oc asce tgd presentation_1-17-2012-es-ap.pptx
TRANSCRIPT
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Model WQMP Update: Key Implications for WQMP
Preparation
Eric Strecker, P.E. Geosyntec Consultants
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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
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Key Take Home Points
!! New BMP selection requirements "! BMP hierarchy "!Menu of LID options "! Feasibility analysis
!! Key implications for WQMP preparation
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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
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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)
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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.
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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
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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
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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
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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!
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Key Implications for WQMP Preparation
!! New menu of BMP options
!! Feasibility screening and related analyses
!! Site design emphasis !! Pathways for regional
opportunities !! Hydromodification
control
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LID Options: Hydrologic Source Controls
HSC-1: Localized On-Lot Infiltration
HSC-2: Impervious Area Dispersion
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LID Options: Hydrologic Source Controls
HSC-3: Street Trees/Canopy Cover
HSC-4: Residential Rain Barrels
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LID Options: Hydrologic Source Controls
HSC-5: Green Roof/Brown Roof
HSC-6: Blue Roof
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LID Options: Infiltration
INF-1: Infiltration Basin
INF-2: Infiltration Trench
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LID Options: Infiltration
INF-3: Bioretention without Underdrains
INF-3: Bioinfiltration (Bioretention with Elevated
Underdrains)
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LID Options: Infiltration
INF-5: Dry Well
INF-6: Permeable Pavement
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LID Options: Infiltration
INF-7: Underground Infiltration
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LID Options: Harvest and Use
HU-1: Above Ground Cisterns
HU-2: Underground Cisterns
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LID Options: Biotreatment
BIO-1: Bioretention with Underdrains (Planter box)
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LID Options: Biotreatment
BIO-2: Vegetated Swale
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LID Options: Biotreatment
BIO-3: Vegetated Filter Strip
BIO-4: Wet Detention Basin
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LID Options: Biotreatment
BIO-6: Dry Extended Detention Basin
BIO-5: Constructed Wetland
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LID Options: Biotreatment
BIO-7: Proprietary Biotreatment
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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?
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Burden of Proof - Example
Project Site LUST Site
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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?
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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
n
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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
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Infeasibility Screening
Out of Service
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Infeasibility Screening
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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
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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
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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)
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Example TGD Resources
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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
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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
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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
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Site Design Criteria !! Creativity in site design can improve feasibility and
yield cost savings
!"# !"#
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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
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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)
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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
1
2
3
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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
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Example – Sub-watershed Planning Scale
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Hydromodification
Lower Santiago Creek (Credit: SCCWRP)
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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
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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
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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
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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 [email protected]