective criteria to support plan development and review

Criteria for site design to achieve maximum feasible retention

Criteria for design of biotreatment BMPs to achieve maximum feasible retention


Appendix XII. Conceptual Biotreatment Selection, Design, and Maintenance Criteria

Provides lists of criteria that differentiate biotreatment BMPs from conventional treatment controlsIntended to be used to check detailed designs

Appendix XIII. Threshold Incremental Benefit Criterion

Describes conditions under which a well-designed biotreatment BMP would be considered equivalent to retention BMPs


Appendix XIV. BMP Fact SheetsEach fact sheet:

• Lists OC-specific design criteria• Describes approach for sizing and design (refers to

applicable sections of Appendix III)• Provides references to detailed design manuals

Appendix XV. WorksheetsIncludes a list of worksheets with hot links to the locations of the worksheets in the document

Anatomy of a BMP Fact Sheet (Appendix XIV)

Description

BMP category for feasibility screening

Site factors that present opportunity for BMP type

OC-specific design criteria


Simple sizing instructions

Capture efficiency (nomograph) sizing instructions

Instructions refer to methods and worksheets in Appendix III


Suggestions for using BMP in a treatment train

Additional design references (some manuals contain more detailed design guidance)


Appendix XVI. ExhibitsRainfall zonesInfiltration feasibility constraintsNOC Hydromodification Susceptibility Maps

Appendix XVII. Sanitary Sewer I&IPlaceholder for potential appendix to be developed

Design Capture Storm Depth

Infiltration Feasibility Constraints

Hydromodification Susceptibility

Example Uses of the TGD

Not intended to be read from cover to cover…

Case 1:

Case 2:

Case 3:

Questions