The Chapter 11 family reads as a continuity-heavy non-GI chapter set in both the 2023 and 2026 manuals: six BMP types, a stable Chapter 9.5 versus 11.3 MTD split, and chapter-specific quantity and quality roles that should not be flattened into one generic fallback narrative.
Chapter 11 in both the 2023 and 2026 NJ Stormwater BMP Manuals remains the non-GI chapter family used when a project needs detention- or treatment-based BMPs that do not meet the definition of green infrastructure. The six BMPs reviewed here are blue roofs, extended detention basins, non-GI MTDs, sand filters with underdrains, subsurface gravel wetlands, and wet ponds.
Read alongside Chapter 9.5, the manuals also keep a stable MTD boundary: GI-qualified MTDs stay in Chapter 9.5, while Chapter 11.3 addresses the MTDs that require a waiver or variance from N.J.A.C. 7:8-5.3. The comparison across the two editions is therefore more continuity-heavy than reorganization-heavy.
The chapter family also gives a practical picture of where these systems fit: blue roofs where roof area dominates or at-grade space is limited, MTDs where installation footprints are constrained, sand filters with underdrains on urban and regulated motor vehicle surfaces, and extended detention at sites expecting larger runoff increases from development.
The manuals draw a clean line between the two MTD chapters. Chapter 11.3 is limited to non-GI MTDs that do not meet the green infrastructure definition and therefore require waiver or variance if they are to be used for stormwater runoff quality. Chapter 9.5 addresses the separate GI MTD subset that does meet the GI definition.
Within Chapter 11.3, the role of a non-GI MTD is narrow but important. It is a proprietary device used to treat stormwater runoff quality, not quantity or recharge. The approved TSS rate is either 50% or 80%, depending on the device's Department certification.
Both editions describe HDS devices as flow-through structures that remove pollutants by settling through a swirling vortex, a baffle system, laminar plates, or a combination of those mechanisms. The chapter's performance treatment stays tied to the individual certification rather than a universal chapter-wide efficiency claim.
Filtration MTDs remove pollutants by passing stormwater runoff through filter media. The manuals keep them as the second certified category and then tie the approved TSS rate, sizing method, and allowable model selection back to the certification letter and published verification report.
Both Chapter 11.3 and Chapter 9.5 require the device to have a Department-issued certification letter and to be sized in accordance with the published verification report. That is the core acceptance path the manuals actually state.
GI MTDs in Chapter 9.5 explicitly tie the 80% TSS rate to NJCAT verification and NJDEP certification. Chapter 11.3 uses NJCAT verification in its configuration rules and cites the TARP reciprocity protocol in the chapter references, but it does not create a separate standalone certification-process story beyond those materials.
The MTD chapters are more specific about sizing than the earlier draft suggested. Both editions say the designer must know the Water Quality Design Storm peak flow rate, contributory drainage area, and physical size limits of the installation area before selecting a device. The device must then be accepted through a Department-issued certification letter and sized in accordance with its published verification report.
The design criteria remain concrete across both editions: future connections are prohibited if they would exceed the existing MTD's maximum stormwater quality treatment flow rate; the device must be installed in the same configuration used during NJCAT verification; HDS inlet geometry must match the tested setup; and blind downstream connections are prohibited.
Blue roofs remain controlled rooftop detention systems used for stormwater runoff quantity only. They are most effective where roofs dominate site impervious cover or where little at-grade space is available for other BMPs.
Extended detention basins remain non-GI settling BMPs that can address quantity and, with waiver or variance, water quality. Their approved TSS range is tied to detention time rather than to a flat single performance value.
Chapter 11.4 remains the non-GI sand-filter chapter in both editions. It is the underdrained chapter, distinct from the infiltrating sand filters addressed in Chapters 9.9 and 10.3.
Subsurface gravel wetlands remain quality-only non-GI BMPs built around a surface marsh and submerged gravel cells. The chapters describe settling, vegetation uptake and filtration, and denitrification in the saturated gravel zone.
Wet ponds are already titled Wet Ponds (Non-GI) in both editions. They remain permanent-pool BMPs whose TSS credit depends on the ratio of permanent pool volume to the Water Quality Design Storm volume and, if used, extended detention.
| BMP Type | Chapter-Stated Performance | Dominant Mechanism | Chapter 11 Role |
|---|---|---|---|
| Blue roof | No chapter-stated TSS rate | Controlled rooftop detention | Quantity only, with waiver or variance |
| Extended detention basin | 40-60% TSS depending on detention time | Settling | Quantity and quality, with waiver or variance |
| Non-GI MTD | 50% or 80% TSS depending on certification | HDS settling or filtration media | Quality only, with waiver or variance |
| Sand filter with underdrain | 80% TSS | Settling, filtration, adsorption | Quantity and quality, with waiver or variance |
| Subsurface gravel wetland | 90% TSS; chapter text also describes 90% nitrogen removal | Settling, vegetation uptake, denitrification | Quality only, with waiver or variance |
| Wet pond (Non-GI) | 50-90% TSS depending on pool ratio and extended detention | Permanent-pool settling and detention | Quantity when on-line, and quality, with waiver or variance |
The useful comparison point is that each BMP chapter states its own treatment logic instead of collapsing the whole family into one shorthand. Extended detention basins are detention-time BMPs, wet ponds are permanent-pool-ratio and detention BMPs, sand filters with underdrains are chapter-stated 80% TSS filters, non-GI MTDs depend on product certification, subsurface gravel wetlands are the denitrification chapter, and blue roofs remain detention-only.
| Topic | 2023 | 2026 | Practical Reading |
|---|---|---|---|
| Chapter 11 family | Full non-GI family already present | Full non-GI family still present | Continuity outweighs novelty |
| GI vs non-GI MTD split | Chapter 9.5 GI / Chapter 11.3 non-GI | Same split remains | Stable classification boundary |
| Blue roof drain rule | 72-hour drainage rule stated | Same 72-hour drainage rule stated | No new minimum-release narrative supported |
| Sand filter with underdrain | Chapter 11.4 non-GI underdrained filter | Same chapter role and core criteria | Compare as parallel chapters, not as newly introduced content |
| Subsurface gravel wetland | 90% TSS and chapter-stated nitrogen-removal language | 90% TSS table and continued denitrification / nitrogen-removal language in chapter text | No support for an invented percentage jump |
| Wet pond placement | Wet Ponds (Non-GI) already in Chapter 11.6 | Same title and chapter role | Better read as continuity than relocation |
Chapter 11 remains the part of the BMP Manual that explains what happens when a project must use non-GI detention or treatment measures. The six BMP chapters do not form a single interchangeable fallback category; instead, they divide into quantity-only, quality-only, and mixed quantity/quality tools, each with its own waiver-or-variance posture and chapter-backed performance logic.
For designers and reviewers, the more useful takeaway is precision rather than broad narrative. Blue roofs should be read as rooftop detention with a 72-hour drain requirement. MTDs should be sized from certification letters and published verification reports. Extended detention, sand filters with underdrains, gravel wetlands, and wet ponds should be read through their own chapter tables instead of through a generic non-GI shorthand.