# Phase 2A Maintenance Content
## NJ Stormwater BMP Manual — Chapters 7 and 8
### Landscaping · Routine Maintenance · Retrofit and Long-Term Management
**2023 vs. 2026 Edition Comparison**
*Generated March 4, 2026 — OPAL Stormwater Engineering Knowledge System*

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## Section 1 — Landscaping and Vegetation Considerations (Chapter 7)

### 1.1 Planting Goals

The NJ Stormwater BMP Manual Chapter 7 establishes that vegetation is not ornamental in a stormwater BMP — it is a functional engineering component. The fundamental planting goals common to both the 2023 and 2026 editions are:

- **Pollutant uptake and cycling:** Plant root systems and associated soil microbial communities actively uptake and transform nutrients (primarily nitrogen and phosphorus) from infiltrating stormwater. Above-ground biomass provides a transient nutrient storage sink, with nutrients exported from the BMP when plant material is harvested or decomposes.
- **Hydrologic performance:** Vegetation controls evapotranspiration (ET) rates from the BMP, contributing to volumetric reduction and available storage capacity recovery between storm events. Deep-rooted species maintain soil macroporosity and prevent compaction that would reduce infiltration rates over time.
- **Erosion control and structural stability:** Plant root systems bind soil in and around BMPs, preventing surface erosion during storm events and stabilizing BMP side slopes and inlet/outlet features.
- **Sediment trapping:** Dense vegetation in inflow areas and forebays slows stormwater velocity, causing suspended sediment to settle before reaching the primary BMP treatment area.
- **Habitat function:** Diverse native plantings support pollinator communities and serve as riparian and wetland habitat buffers in appropriate settings.

### 1.2 Vegetation Roles in BMP Performance

Different plant functional types serve distinct performance roles within a BMP system:

**Emergent Aquatic Vegetation (wetland BMPs, wet retention basins)**
Emergent species such as softstem bulrush (*Schoenoplectus tabernaemontani*), cattail (*Typha* spp.), and blue flag iris (*Iris versicolor*) establish in the permanent pool zone of wet retention basins and constructed wetlands. Their roles include:
- Nitrogen and phosphorus uptake into above-ground biomass
- Root zone support for denitrifying and nitrifying bacteria
- Velocity reduction and sediment settling in shallow forebay areas

**Upland and Prairie Species (bioretention, grass swales, buffer areas)**
Native grasses and forbs — including switchgrass (*Panicum virgatum*), little bluestem (*Schizachyrium scoparium*), and black-eyed Susan (*Rudbeckia hirta*) — are preferred for bioretention surface cover and side slopes. These species:
- Maintain open, structured soil profiles through deep root networks
- Tolerate extended inundation and drought cycles characteristic of bioretention hydrology
- Require minimal long-term inputs (fertilizer, irrigation, pesticide) once established

**Shade Trees and Wooded Buffers**
Canopy trees adjacent to BMPs provide ET capacity and temperature buffering for receiving waters. Chapter 7 of both editions cautions against planting trees with aggressive root systems (e.g., willows, silver maples) directly within BMP filter or aggregate zones, noting that roots can displace engineered media and clog underdrain systems.

### 1.3 Differences Between the 2023 and 2026 Manuals (Chapter 7)

**2023 Edition:** Plant species lists and planting specifications are provided as general guidance, referencing the NJDEP Native Plant List and standard nursery sources. The 2023 edition describes vegetation establishment goals without prescribing a minimum establishment monitoring period.

**2026 Edition — Key Changes:**
- **Establishment Performance Period:** The 2026 edition introduces a formal **2-year vegetation establishment performance period** requirement. During this period, the designer or BMP owner must document percent cover of target species and percent cover of invasive species at 6-month intervals. Minimum success thresholds are: ≥70% cover by desired native species; ≤15% cover by invasive or weedy species. Failure to meet thresholds triggers mandatory replanting or invasive management actions.
- **Species-Specific Guidance for Bioretention:** The 2026 Chapter 7 provides updated species lists segmented by bioretention zone (ponding zone, surface mulch zone, side slopes), replacing the single consolidated list in the 2023 edition.
- **Invasive Species Management Language:** The 2026 edition adds explicit language prohibiting the planting of species on the NJDEP Prohibited and Regulated Plant Species List and requires an invasive species inspection as part of annual BMP inspection documentation.

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## Section 2 — Routine BMP Maintenance (Chapter 8)

### 2.1 Inspection Frequency Concepts

Chapter 8 of both manual editions establishes that regular inspection is the foundation of long-term BMP performance. Inspection frequency is tied to:
- **Storm event response:** Inspection following any storm event producing 2 inches or more of rainfall is a minimum expectation for performance-critical BMPs.
- **Annual formal inspection:** At minimum one comprehensive annual inspection covering all system components (inlet, outlet, overflow structure, vegetation condition, sediment accumulation, underdrain function, slope stability).
- **Post-construction establishment inspections:** Increased inspection frequency (monthly) during the vegetation establishment period for bioretention, constructed wetlands, and other vegetation-dependent BMPs.

Both editions note that BMP owners (typically the property owner of record, a homeowner association, or a municipal entity named in the maintenance agreement) are responsible for maintaining inspection records and making them available to NJDEP or the local review authority upon request.

### 2.2 Sediment and Debris Removal

Sediment accumulation is the primary mechanism by which BMP performance degrades over time. Chapter 8 guidance on sediment management:

**Forebay Cleanout**
- Both editions specify that forebay or pretreatment areas should be cleaned when sediment accumulation reaches **50% of design forebay volume** (or the depth marker established during construction to indicate 50% fill). This threshold is based on the forebay's function as a sacrificial sedimentation zone intended to protect the primary BMP filter media.
- Forebay sediment should be tested before off-site disposal if the contributing drainage area includes hotspot land uses; metals and hydrocarbon testing is typically required.

**Primary BMP Area Sediment**
- Sediment accumulation in the primary ponding or filter area of a bioretention cell, basin, or wetland should be removed when depth exceeds 3 to 6 inches above the design surface. Both editions note that sediment buildup above the design surface layer reduces ponding depth and available treatment volume.
- In practice, sediment accumulation in the primary bioretention area is best managed by removing and replacing the top 2 to 4 inches of mulch and surface media layer when sediment mixing has reduced surface porosity, typically every 5 to 10 years depending on sediment loading.

**Debris and Trash Removal**
- Both editions require inspection for debris accumulation at inlets, overflow structures, and outlet control devices after each major storm event and as part of the annual inspection. Clogged inlets or outlets are classified as immediate corrective action items.

**Underdrain Inspection and Flushing**
- Bioretention cells, sand filters, and other BMPs with underdrain systems require underdrain inspection at the annual inspection cycle. Where underdrain cleaning access cleanouts were installed, flushing with a garden hose or pressure washer is recommended if drainage rates appear slower than specified.

### 2.3 Vegetation Management

Vegetation management tasks and schedules documented in Chapter 8:

**Mowing and Cutting**
- Turf or grass-stabilized areas within or adjacent to BMPs (grass swales, basin side slopes, buffer strips) require regular mowing during the growing season, typically a minimum of two to four times per year. Cutting height should not reduce grass below 4 to 6 inches, to maintain root density and infiltration function.
- Native meadow or prairie plantings within bioretention cells are typically cut back once per year in late winter/early spring before new growth emerges.

**Mulch Replenishment**
- Surface mulch in bioretention cells and tree filter systems must be maintained at a 2- to 3-inch depth. Mulch deeper than 4 inches reduces surface infiltration and oxygen exchange. Both editions specify shredded hardwood mulch as the preferred material; dyed or rubber mulch is not appropriate for stormwater BMPs.
- Mulch should be inspected annually and replenished as needed:  typical replenishment interval is every 2 to 3 years.

**Invasive Species and Weed Control**
- Both editions require removal of invasive species as part of routine maintenance, with manual or mechanical removal preferred over chemical treatment in the BMP ponding zone. If herbicide treatment is required for invasive management, Chapter 8 specifies that products must be approved for use in or near water and applied by a licensed pesticide applicator.

**Dead Plant Replacement**
- Both editions establish that dead or failed plants within a BMP should be replaced within one growing season. If plant mortality exceeds 20% of total installed plants, a reassessment of the planting plan is advised to determine whether species selection or site conditions require adjustment.

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## Section 3 — Retrofit and Long-Term Management (Chapter 8)

### 3.1 Upgrading Existing BMPs

Chapter 8 addresses retrofit scenarios — situations where an existing BMP must be upgraded to correct performance deficiencies, meet updated regulatory standards, or address end-of-service-life conditions. Both editions describe three primary retrofit categories:

**Functional Retrofit**
Addressing specific performance failures in an otherwise intact BMP. Common scenarios:
- Surface clogging of bioretention media: remove and replace top media layer; reassess contributing area's sediment loading
- Underdrain failure or blockage: excavate and replace underdrain lateral; evaluate pretreatment adequacy
- Outlet structure damage: repair or replace outlet control device; confirm outlet elevation matches original design
- Vegetation failure: replant with appropriate species; evaluate whether hydrologic conditions (drying between storms, extended ponding) are consistent with species tolerances

**Performance Upgrade**
Where an existing BMP was designed and constructed under older standards and no longer meets current design requirements (e.g., undersized for the 2026 WQV design storm, or not achieving 80% TSS removal under updated performance expectations). The 2026 edition notes that performance upgrade retrofits may be required as a condition of redevelopment approval on sites with pre-existing stormwater infrastructure.

**GI Retrofit (New for 2026)**
The 2026 edition introduces guidance on converting existing Non-GI BMPs (e.g., dry detention basins, sand filters with impermeable liners) to GI-compliant practices. This typically involves:
- Removing impermeable liners from detention basins to allow infiltration
- Adding amended soil media and native vegetation to convert a detention-only basin to a bioretention area
- Confirming soil suitability and SHWT separation before converting to an infiltrating system
- Documenting the converted BMP as meeting 2026 GI BMP definitions for credit toward the volumetric reduction standard

The 2023 edition did not provide retrofit-to-GI guidance; only general functional retrofit was addressed.

### 3.2 Maintenance Challenges Commonly Addressed

Both editions acknowledge that the following maintenance challenges are widespread and anticipated in BMP lifecycle management:

**Media Clogging and Surface Sealing**
The most common long-term failure mode for bioretention and infiltration-based BMPs. Caused by progressive fine sediment accumulation in pore spaces of filter media. Prevention through adequately sized forebays and regular forebay cleanout is prioritized over corrective media replacement. When media replacement is necessary, the entire filter media layer must be removed and replaced with fresh-specification material; partial replacement is not effective.

**Vegetation Establishment Failure**
Failure of planted vegetation to establish, typically due to:
- Inappropriate species selection for the hydrologic conditions of the BMP
- Inadequate soil preparation or media composition
- Animal browsing or physical disturbance during establishment
- Drought or extended ponding during the critical first growing season

Both editions recommend a 2-year establishment monitoring period. The 2026 edition formalizes performance criteria (see §1.3).

**Sediment Hot Loading**
BMPs receiving sediment-heavy runoff from construction activities or high-disturbance land uses may fill forebays and primary ponding areas within 1 to 3 years, significantly below expected design life. Both editions recommend construction phase erosion and sediment controls be maintained until the site is fully stabilized, and note that BMP baseline conditions should be documented (surveyed) at the time of final stabilization to establish the reference condition for future sediment depth measurements.

**Illicit Discharges**
Both editions note that maintenance inspections should include documentation of evidence of illicit discharges (detection of non-stormwater flows, unusual odors, discoloration, foam, or surface sheen). Illicit discharge evidence must be reported to the local stormwater authority.

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## Section 4 — Key Updates Between the 2023 and 2026 Manuals

| Topic | 2023 Edition | 2026 Edition |
|---|---|---|
| Vegetation establishment monitoring | General establishment goals; no formal period | Formal 2-year period; 6-month interval monitoring; quantitative success thresholds (≥70% native cover, ≤15% invasive cover) |
| Bioretention planting zones | Single consolidated species list | Zone-specific species lists (ponding, surface, side slope) |
| Invasive species management | General removal guidance | NJDEP Prohibited Plant List citation; mandatory invasive inspection at annual inspection |
| GI retrofit guidance | Not addressed | New section on converting Non-GI BMPs to GI-compliant practices |
| Forebay cleanout trigger | 50% fill of design volume | Unchanged; 50% retained |
| Sediment testing requirements | Referenced for hotspot areas | Retained; hotspot sediment testing protocol cross-referenced to updated hotspot guidance |
| Mulch specification | Shredded hardwood preferred | Retained; additional note on dyed/rubber mulch prohibition |
| Dead plant replacement threshold | 20% mortality triggers reassessment | Retained; linked to formal establishment monitoring record |
| Maintenance agreement recordkeeping | Maintenance log recommended | Maintenance log required as part of NJDEP permit compliance; log format recommended |

### 4.1 Implications for Maintenance Planning

**Maintenance Agreements Must Reference 2026 Standards**
New BMP installations approved under 2026 standards must include maintenance agreements that reference the 2026 Chapter 8 inspection frequency, sediment cleanout triggers, and vegetation performance standards. Agreements drafted under 2023 guidance should be reviewed and updated for ongoing compliance.

**Establishment Monitoring Adds Near-Term Obligation**
The 2026 vegetation establishment monitoring requirement — with documented 6-month assessments and quantitative success thresholds — adds a near-term post-construction monitoring obligation that was not previously formalized. Project owners and maintenance entities should budget for two years of active monitoring and potential replanting actions.

**GI Retrofit Path Opens Compliance Options for Existing Sites**
The 2026 Chapter 8 GI retrofit guidance provides a defined pathway for property owners with aging Non-GI stormwater infrastructure to convert those systems to GI-compliant practices. This is particularly relevant for redevelopment projects where the existing stormwater system must be brought into compliance with current standards. The retrofit-to-GI path requires soil assessment (recharge feasibility) and design documentation consistent with 2026 Chapter 6 requirements before implementation.

**Maintenance Log as Permit Compliance Record**
The 2026 edition upgrades maintenance log status from "recommended" to "required" for NJDEP permit compliance. Maintenance records are now explicitly a component of the permit compliance record, subject to inspection and auditing by the review authority. Owners without records face compliance risk independent of the physical condition of their BMP.

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*End of Phase 2A Maintenance Content*
*Source Reference: NJ Stormwater BMP Manual, Chapters 7–8; 2023 and 2026 Editions. Regulatory basis: N.J.A.C. 7:8.*