Stormwater regulations vary significantly by jurisdiction, but the core requirements are consistent across most of the United States. This guide provides a practical compliance checklist for drainage contractors working on residential and light commercial projects.
Disclaimer: This is a general reference guide. Always check your specific local and state regulations. Requirements change frequently, and fines for non-compliance can be substantial.
When Stormwater Permits Are Required
Most projects trigger stormwater requirements when they disturb a certain amount of land:
| Threshold | Typical Requirement |
|---|---|
| Under 1 acre disturbed | Local grading permit only (varies) |
| 1 - 5 acres disturbed | NPDES Construction General Permit (CGP) + SWPPP |
| > 5 acres disturbed | NPDES CGP + SWPPP + enhanced BMPs |
| Any size in MS4 area | Local MS4 permit requirements apply |
NPDES = National Pollutant Discharge Elimination System CGP = Construction General Permit SWPPP = Stormwater Pollution Prevention Plan MS4 = Municipal Separate Storm Sewer System
Many municipalities have lower thresholds. Some require a stormwater plan for any project that adds more than 500 square feet of impervious surface.
Pre-Construction Checklist
Before breaking ground, verify the following:
Permits and Plans
- Local grading permit obtained
- NPDES CGP filed (if > 1 acre disturbance)
- SWPPP prepared and on-site (if required)
- Stormwater management plan approved by reviewing agency
- Erosion and sediment control plan approved
- 811 utility locate completed (call 48-72 hours before digging)
- Adjacent property notification (if required by local code)
Design Requirements
- Post-development peak flow does not exceed pre-development peak flow for the design storm
- Water quality volume (WQv) addressed (first 1 inch of runoff treated, typical)
- Channel protection volume addressed (if required)
- Flood control addressed for 100-year storm (if required)
- Downstream analysis completed (verify no adverse downstream impacts)
- Impervious area limits met per local code
Use the SCS Curve Number Calculator to compare pre- and post-development runoff.
Common Design Storm Requirements by Region
| Region | Typical Design Storm | Channel Protection | Flood Control |
|---|---|---|---|
| Northeast US | 2-yr, 10-yr, 100-yr | 1-yr, 24-hr | 100-yr |
| Southeast US | 2-yr, 25-yr, 100-yr | 1-yr, 24-hr | 100-yr |
| Midwest US | 5-yr, 10-yr, 100-yr | Varies | 100-yr |
| Southwest US | 10-yr, 25-yr, 100-yr | Varies | 100-yr |
| Pacific Northwest | 2-yr, 25-yr, 100-yr | 2-yr, 24-hr | 100-yr |
Check your jurisdiction. These are generalizations. Your municipality, county, or state may differ significantly.
Erosion and Sediment Control
Required BMPs During Construction
At minimum, most jurisdictions require:
| BMP | When Required | Maintenance Frequency |
|---|---|---|
| Silt fence | Perimeter of disturbed area | Inspect weekly + after every 0.5” rain |
| Construction entrance | Every vehicle access point | Replenish stone as needed |
| Inlet protection | Every storm drain inlet on-site or adjacent | Inspect weekly + after rain |
| Sediment basin/trap | Sites > 1 acre with concentrated flow | Clean at 50% capacity |
| Slope protection | Any slope > 3:1 (H:V) | Inspect weekly |
| Dewatering controls | When pumping water from excavations | Continuous during pumping |
| Stabilization | Exposed soil idle > 14 days (7 days in some states) | Inspect weekly |
Common Violations and Fines
| Violation | Typical Fine Range |
|---|---|
| No SWPPP on-site | $1,000 - $10,000 |
| Failed silt fence not repaired | $500 - $5,000 |
| Sediment discharge to waterway | $5,000 - $50,000+ |
| No inlet protection | $500 - $5,000 |
| Disturbing more area than permitted | $2,500 - $25,000 |
| Working without required permit | $5,000 - $50,000+ |
Post-Construction Requirements
Many jurisdictions require permanent stormwater management facilities:
Common Post-Construction Requirements
- Detention/retention facility sized for the required design storms
- Water quality treatment for the first 1 inch of runoff (typical)
- Maintenance agreement recorded on the property deed
- As-built drawings submitted to the reviewing agency
- Maintenance schedule and responsible party identified
- Annual inspection requirement acknowledged
Detention Sizing Quick Check
Most jurisdictions require that post-development peak flow matches pre-development peak flow for specified design storms. Use these calculators to verify:
- Rational Method Calculator — Quick peak flow estimate
- SCS Curve Number Calculator — Runoff volume comparison
- Pond Sizing Calculator — Detention facility sizing
State-Specific Resources
Most states have a stormwater design manual that specifies the exact requirements for your jurisdiction. Here are common sources:
| Resource | Where to Find It |
|---|---|
| State stormwater manual | State DEQ or DOT website |
| Local MS4 requirements | City/county stormwater department |
| NPDES CGP | EPA eNOI system (federal) or state environmental agency |
| IDF curves / rainfall data | NOAA Atlas 14 (precipitation frequency estimates) |
| Soil data | USDA Web Soil Survey |
| Floodplain maps | FEMA Flood Map Service Center |
Inspection Checklist for Active Sites
Use this checklist during weekly and post-storm inspections:
Weekly Inspection Items
- All silt fences intact and properly staked
- No sediment has overtopped silt fences
- Construction entrance is functioning (no sediment tracking onto road)
- All storm drain inlets are protected
- No discolored water leaving the site
- Exposed soil areas are stabilized or actively being worked
- Sediment basins/traps are below 50% capacity
- Material stockpiles are protected from erosion
- Concrete washout area is contained and not overflowing
- SWPPP is on-site and up to date
Post-Storm Inspection (within 24 hours of 0.5” rain)
- All items from weekly inspection
- Repair or replace any damaged BMPs
- Remove accumulated sediment from BMPs
- Check for erosion channels or gullies
- Verify no discharge of sediment-laden water off-site
- Document conditions with photos and log entry
Related Calculators
- SCS Curve Number Calculator — Pre/post development runoff comparison
- Rational Method Calculator — Peak flow estimation
- Pond Sizing Calculator — Detention/retention sizing
- Swale Calculator — Vegetated swale design
- Time of Concentration Calculator — Watershed timing