C.3 Stormwater Compliance for Bay Area Projects
From treatment sizing through agency sign-off. Calichi Design Group designs C.3 stormwater compliance for Bay Area developers, architects, and public agencies under MRP 3.0 and the local watershed program (ACCWP, CCCWP, SCVURPPP).
Does your project trigger C.3?
Under MRP 3.0, the threshold dropped from 10,000 SF to 5,000 SF for most projects. Three tiers determine what your scope is.
| Tier | What triggers | What’s required |
|---|---|---|
| Small projects 2,500 – 4,999 SF impervious |
Single-family residential or small commercial creating or replacing 2,500 SF+ of impervious area. | Site design measures only. Self-treating areas, pervious pavement, disconnected downspouts. |
| Regulated projects 5,000 – 9,999 SF impervious |
Most new development and redevelopment in this size range, post-MRP 3.0. | Stormwater Control Plan + bioretention or alternative LID treatment sized to the contributing area. |
| Large projects 10,000+ SF impervious |
Most multifamily, commercial, mixed-use, and public works projects. | Full C.3 package: SCP, treatment sizing, hydromodification (HMP) where applicable, O&M agreement. |
What we deliver
Calichi handles the full C.3 scope, from concept-stage feasibility to agency-stamped construction drawings.
Stormwater Control Plan
Full SCP narrative + exhibits matching your watershed program (ACCWP, CCCWP, SCVURPPP, others).
Bioretention design
Sized facilities with verified contributing areas, plant lists, sub-base specs, underdrains, overflow control.
Hydromodification (HMP)
HMP applicability analysis, BAHM modeling, detention sizing for hillside and stream-impacting sites.
Self-treating area credits
Provision E.12 self-treating credits sized into the calculation to reduce the regulated treatment area.
O&M agreements
Operation & Maintenance plans and recorded agreements that satisfy agency requirements.
Plan check response
Already in plan check with C.3 comments? We can pick up mid-cycle and respond to agency comments.
Free initial scope review
Send us your project size, location, and watershed program. We’ll tell you what your C.3 scope looks like — no obligation, no proposal until you ask.