Phase 2C - Large-Scale Green Infrastructure (GI) Systems¶
Source Documents: - 2023: BMP 10.1, BMP 10.2, BMP 10.3, BMP 10.4, BMP 10.5 - 2026: BMP 10.1, BMP 10.2, BMP 10.3, BMP 10.4, BMP 10.5
Overview¶
The Chapter 10 family remains the larger-footprint green infrastructure and stormwater BMP set used when projects need more storage, longer flow paths, larger pretreatment zones, and more formal hydraulic analysis than the Chapter 9 small-scale family typically provides. The 2023 and 2026 manuals read best when Chapter 10 is understood as a BMP-specific family rather than as a single acreage threshold, with each chapter tied to the contributory-drainage limits in the GI rules and to its own design criteria for quantity, quality, recharge, and maintenance. (2023 BMP 10.1-10.5; 2026 BMP 10.1-10.5)
Across both editions, the Chapter 10 family includes large-scale bioretention, infiltration basins, sand filters designed to infiltrate into subsoil, standard constructed wetlands, and GI wet ponds. The underlying design logic is continuity rather than wholesale reclassification: the major systems remain in place, but their compliance role depends on configuration, rule context, and the function actually being claimed in the stormwater report. (2023 BMP 10.1-10.5; 2026 BMP 10.1-10.5)
Section 1: Overview of Large-Scale Green Infrastructure¶
1.1 Purpose and Role in Stormwater Management¶
Large-scale GI systems continue to serve several stormwater functions at once. Depending on the BMP and configuration, they can provide storage, attenuation, filtration, settling, biological treatment, infiltration into subsoil, or reuse-based retention. The chapters repeatedly frame these systems as tools for stormwater runoff quantity control when designed as on-line systems, while quality and recharge claims remain tied to the specific GI-rule limits and any required waiver or variance. (2023 BMP 10.1-10.5; 2026 BMP 10.1-10.5)
1.2 Typical BMP Types in the Chapter 10 Family¶
The family is best understood BMP by BMP:
- Large-scale bioretention remains a vegetated soil-bed system that may either infiltrate into subsoil or discharge through an underdrain.
- Infiltration basins remain recharge-oriented systems that rely on highly permeable components and native-soil infiltration.
- Sand filters in Chapter 10 continue to mean the infiltrating type; the underdrained type is excluded from the GI chapter.
- Standard constructed wetlands remain open marsh systems with three categories: pond, marsh, and extended detention wetlands.
- GI wet ponds remain quantity-oriented permanent-pool systems that qualify as GI only when the chapter's native-vegetation and beneficial-reuse conditions are met. (2023 BMP 10.1-10.5; 2026 BMP 10.1-10.5)
1.3 Large-Scale Reading Versus One-Threshold Shorthand¶
The manuals do not support the earlier shorthand that Chapter 10 systems are simply the BMPs for facilities "typically exceeding one acre of impervious surface per facility." Large-scale treatment in the manuals is tied instead to the GI-rule concept of BMPs exceeding the contributory-drainage limits in N.J.A.C. 7:8-5.3(b), along with chapter-specific geometry, hydrology, pretreatment, and compliance conditions. Large-scale bioretention is a good example: both editions say there is no contributory drainage area maximum within Chapter 10.1 itself, even though the rule context still matters for what the BMP can satisfy without waiver or variance. (2023 BMP 10.1; 2026 BMP 10.1)
Section 2: Design Characteristics of Large-Scale GI Systems¶
2.1 Large-Scale Bioretention Systems¶
Both editions describe large-scale bioretention as a flexible family rather than a single configuration. The BMP may be designed with an underdrain or to infiltrate into subsoil, and both manuals explicitly say that no contributory drainage area maximum applies within Chapter 10.1 itself. What changes with scale is the level of design detail: Chapter 10.1 addresses pretreatment, on-line versus off-line routing, access, post-construction testing, tailwater, and the differences between underdrained and infiltrating systems in far more detail than a simple "large system" label suggests. (2023 BMP 10.1; 2026 BMP 10.1)
For infiltrating large-scale bioretention, both editions require soil testing consistent with Chapter 12, use of the slowest tested permeability with a factor of safety of 2, a minimum subsoil design permeability rate of 0.5 inches per hour, and groundwater mounding assessment where infiltration could create adverse hydraulic impacts under N.J.A.C. 7:8-5.2(h). The chapters support mounding analysis and Chapter 12-consistent testing, but they do not establish a universal LPSS requirement or a fixed 3,000 sq ft trigger for all Chapter 10.1 work. Underdrained systems remain part of the chapter family in both editions, but they are treated as filtered-discharge systems rather than recharge BMPs. (2023 BMP 10.1; 2026 BMP 10.1)
2.2 Infiltration Basins and Large-Scale Sand Filters¶
Infiltration basins remain the clearest recharge-oriented large-scale BMP in the Chapter 10 family. In both editions, they carry an 80% TSS removal rate, require Chapter 12-consistent soil testing, require a minimum 2-foot separation from the seasonal high water table, and must drain the design storm within 72 hours using the slowest design permeability rate. The chapters also keep the same practical cautions: infiltration is prohibited where high pollutant loading is anticipated, adverse hydraulic impacts must be assessed with reference to Chapter 13, and pretreatment is essential, especially for subsurface systems and non-roof runoff. (2023 BMP 10.2; 2026 BMP 10.2)
Chapter 10.3 follows the same large-scale infiltration logic for sand filters designed to infiltrate into subsoil. Both editions say the underdrained sand filter does not meet the definition of GI and is not included in this chapter. The Chapter 10.3 BMP is therefore the infiltrating sand filter, with an 80% TSS removal rate, pretreatment zone, infiltration through subsoil, and the same basic rule structure for quantity, recharge, and quality claims: quantity may be satisfied directly when the system is on-line, while recharge and quality for systems exceeding the rule's contributory-drainage limits require waiver or variance. The practical design message is that large-scale sand filters remain part of the Chapter 10 family, but only in their infiltrating GI form. (2023 BMP 10.3; 2026 BMP 10.3)
2.3 Standard Constructed Wetlands¶
The manuals do not frame standard constructed wetlands as GI only when they infiltrate into native soils without a liner. Instead, both editions present standard constructed wetlands as GI BMPs for quantity purposes, with water-quality use tied to waiver or variance. They also describe three categories of standard constructed wetlands, each with its own minimum inflow drainage area: 25 acres for pond and marsh categories and 10 acres for the extended detention category, with smaller drainage areas possible only if a water-budget analysis demonstrates that the required water depths can be maintained. (2023 BMP 10.4; 2026 BMP 10.4)
The design details remain configuration-driven rather than infiltration-driven. Both editions emphasize pretreatment, permanent-pool and marsh-zone allocation, vegetation density, and site constraints such as soils and groundwater conditions. They also say the soils must be sufficiently impermeable to maintain system hydrology, or else soil modification or an impermeable liner may be necessary. GI status in this chapter therefore turns on the chapter framework itself, not on a blanket no-liner condition. (2023 BMP 10.4; 2026 BMP 10.4)
2.4 GI Wet Ponds¶
Both 2023 and 2026 already describe GI wet ponds, not a newly reclassified non-GI category. In both editions, a wet pond qualifies as GI only when the design maintains at least a 10-foot-wide area of native vegetation along at least 50 percent of the shoreline and includes a stormwater retention component designed for beneficial reuse. Both editions also say GI wet ponds can only be used to satisfy stormwater runoff quantity standards unless a waiver from the GI requirements is obtained, and only with waiver or variance may they receive water-quality credit. (2023 BMP 10.5; 2026 BMP 10.5)
The actual Chapter 10.5 performance framework is also more specific than the earlier shorthand. The chapter ties TSS removal to the ratio of permanent pool volume to the Water Quality Design Storm volume and, if extended detention is provided, to detention time. The minimum permanent-pool ratio is 1:1 for 50% TSS removal; the maximum is 90% TSS when the system has 24 hours of extended detention and a 3:1 ratio. Both editions also keep the 20-acre minimum inflow drainage area, subject to a water-budget demonstration for smaller sites, and require beneficial reuse to be included in that budget analysis. (2023 BMP 10.5; 2026 BMP 10.5)
Section 3: Hydrologic and Treatment Performance¶
3.1 Quantity and Routing Functions¶
The Chapter 10 family remains important because all five BMP chapters tie the systems to stormwater runoff quantity control when they are designed as on-line systems. Large-scale bioretention, infiltration basins, and infiltrating sand filters store the Water Quality Design Storm and then discharge by infiltration or controlled overflow, while standard constructed wetlands and GI wet ponds use permanent-pool and detention-based routing to attenuate larger events. The chapters consistently require designers to think about overflow stability, access, pretreatment, and in several cases tailwater effects on hydraulic performance. (2023 BMP 10.1-10.5; 2026 BMP 10.1-10.5)
3.2 Water-Quality Treatment¶
Water-quality treatment varies across the Chapter 10 family and stays tied to the values stated in each chapter. Large-scale bioretention remains the most variable of the family, with both editions giving an 80-90% TSS removal range depending on vegetation selection and soil-bed depth. Infiltration basins and infiltrating sand filters remain 80% TSS BMPs. Standard constructed wetlands remain 90% TSS BMPs, but only with the waiver-or-variance context stated in the chapter. GI wet ponds remain 50-90% TSS BMPs, with the actual removal rate tied to permanent-pool volume ratio and, where used, 12-24 hour extended detention. (2023 BMP 10.1-10.5; 2026 BMP 10.1-10.5)
3.3 Recharge, Pretreatment, and Site Suitability¶
The family also separates itself through how recharge and pretreatment are handled. Infiltration basins and infiltrating sand filters are explicitly recharge-oriented but prohibited where high pollutant loading is anticipated. Large-scale bioretention can be configured for infiltration or underdrain discharge, which changes whether recharge is even on the table. Standard constructed wetlands do not allow groundwater recharge in their chapter tables. GI wet ponds likewise do not allow recharge, and their GI identity depends instead on shoreline vegetation and beneficial reuse. Across the family, pretreatment remains a recurring design element, especially for infiltration-based BMPs and for systems expected to handle heavier sediment loads. (2023 BMP 10.1-10.5; 2026 BMP 10.1-10.5)
Section 4: Key Updates Between the 2023 and 2026 Manuals¶
4.1 Continuity Is the Main Story¶
The dominant comparison point is continuity. The five Chapter 10 BMP families are present in both editions, and the underlying compliance structure is already recognizable in 2023: large-scale GI BMPs may satisfy quantity directly, while quality and recharge claims above the contributory-drainage limits require waiver or variance under the GI rules. The 2026 manual continues and clarifies a framework already visible in the 2023 chapters rather than introducing a wholly new large-scale GI regime. (2023 BMP 10.1-10.5; 2026 BMP 10.1-10.5)
4.2 Large-Scale Bioretention Is Easier to Read in 2026, Not Wholly New¶
The 2026 source set does make the separation between small-scale and large-scale bioretention easier to read because Chapter 10.1 is explicitly titled Large-Scale Bioretention Systems, while Chapter 9.7 continues to address the small-scale family. That clearer labeling does not create a universal one-acre pivot or a new Chapter 10 threshold for the whole family. The more useful comparison is that 2026 makes the chapter boundary more legible, while the core Chapter 10.1 design logic remains materially continuous with 2023. (2023 BMP 10.1; 2026 BMP 10.1; 2023 BMP 9.7; 2026 BMP 9.7)
4.3 Wet Ponds and Constructed Wetlands Were Not Newly Flattened Into Non-GI Stories¶
Both editions already treat standard constructed wetlands as GI BMPs for quantity, with quality use tied to waiver or variance. Both editions also describe GI wet ponds with the same native-vegetation-perimeter and beneficial-reuse conditions, the same minimum inflow drainage area, and the same TSS framework tied to permanent-pool ratio and detention time. The 2023-2026 comparison is therefore continued chapter-specific GI treatment, not a newly imposed 2026 non-GI blanket rule. (2023 BMP 10.4-10.5; 2026 BMP 10.4-10.5)
4.4 Sand Filters and Infiltration Chapters Remain Stable¶
The same continuity applies to sand filters and infiltration basins. Both editions limit Chapter 10.3 to the infiltrating sand-filter configuration and exclude the underdrained type from the GI chapter. Both editions also carry the same Chapter 10.2 structure for infiltration basins: Chapter 12-consistent soil testing, 72-hour drawdown, minimum SHWT separation, pretreatment, and hydraulic-impact analysis with reference to Chapter 13. There is no broad evidence here for a new 2026 protected-water-supply setback regime or a universal new documentation package for all large-scale GI submissions. (2023 BMP 10.2-10.3; 2026 BMP 10.2-10.3)
4.5 Summary of Changes¶
| Topic | 2023 | 2026 | Practical Reading |
|---|---|---|---|
| Chapter 10 family | Full five-BMP family in place | Full five-BMP family still in place | Read as continuity, not a new program |
| Large-scale bioretention | Chapter 10 bioretention already established | Explicitly titled large-scale bioretention | 2026 makes the small-scale/large-scale split easier to read |
| Standard constructed wetlands | GI for quantity, quality with waiver/variance | Same core framework | Not a new liner/no-liner GI rule |
| GI wet ponds | GI wet ponds already tied to native vegetation and beneficial reuse | Same core GI wet-pond framework | Not a blanket 2026 non-GI reclassification |
| Infiltration basins and sand filters | Chapter 12 and Chapter 13 integration already present | Same core integration remains | Stability outweighs novelty |
Section 5: Practical Implications for Stormwater Design¶
5.1 Match the BMP to the Claimed Function¶
The strongest practical takeaway is that large-scale GI should be documented according to the function actually being claimed, not according to broad chapter shorthand. If the design is claiming quantity control, the report should show the on-line or routing logic that makes that claim work. If the design is claiming recharge, the report must address infiltration-specific site conditions and GI-rule limits. If the design is claiming water-quality treatment, the chapter-specific waiver-or-variance conditions and the actual BMP performance framework matter. That is a more useful design approach than assuming every Chapter 10 BMP satisfies the same regulatory objectives in the same way. (2023 BMP 10.1-10.5; 2026 BMP 10.1-10.5)
5.2 Soils, Groundwater, and Pretreatment Stay Central¶
For infiltration-led BMPs, the chapters consistently point designers back to soil conditions, SHWT separation, Chapter 12-consistent testing, and Chapter 13 groundwater-mounding analysis where hydraulic impacts are possible. They also keep pretreatment visible, especially for infiltration basins and sand filters, and require realistic attention to access, post-construction testing, and maintenance. The practical implication is that a large-scale GI report should document actual subsurface and pretreatment conditions rather than rely on generic statements about Chapter 10. (2023 BMP 10.1-10.3; 2026 BMP 10.1-10.3)
5.3 Large Wet Systems Need Chapter-Specific Documentation¶
For standard constructed wetlands and GI wet ponds, the practical questions are different. Designers need to show the selected wetland category or GI wet-pond configuration, the role of permanent storage and vegetation, the applicable minimum inflow drainage area or water-budget demonstration, and any beneficial-reuse or shoreline-vegetation elements that make the GI claim possible. Tailwater, overflow safety, and realistic maintenance obligations also remain part of the large-system story in both editions. The better report voice for these BMPs is precise and chapter-specific, not a blanket statement that every wet system in Chapter 10 has become non-GI or universally triggers the same submission package. (2023 BMP 10.4-10.5; 2026 BMP 10.4-10.5)