Model WQMP Update: Key Implications for WQMP

Preparation

Eric Strecker, P.E. Geosyntec Consultants

Acknowledgements

!! Orange County Stormwater Program: "! Richard Boon "! Chris Crompton "! Mary Anne Skorpanich

!! Consulting Team: "! Geosyntec

•! Aaron Poresky •! Lisa Austin

"! CDM •! Don Schroeder •! Dan Bounds

!! Advisory Groups: "! Permittees (PAG) "! Technical (TAG) – Other agencies, building industry, NGOs

Key Take Home Points

!! New BMP selection requirements "! BMP hierarchy "!Menu of LID options "! Feasibility analysis

!! Key implications for WQMP preparation

Previous WQMP

!! New and Re-Development required to provide treatment for Water Quality Design Storm

!! Consider LID !! Consider well-performing treatment

BMPs !! CEQA for large projects often was key

driver for source, site planning, and treatment controls

Common BMPs under Previous Model WQMP

!! Cartridge media filters !! Mechanical separators !! Grass- or concrete-lined

extended detention basins

!! Vegetated swales !! Retention and

biotreatment driven by project opportunities or other factors (CEQA, LEED)

New LID Requirements

!! Priority Projects must infiltrate, harvest and use, evapotranspire, or if above not feasible, biotreat/biofilter, the 85th percentile, 24-hour storm event (Design Capture Volume).

"! A properly designed biotreatment system may only be considered if infiltration, harvest and use, and evapotranspiration (ET) cannot be feasibly implemented for the full design capture volume.

"! In this case, infiltration, harvest and use, and ET practices must be implemented to the greatest extent feasible and biotreatment may be provided for the remaining design capture volume.

LID BMP Selection Hierarchy On-site Retention BMPs

Example: infiltration trench

On-site Biotreatment BMPs

Example: stormwater planter

Subregional/Regional Retention BMPs

Example: groundwater recharge basin

Subregional/Regional Biotreatment BMPs

Example: constructed wetland

If qualifying regional opportunities exist (more on this later)

Rigorous feasibility “gates”

Alternative Compliance

Surface Water vs. Groundwater

(and Evapotranspiration!) 8

!! Surface water regulators/ environmental groups want to push stormwater into the ground as much as possible

!! Groundwater regulators and users are concerned about this

Surface Water Regulators/NRDC

Groundwater Regulators / Water Agencies

Runoff

Infil

tratio

n

Evapotranspiration

Technical Guidance Document

!! Product of 18 month plus stakeholder process

!! Provides technical guidance for developing Project WQMPs "! Assist in practical, objective interpretation of

permit-based requirements

"! Provide recommended processes for developing plans and demonstrating conformance

!! Provides technically-based feasibility criteria

!! Provides supporting information for BMP selection, analysis, and design

TGD Preparation Challenges

!! Provide rigorous technical defense for criteria as well as rigorous feasibility criteria

!! Attempt to accommodate all foreseeable project scenarios

!! Bridge separate requirements in NOC and SOC permit areas

!! But it needs to be usable!

Key Implications for WQMP Preparation

!! New menu of BMP options

!! Feasibility screening and related analyses

!! Site design emphasis !! Pathways for regional

opportunities !! Hydromodification

control

LID Options: Hydrologic Source Controls

HSC-1: Localized On-Lot Infiltration

HSC-2: Impervious Area Dispersion

LID Options: Hydrologic Source Controls

HSC-3: Street Trees/Canopy Cover

HSC-4: Residential Rain Barrels

LID Options: Hydrologic Source Controls

HSC-5: Green Roof/Brown Roof

HSC-6: Blue Roof

LID Options: Infiltration

INF-1: Infiltration Basin

INF-2: Infiltration Trench

LID Options: Infiltration

INF-3: Bioretention without Underdrains

INF-3: Bioinfiltration (Bioretention with Elevated

Underdrains)

LID Options: Infiltration

INF-5: Dry Well

INF-6: Permeable Pavement

LID Options: Infiltration

INF-7: Underground Infiltration

LID Options: Harvest and Use

HU-1: Above Ground Cisterns

HU-2: Underground Cisterns

LID Options: Biotreatment

BIO-1: Bioretention with Underdrains (Planter box)

LID Options: Biotreatment

BIO-2: Vegetated Swale

LID Options: Biotreatment

BIO-3: Vegetated Filter Strip

BIO-4: Wet Detention Basin

LID Options: Biotreatment

BIO-6: Dry Extended Detention Basin

BIO-5: Constructed Wetland

LID Options: Biotreatment

BIO-7: Proprietary Biotreatment

Feasibility Criteria

Deeper infiltration Underdrains discharge to storm pipe

Retention Biotreatment

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

Burden of Proof - Example

Project Site LUST Site

Physical Limitations •!Soil infiltration rate •! Limiting soil horizons •!High, mounded

groundwater •! Low demand for harvested

water

Economic and Societal Factors •! LID space

requirements •!Dense development

goals •!Reclaimed water •!Costs

Risk of Impacts •!Groundwater and/or

soil contamination •!Groundwater source

protection •!Groundwater

mounding •!Geotechnical,

setbacks •! I&I and ephemeral

streams

What makes a BMP infeasible?

Types of Feasibility Analysis

!! Infeasibility Screening "! Would use of the BMP cause risks to property, human

health, or environment (substantial evidence)? "! Is the BMP safe, but not likely to be effective?

!! Design for Maximum Feasible Retention "! What does it mean to retain on site to the MEP? "! What criteria must be met to demonstrate this?

!! Design for Maximum Feasible Retention plus Biotreatment "! What does it mean to retain plus biotreat on site to the

MEP? "! What criteria must be met to demonstrate this?

Sele

ctio

n D

esig

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Infeasibility Screening

!! Yes/No questions answered as part of BMP selection process

!! Section 2.4.2.4 of TGD

http://invw.org/content/ballard-rain-gardens-a-green-solution-gone-wrong

Infeasibility Screening

Out of Service

Infeasibility Screening

Summary of Key Feasibility Considerations and Associated Implications

Infiltration rates •! Field testing may be required for feasibility screening and is generally required to support infiltration BMP design

•! Professional judgment is needed to select appropriate factors of safety to account for uncertainty and clogging

•! Projects with rates below 0.3 in/hr (at FS = 2) will not be required to fully infiltrate the design storm; partial infiltration design is required in these cases

Groundwater quality •! Infeasibility determination requires substantial evidence

•! May require significantly greater exploration and/or coordination with OCWD or other agency

Geotechnical issues •! Geotechnical engineers will be generally be asked to provide greater support for determinations of feasibility

•! There will be pressure to reduce margin of safety in geotechnical design

Summary of Key Feasibility Considerations and Associated Implications (continued)

Site water balance •! In some areas, analysis of full water balance may be required to evaluate potential for impacts related to infiltration

•! Unseasonal baseflow may impact ephemeral channel biology

Required site area •! Site design must allow room for BMPs •! WQMPs may need to demonstrate that site design

criteria have been met •! Backstop table of % of site is in place to ensure

projects are not asked to give up too much site

Inflow and infiltration •! Projects in high I&I basins required to evaluate potential impacts on I&I and mitigate if possible

Harvest and use demand •! Infeasibility determination requires tabulation of project demand for harvested water – simple screening metrics have been developed

•! Some project types will need to incorporate harvest and use before moving to biotreatment

Key TGD Resources for Feasibility Analysis

!! Section 2.4.2.4: Infeasibility screening criteria "! Plus detailed technical appendices on infiltration testing,

groundwater protection, harvest and use screening, and others

!! Worksheets and nomographs for feasibility screening and sizing

!! Appendix XI: Criteria for designing BMPs to achieve maximum feasible retention and biotreatment "! Criteria for BMP design "! Criteria for opportunity evaluation "! Criteria for site design to allow BMPs

!! Example thought processes for demonstrating conformance with new LID requirements (Section 2.4.3.4)

Example TGD Resources

Implications of Updated Model WQMP on Site Design

!! Minimize impervious area

!! Maximize natural infiltration capacity

!! Preserve existing drainage patterns and time of concentration

!! Disconnect impervious area

!! Protect/restore vegetation

!! Protect channels

!! Minimize land disturbance

TGD Section 3

Perform conceptual drainage and

preliminary site BMP planning concurrently

Design site to allow space for BMPs near existing

connections to storm drain

Design site to minimize conflicts

between infiltration and geotech

Identify areas that can be “self-

retaining” and isolate them from the drainage plan

Site Design Process

Site Design Criteria

!! Incorporate applicable hydrologic source controls

!! Allow recommended area in site design for BMPs

!! Locate BMP set-aside areas where they can accept runoff

!! Locate BMP set-aside areas over infiltrative soils as practicable

!! Discretion is required by prepare and reviewer

Site Design Criteria !! Creativity in site design can improve feasibility and

yield cost savings

!"# !"#

Implications of Updated Model WQMP on Regional Opportunities

On-site Retention BMPs

Example: infiltration trench

On-site Biotreatment BMPs

Example: stormwater planter

Subregional/Regional Retention BMPs

Example: groundwater recharge basin

Subregional/Regional Biotreatment BMPs

Example: constructed wetland

Potential use based on

opportunities and analyses

Selection based on rigorous feasibility analysis

Alternative Compliance

Potential advantages of Regional BMPs

!! Manage and monitor quality of infiltrated water

!! More efficient connection to aquifer

!! Institutional operation and maintenance

!! Address existing development

!! Economy of scale !! Facilitate meeting land

use density goals Freshwater Marsh at Playa Vista

Anaheim Lake – Existing OCWD Recharge Facility

Arroyo Park - Newport Beach, CA (flood control)

Criteria for Regional BMPs !! Outside of Waters of the US (WOUS)

and provides treatment before discharge to a WOUS

!! Sufficiently sized to treat remaining DCV from participating tributary area

!! Provides equal or greater overall benefit than would be achieved by on-site LID; addresses primary POCs with at least “M” effectiveness

!! Retention prioritized over biotreatment if both opportunities are equally feasible

!! Adequately maintained for the life of the project

!! Operational to serve the project before occupancy

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Potential Pathways to Use Regional BMPs

Project WQMPs !! Demonstrate on-site

retention is infeasible, or that a regional BMP would provide greater benefit

!! Provide demonstration of capacity dedication for project

!! Describe funding, timing, and O&M of regional BMP

Watershed Infiltration and Hydromodification Management Plans (WIHMPs)

!! Can identify regional opportunities and framework for sub-watershed planning

!! Can contain categorical feasibility analyses

!! Benefit equivalency analysis !! Funding, timing, and O&M

Example – Sub-watershed Planning Scale

Hydromodification

Lower Santiago Creek (Credit: SCCWRP)

Implications of New Hydromodification Control Criteria

!! If downstream channels are susceptible to hydromodification, then projects must eliminate or mitigate hydrologic conditions of concern

!! North County and South County have very different requirements

!! LID can help meet hydromodification criteria but conformance is demonstrated separately in WQMP

Hydromodification Control

!! North Orange County "! Based on matching 2-yr volume and time of concentration "! Existing condition is the pre-project condition "! Fall-back options are available if matching volume or Tc are not

feasible "! In-stream options are available

!! South Orange County "! Interim criteria are based on flow duration control, continuous

simulation "! Baseline condition is pre-European "! No fall-back option for infeasibility "! BMP volumes are generally 2 to 5 times larger than LID criteria "! Draft HMP submitted to SDRWQCB in December 2011 includes

somewhat more flexible criteria

Summary

!! Most significant implications of new LID requirements include: "! New menu of BMP options "! Feasibility screening and related analyses "! Site design emphasis "! Pathways for regional opportunities "! Hydromodification control

!! As a result, the WQMP preparation process has gotten more complex and control requirements will often be more expensive

!! However, resulting BMPs are expected to be more effective

More Information http://www.ocwatersheds.com/WQMP.aspx It has links to the: !! Model WQMP !! Technical Guidance Document !! Interim Hydromod Tool and related documentation !! Planning Dept WQ website !! Help Desk

Eric Strecker estrecker@geosyntec.com