Overview of Large-Scale Green Infrastructure
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.
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.
| BMP Type | Chapter | Primary Design Logic | Practical Reading |
|---|---|---|---|
| Large-Scale Bioretention | 10.1 | Vegetated soil bed; underdrained or infiltrating | No contributory maximum within the chapter itself |
| Infiltration Basins | 10.2 | Native-soil infiltration with pretreatment | GI chapter BMP with quantity on-line and infiltration-specific testing |
| Sand Filters | 10.3 | Pretreatment + sand filtration + infiltration | Only the infiltrating type is included in Chapter 10.3 |
| Standard Constructed Wetlands | 10.4 | Open marsh treatment with pond, marsh, or extended detention categories | GI for quantity; quality only with waiver or variance |
| GI Wet Ponds | 10.5 | Permanent pool, native vegetation perimeter, and beneficial reuse | Not a blanket non-GI chapter; criteria are chapter-specific |
Reading Chapter 10 Without Over-Shorthand
Chapter 10 is better read BMP by BMP than as a single "greater than one acre" story. Large systems may satisfy quantity directly when on-line, while recharge and quality claims above the GI-rule limits stay tied to waiver-or-variance language and the actual chapter configuration.
Design Characteristics
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 detail around pretreatment, routing, post-construction testing, access, and the difference between infiltrating and underdrained systems.
Infiltration Basins and Infiltrating Sand Filters
Infiltration basins remain the clearest recharge-oriented large-scale BMP in the family, while Chapter 10.3 continues to cover only the infiltrating sand-filter configuration and excludes the underdrained type from the GI chapter. Both chapters retain the same central design themes in 2023 and 2026: Chapter 12-consistent testing, 72-hour drawdown, pretreatment, and Chapter 13 hydraulic-impact review where infiltration may affect groundwater conditions.
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 already present them as GI BMPs for quantity purposes, with water-quality use tied to waiver or variance. Their design turns on category selection, water budget, hydrology, vegetation, and site conditions rather than on a simple liner-versus-no-liner test.
GI Wet Ponds
Both editions already describe GI wet ponds rather than a newly reclassified non-GI category. A wet pond qualifies as GI only when it maintains at least a 10-foot-wide native-vegetation perimeter along at least 50 percent of the shoreline and includes a stormwater retention component for beneficial reuse. Its quality credit remains tied to waiver or variance, and its performance depends on permanent-pool volume ratio and detention time rather than a simple permanent-pool shorthand.
Hydrologic & Treatment Performance
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. Water-quality and recharge claims, however, remain chapter-specific and often depend on GI-rule limits, waiver-or-variance language, and the chosen configuration.
| BMP | Primary Mechanism | Chapter TSS Reading | Hydrologic Note |
|---|---|---|---|
| Large-Scale Bioretention | Settling, vegetation uptake, and soil-bed filtration | 80-90% | Underdrained or infiltrating; quantity on-line |
| Infiltration Basin | Settling, filtration, and biological/chemical activity | 80% | Recharge-oriented with 72-hour drawdown and Chapter 13 review |
| Infiltrating Sand Filter | Pretreatment, sand filtration, and adsorption | 80% | Only infiltrating type included in Chapter 10.3 |
| Standard Constructed Wetland | Settling and vegetative uptake/filtration | 90% | Quality only with waiver or variance; category-specific drainage areas |
| GI Wet Pond | Sedimentation and biological processing in permanent pool | 50-90% | Quality tied to permanent-pool ratio and 12-24 hour detention |
The most accurate Chapter 10 comparison is not a single performance story, but a family of BMPs that reach quantity, quality, recharge, and reuse goals through different mechanisms and under different rule conditions.
Chapter 10 Family ReadingKey Updates: 2023 to 2026
Most Useful Reading: Continuity With Clearer Labeling
- The five Chapter 10 BMP families remain in place in both editions.
- 2026 makes the small-scale and large-scale bioretention split easier to read, but it does not create a universal one-acre Chapter 10 rule.
- Wet ponds and constructed wetlands already had chapter-specific GI treatment in 2023; they were not newly flattened into a simple 2026 non-GI storyline.
| Topic | 2023 | 2026 | Change Type |
|---|---|---|---|
| Chapter 10 family | Five large-scale BMP chapters in place | Same five-BMP family remains | Continuity |
| Large-scale bioretention | Chapter 10 bioretention already established | Explicit large-scale chapter title sharpens the split from Chapter 9.7 | Clearer Labeling |
| Standard constructed wetlands | GI for quantity; quality with waiver or variance | Same core framework remains | Continuity |
| GI wet ponds | Native vegetation + beneficial reuse already required | Same GI wet-pond framework remains | Continuity |
| Infiltration basins and sand filters | Chapter 12 and Chapter 13 integration already present | Same core testing and mounding structure remains | Continuity |
Practical Implications for Stormwater Design
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.
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.
Large Wet Systems Need Chapter-Specific Documentation
What the Chapter 10 Wet-System Narrative Should Actually Show
- The selected wetland category or GI wet-pond configuration
- The applicable minimum inflow drainage area or water-budget demonstration
- Native-vegetation and beneficial-reuse elements where GI wet ponds are claimed
- Pretreatment, overflow safety, tailwater, and maintenance-access provisions that are actually shown in the chapter
- Chapter-specific quantity, quality, and recharge claims instead of a generic submission package imported from elsewhere