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Green Infrastructure Requirement

Regulatory Summary

N.J.A.C. 7:8-5.3 establishes that all stormwater runoff from new impervious surfaces in a major development must be managed through Green Infrastructure (GI) practices to the maximum extent feasible. The design target is to capture 100% of the Water Quality Design Storm (1.25 inches of rainfall in 2 hours) through GI measures before any Non-GI alternative is considered.

The January 2026 amendments to N.J.A.C. 7:8 represent a fundamental shift in how GI compliance is defined and demonstrated — moving from a qualitative preference to a quantitative, volumetric performance standard.

Definition Change: What Qualifies as GI

Aspect July 2023 January 2026
GI definition Practices that "manage stormwater using natural processes including infiltration, evapotranspiration, and reuse" Practices that demonstrate measurable volumetric reduction consistent with BMP Manual Chapter 14 standards
Qualification test Qualitative — practice type determined GI status Quantitative — must show retained volume; detention-only or treatment-only practices do not qualify
Non-GI category Not formally defined Explicit "Non-GI BMP" classification for practices that treat but do not reduce volume

GI vs. Non-GI BMP Classification

The 2026 rules formally classify all BMPs into two tiers:

Green Infrastructure (GI) BMPs — Practices achieving volumetric reduction through infiltration, evapotranspiration, or rainwater reuse:

  • Bioretention systems (small-scale and large-scale)
  • Dry wells
  • Infiltration basins
  • Pervious paving systems
  • Cisterns and rainwater harvesting systems
  • Green roofs (only when paired with cistern/reuse for volume credit)
  • Constructed stormwater wetlands (with infiltration component)

Non-GI BMPs — Practices providing water quality treatment without volumetric reduction:

  • Non-GI Manufactured Treatment Devices (MTDs)
  • Non-GI Wet Ponds
  • Non-GI Extended Detention Basins
  • Sand Filters with Underdrain
  • Blue Roofs (when not connected to reuse system)

Hierarchical GI Application (2026)

The 2026 amendments codify a compliance hierarchy that engineers must follow in sequence:

  1. Maximize GI volumetric reduction for the Water Quality Design Storm on-site
  2. Satisfy groundwater recharge using only infiltration-based GI practices
  3. Apply Non-GI treatment to remaining WQV runoff not managed through GI to achieve 80% TSS removal
  4. Size flood control practices for 2-year and 100-year peak flow standards

Before proposing any Non-GI BMP, the engineer must submit a GI Feasibility Analysis documenting site-specific constraints that prevent full GI implementation. Generic statements such as "GI is infeasible due to site constraints" are explicitly rejected under the 2026 rules without supporting data.

Engineering Interpretation

Design Workflow Under the 2026 GI Standard

The 2026 GI requirement changes the design sequence for water quality compliance:

  1. Calculate the Water Quality Volume (WQV) for the site using the 1.25-inch/2-hour design storm
  2. Design proposed GI BMP(s) based on site conditions, soils, and available area
  3. Calculate the Volumetric Reduction Volume (VRv) per BMP Manual Chapter 14
  4. Compare VRv to WQV:
    • If VRv >= WQV: Full GI compliance achieved; no TSS removal calculation required
    • If VRv < WQV: Calculate the residual volume (WQV - VRv) and size a Non-GI BMP for the residual at 80% TSS removal
  5. Document the GI feasibility analysis explaining why full VRv could not be achieved (if applicable)

GI Feasibility Analysis Requirements

The 2026 rules require the following documentation when Non-GI alternatives are proposed:

  • Soil investigation results — In-situ infiltration testing (falling head permeameter or ASTM D5126); estimated rates from soil texture alone are not acceptable for design
  • Seasonal High Water Table (SHWT) depth — Field-confirmed through borings with redoximorphic features; SSURGO screening data alone is insufficient
  • Setback constraints — Distances to foundations, wells, septic systems, and property lines
  • Hotspot screening — Whether the site or portions of it are classified as stormwater hotspots where infiltration is prohibited
  • Available permeable area analysis — Evaluation of site layout options for GI placement

Impact on MTD-Reliant Designs

Projects that previously relied on Manufactured Treatment Devices as the primary stormwater quality measure must now:

  1. Demonstrate why GI practices are not feasible before defaulting to an MTD
  2. Use the MTD exclusively for residual water quality treatment, not as the primary compliance strategy
  3. Document that the MTD achieves required TSS and nutrient removal for the portion of runoff not managed through GI

BMP Implications

The GI/Non-GI classification directly determines which practices can be used and in what order:

Practice GI Status Recharge Credit Volumetric Credit WQ Treatment
Bioretention (no liner) GI Yes Yes Yes
Pervious Paving GI Yes Yes Yes
Dry Wells GI Yes Yes Limited
Infiltration Basin GI Yes Yes Moderate
Green Roof + Cistern GI No (ET only) Yes Moderate
Green Roof (standalone) GI (limited) No Partial Moderate
Sand Filter w/ Underdrain Non-GI No No Yes (TSS)
Wet Pond Non-GI No No Yes (TSS)
Extended Detention Basin Non-GI No No Yes (TSS)
MTD Non-GI No No Yes (TSS)

Key BMP Pages

Cross References