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Staff Presentation 080311 Gtg
 

Staff Presentation 080311 Gtg

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    Staff Presentation 080311 Gtg Staff Presentation 080311 Gtg Presentation Transcript

    • Revised Draft Construction General Permit: Approach and Overview March 2008 State Water Resources Control Board Division 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 Possible Measures Desired Outcomes Dischargers and Regulators monitor receiving water outcomes WQ Stream Protection Dischargers and Regulators measure behaviours, Outcomes like pollution prevention and financial drivers/outcomes Behavioural Non-Filers Become Filers. Outcomes Dischargers monitor effluent quality Dischargers monitor hydromodification changes Compliance w/ WQ Outputs Numeric Effluent Regulators compile and share information with all Limits (e.g., CIWQS, SWAMP, etc.) Compliance w/ “Narrative” Dischargers and Regulators conduct and measure Behavioral Outputs and record inspections / audits Requirements Dischargers and Regulators record violations
    • Permit Reissuance Goals 1)Adopt a risk-based permit approach 2)Improve “performance” measurement of program 3)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
    • 2000's – Sacramento Area 1950's – Sacramento Area
    • Hydrologic Cycle From Lake (2004)
    • Pre-development Aggradation Phase -hillslope erosion is largest sediment source -width:depth may increase or stay constant - cross-sectional area increases 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 Urbanization tends to increase storm water runoff: Pre-Development peak flows Post-Develop. Runoff volume frequency Time 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 RUSLE Sediment Discharge Risk Evaluate Site and Receiving Water (RW) Info Characteristics of RW, site & RW Risk BU’s RW Risk combined w/ Sediment Risk Tiered Implementation and Monitoring Requirements (site specific)
    • 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 Risk using RUSLE to estimate Low Sediment Yield Estimate: <1 ton per acre per Low year Moderate Sediment Yield Estimate: between 1 - 74 Moderate tons per acre per year High Sediment Yield Estimate: between 75-499 tons High per acre per year Extreme Sediment Yield Estimate: greater than or Extreme equal to >=500 tons per acre per year
    • 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) Risk based on the sensitivity to receiving water and project capability to cause adverse effects Low Potential to Adversely Impact RW: low Low sediment sensitivity WB and/or low risk of discharge causing or contributing to harm Moderate Potential to Adversely Impact RW: Moderate moderate sediment sensitivity WB and/or moderate risk of discharge causing or contributing to harm High Potential to Adversely Impact RW: high High sediment sensitivity WB and/or high risk of discharge causing or contributing to harm
    • Risk and Requirements Combined Risk Level Matrix Sediment Risk Low Medium High Extreme Low Level 1 Level 1 Level 2 Level 2 Receiv ing Water Risk Medium Level 1 Level 2 Level 2 Level 3 High Level 2 Level 2 Level 3 Level 4
    • 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