1. Revised Draft Construction
General Permit:
Approach and Overview
March 2008
State Water Resources Control Board
Division of Water Quality
Storm Water Section

2. 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)

3. 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.

4. Construction =
WQ threats
+
+

5. 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

6. 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.

7. Population and New
Development Pressure –
Projected for CA between 1990
and 2040

9. Sediment Discharges

10. 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

18. Hydromodification Impacts

24. 2000's – Sacramento Area
1950's – Sacramento Area

25. Hydrologic Cycle
From Lake (2004)

26. 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

27. After Lane (1955) as cited in Rosgen (1996)

29. Increase in Bankfull Discharge
Urbanization tends to
increase storm water
runoff:
Pre-Development
peak flows Post-Develop.
Runoff
volume
frequency
Time
From Haltiner (2006)

30. 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

31. 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)

32. 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)

33. 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

34. 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.

35. 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

36. 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

37. MS4 Coverage

40. 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

48. Rain chains and
mulch combo
Sacramento, CA