staff presentation 080311 gtg

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