6.3 Final Stabilization Verification, Final Inspections, and Notice of Termination

Criteria for Final Stabilization Under the EPA CGP and State Permits

A widespread misconception among construction superintendents is that stormwater permit obligations end as soon as building construction finishes and paving crews demobilize. Under the Clean Water Act and the EPA Construction General Permit (CGP Part 8), permit coverage—and the legal obligation to conduct routine inspections and maintain controls—continues uninterrupted until the site satisfies all final stabilization requirements and the operator submits a valid Notice of Termination (NOT).

The Standard 70% Uniform Perennial Vegetative Cover Rule

Under EPA CGP Part 2.2.14b (and most state general permits), final stabilization of unpaved disturbed areas requires establishing uniform, perennial vegetative cover over 100% of the disturbed area at a density of at least 70% of the native background vegetative cover that existed prior to earth disturbance (or installing permanent non-vegetative stabilization such as buildings, asphalt/concrete pavement, permanent gravel subbases, gabions, or engineered rock rip-rap).

Three technical components of this rule are heavily tested on the CESSWI examination:

1. Perennial Vegetation Only: The established vegetation must consist of perennial species that persist year after year. Lush green stands of annual nurse crops (such as annual ryegrass, winter wheat, or oats) used for temporary stabilization do not qualify for final stabilization because annual plants die off at the end of the growing season, leaving bare soil exposed to erosion.
2. Uniformity Across 100% of the Disturbed Footprint: The vegetative cover must be uniformly distributed with no large bare patches, rills, gullies, or washouts. A 10-acre site with $90\%$ turf density across 9.5 acres and a bare, eroding $0.5\text{-acre}$ cut slope fails final stabilization.
3. Relative to Pre-Construction Native Background Density: The $70\%$ threshold is a percentage of the undisturbed native background cover, not an absolute $70\%$ ground cover requirement in every climate.

Worked Numeric Examples of the 70% Background Cover Rule

The minimum required final vegetative cover is calculated using the formula:

$$\text{Minimum Required Final Cover (\%)} = 70\% \times \text{Undisturbed Native Background Cover (\%)}$$

• Example 1 — Arid or Semi-Arid Rangeland ($50\%$ Native Cover): Suppose a utility substation is constructed in a semi-arid rangeland where undisturbed native bunchgrass and shrub vegetation adjacent to the site naturally covers $50\%$ of the ground surface (leaving $50\%$ natural bare soil between plants). To satisfy final stabilization across the unpaved disturbed area, the operator must establish uniform perennial vegetation covering at least:

$$70\% \times 50\% = 0.70 \times 0.50 = \mathbf{35\%}\text{ of the ground surface}$$

• Example 2 — Humid Temperate Region ($100\%$ Native Cover): Conversely, if a commercial site is constructed in a humid region where undisturbed native pasture or woodland floor covers $100\%$ of the ground surface, final stabilization requires uniform perennial vegetation covering at least:

$$70\% \times 100\% = 0.70 \times 1.00 = \mathbf{70\%}\text{ of the ground surface}$$

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Regulatory Exceptions and Special Final Stabilization Pathways

The EPA CGP recognizes three specialized land-use and climatic scenarios where the standard immediate $70\%$ perennial turf rule is modified:

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Conducting the Final Inspection Prior to Notice of Termination (NOT)

Under EPA CGP Part 8.2, an operator must submit an electronic Notice of Termination (NOT) within 30 calendar days of meeting final stabilization or transfer eligibility. However, filing an NOT prematurely—while temporary silt fences remain in the ground or before a permanent detention basin is cleaned out—constitutes a false certification under 40 CFR § 122.22.

Before recommending that the operator certify and submit the NOT, the CESSWI inspector conducts a comprehensive four-part Final Closeout Inspection:

1. Verify 100% Permanent Stabilization and Zero Active Erosion

Walk every cut-and-fill slope, drainage swale, utility corridor, stockpile footprint, and discharge outfall. Confirm that all unpaved disturbed surfaces meet the $70\%$ uniform perennial vegetative cover standard (or permanent rock/pavement armoring) with zero active rills, gullies, headcuts, piping, or bare scars.

2. Verify Complete Removal of All Temporary BMPs and Stabilization of Their Footprints

Confirm that every temporary erosion and sediment control device has been physically removed from the property and off-site outfalls:

• Pull out all synthetic silt fences, wooden stakes, metal T-posts, plastic-netted wattles, temporary rock check dams, gravel bag berms, and concrete washout liners.
• Critical Trap: Do not overlook temporary storm drain inlet filter bags, fabric under-grate inserts, and curb-inlet gravel bags. Leaving temporary inlet filters inside storm drains after construction causes severe post-construction street flooding when the fabric blinds with leaf litter.
• Any narrow trenches, stake holes, or bare soil strips disturbed during the removal of temporary BMPs must be backfilled, seeded with perennial seed, and mulched.

3. Verify Cleanout and Conversion of Permanent Post-Construction Stormwater Facilities

During active construction, permanent post-construction stormwater management facilities—such as dry extended-detention basins, wet retention ponds, bioretention rain gardens, and infiltration basins—are frequently utilized as temporary sediment basins or protected from construction runoff. Prior to NOT submission, the CESSWI must verify that:

• All accumulated construction sediment and silt has been excavated and removed from the basin floor and forebay down to the exact post-construction design invert elevations.
• Compacted infiltration and bioretention subgrades have been scarified/ripped and filled with specified engineered bioretention soil media and permanent plantings.
• Temporary outlet controls—such as perforated riser filter wraps, temporary stone weirs, and floating surface skimmers—have been removed, and the permanent post-construction outlet structure (low-flow orifice plates, permanent trash racks, anti-vortex baffles, and emergency spillways) is fully installed and operational.

4. Verify Complete Site Demobilization and Good Housekeeping Closure

Confirm that all heavy machinery, jobsite trailers, staging containers, aboveground fuel storage tanks, chemical totes, waste dumpsters, portable sanitary toilets, and aggregate stockpiles have been removed from the site, and that any minor oil drips or concrete splatters have been cleaned and remediated.

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Once all four closeout conditions pass inspection, the CESSWI records date-stamped closeout photographs of every stabilized slope, converted post-construction basin, and receiving water outfall, signs the final inspection report, and instructs the operator to submit the Notice of Termination (NOT) within 30 calendar days and retain the complete SWPPP archive for at least 3 years.