Los Angeles County (Unincorporated)
Los Angeles County Department of Public Works
CountyMS4 Phase IVerified 2026-03
Local Permit / Authorization
- Permit Required
- Yes
- Permit Name
- Grading Permit with LID Standards Compliance
- Submit To
- Los Angeles County Department of Public Works
- Lead Time
- Plan review 4–8 weeks; LID compliance reviewed as part of grading/building permit
- Application Method
- Online via LA County Department of Public Works; LID plan submitted with permit package
- Fee
- Grading permit fees based on earthwork volume; LID plan review included
Water Quality Standards
- Impervious Cover Limit
- No countywide cap; projects creating ≥ 500 sq ft of new or replaced impervious surface in unincorporated areas trigger LID requirements (one of the lowest thresholds in CA)
- On-Site Treatment Required
- Yes
- Detention Required
- Yes
- Detention Standard
- Retain the 85th-percentile 24-hour storm on-site; if infeasible, biofiltration of 1.5× the design volume. County's LID Standards Manual governs sizing and selection.
- Turbidity Standard
- Must comply with state CGP and LA County MS4 Permit (Order R4-2012-0175 as amended) receiving water limitations
Local SWPPP / Drainage Plan
- Local Plan Required
- Yes
- Plan Name
- Erosion and Sediment Control Plan (construction); LID Plan / Standard Urban Stormwater Mitigation Plan (post-construction)
- PE Stamp Required
- Yes
LID Plan must be prepared by a registered Civil Engineer. LA County is the principal permittee under the LA County MS4 Permit, with 84 co-permittee cities.
Local Inspection Requirements
- Requirements
- County inspects grading and erosion control during construction. Post-construction LID facilities require recorded covenants and maintenance agreements. Annual self-inspection and periodic county verification.
- Inspector Qualification
- QSP/QSD per state CGP; no additional county certification
Special Overlay Zones
Significant Ecological Area (SEA)
Trigger: Properties within mapped SEAs containing sensitive habitats, wildlife corridors, or rare species
Restriction: Reduced development footprint; enhanced erosion controls; biological studies required; conditional use permits for development
Hillside Management Area
Trigger: Properties in designated hillside areas with slopes ≥ 25%
Restriction: Reduced grading; enhanced erosion and sediment controls; geology and soils reports required; haul route approval
Santa Monica Bay Watershed
Trigger: Properties draining to Santa Monica Bay
Restriction: TMDL-driven requirements for bacteria, DDT/PCBs, and metals; enhanced dry-weather runoff controls; trash reduction BMPs required
Design Manual
- Manual Name
- LA County LID Standards Manual
Official Resources
Jurisdiction Notes
LA County is the principal permittee under one of the largest and most complex MS4 permits in the country (Order R4-2012-0175). The 500 sq ft trigger threshold for LID requirements in unincorporated areas is among the most aggressive in California. The County's Enhanced Watershed Management Programs (EWMPs) add watershed-specific requirements on top of the base MS4 permit.
Remember: These local requirements are in addition to the SWRCB state construction permit. Both must be satisfied before breaking ground.
Disclaimer: This information is provided for general reference only. Always verify requirements directly with Los Angeles County Department of Public Works and the agency website before beginning construction.