staff presentation 080311 gtg
TRANSCRIPT
Revised Draft Construction General Permit:
Approach and Overview
March 2008
State Water Resources Control BoardDivision of Water Quality
Storm Water Section
Announcements
• USEPA Effluent Limitation Guidelines for Construction Activities– http://www.epa.gov/guide/construction/ – Nothing noted on the web, yet – but staff heard this
process is being restarted from USEPA staff at CASQA Mtg. in March 2007
• Our Process – next steps– Release a new “final” draft this Spring (after these
workshops)– Schedule Board hearings / meetings to consider
adoption (as early as August, more likely later)
Construction Activity Threats
• Two-fold – construction projects over an acre have the potential to cause impacts to our beneficial uses of water both during and after the project.
• During – potential for sediment and erosion discharges.
• After – potential for hydromodification impacts as a result of how the new landscape functions.
+
+
=Construction WQ threats
Performance Measurement for Storm Water Program
WQ Outcomes
Behavioural Outcomes
WQ Outputs
Behavioral Outputs
Dischargers and Regulators monitor receiving water outcomes
Dischargers and Regulators measure behaviours, like pollution prevention and financial drivers/outcomes
Dischargers monitor effluent quality
Dischargers monitor hydromodification changes
Regulators compile and share information with all (e.g., CIWQS, SWAMP, etc.)
Dischargers and Regulators conduct and measure and record inspections / auditsDischargers and Regulators record violations
Stream Protection
Desired Outcomes
Non-Filers Become Filers.
Compliance w/ Numeric Effluent Limits
Possible Measures
Compliance w/ “Narrative”Requirements
Permit Reissuance Goals
1)Adopt a risk-based permit approach 2)Improve “performance” measurement of
program3)Establish a standard to avoid, minimize and
mitigate hydromodification impacts associated with all new and re-development projects triggering the construction activity permit.
Population and New Development Pressure –
Projected for CA between 1990 and 2040
Sediment Discharges
Direct Erosion / Sediment Control Requirements
• Old model used SWPPP as main vehicle• New approach to use Rain Event Action
Plan (REAP) as primary tool (SWPPP becomes more a master document/library)
• Requirements based on principles of “soil loss” (e.g., soil type, length:slope, etc.)
• Prevention and planning incentives
Hydromodification Impacts
1950's – Sacramento Area2000's – Sacramento Area
Hydrologic Cycle
From Lake (2004)
Aggradation Phase
- hillslope erosion is largest sediment source
- width:depth may increase or stay constant
- cross-sectional area increases
Pre-development
Erosional Phase
- channel erosion is largest sediment source
- width:depth increase eventually
- cross-sectional area increased to accommodate larger bankfull discharge
After Lane (1955) as cited in Rosgen (1996)
Increase in Bankfull Discharge
Run
off
Time
Pre-Development
Urbanization tends to increase storm water runoff:
� peak flows
� volume
� frequency
Post-Develop.
From Haltiner (2006)
Runoff Reduction
• Remains essentially the same – match volume and time of concentration of pre-construction hydrology
• Construction permit requirements will not apply if a project is within the jurisdiction of an MS4 permit
• Staff believes a simple, runoff reduction credit system is best for the “rest of CA”
• Staff wants to help develop a statewide WQ control plan/policy to address hydromod issues
Estimate Annual “Undisturbed” Sediment Yield�
Sediment Discharge Risk
Evaluate Site and Receiving Water (RW) Info�
RW Risk
RW Risk combined w/ Sediment Risk�
Tiered Implementation and Monitoring Requirements (site specific)
RUSLE
Characteristicsof RW, site &
BU’s
Overview
• Risk broken into two elements – sediment yield and RW sensitivity to sediment
• Risk then drives level of requirements – both implementation and monitoring
• Risk framework based on Southwestern Australia approach
• Turbidity Action Level is site-specific and dynamic, uses MUSLE, applies to all sites
• Turbidity AL limit (1000 NTU) will apply to all sites – exceedance of this value will constitute a violation (and more action)
Sediment Yield Riskusing RUSLE to estimate
High Sediment Yield Estimate: between 75-499 tons per acre per yearHigh
Extreme Sediment Yield Estimate: greater than or equal to >=500 tons per acre per yearExtreme
Moderate Sediment Yield Estimate: between 1 - 74tons per acre per yearModerate
Low Sediment Yield Estimate: <1 ton per acre per yearLow
Receiving Water Sensitivity Risk
• Point system• Based on Watershed and Site
Characteristics– E.g., discharge to salmon streams = 10 points– ATS = deduct 10 points– Etc.
Receiving Water (RW) Riskbased on the sensitivity to receiving water and project
capability to cause adverse effects
High Potential to Adversely Impact RW: high sediment sensitivity WB and/or high risk of discharge causing or contributing to harm
High
Moderate Potential to Adversely Impact RW:moderate sediment sensitivity WB and/or moderate risk of discharge causing or contributing to harm
Moderate
Low Potential to Adversely Impact RW: low sediment sensitivity WB and/or low risk of discharge causing or contributing to harm
Low
Risk and Requirements
Level 4Level 3Level 2Level 2High
Level 3Level 2Level 2Level 1Medium
Level 2Level 2Level 1Level 1Low
ExtremeHigh MediumLow
Receiving
Water Risk
Sediment Risk
Combined Risk Level Matrix
MS4 Coverage
Examples of Runoff Reduction
Measures
– Soil quality improvement (porosity)
– Native and drought tolerant vegetation
– Trees– Permeable pavement– Riparian buffers– A general reduction of
connected, impervious surfaces in runoff pathways
– Bioretention– Disconnected downspouts/rain
chains/rain barrels
Rain chains and mulch combo
Sacramento, CA